my fuel gauge is significantly inaccurate, where the fuel is nearly empty and it reads about a quarter of a tank. How do you adjust or calibrate the gauge so it reads correctly.

I don't think you can.  But I didn't stay in a HI Express last night either.

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Depends...does the gauge show to be accurate up until that point, or is it off all across the board?
If it works until the fuel gets low, I would suspect a bad sender unit. If it is wonky from top to bottom, it could be a bad resistor, or the gauge itself.


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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Honestly....this was my dad's car befor he handed it down. He told me the gas gauge was off and to refill at 125 miles. Might experience is at 125 miles the car is at 1/4 tank...he is a physicist so maybe his impreaaion is off by a factr greater than the rest of us. Is there a calibrating technique that I should know?

I agree with Joel. I'd bet the sending unit in the tank is kaput. Regardless, you'll have to remove the sending unit from the tank to either test it with a Ohm meter or replace it. There are little brass contact strips that the float arm contact constantly swings up and down as the fuel sloshes around. There could possible be a bad spot the a couple of those brass strips. 

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GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.

Hi Sarge.... When I fill the tank completely it reads full....as I use gas the guage goes down but (according to my dad, I have not ran it put of gas tomprove or disprove the veracity of my physycist/engineer father's description) when the gas gauge hits 1/4 the car is actually on fumes.

It's possible that the bladder inside the tank is deformed, and the float is hanging up on it at about 1/4 tank, if the gauge appears to read properly until it gets to that spot. Don't think you can look down into the tank on a '75-'82 car, like you can the older ones, to see if the float is hanging. Ya may have to just pull the sender out(from the top) as Darryl stated, and have a look-see from there.
Afaik, there are no "calibrations" to be done on the sender/gauge unit...they either work, or they don't. Not sure if the later cars have the resistor on the gauge itself, but those can cause a fluctuating/bouncy reading on the gauge, as well as incorrect readings. At this point, I think I would disconnect the gauge wire AT the sending unit, and ground it. If the gauge goes to EMPTY then, you'll know the problem is with the sender unit/float. If the gauge does NOT go to EMPTY, and stops at 1/4, then your gauge itself is wonky, and will need to be either replaced, or repaired.

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Joel Adams
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I just rebuilt the sending unit in my '80 with the help of an article from Corvette Enthusiast from October 2006. According to the article, the sending unit should have a smooth 0 to 90 ohms resistance as the float arm moves from empty to full. Might have been the other way around. In any case, you should see my point. Remove the sending unit and measure the resistance as you move the float back and forth. If it jumps or doesn't reach the full range, you should open it up and clean it with some carb cleaner. Check the quality of the contact.

|UPDATED|6/11/2015 3:53:21 AM (AZT)|/UPDATED|


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hi   sarge81 is right  that's is to only way  to check,many factors are at work   no gas tank that I have worked on is perfect   some will say 1/2 tank when only 1/4 tank,my company built fire trucks we made are own tanks some 50 gals or more,using factory sending units  we bent arms to make some what acurant  1/2 tank does not ment 1/2 tank left  not true  do as sarge81 sezs   than you can replace  this many not change gauge   many factors  remove is the only way   dwa

0 ohms is empty.  90 ohms is full.  disconnected it will read over (past) full.

|UPDATED|6/11/2015 7:46:54 AM (AZT)|/UPDATED|

Let me see if I have this straight and correct me if I'm wrong. 

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GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.

I had wanted to ask someone knowledgeable about this because when I read Knudsen's "Star Spangled Sports Car", he had said in there that the 78-82's had a hard liner and that 77 was the last year of a bladder.  I was confused/surpised because I had always heard that all C3's had a bladder, and I have never had my tank off/out to check.  I guess mine works the opposite since it was my understanding the tanks were 24 gallons, but when mine reads empty the most I have ever put in it is about 18 gallons and I always thought 6 gallons was a lot to have for "reserve".


