Main.TrailIndexPage | Fuel System | Fuel Pump

Fuel Pump

This component is part of Fuel System.


The Fuel Pump delivers the fuel from the Fuel Tank to the Fuel Injector.

The W113 series of cars uses one of two types of fuel pumps:

Bosch Fuel Pumps
Bosch p/nW113 TypeDelivery PeriodMercedes p/nComment
0 442 200 006230SLApr 63 - Jan 65001 091 13 01"Tall" Pump
0 442 200 008230SLFeb 65 - Mar 66001 091 13 01"
0 442 200 007230SL/250SLApr 66 - Nov 67001 091 13 01"
0 442 200 007280SLDec 67 - May 69001 091 46 01"Tall" Pump until VIN 010241
0 442 201 002280SLMay 69 - prod. end001 091 52 01"Short" Pump from VIN 010241


The fuel pump is reponsible for delivery of fuel from the fuel tank to the fuel injector. There are two styles of pumps used on the Pagoda.

The pumps are electrically driven, 12 volt DC (direct current), low pressure pumps of the rotary vane type. The early (tall) electric fuel pump are of the Dry motor variety in that the motor portion of the pump is sealed from the vane portion of the pump and fuel does not flow through the armature/brush areas.

The later (short) electric fuel pump are of the WET Motor variety in that the motor portion of the pump is not sealed from the vane portion of the pump and fuel flows through the armature/brush areas. This fuel flow cools, lubricates and cleans the brushes and commutator.

For more functional and operational details please refer to the articles referenced above.


Link to related components where appropriate.

How to fix a gelled-up pump

The consequence of leaving a fuel pump (either the Early (tall) electric fuel pump or Later (short) electric fuel pump style) sit for long periods without drainage, is that the pump will be "gelled" up.

The recommended procedure is to dissassemble and clean out the fuel pump. With the Later (short) electric fuel pump, this is pretty easy and all you'll be replacing are the -o-ring seals unless there are other problems in there that you may want to fix--like worn down brushes.

With the old style Early (tall) electric fuel pump, you can try running lots of clean gasoline through it in the hopes that it will flush everything out, but experience of pulling dozens of these apart, is that the two chambers covered by the side plates really get gunked up badly over time.

If the pump is not leaking, you can try partially disassembling for a more thorough cleaning. It's just that there is a high probabilty of doing more unintended damage to this pump since the bottom plate and side plate screws have a real tendency to break off when trying to remove them (see also the article Early (tall) electric fuel pump rebuild). The side plates and bottom have to come off to do the cleaning properly and if you can get it this far, you might want to go the extra step and do a rebuild it while it's apart.

There are repair kits available from MB sources for the newer, small style pump that will contain the brushes. You can also special order these from a number of brush manufacturers--you'll need to carefully measure the originals and specify a copper-carbon type brush. On the smaller pump you just need to make sure that the brushes have a small cut-out where the brush shunt wire enters the brush. Otherwise you'll have a difficult time slipping the brushes under the brush holder to solder them in place. You'll see what I'm talking about once you disassemble and take a good look at the original brush. Repair kits and brushes for the old pump are not available through MB. The brush dimensions are different on the older, large style pump, and you don't need to worry about this cut-out on the larger, old style pump. However, the brushes are annoying to replace, and unless they show visible signs of wear, do not replace them.

Fuel Pump Test

The flow rate of 1 litre per 15 seconds should be the flow rate measured from the return line at the tank end. The high volume is needed for the fuel tank pick up to work properly. The flow from the return line goes into the fuel strainer assembly (flower pot) through a venturi port, this creates a suction that draws more fuel in and fills the flower pot up to a higher level than the rest of the tank. This helps prevent fuel starvation when cornering and braking at a low fuel level.

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.

There is only one fuel filter, which is by the engine. In the gas tank there is a drain plug that has a built-in screen and then there is a plastic baffle/screen built in the tank. When you change the paper fuel filter, tear open the old one and look to see what is being filtered. If there is lots of junk, then it is time to remove the drain plug and see what is in the tank.

