350SL Fuel Gauge

[keith mathison]

I am the proud owner of a 350SL 1979. My problem is the fuel gauge is not showing the correct amount of fuel in my car. When I fill the car with petrol, the fuel gauge points towards the F. As the petrol is consumed, the fuel gauge does not go past the ¼ marker. Since the gauge does not go past this point the red warning light never comes on to show I?m now using the reserve fuel. I?ve no way of knowing how much fuel is left in the car.
Can anyone tell me how to rectify this problem

Many thanks.

 

[Andy]

Hi

I would guess that the fuel sender guage is at fault. To get to it you have to remove the partition at the back of the boot. Held in with loads of 10mm bolts. The reserve light usually stills comes on if the vheicle is using the reserve fuel. Whether the guage is reading correctly or not. Does the light come on with the ignition & go off when started.


Regards

Andy @ www.mercedesservicing.com

 

[keith mathison]

Andy,
No, the light does not come on with the ignition. In fact it does not come on at all. Since discovering this problem I normally fill the car with petrol as soon as it reaches the ¼ mark to make sure I don?t run out of petrol.This fuel gauge cost £79 + vat. ?(money non refundable). How certain are you this may be the fault & not any thing else?

 

[Arnie]

Hi,

I had this problem on my last car and changed the sender to no avail. It might have been the gauge itself, but never found out. Also someone told me that there is also some interface electronics between sender and gauge, but I didn't fiind them.

 

[keith mathison]

Arnie
I imagine there would be electrical connection connected to the sender gauge to send the information (eg the amount of petrol in the tank) back to the display unit. But remember when I fill-up the car, the gauge tell me the petrol tank is full but not when its past the ¼ mark. That may suggest the interface electronics is ok.

 

[Arnie]

Usually, the sender connects straight to the gauge, but as I said, I am not sure with these cars.

It could be that the sender gets stuck at the 1/4 way point and this is what I thought was the problem with mine, but having changed the sender, it was still the same.

Your low-fuel lamp should, however briefly light when you first turn the ignition as a sort of "bulb-check". You may therefore have a faulty lamp too.

I'd check the sender to be sure and then have a look at the gauge. Maybe Andy can say whether there are any additional electronics. Do you have a haynes manual? You could also go to your dealer's parts dept and if you ask nicely they should be happy to print off the EPC pages for the fuel guage system so that you can see what all the bits are.

 

[Malcolm Brown]

Correct - the sender connects straight to the gauge and to the reserve light. On the sender, pin 1 (blue/black wire) -> guage; pin 2 (blue/green) -> reserve light; pin 3 (brown) -> earth. The sender has a switch that closes at a given level (about 10 litres?) to operate the reserve light.

I'm with Arnie on this. If the reserve light is illuminated at ignition on (before starting), then it's probably the sender, otherwise its probably the reserve light. Or an electical connection, of course.

 

[njpumphrey]

E300TD Fuel gauge problem

I have just the same problem with my "new" E300TD. The chap I bought it from said he had once been caught out and has filled it up early eversince. Would there be any more wisdom out there on what could cause this fault and how to fix it? It is just a little niggle with an otherwise superb car, but it would be lovely to sort it out.

 

[turnipsock]

I thought the low fuel warning light was independant of the gauge. I would think that the problem is related to the sensor float, initially.

As the fuel level drops the resistance increases, it should get to about 80 ohms when the tank is empty. It sould be about 2 ohms when full.

"Does the reserve warning lamp light up when you switch on the ignition?" You say that it doesn't so it looks like you have a problem there as well.

The gauge and warning light are easy to check. The gauge is a bit like an ampmeter, so when the resistance increases the current drops and the gauge falls to zero.

 

[njpumphrey]

Apologies - my problem is not quite the same since the light does come on with the ignition. Thanks for your help Turnipstock - it looks like I am going to be getting my ohmeter out today!