Fluctuating gas tank needle

[7mgte808]

Ok I tried searching and I want to apologize in advance if this is covered already, but recently my gas tank needle in my tach has been acting irratic. I would fill in a full tank of gas and less then 5 miles later the tach would read 3/4 tank. Sometimes the needle would drop to below empty and then go back up to the 3/4-full tank mark. Any ideas of what this could be?

Also, the low coolant warning light goes on when I start my car. I just checked my cap, and coolant level and topped it off a bit. Still reading that error.

Thanks everyone.

 

[gtsfirefighter]

Maybe your fuel sending unit is going bad. Also check the fluid level in the coolant reservoir bottle. I put some coolant in there and my light went off.

 

[ValgeKotkas]

Mine tank needle shows nothing I don't complain.

 

[Nick M]

Sounds like bad wiring to me. The sending unit varies resistance between the guage and ground. I haven't had one out in some time, so I don't remember which way, but it will either be this way, or the opposite.

If the guage is grounded with its proper supply voltage, you will show full. Or the opposite.

It has two sets of wound wires. They both make a magnetic field when powered. The difference between the strength of magnetic fields moves the needl up or down. The sending unit changes the set of windings, so the needle moves. I just don't remember if the resitance increases or decreases as the fuel level drops in the tank.

You should get the electrical wiring diagram for your year, and a volt meter. Check the voltage supplies, and the ground points. If you can get to your sending unit harness, unplug it, and watch what the guage does. Then ground it and watch what the guage does. If it moves, then I highly doubt it is the guage.

That being said, it could be the sending unit as already mentioned. I would think of the guage last.

edit: Welcome to the board.

 

[7mgte808]

Maybe your fuel sending unit is going bad. Also check the fluid level in the coolant reservoir bottle. I put some coolant in there and my light went off.

Problem solved with the coolant light. I guess the reservoir was low. Also, will check up on the fuel sending unit. Thanks everyone for the response and I'm glad to finally own a supra. :icon_bigg

 

[mickyg]

I had this problem on on my Cressida - actually affected my tachometer as well. Re-soldering the connections on the back of the meter elements fixed it for me. I think the connections get loose over time (over 20 years in my case!). Checking the wiring on the fuel sender in the tank would likely be a bit easier though. Also might be worth double checking the wiring harness to the gauge cluster to make sure it's not corroded or loose. Saves you from tackling the soldering job if it's not necessary!

 

[Nick M]

Your gas needle fluctuated from being low on coolant?

 

[Clip]

thats fricking crazy, try draining your 87 octane coolant and putting in a 50/50 mix of antifreeze and water. course, you could always go with more water if you wanted better cooling with less temperature protection

welcome to the boards, glad you got the problems taken care of!

 

[KeithH]

Fuel sending unit is dirty...

http://www.supras.com/06/techcenter/display.php?QID=47

 

[jdub]

^^^ Bingo!

You can clean the contact with some carb cleaner and a cotton swap to remove the varnish build-up.

 

[iwannadie]

i had the same problem. i replaced the battery and havent had the problem since. not sure if its related or not, but it seems fixxed sofar lol.

 

[Adjuster]

Test.

 

[cheverlot]

does any one know if you can get the sender aftermarket if so how much and were can you get it