Frank Mallory says: I think there is another screen in the electric pump. To clean it, simply reverse the pump leads and run the pump backwards for a few seconds. This is usually done only if you think you have blockage at the pump, not part of scheduled maintenance. The only fuel filter subject to scheduled maintenance is the fine fuel filter up front. After changing it, be sure to bleed the filter housing via the small horizontal screw on top.

I would appreciate inputs regarding installation of the fuel pump on my 230 SL. I'm planning to reinstall the original fuel pump, which has been out of the car for a year. Now my question: does the fuel in the pump have access to the electric motor and its brushes? If so, is there a procedure for getting the air out of the pump before applying voltage, in order to prevent ignition of an air-fuel mix inside the pump?

Will: from my experience, the fuel does surround the brushes and armature of the electric fuel pump. The fuel acts to cool and lubricate the motor. I have also wondered if one could cause an explosion when first filling a dry tank and pump. But, it has never happened in all the years I have been doing this. Just pour gas into the tank, the gas runs into the pump and then you start the car. So far I am still alive to tell you somehow it works.

The hardest part of changing the fuel pump is not getting soaked in gas when you disconnect the line from the gas tank. What I do is to have a bucket under the line and when I remove it from the pump stick an old spark plug in the line, if it drips just tighten a clamp over it. The return line from the tank to the pump needs to be plugged also, a large screw works well for this line. On my car the nuts holding the screws that hold the pump bracket were not captive. I had to rig a wrench to hold the nuts in the trunk. The electric connection needs to be on the proper poles for the pump to run. There was no need to bleed the pump after installation. Entire job should take about 1 - 2 hrs.

The electric fuel feed pump has a ring seal that seals the motor shaft from the pump vane assembly. There is no fuel at any electrical parts on the pump. The pump housing consists of a vane pump, a seal, the housing, an inlet connection, outlet connection with check valve, o-rings and fittings.

Frank: you can improvise a fuel line clamp by taking a pair of vise grip pliers and placing a large socket on each jaw. Adjust the pliers so that when it locks, the fuel hose is squeezed shut between the sockets. I think the original 113 fuel pump became unrebuildable for some reason, so that nearly everybody converted to the small-design pump when the original one stopped working

In my car the original fuel pump was removed and exchanged by a rebuilt one. The problem is that it is very noisy, specially from the inside of the car. I have discovered that is not just noise, is the vibration of the pump what makes this anoying sound, the original metal piece surrounding the pump is not there and I guess that's the problem, any solutions?

Frank: if your car had a large-design pump that was converted to small-design, there is or was a mounting kit for this conversion. There are rubber standoffs that go between the pump and the body. If these are broken or missing, it could be causing the vibration. A W 113 pump should be barely audible from inside the car.

The pumps for the early W 113's had a dry motor I believe. There is a mechanical seal on the shaft which keeps fuel from entering the motor. Between the motor and the seal itself there is a drain with a tube to let any leakage escape. I had one that had a good leak coming out of the tube. I took the pump apart and stretched the metal bellows on the pump to put extra pressure on the seal and I also used silicone sealant on the shaft around the seal before putting it together. Worked like a charm with no leaks. MB does not supply rebuild kits for the older style pump and they recommend using the newer style which does have a wet motor ( you have to buy or make a mounting flange). They are pretty easy to rebuild just make sure you put the motor case on the same way it came off. If the poles are reversed the motor turns backwards. You don't know how long I spent trying to figure out wat was happening. I took it apart several times, half the time I got the poles right but the pump would leak for some reason or another when I did it get it right necessitating its removal again.

How tough is it to rebuild a fuel pump? How can I determine if I should do this, have it professional reconditioned (Bosch?), or replaced? What parts do I need?

