Crazy gas gauge - is it the gauge or the sender? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Number21 · 10-20-2010, 08:42 PM

The gas gauge on my '73 is constantly changing levels regardles of what is in it, even if I'm parked on a level surface. It never pegs completely to one side or the other, so I'm guessing it's not shorting out somewhere.

How do I know if the gauge is bad or the sender in the tank is bad? If the gauge turns out to be bad, can I steal the good one out of my '79?

James McClure · 10-20-2010, 09:25 PM

21, A 46 ohm resistor should center guage. I use an old volume control. Wire to sender grounded should read empty. Open circut will go over full. Make sure the tank itself is well grounded. Chances are it's the sender, but dash guages do fail. Don't overlook the wireing under the truck, especially if it has dual tanks. jim

SCOTI · 10-20-2010, 10:41 PM

The one in my 74 bounced alot but it appeared to actually be changing w/the level in the tank (fuel slosh when moving down the road). If the truck was sitting still & the gas/liquid was still, the needle was still.

Is your gauge needle moving even if the truck has been perfectly still?

Number21 · 10-20-2010, 11:09 PM

Quote:

Originally Posted by SCOTI

Is your gauge needle moving even if the truck has been perfectly still?

Yep, just warming up in the drive way I can go from half a tank, to a full tank, and then back to a quarter, within a few minutes.

It moves a lot but not fast enough to keep up with sloshing.

SCOTI · 10-20-2010, 11:32 PM

Start w/inspecting the ground @the tank.

GMC Guy · 10-20-2010, 11:36 PM

Quote:

Originally Posted by SCOTI

Start w/inspecting the ground @the tank.

x2

tucsonjwt · 10-21-2010, 08:33 AM

If you search here you will find several threads on erratic gas gauges. I did a lot of research when my gauge was not working properly and determined that I needed new sending units on my dual tanks. I actually needed a new gauge, so I don't think all of the tests recommeded are 100% foolproof. I suggest installing a known good gauge to see if that helps. Dropping a tank or lifting a bed takes quite a while and can be a dirty job. Removing an instrument cluster and replacing a fuel gauge is a clean .5 hour job. You can buy a new aftermarket gauge for about $50. If it is not the gauge, you might be able to return it. If you can get your hands on a known good working used gauge that would be better for a test. Note: if you replace your sending unit(s) with Spectra brand, your gas gauge will move when your vehicle moves (about 1/4 tank range). However, AC/Delco sending units cost about 3X as much - I'll put up with the moving gauge.

10-20-2010, 08:42 PM	#1
Number21 Registered User Join Date: Aug 2009 Location: Oregon Posts: 611	Crazy gas gauge - is it the gauge or the sender? The gas gauge on my '73 is constantly changing levels regardles of what is in it, even if I'm parked on a level surface. It never pegs completely to one side or the other, so I'm guessing it's not shorting out somewhere. How do I know if the gauge is bad or the sender in the tank is bad? If the gauge turns out to be bad, can I steal the good one out of my '79? __________________ '73 K20 Cheyenne Super Camper Special 350/TH350/NP205 sittin' on 33's. You can set my truck on fire and roll it down a hill, and I still wouldn't trade it for a Coupe de Ville.

10-20-2010, 09:25 PM	#2
James McClure One shot, one kill. Join Date: Dec 2007 Location: Saratoga Springs NY Posts: 859	Re: Crazy gas gauge - is it the gauge or the sender? 21, A 46 ohm resistor should center guage. I use an old volume control. Wire to sender grounded should read empty. Open circut will go over full. Make sure the tank itself is well grounded. Chances are it's the sender, but dash guages do fail. Don't overlook the wireing under the truck, especially if it has dual tanks. jim __________________ 1984 K20 350M engine with 465,000 miles. Well, it's finally done!! Almost 2 years of work, but it was really worth the effort. Little stuff left to do is mount winch, wet sand & buff out and build belly pan\running boards. Body work takes lots and LOTS of beer!!!! God, Guts and Guns made America and God, Guts and Guns will preserve it! The worst thing you could do is get into my sights, but that don't matter, you'll never know it, cause you'll never hear the shotJim or Paladin whichever you choose.

10-20-2010, 10:41 PM	#3
SCOTI Registered User Join Date: Apr 2001 Location: DALLAS,TX Posts: 22,064	Re: Crazy gas gauge - is it the gauge or the sender? The one in my 74 bounced alot but it appeared to actually be changing w/the level in the tank (fuel slosh when moving down the road). If the truck was sitting still & the gas/liquid was still, the needle was still. Is your gauge needle moving even if the truck has been perfectly still? __________________ 67SWB-B.B.RetroRod 64SWB-Recycle 89CCDually-Driver/Tow Truck 99CCSWB Driver All Fleetsides @rattlecankustoms in IG Building a small, high rpm engine with the perfect bore, stroke and rod ratio is very impressive. It's like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar..... *Cubic inches is like Indiana Jones with a cheap pistol.*

10-20-2010, 11:32 PM	#5
SCOTI Registered User Join Date: Apr 2001 Location: DALLAS,TX Posts: 22,064	Re: Crazy gas gauge - is it the gauge or the sender? Start w/inspecting the ground @the tank. __________________ 67SWB-B.B.RetroRod 64SWB-Recycle 89CCDually-Driver/Tow Truck 99CCSWB Driver All Fleetsides @rattlecankustoms in IG Building a small, high rpm engine with the perfect bore, stroke and rod ratio is very impressive. It's like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar..... *Cubic inches is like Indiana Jones with a cheap pistol.*

10-21-2010, 08:33 AM	#7
tucsonjwt Registered User Join Date: Jul 2007 Location: Tucson, AZ Posts: 3,189	Re: Crazy gas gauge - is it the gauge or the sender? If you search here you will find several threads on erratic gas gauges. I did a lot of research when my gauge was not working properly and determined that I needed new sending units on my dual tanks. I actually needed a new gauge, so I don't think all of the tests recommeded are 100% foolproof. I suggest installing a known good gauge to see if that helps. Dropping a tank or lifting a bed takes quite a while and can be a dirty job. Removing an instrument cluster and replacing a fuel gauge is a clean .5 hour job. You can buy a new aftermarket gauge for about $50. If it is not the gauge, you might be able to return it. If you can get your hands on a known good working used gauge that would be better for a test. Note: if you replace your sending unit(s) with Spectra brand, your gas gauge will move when your vehicle moves (about 1/4 tank range). However, AC/Delco sending units cost about 3X as much - I'll put up with the moving gauge. Last edited by tucsonjwt; 10-21-2010 at 08:34 AM.



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