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Sticking Fuel Gauge

Sticking Fuel Gauge

Finally the snow is going and the rain has washed the salt off the roads. I took my XK140 ots out for about an hour. All is well after a long winter except the gas gauge. Whenever the gas moves in the tank the needle will for a moment slam to the top then return to indicating its' level. Any ideas? Bill 1955 XK140 ots

Sounds like you're losing contact momentarily between the wiper and the wire-wound resistor (fuel level sensor). Correct solution would be to pull and clean or replace the sending unit. Might be due to corrosion from sitting for a while - Run it around for a week and see if things improve (the wiping action of the slide on the wire may 'scrape' off some oxide coating). If you pull the sensor for refurbishment, be sure to drain the fuel tank first, pull the bottom filter/plug, open the filler cap, and flush it well with compressed air (or carbon dioxide) first, to preclude the popssibility of a spark-induced explosion! Oh, yes, disconnect the battery, too!

Good luck! This might actually 'heal' itself with a little time (I am always suspicious of self-healing hardware, however!). - Larry Schear Twin Cam, Inc.

These gauges go to full scale when the wire to the sender is disconnected. It could be a loose connection at either end. - MIke Morrin Finally the snow is going and the rain has washed the salt off the roads. I took my XK140 ots out for about an hour. All is well after a long winter except the gas gauge. Whenever the gas moves in the tank the needle will for a moment slam to the top then return to indicating its' level. Any ideas? Bill 1955 XK140 ots

Sounds like you're losing contact momentarily between the wiper and the wire-wound resistor (fuel level sensor). Correct solution would be to pull and clean or replace the sending unit. Might be due to corrosion from sitting for a while - Run it around for a week and see if things improve (the wiping action of the slide on the wire may 'scrape' off some oxide coating). If you pull the sensor for refurbishment, be sure to drain the fuel tank first, pull the bottom filter/plug, open the filler cap, and flush it well with compressed air (or carbon dioxide) first, to preclude the popssibility of a spark-induced explosion! Oh, yes, disconnect the battery, too!

Good luck! This might actually 'heal' itself with a little time (I am always suspicious of self-healing hardware, however!). - Larry Schear Twin Cam, Inc.

These gauges go to full scale when the wire to the sender is disconnected. It could be a loose connection at either end. - MIke Morrin

Dear friends

Now that my 120 dhc is finally in my garage and the weather is fine here in Switzerland I drive the car everyday. It works marvelously. O.K. Once the traffic lights and the horn ceased to work, but the next day when I tried to fix it, it already worked well again.

But now I have a sticking fuel gauge. It stays on a level where the light for fuel just has gone on, and doesn't move even when I have twiced filled it up. In the beginning it was the same but after a while it worked again, now it doesn't. Any hints what I could do? - Zoran Mitrovic

Zoran,

(I am making the assumption that the fuel sender setup is the same on a 120 and a 150.) There are two wires on the sender on the side of the fuel tank. Remove both wires. Fuel gauge should go to empty and light should go off. Ground both wires to chassis. Fuel gauge should go to full and light should come on. This checks out the fuel gauge and the wiring. Assuming this works, and I suspect it will, you may have a problem with the float. It may have a hole in it rendering it unable to float. On a 150 it is possible that if the float wire is bent improperly, interference with the side of the tank (where the relief for the spare tire is) will cause it hang but I think the shape of the 120 tank is different. I will defer to those who have 120's. - Dick White Zoran, The 120 gas gauge sending unit is located on the top of the tank. If the gauge is sitting at empty and the light is on, the float has probably has a leak. In a earlier E-mail from Dick White he tells you how to check the gauge & wiring.

If the gauge is good and the sending unit suspect, then plan to take out the sending unit. Here are steps to remove the unit & repair the float.

1. Remove the wood floor in the boot covering the center top of the tank. The gas filler cover may have to be removed. (depends on the floor design) 2. Remove the small nuts and washers attaching the wires to the sending unit. Put in safe place! 3. Remove the screws attaching the sending unit to the tank. Again, put in safe place. Rotate the unit slightly to break the seal and remove. 4. Shake the sending float and listen for liquid sloshing. If yes, then force the liquid out of the sending unit. This can be done by shaking or enlarging the pin hole slightly. I do not suggest using heat because of the gasoline fumes. Coat the float with gas tank sealer once the gasoline is out of the float. 5. If the float is OK, then use an ohmmeter to check the internal reostat. Ground one probe of the meter on the unit body and the other on the one of the terminals. Movement of the float arm should show one of two signatures depending on the terminal being touched. One signature will be an even and smooth motion of the ohmmeter needle. The other will be either a zero ohm at one certain end of the travel or infinite at the rest. If this doesn't happen, the sending unit has one or both sides not working. I've seen some e-mails on this part so won't elaborate until we know more! 6.Use new gaskets! Reverse steps 1, 2, and 3 to place the unit on the tank - Cleo Bay

Cleo, I've been noting the discussion on the fuel gauge question for Zorans 120, and over the weekend I noticed that the guage on my 150 is doing a similar dance. It seems to be stuck at 1/4 tank even at fill up, although it does move toward empty as you would expect as you use up the fuel. I suspect a leaking float. Any idea as to how to get to the float on the 150DHC ??

Bill Burke

Bill,

The fuel gauge sender assembly on the 150 is mounted to the side of the tank. You don't have to remove anything to get access. Otherwise, follow the same instructions suggested by Cleo Bay for the 120. Use lots of WD40 to loosen the screws first. The screws holding the assembly to the tank for the 150 are available from a good hardware store (#5-40) but you don't want to have to extract the broken bits (I broke two of mine). The gaskets are available from several suppliers. I got mine from British Auto/USA. Also, be careful not to bend the wire that the float is attached to. It can hang on the back of the tank where the spare tire relief is as it travels up and down. - Dick White

Fuel 'floats', weird fix, but it works. Sometimes its really difficult to get the fuel out of a float (carb or fuel tank floats) in that the hole that let the fuel in, often a hairline crack, wont let the fuel out so easily. When I had the problem I reluctantly tried a fix that a fellow Jag club member suggested: OUT OF DOORS - put the float in a pan of boiling water, I used a small camp stove, the fuel will boil out in a hurry and the fumes wont be a problem in that: A. you're out of doors, B. there are only a little fumes, and C. If you are like me, you will be out of range if something bad does happen. The procedure worked like a charm, since them I have done it several times, alternately soldering up the cracks or using Epoxy glue, either seems to work fine. - David M Drenzek

To correct leaking carb. floats, I've had great success in the past using red Loctite. Use the Loctite cleaner/accelerator if desired. After making sure the float is completely emply and dry (a few days in the hot sun does the trick) I just flow a little red Loctite around the seam. It will always find the smallest leak and the seal will not break down in gasoline. - David Sales

Suggestion: get water boiling, remove from heat so that ebullition stops and then AWAY from naked flame, dangle float in the water on some wire. REMOVE AS SOON AS ANY BUBBLES THAT EMERGE STOP. If you don't, you'll end up with water and not petrol in the float. Petrol's volatile enough to not need water at more than about 190 deg F to get it to evaporate. So long as there's more pressure in the float due to the "evaporating" petrol, you'll get it all out.

If the pinhole/crack can be identified, I personally would clean the area with emery paper/wire wool, heat with a SMALL electric soldering iron and then seal after fluxing, with a good non-rosin cored tinman's solder. Personal choice, though..... your mileage may vary, as they say. - Dick Clements

If you have any questions or comments send e-mail to: ted@jag-lovers.org
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