I rebuilt mine a couple of years ago (in the driveway, with gas spilling on my face). Once I got it on the bench I broke most of the (aluminum?) screws getting them out. I re-tapped it and put in brass screws. Bought a rebuild kit from Star Quality - had some gaskets and brushes for the motor. Mine has been working just fine for the past couple of years, but not sure I would do it again.

Do you know where to get the rebuilt fuel pumps for $250 (half the price of new-$500) ? Also the rebuild kits seem to only include brushes and seals. Can you completely rebuild these pumps just with the MB kit? What about the actual parts (vanes and bearings etc.) of the pump?

I just replaced my fuel pump and don't want to toss the original. The motor works, but the pump section is completly clogged with rust and crud. This is the large type electric pump that was original with the car in '68. I hear these are worth their weight in gold (I assume only if working). I've seen the rebuild kits which do not seem to address the pump section. This would be a massive rebuild as most of the hardware is fused. I tried to get into the inlet section to clean the screen and the screws would not turn. Probably a lost cause, but as rare as these are, I'd hate to toss it. Any ideas?

Will Samples says: I do not believe the old style, large fuel pump is able to be successfully rebuilt. There is a proprietary seal inside that is not available. Anyway, I tossed all mine. Let me know if the pumps can be reworked.

I was able to stop a leak on the old style pump. I pulled the pump section apart which contained a mechanical seal to stop any gas from leaking out the shaft. It consists of a bellows which push against a sealing ring. I used some silicone sealant around the shaft itself and the bellows (not on the moving surface). I then stretched the bellows a little to put a little more pressure on the sealing ring when put back together. I was pleasantly surprised when the pump worked without any leakage. I am sure I got a little lucky but maybe it will save someone a lot of money and keep there car a little more original since the old style pump is no longer available as far as I know.

There is apparently a filter inside the fuel pump that gets clogged with rust from the tank. Could be that this has clogged again since you replaced the pump. This filter is another undocumented feature from MB. I have not cleaned it on mine yet either but someone told me that it is definitely there.

I wonder how many good fuel pumps have been replaced and discarded by frustrated owners. It sounds like your mechanic is "grasping at straws" with the suggestion of filling the fuel tank. My problem of sputtering with a loss of power was due to rust in the fuel tank flaking off and impeding the flow of fuel through the filter in the bottom of the tank. I discovered the problem by running a simple test recommended by MB. Simply disconnect one of the rubber fuel feed hoses either at the fuel pump or at the engine and direct it to a container. Turn ignition switch one notch to turn on fuel pump for 15 seconds. Fuel pump should deliver 1 liter of fuel in 15 seconds. When I ran the test, I had much less fuel in the container so I knew my engine was starving for fuel. When your tank is near empty, drain the remaining fuel into a large gas can using the fuel pump to pump it out. You'll be able to reuse the fuel later. With the tank empty, use a large hexnut or allen wrench to unscrew the filter at the bottom of the tank. The filter is cylindrical mesh about 3 inches tall and 1 inch diameter. You can clean it or replace it. It is readily available from MB dealer or other suppliers. Someone reported similar symptoms that were caused by inoperative venting of the fuel "compensating" tank. To test this, loosen your gas cap to allow venting, then drive as normal to see if the symptoms go away. Lastly, I noticed that you do not mention that your ignition points were replaced and gapped. This can also cause the same symptoms. (I know because I've experienced it! Double check the ignition timing and check that there is no "play" in the distributor.

The filter is a mesh filter at the inside bottom of the fuel tank, not in the pump itself.

Joe Alexander: the filter screen in the fuel pump can be removed and cleaned by removing the fuel intake hose on the electric fuel pump amd unscrewing the fitting on the fuel pump. The filter screen is under this fitting.

