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Gas guage not reading correctly...


720buck

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Hey ya'll.   I was wondering if someone has had this problem before... I drive a 720 1980's pick up that I picked up as a daily communter.  It's got around 148,000 miles on it...  I live on top of a hill but my parking is flat .    When I fill up my tank it only goes up to 4/6 on the fuel gauge which will continue to read that as it goes down within me driving it around town.  However when I back the truck down a hill to pull out of my driveway the fuel guage reads full. 

 

What exactly Is going on?  I admit I'm not very knowledgable with this at all so bare with me.  I'm always up to learning something new.

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Float not adjusted correctly, or it's starting to sink.  Only way to fix it is to pull the tank, though, to get to the sender. 

 

My '76 does a similar thing, though it's an oversize aftermarket tank with no baffles so I have as much as a 1/3 gauge deflection from stopped to accelerating, and accelerating up hills to braking down hills makes the gauge read as much as 1/2 tank different.  It does read full when full, though.

 

I just live with it.  It's not worth the hassle of possibly breaking off the mounting bolts just for a gas gauge that's a little off.  

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Oh, you can pull the drain plug, drain the tank, then see where the gauge actually sits when the tank is really empty (plus you'll flush some of the crap out of the tank, while running it dry would get it in the fuel lines).  Almost every car I've had, the gauge still moves off the peg (vs where it sits with the ignition off) even with the tank dry.  My '74 is notoriously bad, the tank is empty right when the gauge hits the "E" line.  On my '76, that same "E" line is 1/4 tank.

 

Rule I've used to figure out "range" is I'd fill the tank normally, then drive 200 miles as exactly as possible.  Then fill the tank again to see how much it used.  If I have a trip odometer (620s don't, unfortunatlely) I use that more than the gauge to decide when to fill (since I don't want to be having to fill up in Seattle or Bellevue, I plan it so I'm filling in Tacoma where gas is 20-30 cents cheaper).  I try to never let the tank have less than 2 gallon in it, though with the tiny 11.7 gallon tank my 74 has, that's why it's run out on the way to the gas station.

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