fuel tank capacity

[langa01]

Hello all,

For the first time today I ran out of fuel, luckily as I was driving to the petrol station so I got there with the inertia..(just). I filled up the tank very carefully (ie slowly) and it took 49.7 litres which seems to indicate that the tank holds just 50 litres. Now according to the manual (1971 280SL) the tank should hold 82 litres! This tank is a replacement of the old tank that had rust and i bought it via one of the MB spares suppliers (not MB official) and even though this was many years ago I am only now starting to drive the car following a lengthy restoration. The tank has no dings etc so the shape is completely unaltered. The question is, would it be at all possible that I was sold the "wrong" tank? is there any other MB that may use a similarly shaped tank but with reduced capacity (I guess the only way would be if it is a slimmer tank...)? Any help would be greatly appreciated. Many thanks

[Jordan]

As far as I know there was no 50 litre tank, only 65 litre on the 230SL and 80 litre on the 250 and 280SL.  Don't know when the actual change occurred but you can read more about it here.  https://www.sl113.org/wiki/Fuel/Tank

[Benz Dr.]

82 liter tank started with 250SL production. It's possible to fit the larger tank on the late 230SL.

[Kevkeller]

Maybe your tank wasn’t empty.

[Pawel66]

Or you did not fill it full, e.g. if the pump nozzle was long and you stuck it long..

I do not remember dimensions of the tank, but let's assume it is roughly 0.8mx0.8m. Then each 1cm of fuel level is good 6 liters.

You may also have some of the channels in the flower pot blocked.

It is also a simple look at the picture in tech manual and see how the tank looks like and how it fills the space. Then you can insert a hand on the fuel pump side and feel the distance to the trunk floor, wich is, more or less, between 1 and 2 cm.

[langa01]

Thank you so much for all your replies. I have been thinking about this today (it is really puzzling) and one theory that is evolving is that the fuel pump may be wrongly connected to the return side of the tank (ie the upper pipe) instead of the feed lower feed pipe and therefore the pump is not able to suck fuel past a certain level. That will explain (Perhaps) that the car runs out of fuel after 50 litres where in fact there are other 32 litres sitting there but not accessible to the pump! I don't think blockage of the flower pot etc is a likely cause given that the tank is brand new so tomorrow I shall have a good look at those connections to check if my theory holds any water (or rather fuel). I don't really know if this connections are potentially interchangeable so as to be the possible cause of the problem. All I have been able to do so far is some desk research but have not been underneath the car to see.
Keep you posted on this but in the meantime any other ideas are more than welcomed.

[mrtzmd]

The fuel feed and return lines are different diameters and I do not think the car would have ran if the pump was not connected properly. My guess is you may have a blockage at the drainage screen or a non oem tank. Good luck.

[enriquegarcia]

Seems very unlikely that you mistakenly installed a new tank half the size of the old. Did the reserve warning light come on before you ran out of gas? If the mystery persists, simply run the experiment again and when the engine dies for lack of gas, check contents of the tank by removing the fuel sender from inside the trunk. My bet is that you will find it is half full. Good luck!

[Pawel66]

Seems very unlikely that you mistakenly installed a new tank half the size of the old. Did the reserve warning light come on before you ran out of gas? If the mystery persists, simply run the experiment again and when the engine dies for lack of gas, check contents of the tank by removing the fuel sender from inside the trunk. My bet is that you will find it is half full. Good luck!

This is a great idea. When you remove the sender, have a new gasket ready just in case (you probably have a new one, but it is easy to tear it). Slide out the sender very slowly out of the tank as fuel may be inside - it is flowing out of the sender very slowly. And be generally careful when working with fuel.

[Mike K]

I've had exactly the same issue with my '71 280SL. I replaced the tank with a new tank 5 years ago and have never been able to get more than about 50litres into it. The old and new replacement tank looked approximately the same size to me; I was so happy to get rid of the old rusted tank that I never bothered to compare actual dimensions when I fitted the new one.

I've emptied the tank through the bottom drain where the fuel filter screws in and then refilled, and still can't get more than 50 litres into the tank.

It's worth noting that I also replaced the fuel pump with a new Bosch pump as well as a new fuel sender and new fuel lines.
The only explanation that I can come up with is that I suspect these non OEM replacement tanks have a smaller capacity than 80 litres.

Compared to the grief I had with the original rusted fuel tank,  I've decided to live with the reduced fuel capacity of the new tank and am happy to have no more fuel flow issues. 

Best
Mike

[Tyler S]

Just a note about service station gas pumps. If your tank vent lines are blocked, the gas handle will continue to click off  as if the tank is full when it is actually less than. Pulling back slightly on the gas nozzel boot will allow vapor to escape and not build up in the tank.

I have also seen 1 aftermarket tank that had the fill pipe welded in that was protruding more than 2 inches into the inside of the tank. Along with the blocked vent line, it effectively created an air pocket in the top of the tank and couldn't be completely filled. 

[Mike K]

Thanks Tyler, in my case I cleared the vent lines as well.

The fuel gauge also indicates full once I've put the 50 litres in.
Would it show full if there was an air pocket in the tank?

Best
Mike