Apr 27, 2010
Sherwood Park
1998 roadster 6spd
Hi guys, well, I am having a bit of trouble with this. I have been using Seafoam, but not at every fill and now I may have to use it more often.

What's happening is slightly different (I think) than what I have read about. If I fill up from empty, even with a full tank, I get in the car and the guage reads about 1/2. But, after driving it for some miles, the guage slooooowly creeps back to full.

Is Seafoam the answer? Is it just a matter of cleaning up the tank transfer orfice? What confuses me about this is, if the tank transfer from one to the next is slow, how can the guage read half now and full later? What I mean is, if the tank transfer is not occurring, the guage should read half because there is only half- gas is not getting to the other tank at all.

Do I have a guage/sending unit issue? Or do I have an understanding problem- I am not "getting" the real problem?


My car has done this off and on. I think it is just one of those C5 things. I don't think this is something that Sea Foam fixes as it's not a build up of material that is throwing off the gauge but I may be wrong. One day I may splurg to replace the sending units but the $1500 it will cost could be used in other areas right now. I may have a bead on a cheap fix if you can get the tanks out yourself but will have to find it.

My car also drops to E when at the 1/3 tank mark. If I drive it a while longer, it comes back! I think this is more where Sea Foam works as it removes the buildup that keeps the fuel sending unit from reading the level. Sea Foam fixed this a couple summers ago for me and I may throw more in, but I rarely let it get below half a tank anyway.

In the meantime, use your trip odo. If your gauge or sending units should shat the bed, then at least you can go by that to know when to refuel.
Tank Half Full

I bought my car in NC 5 Yrs ago and was driving back through Cape Hatteras when the 1/2 full tank went to 0 on the gauge, with all the alarm bells and whistles going off. At that point I filled it up and it would only take enough fuel for 1/2 tank. When I got back home I put in a couple bottles of Chevron Techron and switched to Shell detergent gas and the problem only occured once since. It has been OK for the last 5 years and I annually put in a bottle of Techron at the end of the season before storage. (which I buy at Target or Walmart in the US)
Sounds like there is more of a detector failure in your case especially after treating it and having the buildup respond to Sea Foam.
I only use Sunoco Ultra 94 in the car and put a container of Techron in the car every once and a while.
The Seafoam works sometimes but if the resistive coating on the tank level indicator has been eaten away
then you will have to drop the tank and have the tank level sensor replaced.
I dont think its a cheap option so you should keep trying the Techron or the seafoam for a while.

There is a little resistive strip that is mounted on a circuit board and a conductive wiper on the level arm, this can
have a buildup of gunk on the strip so you do not get a proper reading. It can also be eaten away in spots
so the tank gauge will only work at certain levels but not at others.
Last edited:
Thanks for that explanation of how the tank float works, makes perfect sense...I remember reading awhile back about how to drop the tank for the do-it-yourselfer and it didn't seem too hard. I just don't want to have to do it if I can avoid it. This is my wife's car and I wouldn't want to screw something up in trying to fix it myself. She loves it and could not stand to be without it.
I had the same problem as well after getting the car a few years back . Did some playing with different PREMIUM fuel only from different gas companies. So far after going to ESSO fuel I have not had a single problem with the gas gauge going to empty around half a tank . Just my experience but might be worth a try and no I do not work for ESSO as well . lol
Just thought I'd update the situation. I started using Seafoam again, which seemed to alleviate the problem. The guage is swinging easily again, and reads full after I sit in the car after fillup.

Seafoam, however, just changed thier packaging, which now leaks!! Every can I checked on the shelf had an oily coating, and on some, you could see how it was leaking around the newly designed nylon cap. Just me complaining, but I hate it when companies move away from something that works just for the sake of change- and the "improvement" is worse than the original.

And I forgot to add previously- I only run Esso Premium.
You should contact Sea Foam and complain. They may send you some free Foam! Who knows. That is lame that their product leaks. My car half gauged me the other day so I believe I'll throw a bottle or two through my car as well.
I had the same problem on my 02 a couple of years back and ever since I started using our GM Fuel System Treatment every so often I haven't had a problem since. I use it in all my cars and have had great success with it.

If anyone wants to try it, let me know. The regular price on a 591ml bottle is $26.35 but I will sell them to anyone here for $14.19 if you mention the words "Car Club".

Last edited:
Old Thread: Hello . There have been no replies in this thread for 100 days.
Content in this thread may no longer be relevant.
Perhaps it would be better to start a new thread instead.

Similar threads

Users who are viewing this thread