Calibrating fuel gauge

**tangiers** · 18th October 2010, 03:36 PM

My fuel gauge worked properly until I had my fuel tank replaced with an aluminium tank. Now, when the tank is full, the gauge shows half-full. The needle does go down as the tank empties but will never go beyond a half-tank. I told the mechanic that replaced the tank that I thought it might be necessary to re-calibrate the gauge (I'd Googled the problem) but after leaving it their for a week was told that the problem was that the float had a leak. The float was replaced but I discovered (after taking the car home and filling the tank) that the problem is still there. I don't have it in me to drive out to the mechanic again and wait another week to get the car back (and my wife is unlikely to agree to picking me up again!).

Am I correct in my diagnosis?
And if so, anyone had experience in re-calibrating a SIII gauge?

**Timj** · 18th October 2010, 04:16 PM

If the tank us the same size as the one it replaced then there should be no need to recalibrate. Actually I will rephrase that slightly, if it is the same internal height. The sender works just on changing resistance based on the height of the float. If it still travels the same distance down from full to empty then there will be no difference. If the height of the tank has changed then you might need to look for a different sender or look at different ways to bend or extend the arm on which the float is mounted so that it's full travel is between full and empty. If that is not the issue then I would be looking at earthing issues with the change of tank material and possibly mountings.

TimJ.

**stage one** · 19th October 2010, 08:25 AM

I guess you could pull it out and move the float/arm up and down very slowly and see what happens?

**Randylandy** · 19th October 2010, 09:03 AM

I know in Aircraft youcan re caliberate the fuel gauge easyly must be some way to do it

**tangiers** · 19th October 2010, 11:12 AM

Originally Posted by Timj

If the tank us the same size as the one it replaced then there should be no need to recalibrate. Actually I will rephrase that slightly, if it is the same internal height. The sender works just on changing resistance based on the height of the float. If it still travels the same distance down from full to empty then there will be no difference. If the height of the tank has changed then you might need to look for a different sender or look at different ways to bend or extend the arm on which the float is mounted so that it's full travel is between full and empty. If that is not the issue then I would be looking at earthing issues with the change of tank material and possibly mountings.

TimJ.

Tim, I think you may be on to something with the earthing. The tank is the same capacity and I wouldn't imagine the shape would be any different. I will try to see if I get a better earth what the result is.

**weeds** · 19th October 2010, 12:09 PM

a baffle is not restricting the gauge?

**Mick_Marsh** · 19th October 2010, 01:33 PM

My Mercedes fuel gauge is being calibrated as we type.
The mechanic has sent the gauge and sender to an automotive instrument repair place. I can find out who it is if you wish but best you find one locally.

**101RRS** · 19th October 2010, 01:46 PM

Originally Posted by weeds

a baffle is not restricting the gauge?

Or the side of the tank. I took the sender out of my tank and did not note its orientation. When the sender went back in I just put it in the way I thought it should go and then had the same problem.

As the fuel went down, the float was hitting the side of the tank and staying there.

Garry

**tangiers** · 21st October 2010, 10:50 AM

It doesn't have baffles (makes an awful noise when you stop!). Something obstructing the float makes sense: the needle on the gauge seems to be stuck on the half tank mark for a very long time before it actually starts going down. If there was a bad earthing (or a calibration issue), one might expect that the gauge would go down normally (albeit reading inaccurately) from the half-full mark. However, if the float was obstructed so it couldn't go up all the way to the top to reflect a full tank, it would stay in that position until the fuel level dropped to a level where the float started to drop itself?

Thanks for all the responses.

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