My Petrol Gauge

[Mikejj]

I have had the same petrol gauge and sensor since the original build some years ago. It was supplied by Marlin as part of the kit. It has never worked properly, however. When I fill the tank, it only registers just over "half full". Since I have no confidence in it, I hesitate to see how gauge registers when I am low in fuel. Has anyone else had this problem and how to I rectify it? Any help would be appreciated!

[CABRIOBOB]

Re: My Petrol Gauge

Apart from buying a new gauge and sender unit with matching ohms value or contact ETB instuent for advice. I have rebent the tank float arm on several cars and this has improved the problem to about 90% plus in most cases.

[Mikejj]

Re: My Petrol Gauge

Thanks Bob. I thought of bending the float tank arm. I will try this first. Thanks for your suggestion
Mike.

[greyV8pete]

Re: My Petrol Gauge

Hi Mike.
I have the same problem. Mine only reads 3/4 full on a full tank. I have never run it below 1/4 on the gauge, even though I carry a spare, as I don't want to ruin the HP fuel pump if it runs dry. I have the 3.9i engine. Re my other thread about the rear diff support failure, while I was moving the tank back and upgrading the support straps, I found a slight fuel leak around the sender flange so I am also planning to bend the float arm down a bit while it is out. Peter.

To Cabriobob - How much did you bend the float arm? Peter.

[CABRIOBOB]

Re: My Petrol Gauge

Peter,
It all depends on what type of float you have. Firstly to test the gauge, remove the sender wire from the float and hold to an earth to see if you gauges goes to full. If you get the float out of the tank and conect the wire to it, switch on the ignition and move the float from the lowest position and the gauge should read empty, then lift the float to the top and the gauge should show full. note the position of the float and arm inrelation to the top of the tank (flange base of sender) when gauge shows full, also if the float is higher then the arm on the sender so allowing the gauge to read less if the sender was in the tank and full of fuel. All you need to do is rebend the the arm slightly allowing the float end to lower then retest by resetting the sender back in the tank.

[Mike]

Re: My Petrol Gauge

Peter,
It all depends on what type of float you have. Firstly to test the gauge, remove the sender wire from the float and hold to an earth to see if you gauges goes to full. If you get the float out of the tank and conect the wire to it, switch on the ignition and move the float from the lowest position and the gauge should read empty, then lift the float to the top and the gauge should show full. note the position of the float and arm inrelation to the top of the tank (flange base of sender) when gauge shows full, also if the float is higher then the arm on the sender so allowing the gauge to read less if the sender was in the tank and full of fuel. All you need to do is rebend the the arm slightly allowing the float end to lower then retest by resetting the sender back in the tank.

...............and if you find the range on the guage is not sufficient, you could shorten the arm length. It's easy enough to cut the end off and solder it back on shorter: or put a small V\ bend in the arm to use up some length.

I am not an electrician, but if you add a resistor in parallel to the sender, I believe that reduces the resistance, and therefore increases the range of the gauge? Could an electrician please confirm that this is correct before someone tries, please?!

[greyV8pete]

Re: My Petrol Gauge

Hi Cabriobob & Mike. Many thanks for the feedback. I will have a play with it once the diff is back in. Meantime back to the decorating Peter.

[greyV8pete]

Re: My Petrol Gauge

Help! I have just finished resealing the fuel sender with a new gasket and some blue hylomar. While it was out I bent the arm up a bit as it wasn’t allowing the float to reach the top of the tank. I now wish I hadn’t bothered as the calibration is even worse as shown below!

GALLONS FUEL IN (APPROX)	GAUGE READS
EMPTY	Minus1/4 (OFF SCALE)
1	Minus1/4 (OFF SCALE)
2	Minus1/4 (OFF SCALE)
3	Just below the “0”
4	Just On the Zero Line
5	1/8 full
6	¼ full
7	3/8 full

As I am more interested in the “near empty” readings it looks as though I will have to remove the sender again and bend the arm down this time, so that it at least gives a reading when the float is further down in the tank. I can live with ¾ meaning “full” but I can’t live with zero meaning anything from 4 gallons to empty!

No I haven’t yet done the tests that Mike suggested above, as the job has dragged on long enough with all the “add-ons” (see separate forum post) and I really want to get the car back on the road and try out the new diff ratio following fitting of the billet m/c mount. I can easily lift the boot floor plates and tinker with the sender separately once I know what I should be doing.

It occurs to me that the real problem is that the float arm seems too short. It is only about 6” long and the tank is deeper than that so the float will never be able to follow the fuel level at the extremes of max / min.

