Main.TrailIndexPage | Fuel System | Fuel Tank

Fuel Tank

This component is part of the Fuel System.

Definition

The Fuel Tank (Gas Tank) is used to store gas (petrol, German: benzine).

  • Its technical name & common name(s)
  • part # - start year & end year
  • which area it belongs to - engine, transmission, body, injection etc, link back to the relevant section

Function

The fuel tank comprises the following parts:

Describe, in general terms the function of this component. Meaning what is it there for and what role it plays. Describe how it works, the inside mechanism. Use diagrams to explain.

Fuel Tank

Two sizes of fuel tanks are used on the Pagodas. 230 SLs have a 65 liter tank. Early 230 SLs have a vertically mounted spare wheel on the left side of the trunk with its well sticking out under the trunk floor. Later, (after chassis # 007205) the spare wheel mounting was changed to a horizontal position on the right side of the trunk. This allowed for a flat trunk floor and a bigger 80 liter tank could be fitted from November 1965 to the 230 and then to 250 and 280 SLs. The 80 liter can also be fitted to the flat trunk floor 230 SLs but the electric fuel pump has be relocated.

Picture showing the protruding wheel well on the left. Note also the early rectangular electric fuel pump shield. Later shields are cylindrical.

Picture showing the smaller 65 liter tank on a late 230 SL with flat trunk floor.

Picture showing the larger 80 liter tank. Note the slightly different mounting position of the electric fuel pump

For a tabulation of tank filling capacities see: http://www.sl113.org/wiki/Maintenance/Start#FillingCapacities

Tank Inspection:

Inspection of the tank can be done first to determine its condition. Lift the trunk mat and center round plastic cover. Remove the electrical plug then unfasten the five small nuts and remove the fuel sender. With a flashlight, you will be able to view the inside and bottom of the fuel tank. Depending on what you see you may want to just drain the fuel or remove the whole tank for cleaning. You may also need to replace the cork gasket to reseal the fuel sender during re-assembly (part #110-471-0180). Removal of the fuel tank is not difficult. Drain or siphon fuel out. Unplug fuel sender (as described), dis-connect the fuel lines, the rubber seal around the fuel filler, and the three nuts holding the tank in place. During removal the two small vent hoses going to the canister in the trunk can also be unhooked. Once the tank is out it can be taken to a radiator shop to boil out or repair. If the tank is in very bad condition a sealer can be used to line the tank.

The inner workings of the W113 fuel tank are a mystery to most owners. If you ever need to re-condition your tank or service the drain plug/fuel screen this information should be helpful. Here is an illustration of the complex "flower pot assembly" (Note the term flower pot was coined by the Benz Dr. and he will permit this group to use it for now ~)

The drain plug/fuel screen in the fuel tank is the first line of defense to protect the injection system from contamination. This drain plug/fuel screen can be removed using a 22mm allen bolt (7/8") will work. One can make a tool using a 22mm bolt welded on a pipe (see picture). The next photo shows Dan Caron's solution using a 13/16 spark plug socket with the plug gripper removed and reversed on the extension (described in Old Yahoo content). The unit has a rubber o-ring seal which should be renewed. New drain plug/fuel screens are available new if yours is damaged. My old dealer (280-SL)parts book show the number for the filter/plug to be #111 470 0686. The seal is listed as #022 997 0648 (corrected #s 0807). Earlier W113 cars may be a little different. I believe the earliest versions of this drain plug/fuel screen were brass plug with a copper screen while the later units are aluminum plug with plastic screen.

Picture below shows an aluminum plug with plastic screen and the earlier brass plug with copper screen. The copper screen is virtually dissolved away when the tank was cleaned with some sort of acid. Note the very fine mesh screen.

The next photo shows the tank bottom without the flower pot to show how the fuel manifold interacts with the fuel pick up line. Fuel going to the engine must first flow through the screen and into the round "fuel manifold" where it leaves the fuel tank via the metal line. After traveling through the electric fuel pump, fuel lines, main fuel filter, injection pump, left over fuel is returned to the tank via the smaller metal fuel return line and dumped into the "flower pot".

