Hey guy's,
Just as the title read's I just finished putting in a new sending unit, job went fine and did fix the gas gauge(needle was pegged at 3 o'clock). Went for a spin to the gas station to fill it up to check the final outcome or essentially what the gauge would read. Filled it right to the brim to almost over flow the tank and the gauge went to between 3/4 and 7/8..not to the full mark. Just wondering if anyone would know why that is? I never thought to compare the profile or shape of the new one to the old one before I installed the new one or if that would even factor in? Any input is much appreciated.
Thanks,
Trev

 

The profile would be a factor. You can put an ohm meter on the sender at full and see if your reading 90 ohms or not.

 

Thanks Eric, is there much to doing that kind of test and can I do it with the tank still on? I do have a multi meter but that type of testing isn't my strong suit. And the car is my '71 cutlass. Trev.

 

Where did you buy the sender, and what brand is it? I'm aware of a problem with one sender, I had the same thing happen to me. Apparently...the angle of the arm on 1 particular sender is not bent in a way that it will travel to the full position. It can be modified to work.

 

Yes you can do it with the tank in the car. Get on the connector that feeds the sender to the gauge I think its in your trunk (sender side of connector) to ground and set your meter to 200 or 500 ohm scale. Like I said should read 90 ohms with a full tank. To modify the sender arm unfortunately the tank needs to drop.

 

Dude, that kinda' stinks. At least you'll know if you're running out though.

 

Hey mrolds69, it's an OPG product number CH20870 3/8" without return if that helps to narrow it down.
Thanks again Eric, I'll try that test next time I get out to work on it.
And ya Macadoo it does suck a bit but does help overall I guess.

 

Just to follow up, so will the gauge then just stay on this 3/4's to 7/8's mark longer and then start to go down and empty is still empty or will everything be offset slightly and the needle go below empty? probably the first part I'm guessing but i will carry a small gas can till i go through the first tank of gas.

 

My repro sender was a 2 line sender and not from OPG. It was for my 70 GS 455. Before I put it in, I tested it with an ohm meter, it worked perfectly (0-90). After it was in, went to the gas station, and then the same thing happened as yours. I also noticed that sender made my gauge needle float around more than before. I did some research and found somebody else with the same problem. They had a pic of an original + repro side by side, showing the float arms. I guess it just works like normal but doesn't read full. Fixing it is on my long list.........

 

yeah, I have seen this before when the float arms are not quite the same. really have to take time to compare and verify they work right before installing so you don't have to drop the tank again. some can get bent during shipping also and they are easy to tweak out of shape. your gauge is going to go down the same speed I would think but you may also hit E with a 1/4 tank left yet. I would have to fix that...

 

can you add a resistor to attain the 90 at full tank or would that throw off the Empty end of the scale then? The right way is to drop the tank and do a side by side and make the repro behave like the original in every detectable way I guess. Like the manufacturer should have done.

 

it would still be off on the low side . sounds like the arm is bent upwards so there is a huge reserve now lol you have plenty of time to find a station when you hit E

 

Ya i think I'll run a tank through it and see what happens but i will keep a small jerry can of fuel close till I figure out what's what, i won't pull the tank again unless it is way off. I better get an inline fuel filter aswell for if or when the time comes i need it too.

 

Not the same issues but similar.....but just put in a new tank and sending unit. had 1/4 tank, but in 9.6 gallons (was not filling it, just butting a set dollar amount) and gauge is now at full. So unless I am missing something that thank can't be full, or..it is a 17 gallon tank (15 gallon by the math, but that can't be possible).and not a 20..I understand the factory tank for a 70 Cutlass is 20 gallon. So maybe the sending unit float is not bent to the correct angle, unit is bad?.... anyone ran into this issue?...