Never top off with gas?

[Secret Squirrel]

I have an aftermarket rear tank in my 1969 c10.

I was at the gas station filling up. I set the pump on the slowest setting to allow the gas fumes to cycle out of my tank.

I became distracted by a nice corvette (happens way too often with fast/classic cars). I then heard a dripping sound as I continued to gaze at the vette. The smell of gas pulled me out of the trance but my shoe was soaked. Guess I did not have a good seal.

Since that day my fuel gauge has been way off. I think I knocked the float out of adjustment. It reads half full when empty and off scale when full.

Is that why you shouldn't top off your gas tank, besides the dangers of gas spilling as you drive down the road?

Anyone ever have a messed up gas gauge after topping off?

[mrein3]

I've owned my truck since 1994. I've never left the gas station with anything less than two completely full tanks of gas. Both my factory seat tank and aftermarket saddle filled to the brim.

I'm pretty sure these three events, Corvette driving by, full tank, and gas gauge not working are completely unrelated.

Flip your seat forward, pull the brown wire off the fuel sender, key on. I can't remember if ground is full or empty but if you ground that wire then leave it open you should see a full sweep of your fuel gauge.

If the gauge works, you need to trace that wire in your hand and look for an open in it. If the wire is good you need a new sender.

[cdowns]

some people just dont read well


what type of sending unit? some of the uviversals slip, or another thing is poor grounds installed

[67ChevyRedneck]

Nice truck

I have an aftermarket blazer tank that I've filled to the brim many many many times.

It could be a bunch of different things. Bad sending unit, bad wire, bad ground, bad fuel gauge.

The float arm can only go so high, so it's highly unlikely overfilling somehow bent it so it reads 1/2 tank high.

If you had the opposite problem, I would have gussed your float had a hole in it

[Kayotic]

Did Gas possibly spill onto any electrical connections on the tank itself? (don't know how plausible that would be) but could be enough corrosion to cause a week ground.

I would also think it is possible for the float to have slipped...

[mrein3]

Arrogant posters aside I'd still verify the gauge then the wire to the gauge before I dropped the tank to look at the sender.

[chevy_mike]

Completely off topic but what is the color of your truck? Looks great. Paint code would be nice or the name called (not just purple ).

[justagoodolboy]

Originally Posted by chevy_mike

Completely off topic but what is the color of your truck? Looks great. Paint code would be nice or the name called (not just purple ).

X2. I love it.

[Secret Squirrel]

Originally Posted by chevy_mike

Completely off topic but what is the color of your truck? Looks great. Paint code would be nice or the name called (not just purple ).

Paint code is Sherwin Williams 48935 Dark Blue Metalic. It has a mind of its own from purple to black depending on the light. I am happy with it.

[BIG69GMC]

well Mr. Squirrel, just wanted to say one reason i know of that people say not to top off your tank is mostly due to newer cars that have a charcoal canister , when you top off your tank your going to loose some of that extra fuel you squeezed in because the charcoal canister will absorb the fuel and if done excessively could damage your charcoal canister and not really cause any major problems that i have seen. but just wanted to say maybe thats why you have heard "not to top off your tank" being a classic vehicle you shouldnt have to worry about this. unless you have a leaky gas cap like mine lol! .. btw Nice Paint job, it looks good! Dave...

[slomotion]

Another reason to not top off the fuel tank, is the fuel comes out of a cool environment under ground and goes into your tank at a relatively cool temperature. In my case, (in-cab tank) the ambient temps, and the sun beating on the back of the cab causes the fuel to expand at an amazing rate causing the fill pipe to become full of gas, and has in the past overflowed and run down the side of the cab.

[Secret Squirrel]

Thanks for all the advice guys. I even like the smart __ remarks!

I think my tank sender unit crapped out around the same time I overfilled the tank. Previous owner put it in about 3 years ago. When I ground the tank sensor post to the frame the needle goes to empty.

It just threw me for a loop because the gauge still works but its off by 1/2 tank. I am not motivated to change it now ... so I'll just drive it for a bit and fill up before 1/2 tank.

Thanks for all the color compliments as well!!! I have been drooling over all your trucks for years, never thought I would have one of my own.

[Secret Squirrel]

Originally Posted by cdowns

some people just dont read well


what type of sending unit? some of the uviversals slip, or another thing is poor grounds installed

It is a universal sending unit. Not sure of the manufacturer, the previous owner gave me the paperwork on the truck but the sending unit paper is not labeled with manufacture. see pic below.

[Secret Squirrel]

Originally Posted by Kayotic

Did Gas possibly spill onto any electrical connections on the tank itself? (don't know how plausible that would be) but could be enough corrosion to cause a week ground.

I would also think it is possible for the float to have slipped...

No just gas all over my shoe. I may try to clean the crap out of the post and wire connection.

I tried to run a ground from the frame to the screw on the outside of the tank unit. It had no affect on the gauge.

