fuel gauge weirdness

[JohnC]

Just got a new fuel tank sending unit for the C10. I tested the gauge by unplugging the wire from the sending unit and the needle goes to empty, then grounding that wire, the gauge pegs full. So think that suggests that the gauge is fine.
When I put the new sending unit in, and put some gas in, the needle rose appropriately. Next time I drove it, today, I noticed that on start up, the needle was at 1/4 tank (it had been at 3/4 full when I parked it 2 days prior). No gas smell etc so I don't think i leaked. Wiggling the wire on the sending unit, did nothing. A minute or two later the needle just rose back up to near 3/4. So it read low for 1-2 minutes, then read accurately after that. Driving it around it did that same thing every other time I parked it and started up again.
That sounds weird right? Not a big deal but can anyone explain why it might do that?

 

[Chevelle_Nut]

I have had the same issue with replacement sending units in my Gold Chevelle. The first one worked fine for a while then would only go to 3/4 full when filled. I replaced it and the new one hits the full mark and has about 3 gallons in it when on empty . In comparison to the original 50 year old sender in my Bronze Chevelle the needle has always gone above full and when she reads empty, she is out.

I think the problem lies in poor quality replacement sending units.

 

[JohnC]

Thanks. It’s hard for me to understand scientifically why it might do this but as long as it eventually reads right I guess I don’t care if it reads wrong for the first 1-2 minutes. This was the “OER” brand for what’s that’s worth.

I haven’t filled it up completely to see how it reads. I’ll have to do that.

I know my prior sending unit had rust holes in it so I assume it sank to the lowest point on its arc but still read as about 1/4 full.

 

[Chevelle_Nut]

The bad thing about having 2 of the same cars is I compare the 2 against each other.

 

[12stones]

I thought all old Chevy gas gauges worked like that. And the last half of a tank goes a lot faster than the first. That's been my experience with several of them anyway.

 

[Chevelle_Nut]

I thought all old Chevy gas gauges worked like that. And the last half of a tank goes a lot faster than the first. That's been my experience with several of them anyway.

1/2 to 1/4 drops like a rock

 

[JohnC]

Main ain’t that the truth. First half of the tank the gas gauge makes you think you’re getting 30 mpg, last half the tank you think you’re getting 8 mpg. But maybe some of you BB guys with a heavy foot actually do get 8 mpg.

 

[12stones]

My Chevelle does just like yours john. When I first start it, it always shows lower than it should, then it goes up to where it should be. I think the shop Forman hit it on the head.


[/QUOTE]

I think the problem lies in poor quality replacement sending units.