Notice where the fuel return line and the larger (lower) fuel supply line enter the tank. Notice that the metal fuel supply originates at a round collector (manifold) in the center bottom of the tank where it picks up fuel after it is drawn through the drain plug/fuel screen.

Some tanks have rubber connecting pipes within the tank and need care when trying to unclog them:

If you ever need to recondition your tank and coat it with gas tank sealer you should be very careful to cover the screen so sealer will not clog the round collector (manifold and fuel line.

Also be aware of the tiny vent line which snakes along the top of the tank! This must also be kept clear!

This tank seems to have a zinc galvenized coating from the factory and the surface is still in decent condition. The earlier tanks may not be galvanized.

Use extreme caution when working around gasoline! Make sure to have enough empty containers to store the fuel in with good seals. Have an extinguisher and something to absorb spills on hand. Static electricity or things like water heater pilot lights can ignite gas fumes. You may want to do this kind of work in the well-ventilated outdoors. You can pump your tank dry by disconnecting a fuel line in the engine compartment, hooking up a hose and use the electric fuel pump to pump the fuel into containers.

Just be careful or have a professional deal with fuel tanks. Please be sure your gas tank is drained completely and dry before cleaning it. Any contaminated fuel must be disposed of properly to protect the environment and prevent safety hazards.

Picture showing an old rusty tank:

Maintenance

Describe common maintenance procedures, and common faults that may occur. Describe how these may be diagnosed and resolved. Again, include diagrams, photographs and explanations. Where possible, include measures, tolerances, weights etc.

  • Symptoms when it faults
  • How to test if it is faulty - what tools to use
  • How to fix / change

Unfortunately some of the new fuel mixtures, especially those with alcohol content, attack the original protective coating inside older fuel tanks. If you have an old Mercedes and you’re finding black flakes clogging your fuel filter and screens then this may be the case. When the original coating breaks down the tank is vulnerable to corrosion. Just flushing and cleaning the tank is only a temporary solution. The rust will usually return, especially in collector cars which spend much of their lives in not so perfect storage. The solution is to clean and re-coat the tank. A gas tank sealer was developed for the aviation industry where a pure fuel supply is really critical. It is simply fantastic. I used it over the years on many cars, several 190 SLs with chronic rusty and flaking tanks. The cars, after twelve and fifteen years are still doing fine. The coating is alcohol resistant and forms a tough plastic coating impervious to any fuel blend. After cleaning, the sealer is simply poured into the tank and sloshed around, the excess is poured out and the tank is left to air out for a couple of days. The resulting coating, besides protecting the tank from corrosion, also seals minor pin holes and leaky seams. Any rust or dirt particles left after cleaning become trapped in the tough coating and rendered harmless. To do a really good job, remove the tank, take it to a radiator shop and have it boiled out. If the tank is rusty inside, clean with acid, then coat with sealer. Order at least a quart of sealer so you can slosh it around good in those big Mercedes tanks. Use extreme caution when dealing with all that gasoline! Make sure you have enough gasoline containers available to store the gas when draining the system. A fire extinguisher should be kept handy. It might be best done outdoors if you’re doing it yourself. This sealer is available through numerous automotive distributors and aviation stores. The Eastwood co. is supplier to a lot of the old car people. You can probably find a better deal if you shop around. Try some aviation stores.

One other idea that has been reported and should work is to boil the tank out with some caustic soda. Fill it with water and then heat it to a roiling boil on your propane grill. It may sound dangerous but the tank is filled with water and cleaner.

Checking Fuel Return Lines

Disconect the return line in the engine bay and put a short piece of rubber fuel line on it. Use a compressed air line with a long wand on it and fit it into the rubber hose. Place a rag around the end of the hose - you will be happy you did.