[ced935]

Well I don't know too much about cars but I'm trying to learn as much as possible. I'm on Travis AFB too, so if you need somebody to hand you a wrench or help drink beer....give me a holla

[chevy_mike]

Well, from what I can see, it doesn't say what Ohm rating the sender is. There are 4 common ones you'll typically find and it you have the wrong rated sender, your gauge will never read correctly.

For '66+, GM used 0-90 ohms, pre '66 was 0-30 ohms, Ford had their own rated, aftermarket had a funky one too. No idea on Mopar's as I typically haven't seen ones labeled for them.

If you have the box or docs that tell you the ohm rating, that might solve your problem. If not a 0-90 version, you have the wrong one for a stock gauge.

[Legolas894]

I've had no luck with these senders. Ran out of gas twice when reading 1/2 full. Now I just keep track of the mileage. I have a 0-90OHM variable resistor that I use to check the gauge. Gauge works fine-it's always been a sender problem. They're $60 a pop up here so after two, I've given up for now.

Maybe this summer I'll tackle it again.

[BlazinC5]

I am suprized you didn't send out the usual E-mail to everyone. lol But I guess you already know what your buddy near Fairchild AFB would say about your measly 15 gallon aftermarket tank.

[Secret Squirrel]

Originally Posted by ced935

Well I don't know too much about cars but I'm trying to learn as much as possible. I'm on Travis AFB too, so if you need somebody to hand you a wrench or help drink beer....give me a holla

sweet buddy!!! Same here ...

[Secret Squirrel]

Originally Posted by chevy_mike

Well, from what I can see, it doesn't say what Ohm rating the sender is. There are 4 common ones you'll typically find and it you have the wrong rated sender, your gauge will never read correctly.

For '66+, GM used 0-90 ohms, pre '66 was 0-30 ohms, Ford had their own rated, aftermarket had a funky one too. No idea on Mopar's as I typically haven't seen ones labeled for them.

If you have the box or docs that tell you the ohm rating, that might solve your problem. If not a 0-90 version, you have the wrong one for a stock gauge.

Yeah I see your point. That paper is all I have for info on the sensor. The guage worked great for about two/three months.

After top off it went wacked. I'll shoot the prev owner an email and ask where he got the kit from.

[Secret Squirrel]

Originally Posted by BlazinC5

I am suprized you didn't send out the usual E-mail to everyone. lol But I guess you already know what your buddy near Fairchild AFB would say about your measly 15 gallon aftermarket tank.

It is about time you got an account. 15 gallon tank is all I need ... don't you know these trucks get awesome gas milage. My tank never goes under half full!!!!

[Secret Squirrel]

Originally Posted by Legolas894

I've had no luck with these senders. Ran out of gas twice when reading 1/2 full. Now I just keep track of the mileage. I have a 0-90OHM variable resistor that I use to check the gauge. Gauge works fine-it's always been a sender problem. They're $60 a pop up here so after two, I've given up for now.

Maybe this summer I'll tackle it again.

Dang ... looks like i may be trackin my miles as well

[Secret Squirrel]

Originally Posted by BIG69GMC

well Mr. Squirrel, just wanted to say one reason i know of that people say not to top off your tank is mostly due to newer cars that have a charcoal canister , when you top off your tank your going to loose some of that extra fuel you squeezed in because the charcoal canister will absorb the fuel and if done excessively could damage your charcoal canister and not really cause any major problems that i have seen. but just wanted to say maybe thats why you have heard "not to top off your tank" being a classic vehicle you shouldnt have to worry about this. unless you have a leaky gas cap like mine lol! .. btw Nice Paint job, it looks good! Dave...

Thanks I did notice gas leaking out the top of the tank when I parked it in the drive way after it was overfilled. Thought it was the breather? My driveway is angled pretty good.

[chevy_mike]

Okay, if you said it worked fine for a few months, then likely you had the right ohm rating. Another, not uncommon issue with cheaper units is, the float has a small pinhole in it. By overfilling the tank, it submerged the float and allowed fuel into it. Now it doesn't have the same buoyancy and reads low.

Easy way to tell is to remove the sender and shake the float and if you hear any liquid inside, there is your problem. Just another idea to test.

[Secret Squirrel]

Originally Posted by chevy_mike

Okay, if you said it worked fine for a few months, then likely you had the right ohm rating. Another, not uncommon issue with cheaper units is, the float has a small pinhole in it. By overfilling the tank, it submerged the float and allowed fuel into it. Now it doesn't have the same buoyancy and reads low.

Easy way to tell is to remove the sender and shake the float and if you hear any liquid inside, there is your problem. Just another idea to test.

I am tracking what you are saying, but I have the opposite problem. My tank reads halfway when empty and way past full with gas. When I add gas the needle moves toward the full mark. Instead of starting at empty the needle starts at 1/2 way mark.

Since it is an universal float (i.e. adjustable) maybe over filling the tank cause it to slip or get knocked out of adjustment?

Anyone adjusted a universal kit unit? They would have a better idea if that is possible? I have never seen one out of the tank.