'68 GTO Fuel Gauge Has Odd Readings - Pontiac GTO Forum
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post #1 of 8 (permalink) Old 07-26-2019, 12:00 PM Thread Starter
 
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'68 GTO Fuel Gauge Has Odd Readings

I did a search and some reading on this, most others fuel gauges either work or didn't work. It was a wire or sending unit.
My '68 GTO runs out of fuel at about 1/8 of a tank showing, ask me how i know, go ahead, i'll wait.
When I fill it up the orange needle can't be seen until about 6 gallons has been used.
It was reading above half and I put in 13 gallons in last night, with a 20 gallon tank it should have been below half.
Any one have trouble shooting info?
Thanks
John
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post #2 of 8 (permalink) Old 07-26-2019, 06:20 PM
 
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Originally Posted by John Schutt View Post
I did a search and some reading on this, most others fuel gauges either work or didn't work. It was a wire or sending unit.
My '68 GTO runs out of fuel at about 1/8 of a tank showing, ask me how i know, go ahead, i'll wait.
When I fill it up the orange needle can't be seen until about 6 gallons has been used.
It was reading above half and I put in 13 gallons in last night, with a 20 gallon tank it should have been below half.
Any one have trouble shooting info?
Thanks
John

Does not sound like a problem to me. This is not a "modern" car. I can't think of when any of the old gas gauges were that accurate. The tanks are wide and flat, so I don't think you can get as accurate a reading like you do with today's gas tanks which are typically smaller, more compact, and located differently.

You could install a new tank sender, gauge, wiring, etc., but you may still have the same results. Don't let the gauge hit 1/8 as 1/8 may actually not be bone dry "empty," but at the point where the pick-up tube in the gas tank won't be immersed in the remaining gas. This may also account for why when you added 13 gallons, the gauge was over half because you still had 2-3 gallons in the tank that can't be picked up.

I have a '73 Fury that will show full when it is full, but use up a couple gallons and the gauge drops fast, but I know I have more than the gauge says. These old type set-ups can drop real fast from full to half, but then hang at half tank for some time. The gas can also slosh around because of its large size and you can watch the needle move around as you brake, accelerate, go up a hill, go down a hill, or corner hard. Nature of the beast - in my opinion.

It may be wiser to simply know how many miles a gallon the car gets and figure how far you can go on a full tank - when you fill it. Consider the 1/8 level on your gas gauge as your car's "empty" mark.
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post #3 of 8 (permalink) Old 07-27-2019, 08:31 AM Thread Starter
 
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Thanks for the response PontiacJim, been about 25 years since i owned a mid to late 60's car. if it ain't broke i'm not gonna fix it.
One other question related to the Forum, i uploaded a pic for my signature but i don't see it when i look at my threads. Any one know why?
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post #4 of 8 (permalink) Old 07-27-2019, 01:19 PM
 
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Originally Posted by John Schutt View Post
Thanks for the response PontiacJim, been about 25 years since i owned a mid to late 60's car. if it ain't broke i'm not gonna fix it.
One other question related to the Forum, i uploaded a pic for my signature but i don't see it when i look at my threads. Any one know why?

Agreed, leave well enough along until it really gives you a problem, but I think it is fie.

Not sure how the signature pic is done. I have one on my personal data, but it does not show here either. It will also show up if you do a Google search of the forums. Never thought much about it. Let's give it a try.

Looks like if you go to the "Settings & Options" you will see "Edit Avatar." Click on it and it explains what to do to set your picture. I clicked on the circle/dot that reads "Custom Avatar." Then I hit the "Browse" to leaf through my own photos. Found a photo, but prior to upload, I shrunk it down using the Microsoft "Paint" program and the resize feature using the pixels option and got it down to the required size of 110 x 110 pixels.

Boom! There I am.
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post #5 of 8 (permalink) Old 07-31-2019, 08:07 PM
 
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My gauge was behaving as yours, would take forever to move off Full, then a quick descent... would run out at an 1/8 from empty. I just put a new sender in it and now it reads correctly. Or at least as correctly as these gauges ever were. Cheap fix. Mine was original to the car ('67 GTO) so it was probably time anyway. (I put a new gas tank in a couple of years back and I didn't bother to swap out the sender, lazy...)
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post #6 of 8 (permalink) Old 08-02-2019, 09:35 PM
 
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Two thoughts. Ground, ground, ground. You could try taking out the sending unit and bending the float support wire to find a more accurate range.
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post #7 of 8 (permalink) Old 08-03-2019, 12:03 PM
 
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All excellent advice. My brother (the Chevelle guy) made sure his speedometer/odometer was working correctly and then when his gas gauge was wonky, he kept a small pad in the Chevelle and noted date and mileage and gallons whenever he gassed up. He knew what his approx gas mileage was and would gas up again when he had a certain number of miles on the car.

I had a Stude with a wonky sender that I couldn't find a replacement for so I used the "Chevelle method" to keep up with date and mileage when I gassed up. It really wasn't any trouble to do this and neither him or me ever ran out of gas with this method. Old cars just call for out of the box thinking sometimes.

(Jim's post number two says it well, the tanks were different than today's vehicle and a new sender setup may/maynot work.) Brother preferred not to fix it and use the $$$ for other things the Chevelle needed.

Best of luck with your "68, the PO of mine had a new sending unit put in but I figure it's just a matter of time before trouble again, hence the pad in the car.
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post #8 of 8 (permalink) Old 08-15-2019, 09:21 AM Thread Starter
 
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Two tanks of fuel and now the Orange indicator is completely out of sight, been using iPhone Excel, which also tell me i'm getting 13 mpg, I was expecting 8, so i'm happy.
I think every family has a Chevelle family member, even if we don't talk about it in public, LOL.
I am really happy with the work I've done to make this a daily in the summer:
-Aluminum Radiator with twin fans keeps is at 180F.
-The UMI Satge 2 suspension kit just plain old handles, took a few on rams well beyond the recommended speed and it didn't care.
-The MSD box lets it start easier and idle smooth.
-Using Manifold vacuum for idle, how could I get this old and not understand this until I read that article?
Its plain old fun to drive.
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