Remove the fuel cap and have someone stand at the back of the car. Blow a quick shot of air into the line and if it's open you should hear bubbles inside of the fuel tank. If it's not open gas will spray back at you which is why you want the rag around the end of the hose. To check if the return line is plugged remove the hose just before the fuel tank. If the main line is clear under the car then it's likely the return line inside of the tank. I would drain the tank and remove so it can be boiled out. After it's cleaned try to blow air into the return line. If it's still plugged you might be able to open it using a base guitar string and a battery operated hand drill. Works kind of like a roto - rooter. It's going to be full of rust and old dried up fuel. Once it's open you won't have many problems after that. I also test all of the fuel lines coming from the IP with compressed air when I have them off. I've found some that were plugged or nearly plugged which will greatly affect the engine. The CSV line is often plugged with crud because there's very little pressure in the line and very little fuel moves through the line. This line has a larger ID than the high pressure lines to maintain proper volume to the CSV.

Fuel Tank Sealing:

  1. Study the fuel tank information above, understand that the fuel inlet into the flower pot is below the return line.
  2. Read and re-read the instructions on the seal kit. I used the tank seal kit from the Eastwood company. I had to call them to verify the instructions. The Eastwood kit calls for you to buy an additional 2 quarts of acetone (buy two one quart cans) and muriatic acid. The acid is used during the prep process, the dilution is 20:1 water to acid mix. 1/2 gallon.
  3. Pull and cover the fuel tank screen, I used a finger from a latex glove and then some electrical tape wrapped around to seal it well.
  4. Make a cover for the sender unit opening, I used a plastic ice cream top, cut and drilled using the gasket from the sender unit as a template.
  5. Have covers for the fuel return and feed line. I had vacuum covers from a Mityvac kit that fit well.
  6. The main catch to sealing the tank is to follow the instructions, and when sealing the tank to not clog any of the fuel lines.
  7. Have heavy plastic gloves and a face protection. the chemicals used are nasty, if you have a respirator use it.
  8. When it came time to apply the sealer, with the help of another person I coated the sides of the tank, then did the bottom of the tank.
  9. To keep the sealer out of the fuel inlet in the flower pot, I removed the cover for the sender unit so I could see the bottom of the tank, then with the tank standing up, we slowly lowered the tank bottom side down and I watched the sealer as it flowed toward to flower pot, once it was approaching the inlet, we raised the tank just a little and allowed the sealer to just touch the bottom of the flower pot. We did this two times, then angled the tank around to get the sealer on the other side of the flower pot to cover the rest of the bottom of the tank.
  10. Re-install the home made sending unit cover, turn the tank over and seal the top of the tank.
  11. Per the instructions after waiting 8 - 10 minutes, drain off the excess sealant.
  12. Use compressed air to verify the fuel feed and return lines are clear, also check the vent lines. I used an extra guitar string to verify the vent lines were clear. Using the process above I was not too worried about the fuel inlet and return lines being clogged as I never got sealant in the flower pot.
  13. Once the sealant has cured I will verify the flower pot fuel inlet is clear. Probably will use some clear poly line placed into the flower pot and allow some water flow thru the tube to the inlet hole and verify by viewing the fluid flowing out of the flower pot.
  14. The whole process takes about 2 hours, and is an inexpenisve route to attempting a do it your self tank sealing. The eastwood kit was about $50, muriatice acid and 2 qts of acetone was about $10.

This is a lot less than buying a new tank from mb or a repro from k&K - as long as it works.

27 November 2007, at 06:46 EST

Link to related components where appropriate.

Old Yahoo content

I guess I have to give up another one of my secrets.

The drain plug can be removed using a spark plug socket with a hex head on the drive end. This socket should have a rubber insert used to hold a spark plug which you need to remove.

Push the hex end of the socket into the recess of the drain plug. Fit a long extension through the socket into the square drive from the bottom and remove like a regular drain plug.

