MilesA Posted April 24, 2012 Report Share Posted April 24, 2012 Recently the fuel gauge in my TR3A has started to move smoothly from 'full' (when it is) to 'empty' when only about 3 gallons of petrol have been used. Quite alarming the first time it happened. I have read all that I can find on the Forum on this topic but have not see this precise problem recorded previously. Has anyone experienced the same issue? I will be undertaking some basic testing based on what I have read here and in manuals but to test the sender unit, one manual casually says 'remove unit from tank'. I don't have access to the car at present but can the sender unit be removed with the tank in situ? Miles Quote Link to post Share on other sites
Icarus60 Posted April 24, 2012 Report Share Posted April 24, 2012 Miles Suggest: Check that the sender float is floating by looking in the filler cap The sender is on the right side top of the tank and I changed mine without removing or draining the tank by removing the fuel filler pipe and undoing the straps and this gave just enough clearance to withdraw the sender after undoing the securing screws. Before doing this however suggest you measure the resistance of the sender in various positions. I think it should be around 80 ohms full and around 10 or less empty. You can check the higher level by getting a piece of stiff wire and hooking the sender arm through the filler neck and raising the float. If this is all good check the the wiring and ensure that the gauge earth is OK All the best Gerry Quote Link to post Share on other sites
TR Mitch Posted April 24, 2012 Report Share Posted April 24, 2012 the fuel gauge in my TR3A has started to move smoothly from 'full' (when it is) to 'empty' when only about 3 gallons of petrol have been used Miles, I think the issue has been since metrification. If you set your car to burn litres of fuel instead of gallons, it will work again. The problem arises because you are buying fuel in litres (as sold in modern petrol stations) but you are burning it in gallons, so the gauge is misreading. If you burn it in litres, all will be well (Sorry, couldn't resist that one) Quote Link to post Share on other sites
Bob Smith Posted April 24, 2012 Report Share Posted April 24, 2012 Miles, I had a similar problem but cured it running a separate earth from the gauge fixing bracket to a suitable earth point behind the dash. Unless there is a very good earth for the instrument it will give odd readings. Quote Link to post Share on other sites
Don Elliott Posted April 24, 2012 Report Share Posted April 24, 2012 The original senders had a metal can as the float. if it has developed a leak, this can will fill with fuel and then sink - with the gauge "thinking" that the fuel tank is empty. Quote Link to post Share on other sites
Norman D Posted April 25, 2012 Report Share Posted April 25, 2012 I concurr with 2 of the above observations that the guage needs an earth via its fixing clamp to dashboard allthough why is not obvious from circuit diagram. If I unclamp mine and pull it forward it stops working even though it would seem to have power to one side and feed from tank to the other, perhaps there is a bridge circuit inside not obvious from diagram. Quote Link to post Share on other sites
MilesA Posted April 26, 2012 Author Report Share Posted April 26, 2012 TR Mitch - If only it was that simple! Everyone - Thanks for the suggestions which I will work through methodically. Don - If the metal float is leaking, is there proven repair given that it is probably permanently covered in petrol or does one have to locate a replacement float? Thanks - Miles Quote Link to post Share on other sites
Don Elliott Posted April 26, 2012 Report Share Posted April 26, 2012 (edited) New "repro" senders are available. They have a plastic float. The holes are 30 degrees off and you need to bend the long rod about 30 degrees so it doesn't foul with the inner wall of the tank. In the meantime, you can solder the hole in your float can if you find a tiny leak. BUT MAKE SURE TO GET ALL THE FUEL OUT OF IT BEFORE APPLYING ANY HEAT OR YOU WILL BE PUT AWAY AS A "TERRORIST". Edited April 26, 2012 by Don Elliott Quote Link to post Share on other sites
Bob Brennan Posted April 26, 2012 Report Share Posted April 26, 2012 Miles - In Surrey, are you running E-10 gas? Are there alternatives? The E-10, 91 octane available here in Maine, does not make my MG-TC or TR-3 happy. The Obama EPA is promoting E-20 and I fear for the worst. Rotten floats will not be the worst of our problems. Bob Quote Link to post Share on other sites
