Fuel Tank reserve light on first time

[Kayvan]

Got my reserve light to go on for first time ever.....and its bright!

The 2/4,  R label of the gas guage gas always given me angst.  I would much pefer the usual quarters and E.

My needle was below the 2/4 hatch mark &  near the "R" for about 1 week with 2 drives of  50 miles each. 

I was reluctant to drive and thought for sure I would get stranded; and my last few fill-ups are each 10 gallons max, so I knew this reserve area near "R" has a lot of capacity, maybe 2 gallons.

Finally when the needle touched the corner of the R, the light went on. 

The manual says I have 20-22 miles of range. I drove another 10 miles and will fill up....

Nice to know German technology works after 40 yrs.....and that back wash/top up stale fuel is now gone

[JamesL]

My gauge is broken so I refill based on the odometer. Basically a top up at 250 miles or so. That said, I did a haul back from Cornwall the other week and was pretty sure I'd make it home - although only just - as I was through 210 miles but mostly flat out or sat in stopped traffic.

5 miles from home, trusty light came on so I filled up. I am wondering as to the value of stripping my dash to replace the fuel gauge when my system works quite well!

[scoot]

My gauge is broken so I refill based on the odometer. ...5 miles from home, trusty light came on so I filled up. I am wondering as to the value of stripping my dash to replace the fuel gauge when my system works quite well!

Just curious - how do you know that your gauge is broken and that it isn't the sender?  (if it's the sender it is a very easy fix and I would be happy to sell you a used one or you can get one from a scrap yard and clean it yourself...)

[J. Huber]

Yes, it is a bright little guy... Somewhere in the early archives is the first time I saw mine (or it may have been on pagoda113)... Anyway, I had had the car for about 15 years and never saw it -- I was surprised (and glad) it worked so well! I rarely let the tank go below a 1/2 or a 1/4 -- but at least I know I'll get a reminder if I do...

[JamesL]

Just curious - how do you know that your gauge is broken and that it isn't the sender?  (if it's the sender it is a very easy fix and I would be happy to sell you a used one or you can get one from a scrap yard and clean it yourself...)

My mechanic tells me he's checked all the back end stuff and it's all working. So narrowed it down to the gauge end. I have the gauge (Thanks to Mr Caron) and will try that. But have a feeling that I may need to come back to you for a sender!

Actually, my central glass on the cluster is bugging me. When the sun is on it, I can see dirt/grime on the back side of the glass so there's one benefit for getting it off!

[scoot]

The sender is easy to take out (and you may want to replace the $2 gasket).  If you tip the thing back and forth you should get variable resistence on two of the terminals.   If you are, then it's working.  When the float goes all the way to the bottom, it shorts two other contacts that control the empty light - so the two are unrelated actually inside the sender.

[Peter van Es]

Also have a look at Al Lieffrings PUB Presentation. About halfway through he has a very clear diagram of the fuel gauge / reserve light wiring.

Peter

[ejboyd5]

Is it only on the later M-Bs that the reserve light activates as a bulb check when the ignition is first turned on?

[scoot]

Is it only on the later M-Bs that the reserve light activates as a bulb check when the ignition is first turned on?

I have never heard of that or seen that.  I have a 67 250 SL and a 71 250 C.  It doesn't do that on either.  (and it does go on when the tank is low)

[Dave Gallon]

Somewhere in the 1980s (probably with the 126s but I have not checked this fact) Mercedes arranged that all the dash lights come on when the ignition switch is placed in the driving position (position 2 using the traditional naming convention) without the engine running so the driver can verify all bulbs are good. As the electrical systems became more sophisticated (and complicated!) individual lights represent the status of a processor and individual lights are extinguished as the respective processor passes its system test.

While you may want to remove the glass while the center cluster is removed, it is not a requirement to change the fuel level gauge. The gauge is removed out the back of the cluster.

If you replace the fuel level gauge, I would suggest plugging in the center cluster under the dash to verify correct operation before installing the cluster back in the dash. Even if the problem is at the dash end of the circuit, you may find a broken connection in the cluster or cluster wiring.

[Kayvan]

Had a 16 gallon fill up (on 18 gallon 250 SL US tank) today....first time ever. I had driven 10 miles when light came on so, gues there was a half-gallon in there.

I held the trigger at 1/3 power an let it slowly flow in (tried full power and it created some bubbling/weeping at nozzle grommet)

I could have gone another gallon, it clicked off twice, but it was a hot day and didnt want to risk expansion or cap-seal weep.

I would encourage all to let there red-light come on and drive another 10-15 miles.

I think many of us are driving with watered down/topped up/backwash reserve fuel, from multiple fill-ups.

At least it sounds that way from the number of posts on stuck injection pumps, rough idling, etc... probably stemming from stale fuel.

It ran very well.