CAUTION!!!!!!!! NEVER use a trouble light near gasoline. A loose bulb could start a fire with you covered in gas.

It happens far more often than you might think. Don't be stupid.......

Dan Caron

The following is the content from the old Yahoo documents on the site. It needs to be structured and edited in the correct sections of the entire document. After moving particular content to its correct place in the manual, please delete it here.


I am concerned about crud in my fuel tank. I drained it of old standing gas, but did not to a thorough cleaning. The car sat for a long time and there may be rust. Has anyone installed an in-line filter before the fuel pump? Is there any reason not to do this? I know I really need to get into the tank and inspect it and clean if necessary. I just filled the tank and after driving for a while had some problems with stalling. I'm pretty sure it was fuel delivery. What's a good process for cleaning the tank?

I had the same problem with mine. No choice here, you'll have to replace the tank. It is virtually impossible to clean rust out of an old tank. The tank costs about $440 from a good parts house, plus the installation. Unless you're really good at this, I'd leave it to a good shop.

I had the same problem with my tank which was half empty for 28 years (car sat in the corner of the lot). The only solution that is worthy and cost effective and not to mention headache free is to buy a new or good used one. In my case I bought an almost brand-new used one from Potomac German Auto.

I had the same problem with my '67 250 SL. I replaced the fuel tank and it helped. But when the fuel level was below half the engine coughed and sputtered. I finally replaced the fuel pump and now the car runs like a charm. But don't jump the gun. You have to drive it for a few hundred miles first. I degaraged mine this weekend after only 4 months and it ran and drove terrible. This happens every spring. I believe these cars want to be driven. So drive it for a while and take notes.

Will: the fuel tank is pretty hard to clean effectively. You can chemically strip it of rust, but then you need to coat the inside to keep the rust at bay. Problem is the plastic screen inside will also be coated and this makes the tank useless. Another problem with running the car and going through many tanks of fuel to clean the tank is the rust and junk you are trying to get rid of is going through the very expensive fuel pump, ruining it. I agree with everyone that have said “get a new fuel tank”. It is expensive, but if you keep the car in service and the tank full when the car is stored, you will get another 30-40 years of service out of it.

Pete Lesler: to repair your existing tank, find an authorized "Renu" dealer. They have a method of removing all rust and scale and seal the tank before sending it back, they give a lifetime warranty and the cost was $185 five years ago. They advertise in Hemmings.

Will again: I still say it is not possible to pour gas tank liner/sealer in the tanks as used on W 113s due to the plastic basket that holds the fuel lines inside the tank. Anyone out there actually relined a W 113 gas tank and put it into service?

Joe: good point Will, however the plastic basket removes with the 22 mm drain plug. The next item to be concerned with is how to keep sealer from plugging the fuel lines in the tank. The lines go into a collector in the bottom of the tank where the fuel has no chance but to go through the plastic screen before going out of the tank on the way to the fuel pump. Possible solution: cut up a chemical-resistant rubber glove and wire one finger of the glove over the plastic screen, re-install the screen/drain plug. This should keep the sealer from clogging the screen and entering the fuel lines. Always check and clear the vent and fuel lines in the tank after using the sealer! One should also remove the fuel sender before sealing. I just use furnace tape to temporarily close off the filler opening, fuel lines and the opening where the sender goes. I like to take a flashlight and look inside during the process to make sure everything is covered. Before re-installing the tank, remember to clean the coarse screen on the intake side of the fuel pump. This can become clogged and most people do not know it is there. A W 107 series (450 SL etc.) in line fuel filter can be added as a second filter to the system as another line of defense against dirt and rust. It requires a little non-original cut and splice of rubber fuel lines. I wouldn't reccommend it unless you’re really having dirt problems. It will handle the pressure and the volume of a W 113 system just fine. My best advice is keep your tank full during winter storage, drive your car, use a good fuel from a newer gas station ( nice clean new fiberglass storage tanks in newer stations!)