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just thinking  [yits hard]  if car gauge shows 1/4 tank of gas,than fill it up and see how much you put   in   that could tell 1/4  how much fuel you do have   just a thought   dwa

There were NO bladders or liners in the tanks until the '75 model. Earlier cars were nuttin but steel. The tanks are listed as 20 gallon for most years, but the '68-'74 cars have a filler tube extended down into the tank, that will keep you from being able to put any more than 18 gal in them. The '75-'77 cars had a little less fuel capacity due to the bladder taking up space. The '78-'82 cars had different tanks to start with, and I think most of those will hold 20 gal when totally empty...not 100% sure on those.
The '75-'77 bladders can be removed fairly easily thru the filler neck hole, once the neck/sending unit has been removed. The later cars with the less flexible liners can be removed, but not very easily.....usually not worth the effort. Even the rigid type liners can deform over time, and cause problems.


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Joel Adams
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Hello all. I just bought a 80 vette that needs a lot. First thing to fix is the gas gauge:) then speedo. I've read this post and I'm not sure what to do next. When I disconnect the ground to the sending unit the gauge goes past full. As soon as I reconnect it drops to around a quarter full but nothing else. There is probably 15 gal in the tank and no change. I have a limited budget and a little knowledge(which is dangerous) so I just don't want to throw money at parts wishing it works. I'm looking for any and all advice I can get. Thanks

Use your average mpg and the capacity of the tank.  That should tell you how far you can go on a tank.  Just reset your trip odometer.


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Unfortunately the speedometer doesn't work either. That is project number two after I get gas gauge working.

Car pic

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|UPDATED|7/20/2015 4:21:11 AM (AZT)|/UPDATED|

Ground the wire to the sending unit and see if it reads empty.  If so your 80 either has a bad ground from the sending unit in the tank, or a bad sending unit. if not, it's back up to the dash gauge or a bad connection between the two.

|UPDATED|7/20/2015 6:00:18 AM (AZT)|/UPDATED|

OK ...... it may be Aliens but I have to tell this story..... I have been having a problem with my 1980 fuel gauge for 5-6 years.....

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Ok. I think the sending unit is bad. Any advice on best price on finding a replacement?

Ethanol fuel is known to create issues with fuel senders, but since you just changed yours, I'd find it hard to believe it has already caused that problem. Plus...you had the same problem before.
If you still have your "old" sender, plug that thing in(be sure it is grounded to the car/chassis?, turn the key on, and move the float manually, and watch the gauge. See if it will go to full with the float lifted up, and go to empty all the way down.



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Joel Adams
C3VR Lifetime Member #56    
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I checked our Supporting Vendors and Bair's has one listed for $95. He's the cheapest. Make sure you replace the gasket that goes in-between the sending unit and tank. I would also either replace or clean the filter socket (with solvent or carb cleaner) on the end of the pick up tube. 

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GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.

Thanks fir the info. Let me know if you have the old one available please

Bair's Corvette is our sponsor. Mention you are a C3VR member you will get a discount. Great people do business with. We were just there has part of the C3VR gathering.

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EBO,  your fuel was partly shorting your sending unit resistor.  Remember, grounded is empty.  When the fuel was below the level, it was no longer shorted.

You should give Bairs a try for the unit.   They are one of our sponsers.

I'll get back to you Monday and let you know if it's still around. I'm at "Ebo's" for the"Eboland" party rest of the week. 



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GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.

Hey Sarge I hope you had a good weekend at Eboland. Where you able to find the old sending unit and if so what do you want for it. Thanks

Ebo, as already stated the percentage of ground is what determines the fuel gauge reading.  Our cars were made to handle up to 10% ethanol.  Many gas station pumps are now 12 to 15%, even if they say 10%.   The feds made this change allowable several years ago.   The GM owners manuals used to say 10% and the Feds required a recall to "correct" the issue.   GM simply did a recall to the owners manual.  They replaced the page with one that said 12%.

Hi Mitch, yup we had a blast at Eboland. Lots of good food, drink and adventures with a couple tech/repair sessions. I finally made it over to the shop today. Unfortunately the sending unit got tossed. Sorry I couldn't help you out. 



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GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.

Thanks for checking. I think I'm going to try to take it apart and clean it first. If that doesn't work I'll call Bairs.

Just thought I let people know that Bairs doesn't carry the fuel sending unit anymore. They said they had too many problems with them. I did take mine apart today to try to clean it but that turned out to be just a waste of a couple hours:) I'll be ordering one shortly.