Does anyone else know how long their float arm is? Or how long it should be for a “Marlin” O/E gauge?

Peter.

[Mike]

Re: My Petrol Gauge

Help! I have just finished resealing the fuel sender with a new gasket and some blue hylomar. While it was out I bent the arm up a bit as it wasn’t allowing the float to reach the top of the tank. I now wish I hadn’t bothered as the calibration is even worse as shown below!

GALLONS FUEL IN (APPROX)	GAUGE READS
EMPTY	Minus1/4 (OFF SCALE)
1	Minus1/4 (OFF SCALE)
2	Minus1/4 (OFF SCALE)
3	Just below the “0”
4	Just On the Zero Line
5	1/8 full
6	¼ full
7	3/8 full

As I am more interested in the “near empty” readings it looks as though I will have to remove the sender again and bend the arm down this time, so that it at least gives a reading when the float is further down in the tank. I can live with ¾ meaning “full” but I can’t live with zero meaning anything from 4 gallons to empty!

No I haven’t yet done the tests that Mike suggested above, as the job has dragged on long enough with all the “add-ons” (see separate forum post) and I really want to get the car back on the road and try out the new diff ratio following fitting of the billet m/c mount. I can easily lift the boot floor plates and tinker with the sender separately once I know what I should be doing.

It occurs to me that the real problem is that the float arm seems too short. It is only about 6” long and the tank is deeper than that so the float will never be able to follow the fuel level at the extremes of max / min.

Does anyone else know how long their float arm is? Or how long it should be for a “Marlin” O/E gauge?

Peter.

Peter

Plot your figures on a graph and you'll see the answer straight away (- gallons on x axis, gauge on y).
You need to bend your float down by half your tanks depth - if it is possible. The good news is the readings appear to be very linear once they start to register. My quick graph suggests you'll need 12 gallons to register full though.

[greyV8pete]

Re: My Petrol Gauge

Thanks Mike. Yes I did notice the 1/8 increments for every gallon. Will try bending the float down although I suspect that then the gauge will read 3/4, as before, at anything above 1/2 full. First priority now is to have a drive with the new 3.38 diff Peter.

[greyV8pete]

Re: My Petrol Gauge

The fuel gauge error was still fidgeting me so yesterday I pulled the sender out again. I measured the resistance of the sender which on the 20k ohm range was 0.031 in the “full” position and 0.247 in the “empty” position. I then gave up trying to figure how this would help me! I did notice that the sender resistance track is not circular but made up as a printed circuit board with the “windings” parallel and horizontal. The pick up wiper blade swings in an arc across this so the movement / sender resistance output mimics the float movement in the tank. Most ingenious I thought as it is a simple way to achieve a linear output.

I then went back to basics and found a length of wooden dowel which I poked down through the sender hole. I marked the top of the tank on this and measured the distance to the bottom end, which is 7 inches. As it is notionally a 12 gallon tank I then divided this 7 inches into twelve equal marks (each 7/12ths of an inch apart). When I put the dowel back into the tank the fuel level was at the 7^th mark. As I had put 7 gallons in the tank I was really pleased with this! I then bent the float arm down until the gauge reading was just over half full. At least I will now know when I have a half full tank!

I will get a longer length of 8mm dowel and transfer the markings on to this. As the filler neck is quite straight and nearly vertical I can then use this to check the gauge calibration from outside the car and see what “reserve” there is when the gauge reads “empty”. If I keep the dowel in the boot it can also serve as a fuel gauge if the electric one ever packs up! Result! Peter.

[greyV8pete]

Re: My Petrol Gauge

After recent runs fuel gauge now reads 1/8 full. Dowel dipstick shows 4 gallons left. Peter.

[Dane_Rescueman]

Re: My Petrol Gauge

Pete, when I rebuilt "Moll" I chenged my sender to a matched VDO including gauge. I find that my escort van tank has no baffles so the gauge needle can oscillate a lot whilst driving. It is accurate on full but a bit pessimistic on empty - like you I have not run out to find out my actual range for the same HP pump reasons. A year after my rebuild, I started getting soft cut-outs on fast runs. After a short stop it would run again or a while. I expected all sorts of snags such as intermittent prime pump or wiring to both pumps, an air lock in the swirl pot but no. I found the filter clogged with goo. I had sealed my sender unit flange with Hylomar which now certainly looked like it had been eaten away. Hylomar states on the info sheet that it is OK with fuel, oil and antifreeze but can it cope with the greater amount of ethanol in the fuel now? I've cleaned it all off and made thick rubber seals instead. "thinks, doesn't ethanol attack them too?" Oh well, back to the drawing board!