Will, I am not sure I know what you speak of concerning a plastic basket. However, my W 113 tank has been redone, professionally, by a local in my city. The procedure was to remove everything from the tank, then boil it in their vat for 48 hours or so. This removes rust/scale and gas fumes. The latter being most important. Then the tank was coated, with special attention given to the two vent lines on top and the fuel line. I think he actually ran compressed air through these during the drying process. Whatever, the tank is flawless, rustfree, and it has this really neat inside coating. Total cost was $80. After seeing the pix on another MB list a few years ago where a guy tried to dry his tank, after cleaning it at home, with a hair dryer. Resulting in a tank explosion which radically rearranged the tank's geometry and releived a fellow lister of a lot of superficial hair, I decided that $80 was really cheap.

Will, I had a tank renewed by "Renu". It works just fine. They sandblasted the entire inside of the tank, then sealed it. I have had it in service for over three years with no adverse results whatsoever. I guess these guys know what they are doing.

Joe: you can block the fuel line going to the cold start solenoid on the intake manifold, to see if running improves. This will tell you if the solenoid valve is leaking. A correct size steel ball works well, just snug up the fitting on the ball do not overtighten. I DO NOT believe this is your problem. It sounds like you’re starving for fuel. Make sure your fuel filter is clean. If there are large black flakes, a lot of rust or an unusual amount of dirt in the filter you may have to check the screens in the fuel pump and the tank for blockage. I would say it is normal for the pressure in the fuel system to drop when the ignition is off. However it seems that the running pressure is a little low which is usually 14 psi plus or minus 1 or 2 depending on rpms. This low pressure would indicate a blockage or fuel pump problem possibly. Fuel pumps straining to deliver fuel because of blockages or a dying or worn pump will sometimes change tone or get noisier. Where do you have your fuel gauge hooked up? The fuel on these engines circulates back to the tank. The fitting on the return fuel line of the injection pump is a check valve which holds the working fuel pressure in the pump body at 14 psi under normal conditions. When the pressure drops off too much because of fuel delivery problems, all kinds of strange running and starting problems arise.

I had a problem with my 280 SL that developed shortly after I bought it and it nearly drove me crazy. I would be driving along, usually at a pretty good speed, and suddenly the engine would sputter and cut out. This would happen randomly without warning. After sitting for about 5 minutes, the car would usually start right up and be fine. I checked all the normal electrical connections, changed the coil (it looked pretty old), did a tune up and changed the fuel filter. The problem persisted. I knew that I had to determine if the problem was electrical or fuel related. So I hooked up my timing light to one of the spark plug wires, put the timing light in the car, leaving the hood partially open and took off. Then, as the car began to conk out I pulled the trigger of the timing light and determined that the plugs were still getting spark. The problem therefore had to be fuel related. The fuel pump and all the connections appeared fine. It was time to pull out the service manual for some possibilities. Normally, the big blue mercedes service manual has more information than you ever care to read about. But, sometimes, when you are stumped, it is fantastic because it is so thorough. It indicated that the fuel pump should deliver 1 liter of fuel every 15 seconds with the engine off. So, I disconnected the rubber fuel line coming from the pump and put it in a large jar. I then turned on the pump by turning the ignition key one knotch for 15 seconds. It delivered less than half of what it was supposed to! To make a long story short, my frustrating problem had a very simple answer: rust and grud had flaked off of the inside of the gas tank and was impeding the flow of fuel to the engine by clogging the mesh filter at the bottom of the tank. Starved for fuel, the engine would cut out. A simple cleaning eliminated the problem and I eventually replaced the gas tank when I did a full restoration of the car.

How hard is it to take off the gas tank. Mine is empty so that isnt a problem. Is it held on by bolts into the frame ? I dont see any straps so assume this is the case. I see a couple in the back of the tank but havent looked at the front part yet. What do i need to look for there? Anything i should be carefull about beside normal safety issues working around gas and fumes?

