Fuel tank, venting, and fuel gauge

[Melburnian]

Last post for a while I promise. I dont want to be seen as a serial poster!
My '64 230sl manual appears to have a new (er) fuel tank.
The fuel tank has the 2 connections for venting pipes but they are  just blocked off. On the early ( my) car the fuel tank was vented through the fuel cap. There was no venting pipe or the little overflow box attached on the right side of the boot in later models.
My car is suffering  from fuel starvation when the tank is low. If I stop and remove the gas cap theres a rush of air and the car will start.  It's quite possible my fuel cap is not original.So I want to install breather pipes and canister and overflow as per the 280sl.

My fuel gauge is the original float unit which jumps about when the car is in motion.It doesnt give a true reading when fuel is getting low, still showing half a tank.  So...my question is -might my newer fuel tank be shallower than the original so the length of the sender unit is not correct? How can I identify which model fuel tank I have and determine which sender unit  is appropriate? Will I have to alter the fuel gauge also to suit a different sender unit?
Does anyone know a part number for the little expansion/overflow tank that lives in the rear right trunk panel?

I  hoping one of you well learned guys will suggest the easiest solution fo my fuel starvation and incorrect fuel level reading g problems! Thanks, Simon Miles.

[WRe]

Hi,
in the Technical Manual here you'll find a lot of information you need: https://www.sl113.org/wiki/Fuel/Start.
There had been 2 tank sizes: 65 and 82 liters (after chassis number #7205) with 2 different fuel sender's. How much is yours?
Part numbers you'll find here: https://nemigaparts.com/cat_spares/epc/mercedes/1/fg/113044/249/47/001/ or
https://www.sls-hh-shop.de/main/en/mercedes-230-280sl-w113-47-fuel-tank-c-3_76 or https://www.niemoeller.de/en/w113/w113/B044/470/.
...WRe

[Aaron h]

Well, is this "rush" of air the result of a positive pressure or negative pressure?  Since you're having fuel starvation issues I'd have to assume a negative pressure is at play here.  The tank has to breathe.  As gas is taken from the tank and returned the tank can experience negative and positive pressures.  In addition, as the tank gets hot and cools the same will occur. 

You'd probably save a lot of time and money buying the correct fuel lid.  If the current one doesn't have a calibrated pressure relief (positive or negative) then that could be half of your problem.  And yes, if your car originally had the early 65 liter tank, and then later fitted with the 82 liter tank then the sending unit AND fuel gauge would have to be replaced in unison.  The later style sending unit will not let the early fuel gauge read accurately, and vice versa. 

[Pawel66]

I am not a mechanic and my experience is somewhat limited, but if I may:

1. If I had a fuel tank with breathing through the filler cup, I would look for an original fuel filler cup. To install the 280SL breathing system (probably not the latest one, but the open air one) you would need to fit the pipes in the tank, lead the metal lines in the trunk that are screwed to the floor, install the expansion tank and lead the line outside with the cone at the end. To do it properly, you would need to cut out mounting holes in the side trunk panel. It is, I think, even more work and parts with the latest closed breathing system. It also may smell a bit in the trunk at times, it takes attention to keep it tight. It may be simpler and maybe less expensive to stay with original solution. If you decide to go for breathing system - there are hundreds of posts on it on the forum, as well as info in Technical Manual.

2. On the fuel level sensor and gauge: please pay attention to the remark in Aaron h post: if you replace the sensor, e.g. for the later tube type, you also have to replace the gauge in instrument cluster. It will not work otherwise. Maybe you had smaller tank in the car before, then you need to replace both sensor and gauge. But perhaps your sensor float is getting stuck and does not travel to the bottom or the resistor wire is damaged or dirty. Does the reserve light come on? If does light up - you may indeed have components from a smaller tank. If it does not light up, you can test the bulb and if the bulb is ok, it may mean the float does not travel all the way down. It is not a big deal to remove the sensor and refurbish or replace it.

[Melburnian]

Hi Pawell66.
This car is new to me so I am still feeling  way. Its had a multitude of "repairs" and improvements done which are not documented. I just have to continue to familiarize myself with the model.
I am sure the fuel tank was replaced because my 230sl should not have connections for breather hoses on the fuel filler pipe  but mine has them. Because it has them it would be very simple to connect 2 rubber hoses and the small overflow tank that is correct for the 280sl. But I dont see this tank offered on any classic part supplier pages.
The mystery is the wrong reading of the fuel gauge. My gauge tells me I have half a tank of gasoline when it is actually nearly empty. If I have a larger tank, than the original wouldnt I have the reverse problem ie,. the gauge reading empty  when the tank is still half full.
I understand that the gauges and sender units are not interchangeable  but I'm not meen to have to replace both..hoping theres another way. Thanks for your contribution.. cheers

[Pawel66]

I see.

In 280SL you need the long (tube) sender style and corresponding gauge. You said you had the float type gauge and its reading going up and down is annoying. You then need to buy the long style sender and see what the gauge is showing. If the reading is wrong, means you need to buy and replace the gauge to late type. If you take the gauge from a car other than Pagoda - in my opinion it will not work, as the length of the sender needs to correspond to the scale of the gauge.

If you want to keep the current sender: if you want to try if your current sender works from full to empty - you need to check it as I wrote. If it works and you want to keep it and the gauge shows wrong reading, you may need early type gauge. Someone replaced the tank, I have no idea if they replaced sender and gauge together with it.

The seal for fuel gauge is A 110 471 01 80.

Sender and gauge later style (plenty of them around), e.g.:
https://www.niemoeller.de/en/w113/w113/B044/470/15
https://www.sls-hh-shop.de/main/en/54-elektrical-equipment-at-body-54-a-instruments-c-3_2339_82
https://classic-mercedes-parts.com/en/w113-interior/fuel-indicator-late-model-w113-w111-after-008953-0005428803.html
Sender, Mercedes: A 110 542 12 04, $220 but you do not pay shipments.

On the evaporation systems:
There was a US version (enclosed, big expansion tank on the left side of trunk) and open  version.

For open version:
1. On the expansion tank (no clue where in Australia you could find it):

https://www.niemoeller.de/en/w113/w113/B044/470/d47064-expansion-tank
Mercedes dealer, A 115 471 02 68, about $230 (USA $).
Seen on ebay some time ago, now it is gone..

2. Hardware (pipes, brackets, cone, trunk side panel, clips): Mercedes or SLS. It will depend if you get the expansion tank with long hoses or just the tank. Anyway, the plastic nipples will probably brake-off, you will need ot install some small pipes there, but that is for later.

[Shvegel]

Melburnian,
You mean this one?
PM your address to me and it’s your’s free of charge.  It was listed as the big tank I needed but came as the wrong part.  Better on your car than a shelf in my garage.