MilesA Posted April 27, 2012 Author Report Share Posted April 27, 2012 New "repro" senders are available. They have a plastic float. The holes are 30 degrees off and you need to bend the long rod about 30 degrees so it doesn't foul with the inner wall of the tank. In the meantime, you can solder the hole in your float can if you find a tiny leak. BUT MAKE SURE TO GET ALL THE FUEL OUT OF IT BEFORE APPLYING ANY HEAT OR YOU WILL BE PUT AWAY AS A "TERRORIST". Don - Thanks as ever for sharing your experience and photos and I will try and avoid blowing myself up! Miles Quote Link to post Share on other sites
MilesA Posted April 27, 2012 Author Report Share Posted April 27, 2012 Miles - In Surrey, are you running E-10 gas? Are there alternatives? The E-10, 91 octane available here in Maine, does not make my MG-TC or TR-3 happy. The Obama EPA is promoting E-20 and I fear for the worst. Rotten floats will not be the worst of our problems. Bob Bob - I use 97 octane petrol which I believe has 5% ethanol and which has necessitated a recent retune of my Webers (see recent post on this forum) although the car is running really well again. My understanding is that in 2013 there will be a move to 10% ethanol although I believe it is already higher still in some European countries. Others are more expert than me on this subject but it just looks like another headache for classic car owners. Miles Quote Link to post Share on other sites
unclepete Posted May 1, 2012 Report Share Posted May 1, 2012 Miles You are going to have some fun setting the guage up to remotely indicate whats in the tank! After hours measuring the resistance when empty, 1/4, 1/2, 3/4 and full and then trying to replicate this at the adjustable poles on the guage I then found the resistance changed slightly when re-installed and bolted up!! So I now have a guage which shows about 3/4 and does not wobble when tank is full, starts wobbling when about a 1/2 tank then drops to nothing when about 1/4 tank and then I get out open the cap and look at the level with a torch when getting low. I have seen some which are fairly accurate but as long as the indications are consistant all add to their character...... Good luck Uncle Quote Link to post Share on other sites
Andrew Smith Posted May 1, 2012 Report Share Posted May 1, 2012 Well, TuRK's is full when reading full, 3/4 full when at 3/4, half full when reading 1/2 and empty when reading a 1/4, so work that one out ..................learned to live with now though and always carry a torch just like Unc! Cheers Andrew Quote Link to post Share on other sites
Guest ntc Posted May 1, 2012 Report Share Posted May 1, 2012 Dipstick in boot Quote Link to post Share on other sites
MikeTR-6 Posted May 1, 2012 Report Share Posted May 1, 2012 Both my 3a's had erratic fuel gauges , depended on volts in the system , lights on / of heater and so on. 50's / 60's technology with petrol at two bob a gallon . was no excuse to run low then , i never ran out . often that is . Just top it up when it gets to 1/3 empty Mike Quote Link to post Share on other sites
MilesA Posted May 1, 2012 Author Report Share Posted May 1, 2012 Thanks for the additional input - seems I was spoiled before with a reasonably accurate gauge! I will have a crack at finding a solution, but this is one problem I won't waste too much driving time on. Miles Quote Link to post Share on other sites
MilesA Posted May 20, 2012 Author Report Share Posted May 20, 2012 Just to complete this thread. Checked the float and it was riding on the surface of the fuel. Next electrics. The fault was that the earth cable had become disconnected from the sender unit. How the hell that happened is beyond me as it is tucked away behind the boot panel and I had a job to get it back together as the spade was so tight fitting. So normal, accurate service resumed (although I now zero the trip counter every time I fill up). Anyway, all your help was not wasted as I now own a multimeter and have learnt how to use it - as all things electrical just baffle me, this is progress. Thanks all - Miles Quote Link to post Share on other sites
ians Posted May 20, 2012 Report Share Posted May 20, 2012 I fixed mine last week with the same solution. Poor earth on sender unit. After 30 minutes trying to access the sender unit from the boot (with great difficulty I might add) I realised that access is easy if you remove the trim panels inside the car! Dohhhh. Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.