It is a very simple job. Remove the filler neck cover that is located in the trunk and then remove the breather hoses. Remove other hoses and grommets and loosen the bolts holding it in place. It's a piece of cake. I got tired of doing it, though, so I eventually bought a replacement. I kept getting some seepage from the seams and there was a lot of rust flaking on the inside.

Fuel tank/Reserve 230 SL 65/9 Liter Fuel tank/Reserve 250SL/280SL 82/11 Liter (Tabellenbuch PKW)

What is the size of the hex bolt on the gas tank drain at the bottom of the tank? Would it be better to hit the ratchet with a hammer to loosed it or use a breaker bar. I don’t want to rip the threads out of the tank.

I used a 13/16" lug nut with a box end wrench around it and stuck it in the hole in the plug (worked great) and I would hit it before I would use a cheater bar you are less likely to twist out the threads this way as a hitting force rather than a constant turning force. This is the same reason for the design of a pneumatic impact wrench.

Finally got my plug out. Bought a 14mm bolt and matching nut; this hex size is perfect for the 22mm drain plug. Welded nut to bolt to prevent it from turning. Tried breaker-bar first, but no success. As already suggested, it took a good burst of impact wrench to loosen it. Bonus: My plug was personally signed by the guy that made it - someone named Ben Zin!

My 230 SL hasn't been driven for probably 10 years, so I assume whatever gas remains in the tank must be pretty gummy. What's the best way to get the gas out -- take out the plug and drain it, or siphon it out? What’s the best way to clean out the tank -- is it necessary to take it out of the car (looks pretty easy, actually)? Do I need to clean out the fuel pump as well?

The injector pump migh be your main problem since it is warned by specialists over and over that it must never be allowed to dry out because the pistons can seize. It might be a very good idea to take it to a Bosch shop and have them get it working properly without damage.

Naj says: I drained the tank by connecting a piece of hose to the outlet pipe of the electric fuel pump at the tank and running the pump by switching the ignition on. Once empty, also clean the filter which is part of the drain plug. When you refill, you need at least 25 litres of fuel in the tank for the pump to work. Any less and it wont start!. On a different occasion, I was able to start the engine with about 4 liters. I used the pump to put the fuel directly into the flower pot through the outlet line on the tank. I also suggest changing the main fuel filter and making sure there is enough oil in the injection pump before attempting to start engine.

Actually draining the tank by running the electric fuel pump is not such a good idea. I'd use the bottom drain first, then remove the tank and have it professionally cleaned in your case. The biggest cause of seal failure in the electric fuel pumps is running the pump until the tank is dry. This causes fuel tank sediments to get distributed onto the seal faces--there's a rotary bellows seal on the main shaft. Also this seal is designed to operate "wet" so that there is a thin boundary layer of sealing fluid (gasoline) between the two seal faces. This is for sealing, lubrication and cooling--sort of the same principles your oil serves on the engine pistons.

Tom Hanson: be sure to replace the screen / plug in the bottom of the tank.

Rodd: I removed the plastic cap in the trunk to access the fuel gauge sender. I removed that from the tank and used a flash light to see in the tank. WOW, what amazing amounts of material in there! I took a screwdriver and pushed it around to verify what I saw. Unbelieveable! So, I drained the tank and removed it (any one need instructions?). I then took 1/2 gallon of the drained fuel, put it back in the tank, and tried to "wash" out the loose material through the filler neck. Repeated this 4 or 5 times. I got a lot out, maybe 32 cubic inches (4x4x2), maybe less, but there is still more in there. This was the night before the Tech Session at Joe's so I wanted to get it back together and it was getting late. I put it back together and it drove better that weekend. I then filled the tank and drove it a lot this week. It has run through that tank with few of the old symptoms. Now that the tank is almost empty again, I think I will try washing out more loose rust this week. I also plan on cleaning the in-tank filter screen, the in-pump filter screen, and replacing the main fuel filter. This will take care of the majority of the problem, but I really need to take the fuel tank to a radiator shop and have it "boiled out", which I assume is not literally boiling it in water but using some sort of cleaning agent to eat the rust away. Then it will have to be re-coated on the inside. What I've done should hold me over until after I get moved into the new house in the end of September. I may also look at replacing fuel lines as well. I don't know the difficulty or cost of that. By the way, I looked at Star Quality's web site as a reference for pricing a new tank - $825! I'll be boiling & coating, thank you.