Hans Strom: there is a mesh screen at the fuel feed pump inlet, but this is on the small type pump only. The earlier, large pump does not have this. I enclose a few lines from an earlier posting of mine: "Brushes and seals are available as spares for the small type fuel feed pump (fitted from May 1969). Another point to check is the fine mesh strainer (screen) placed onto the inlet hose fitting. The fitting is often very tightly stuck in the pump alloy body, use a good socket to loosen it. Allows you to clean out this filter mesh. I should mention that since the large pump cannot be fully rebuilt (lack of spare parts) many W113s have during the course of time passed been fitted with the newer, smaller type pump.

Got my large-style fuel pump all apart (only broke 7 out of the 14 screwheads!). I found there is rotational "play" between the impellor and the shaft, ie: I can rotate the impellor about 20 degrees or so before it actually starts to turn the shaft. I that how it is supposed to be? The "key" locking the impellor to the shaft is a very small chrome-looking piece, and does not look damaged (ps: Yes, there is a small brass internal filter screen on the inlet side, and a light duty plastic disk check-valve on the outlet side).

Unfortunately, my car sat for ~6 years with 1/4 tank of gas. The rust sediment apparently makes it past the screen in the tank, and because the fuel pump motor itself gets immersed in the gas, the rusted metal particles "short out" the pump intermittently, and cause a reduction in fuel flow. I know that the ultimate solution is a new tank; but has anyone had success with the new "plastic" coatings? I'm going to run a few tanks, and see how it goes.

I just received my mail-order of POR-15 "Fuel Tank Sealer". I just put my fuel pump back together as well. Your 250 pump must be different from my 230, because the electrical part of mine has no contact with fuel. I should be re-doing my tank soon. I don't know how long you can wait because I'm not the fastest guy in the world, but I can let you know my experience when I'm done.

The two fuel pump bearings are standard DIN sized bearings. On later models of the large style pump, they actually used the sealed, lubed for life bearing. I know what you have because I'm working two pumps that have the older, opened style bearing. I'm simply going to replace these with the newer style shielded "sealed for life" bearings. Will get these through Maryland Metrics in Baltimore--they have a web site if your're interested--don't have the URL handy. I've yet to solve the sliding ring seal problem completely, but here's what I've come down to. On the pumps I'm working the main seals look okay. I've removed them as follows. There is a small snap ring on the main shaft right above the seal. You must remove this carefully. After that is removed, there is what they call a tab washer that prevents the seal from rotating independently from the shaft--this should lift right off after snap ring removal. Remove the two nuts that on the motor side that hold the "Can Assembly" (main motor body" and you should be able to lift the entire motor assembly minus the armature off the pump body. This will expose the two small screws that hold the armature plate and other bearing in place--remove the two screws and you should now be able to press the armature out from the pump side. Be sure you've already removed the snap ring I mentioned other wise you'll do a number on the seal. After removing the armature, you'll be able to assess the status of the bearing and the main, seal face, the small o-ring on the main shaft and of course the main bellows seal. All of mine appeared okay although I do intend to replace the small o-rings and to stretch the bellows seal on replacement to ensure more pressure on the seal face. I think all of this will make more sense once you "get in there".

What's the function of this "fuel pressure damper", because I think it's not installed in my 230 SL. Where should it be? What happens if one runs without this damper?

The fuel pressure damper is attached to the LH motormount, immediately behind the fuel filter. It should have 2 fuel lines connected to it. It is connected "in series" in your fuel system, between the injection pump and the fuel return line to the tank. It is supposed to even-out the fuel pressure pulses in the system. I don't think it is a critical part of the system, because mine is stiff as a board, and the car still ran.

Last night I consulted the Spare Parts Book, and it shows that "fuel pressure damper" was introduced since engine number around 3100 -series 10 and 20- (I don't remember the exact number). And mine is 127981 10 002164, so it's correct. As you think, it doesn't seems to be a critical part of the system, because more than 3000 230 SL was made without it !

What is this "fuel screen in electric fuel pump"?. Because I know the main fuel filter on the engine compartment, and the filter attached to the drain plug of the tank, but I don't know this fuel screen in the electric fuel pump.

