Fuel gauge flickering

[Brennie]

Hi
I have an early 230SL.. the fuel gauge kinda works but it’s flickering.. I guess I have the early external float sender unit..
I never really know how much fuel I have left.. a bit disconcerting at times..
where should I be looking to stabilise the needle? And, should I have a low fuel warning light? Mine is the vertical spare wheel early 230…

[rogerh113]

I have had that problem several times with my 230SL in the past, and have resolved it by cleaning the sender.  If memory serves, there is a labyrinth on the bottom white plastic cap that can collect junk. Pretty easy to unscrew the small bottom nut, disassemble the float, and clean it up.  Also make sure the guide wires for the float are clean and everything moves smoothly.  Pretty easy, and with any luck it will work well after that. 

regards -- Roger

[rwmastel]

If memory serves, there is a labyrinth on the bottom white plastic cap that can collect junk.

If there is junk collecting on the sender, then doesn't it mean the fuel tank should be cleaned?

[rogerh113]

The 230sl has gone for years between fuel sender flareups.  I pulled and replaced the tank many years ago, and that is no fun.  Draining the tank is not much fun either, but maybe a service station is better equipped for that.  The sender cleaning can easily be done at home.  During that, it should become clear if particulates are in there, and to what degree. 

One could drain the tank if there is concern there is a buildup of junk in there.  Replacement of the tank is useful if you feel that the tank itself is deteriorating.  One bad gas fill could result in some particulates in the tank.

If the sender cleaning works, and the sender continues to work over time, then a practical solution.  The fuel goes through a filter up at the engine, which addresses a bit of junk getting into the tank via the gas.  Apparently Mercedes expected, and planned for, that.

Sometimes the simple solution is best.  If that doesn't result in a fix, at least more information is available, and then moving on to more aggressive measure might be required for a fix. 

[BobH]

The flickering fuel gauge was probably the reason they changed to the tube type of sender.  The early floats must be like a boat in the ocean, bobbing up and down when the fuel sloshes about.  The tube type probably provides some form of dampening

Not sure you'll ever stop the flickering gauge unless the sender and gauge is replaced with the later tube type

According to the wiring schematics all cars had the low fuel light

[Brennie]

I guess so…I think the gauge and the sender have to be a pair to be properly calibrated..they are not interchangeable are they?
I mean,you can’t replace a float sender with a tube version and expect the gauge to be accurate or,work at all?
Thank you for the info re the warning light…which of the three lights is it supposed to be? Mine must not be working..as is not my “door open “
warning light..the only light I see is the red alternator light..

[BobH]

The later senders have a different resistance range, so won't work with the early gauge.  There is probably a way to change the resistance in the gauge to match the new sender, if you have a degree in resistance, or nuclear physics!.  if not then, yes you need to change the sender and gauge

As far as i know the door open light on the cluster wasn't connected on 230's, this light is just for the low brake fluid, but i may be wrong.  On later cars it was wired for both functions

EDIT, it doesn't look like this lamp was wired for either function on 230's, they don't have the brake fluid level switch fitted

I've never seen my low fuel light illuminate, but i'm guessing the lamp is integral to the gauge, but again, i may be wrong

[rwmastel]

The low fuel light should work, I've seen it on my late 230SL.  There is a very detailed discussion going on in the "Electrical and Instruments" board right now about fuel senders and gauges and testing.  I think it's up to 3 pages of posts!

[Brennie]

Thank you
I’ll head there now…

[franjo_66]

The later senders have a different resistance range, so won't work with the early gauge.  There is probably a way to change the resistance in the gauge to match the new sender, if you have a degree in resistance, or nuclear physics!.  if not then, yes you need to change the sender and gauge

As far as i know the door open light on the cluster wasn't connected on 230's, this light is just for the low brake fluid, but i may be wrong.  On later cars it was wired for both functions



EDIT, it doesn't look like this lamp was wired for either function on 230's, they don't have the brake fluid level switch fitted

I've never seen my low fuel light illuminate, but i'm guessing the lamp is integral to the gauge, but again, i may be wrong

Hi Bob
My 1965 230SL  has the low fuel light and it definitely comes on when level is low.

Best regards

[BobH]

Hello all, i'm not saying the low fuel level lamp doesn't come on, i said all cars have them, it's just that i've never seen mine come on as i don't let the fuel get that low, so i couldn't confirm where the lamp was located.  Brennie's question was "where is the light located" I guessed it's in the back of the gauge, rather than on the cluster with the other warning lamps

[Brennie]

Thank you Bob
I have three little squares where lights should be on my instrument cluster.. one is  blue( high beam) one red( alternator) the third is a mystery.. it doesn’t come on when the door is open( only the under dash courtesy light does that) and I’ve never seen it on for low fuel.. although I too try not to let it get that low, but I’ve been close sometimes.. small tank on an early 230…

[BobH]

Hello Brennie, the third light is the door open/low brake fluid light, this wasn't wired on 230's, so will never illuminate

I think the low fuel light is actually in the gauge itself

[Brennie]

Ah!
I’ll go and look more closely..
Thank you

[franjo_66]

Ah!
I’ll go and look more closely..
Thank you

Yes what Bob mentioned is spot on.
The low fuel light is in the fuel gauge itself. Should have mentioned that in my post !

[getsmart]

If its any help, I measured the resistance of my fuel sender on my early 230sl

full = 12.4 ohms
empty = 192 ohms

If it is flickering it could mean also your fuel sender circuit is going open. This could be caused by dirt/debri or a faulty sender or suspect wiring to/from the sender to the gauge or the gauge itself.

To localise the problem rather than empty the tank initially you could in theory disconnect the cable from the fuel sender and place a resistor (between the 2 wires you've disconnected) with these values or anywhere inbetween and see if it continues to flicker or stays stable. I'd be inclinded to get 2 resistors of around 20 and 180ohms and try both for a period of time.

Alternatively you can measure the resistance of the fuel sender with the cable removed at varying fuel levels.

R/Joe

[AdelaidePagoda]

Mine is a Jan 1964 and has the same flickering fuel gauge. It is stationary when stationary and gets quite the flicker when in motion.
Have never tried to fix it as previous explanations state it is ‘normal’ for the 230’s given the fuel float system. Now I am used to it and know when it is getting low, although I have never seen the low fuel light on so not sure if I should try and see if it works 
Also do not have the open door light wiring.

[rwmastel]

The low fuel light should work, I've seen it on my late 230SL.  There is a very detailed discussion going on in the "Electrical and Instruments" board right now about fuel senders and gauges and testing.  I think it's up to 3 pages of posts!

Again, there is a long, detailed thread about fuel sender units, gauges, testing, wiring, etc.... over in the Electrical and Instruments board.  I recommend you all read that and comment over there, as it's all the same topics.

[ja17]

The "twitching" or flipping needle on the early lever and float systems, was caused by a worn out electrical coil in the sender. The sliding contact in the sender eventually wears through the coiled electrical wires, cutting through the tiny hair size wires. When this happens, the needle reacts by flipping to full and back, until fuel is refreshed in the fuel tank and the sliding contact rests on a good section of the coil. The problem repeats itself when the fuel level allows the fuel sender to again contact the damaged coils. The newer tubular fuel sender does not have this problem. However, as mentioned, with the newer sender, the "aunt maze" of passages built into the bottom of the sender, must be kept clear.