Will: I just finished doing all this to my tank and fuel system, using POR-15 products, and am happy with the results. Let me know if you need any tips. The metal fuel lines under the car were fairly easy to remove, but of course it is a messy proposition if your car is coated with 37 yrs. Of undercoat/oil/grime, as mine is. There are about 5 brackets, held on by a single bolt/nut each, holding the 2 fuel lines and the single brake line. Surprisingly, none of the hardware had rusted, and removed easily (one advantage of oil leaks!) You will need a helper, or some vise-grips, to hold the head of the mounting bolt inside the car while you undo the nut from the bottom. You'll have to remove the LH seat, and lift some carpet, to get to the bolt heads. K&K has the fuel line, but being in a foreign land, I plan to replace it with generic fuel line, and bend it myself to the required shape.

Rodd: hello. Yes, please provide a detailed description of your experience applying the POR-15 coating to your fuel tank. I imagine I will be doing this in October.

Tom: just to clarify, I assume you mean that you used products specially formulated for the inside of the tank that are offered by the manufacturer of POR-15. You did not use the actual rust coverter product known as POR-15, correct?

Will: Correct, I used the "Fuel tank Sealer" made by POR-15 for the inside, and the "regular" POR for the outside. I'll post the whole thing a bit later...

Hi Rodd, here is my fuel tank experience you were asking for: basically, just follow the directions on the products. What I did: Removed my tank after draining, and drying out. Emptied as much garbage as i could by shaking it all around. I then lightly banged it all around, to loosen any stubborn rust. Emptied again. Mine dropped about 1qt. of rustflakes! I considered taking it to be hot-tanked or steam-cleaned, but there is a plastic collector ring about 8"dia/4" high around the bottom drain that might be damaged by those processes. So I took a high pressure water hose to the insides, swirl around and drain, repeat several times till it runs clear. Then used Marine Clean degreaser. Por says to do that until it runs out clear, but if there is any surface rust at all in the tank then no run-off will ever be totally clear. I did mine 4 times, still not running out clear, but figure most important is no grease left - surface rust is ok, the sealer will take care of that. Then used Metal Ready to prepare metal for sealer. Flush, and let tank dry totally. Cover all openings you don't want blocked by sealer - I used duct tape. I also blocked-off the fuel cavity at the lowest point in the tank, below the filter-screen (attached to drain plug) so that sealer wouldn't go in fuel supply tube. Poured in the tank sealer, swirled all around for about 30 mins, then drained - about 80% comes back (not reusable). Use some compressed air to blow through the 2 little tubes, and the fuel-return tube, to make sure they are not being blocked by sealer. The outlet tube I had blocked from the inside, so couldn't clog. I repeated this several times over the first few hours while the sealer was setting up. I turned tank around a few times while drying - I figured if I wanted a thicker coating anywhere, it would be the top inside surface, because that would be uncovered the majority of the time, and the most prone to rusting. The outside of the tank was very rusty as well - I removed as much as possible, first chipping, then with steel brush, then Marine cleaned, and metal readied. The most important was to get all old grease/undercoating off so the POR will stick properly. Then 2 coats of POR rust coating. If your tank is not as bad as mine, you may not have to do everything I did - the instructions on the can of Sealer explain that. The POR goes a long way - i think i used less than 1/2 pint for 2 coats on very rusty tank exterior. Make sure the filter screen comes out with the drain plug; careful with the plastic collector ring; don't clog the little vent tubes/fuel return tube; remove the sending unit.