Rodd: I can't recall exactly where this was oriented on the pump, as this was the first time I've seen it. Basically, where the fuel enters the pump, it passes through a removable connector nut of some type that has a screen built into it. It has only about an 8mm inner diameter or less. I assume the nut w/ screen is replacable as an individual part number, but I haven't looked for that. More simply, it can be cleaned out if clogged. Both fuel pump types have this screen. The filter screen on the drain plug appeared to be a very fine brass mesh, and cleaned up nice and "brassy". If it appears black, it might be worth removing the drain plug and cleaning it. Not sure if this could be the cause of a "miss", but i found my distributor vacuum unit had a small air leak. Not big enough to hear, but when removed the hose from the throttle body and sucked on it, it wouldn't hold the vacuum. It ended up being where the hose entered the vacuum unit, not the diaphram itself.

Joe Alexander: the fuel pump fitting on the left is the output and the mechanism in the fitting is a check valve. I quickly dissassembled three early pumps and found no screen in the two fittings on the right. However the third early pump did have a screen built in the intake fitting! So we can safely say that some of the early pumps had screens and most likely the earliest examples of the early pumps did not. However the screened fitting fits fine in the other two pumps. So someone with an early electric fuel pump could retrofit a screened fitting to their pump if desired. The early pumps are much more difficult to rebuild and parts may not be available. The later 113 electric fuel pumps all have screens built in the intake fitting of the pump. These should be checked for blockage if you are having fuel tank problems. The fitting requires a 27mm wrench size for removal on the later pumps and a 22mm wrench size for removal on the earlier type. Either pump will work fine however the mounting brackets and rubber mounts are different and must be kept with the correct style. Remember that these pumps are feed fuel by gravity and the correct position on the car is critical. If you have rigged the mounting you may be causing some running problems. Now if you are not sure which pump you have the early units are approx 7" long (180mm) and the latter units are approx 5.5" long ( 140mm). My dealers parts book edition "C" shows both styles. It calls for replacement of the early style with the latter. In addition to the latter pump #001-091-4601 the following list of mounting parts must also be used; (1) #108-470-0281 mounting plate, (3) #114-328-0581 metal/rubber buffers (mounts), (1) #113-470-1548 protective cover. The metric hardware required for the change is; (3)# 912004 005100 lock washers, (3) #000934 005004 nuts, (3)#000127 006203 lock washers, (3) 000933 006016 screws. This hardware is not special, but is standard metric nuts and bolts as required. These pumps are expensive new. However rebuilt units and kits are available from some suppliers. Also fuel injected sedans and coupes of the era used the same electric fuel pumps!

All the early pumps that I've disasembled save one have the screen filter. The early one without the filter has a screw on inlet fitting instead of the slip on fitting on the later early model pumps. This particular pump also has a screw that can be removed from the top to allow greasing of the top bearing. These pumps are not any more difficult in my opinion than the newer pumps to re-build. The two bearings are both DIN sized bearings and once you figure how to get the main shaft seal out the pump is relatively easy to disassemble. I also believe the brushes are much easier to replace than on the newer pump because they are much more accessible. The part of this pump that causes the most problems in rebuilding is the main shaft seal. It is a metal bellows mechanical seal. I've not beeen able to find replacements for these but in most cases what I've found is that this seal can be cleaned up, stretched ever so slightly and the rubber o-ring on the shaft itself renewed to ensure a tight fit between the top of the main seal and the armature shaft. Occaissionally the seal will develop a small leak. I've used the POR-15 paste to seal a few of these and it seems to work so far. Aside from the main seal, these pumps typically seize up because they sit with old gasoline in them and the varnish causes the impeller to seize. Many times just removing the bottom cover and freeing the impeller is all that is required to get you going. All the other o-rings needed to seal the pump are readily available. The brushes can be gotten from most electrical repair shops and cut to size if needed. A word of caution though is in order when dissassembling the pumps. Most of these have been in service for a long time and the screws have pretty much "welded" themselves to the aluminum pump body. Before attempting to remove the screws, they need to be thoroughly soaked in penetrant. If they don't move easily, some heat may be in order. Expect to break at least a few of them. If you need any more details in how to go about dissassembling or "rebuilding" let me know.