I will look for those products and attempt ASAP (in a couple weeks?). The exterior of my tank is not undercoated or anything and still has a smooth, rust-free finish. Question: After using the high pressure water to remove rust, how did the Marine Clean degreaser do it's job? Did you let the tank dry overnight before trying the degreaser? Does a wet surface cause a problem? It sounds like this procedure will postpone the purchase of a new tank for several years.

I used the Gas Tank Sealer on my tank. Worked very well. Just make sure you get all of the gas and gas residue out. Go to http://www.por15.com/tankseal_fuelpreserve.html. They should be able to direct you to a local supplier (they even had one in hawaii) or if not you can just order the gas tank repair kit over the internet through them. The POR-15 product is for external uses, like stopping rust on your firewall. Makes it a nice shiny black that supposedly will never rust again. Just don't get it on your hands or it'll be two weeks before it comes off.

The degreaser is water based, so there is no need to let the tank dry before that step. You put the degreaser in, tape up all the openings, swirl it around, then let it "work" for a while in one position before draining it. I repeated this several times, letting it "work" in a different position each time. As I said, my tank was really badly rusted - you may not have to do all these steps. I wanted to do this job right the first time, because like any kind of "paint" work, preparation is 90% of the final product. I am quite confident that my fuel tank will last the life of the car now, and some lucky sod may even buy it from a junkyard in a 100yrs.!

I have not done this on my 230SL but have on a 57 Chevy Pickup I used to own. Put those glass do-thingy-ma-bobs (they kind of look like clear throat lozenge) that you use in a vase to hold the flowers, into the tank. Roll the tank around for about 30 minutes letting the glass beads break up a bit and "cut" the rust out, and wash it out. The abrasive action of the glass on the inside of the tank takes just about any and all rust out of the tank.

Gas Cap

I just bought a book by Lawrence Meredith which had pictures of several restored SLs. They all appeared to have gas caps that were chromed. I was told that the locking gas caps were originaly highly polished aluminum. Does anyone know for sure?

Frank says: a chrome plated cap is the one most frequently encountered on the 280 SL. However, aluminum caps will be encountered on later cars, and the parts catalog lists an optional cap.

Is the ‘70 280 SL supposed to have a "vented" filler cap? I get significant pressure build-up in the tank when it gets warm. Removing the cap releases the pressure and the tank gives a audible sigh of relief. The vapor chamber, valves and all lines test out fine.

When I remove my gas cap, there is never any pressure in the tank, nor a vacuum, as far as I can tell. Before I got a new cap, I think vacuum was in fact building up.

I had pulled over to the side of the road where someone was parked with his 1969 280SL with the hood open. He apparently had a coil failure, and someone was getting one for him. In the meantime we talked about his car, very nice example with mid blue paint and gray leather interior. He mentioned this problem with the gas cap, whenever he removes the cap a gallon or more of gas would come gushing out. I told him that he should check his ventilation system starting from the black plastic line from the engine compartment to the reservior in the tank to the outlet next to the muffler under the bumper, and it was concluded that a rock was wedged into the black plastic line under the floor pan which pinched the vent line shut and caused a lot of excessive back pressure in the tank when it heated up from the outside temperature(mind you this was during the summer), and was relieved when the gas cap was opened. Might want to check that out too.

Section 00-88 of the manual describes the fuel evaporative emission control system for US vehicles. For 1970/71 MB used a setup that prevents fuel evaporative emissions. The compensating tank has a valve system built in that allows outside air to be sucked in when a vacuum exists in the gas tank; if the gas tank is under pressure, however, the excess pressure is vented into the crankcase, where the gases get burned off. So if you wanted to maintain that fuel evaporative emission control system, you wouldn't opt for the "mit Lueftung" gas cap.

Usually, a new cap can be ordered to your existing key code.
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