Rodd: can I clean the fuel filter that is in my gas tank, or do I have to buy a new one? It gets clogged with rust from the inside of the tank. I will be removing it this weekend and would like to have a new one on hand, if necessary. I have not looked at it yet to determine if it's a metal or plastic screen. Also, how big is than recessed hex bolt? It looks like 24mm or so. I'll be needing a tool for that.

The original strainer is a copper or brass mesh. It can be cleaned. The new ones are not as nice. I seem to remember that I was able to find something in my toolbox that worked as a wrench. It might be the same size as a spark plug wrench or something like that. It is not difficult to remove.

Yes, the screen is cleanable. Mine was brass, but I think someone else said there are other materials as well. Some de-greaser and a toothbrush cleaned it up real nice (rinse toothbrush well before re-using :-)). The plug is a 22mm hex - I bought a 14mm dia. bolt and matching nut; the head size is perfect for the 22mm drain plug. Welded nut to bolt to prevent it from turning. Mine was very tight, and i ended up using an impact wrench to rattle it loose. The plug also has an 0-ring - mine was re-usable, but any automotive/hardware store should be able to match it up.

Albert: if you prefer to change it, a new one costs about $17 / Euros, and the part number is 111 470 0686, including the seal ring. There's an exact torque to screw it, because with less torque you may have leaks, and with more torque you may destroy the thread. In my workshop manual you can read: tightening torque for the fuel tank filter is: 0,8 - 0,9 kg m (5,8 - 6,5 ft lbs)

As I feared would happen, the original fuel pump in my 230SL was kaputt, so I've replaced it with the new, smaller version (part 001-091-52-01, adapter bracket 108-470-02-81, two-ended rubber buffer bolts 126-988-00-11). The adapter bracket and pump fit fine, but I'm having trouble installing the protective canister which fits over the pump. The inlet to the pump is lower than on the old one, and the outlet from the pump is higher and comes out at an angle pointing upward instead of straight out as before. I can't find any way to mount the canister so the fuel hoses go through it without way too much chafing. Is it necessary to modify the protective canister when installing a new-style pump? If not, how can the hoses be routed through or around it?

The newer pump goes normally with the other protictive canister which is round and not box-like like yours. Either you cut holes into your old canister our you go and hunt for the newer replacement. It is kind of expensive, if you want, you can even rebuilt it yourself. Sometimes, used (and new) ones show up for instance on ebay.

Albert: the newer protective canister (I think is the third version) for the short pump is MB part number 113 470 1548, and as Achim told you, is not very cheap: a new one costs in MB Classic in Germany 187,27 Euros / $ USA.

Naj: how far down from the trunk floor should the new pump be fitted? The old type pump on a 280 SL I saw nearly scrapes the bottom of the protective cannister while the new pump on my 230SL is about 4 inches off the bottom of the canister.

I've seen these mounted two ways. One way uses the original mounting flange-looks sort of like a "cross"--attached directly to the new circular mounting bracket whcih in turn is attached to the pump via the rubber mounts. This makes for a fairly long "package". I've also seen it mounted where the original "cross" is not used and the circular mounting plate attached directly to the bottom of the car. When I had the smaller pump in my car this is how the shop installed it. I could not use the original shield because the holes were not located where the hoses could go to the pump. I later replaced this pump with a rebuilt larger style pump and I've now got the original shield installed. While I had the smaller pump installed it worked properly as mounted. As long as the fuel pump intake is below the level of the fuel tank outpipe I don't think it matters a whole lot how high the pump is. Gravity is what gets the fuel to the pump--I don't think the pump provides a whole lot of suction on the tank side.
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