gas cap stuck - PeachParts Mercedes-Benz Forum

speeddemon2008 · #1 07-14-2008, 03:04 AM

Well went to the gas station today and had to fight to get the cap off. Finally got it though. Then went to put it on and it would not click shut. Got home to figure things out better and it did finally click shut, but now I cant get it off. Any suggestions on this?

My car is an 89' 300se
Thanks Jacob

rocky raccoon · #2 07-14-2008, 07:17 AM

Gas caps today seem to all be constructed using inner and outer subassemblies that are constructed to "release" (click) when tight thus maintaining a fixed pressure in the fuel tank. That mechanism is failure-prone.

I had a similar problem on the fuel cap on my BMW motorcycle. To get the cap off, I carefully drilled a small hole through the outer cap going through the upper side of the inner cap without going completely through. If you then take the drill bit out of the drill, you can reinsert it in the hole effectively pinning the outer and inner assemblies together allowing you to remove the cap. In my case, I put a sheet metal screw into the hole permanently fastening the two parts of the cap and defeating the "clicker" assembly. Still works great after six years.

speeddemon2008 · #3 07-14-2008, 11:34 AM

thats pretty funny. dont know if i want to drill in case i get any shavings into the tank. I will see what i can do...

BENZ-LGB · #4 07-14-2008, 03:48 PM

Do you want to risk a spark, or heat from the drill, setting off a gas fire?

I had the same problem happen with my '89 300TE. I managed to pry the gas cap off by inserting a screw driver between the edge of the cap and the edge of the filler neck. The I "jiggled" the screwdriver as I turned the cap in an effort to "pop" the cap off. If you are able to align the "hooks" in the bottom of the cap with the "openings" on the filler neck while using the screwdriver as a lever you will be able to pry or pop the cap off.

In my case it was an old and broken gas cap that caused the problem. The bottom of the cap has a plastic part, that turns (as you close the gas cap) and locks the cap in place. This part gets old and worn and then when it locks it won't disengage from the filler neck.

The filler neck is made out of a soft metal (aluminum?) so be careful not to distort it. If you damage the filler neck, you will have to replace the entire tank because the filler neck is an integral part of the tank.

Good luck.

rocky raccoon · #5 07-14-2008, 07:31 PM

Shavings issue: Don't drill all the way through. If you do, the cap will not hold pressure. If you screw up and go all the way through, your fuel filter will easily handle a few shavings.

Spark issue: The inner cap is of aluminum thus will not spark.

crashone · #6 07-14-2008, 09:27 PM

Put a big (15'') adjustable wrench on it so you can get some leverage, when it comes off, turn it upside down and spray it down with WD40. Work it on and off the filler tube, spray somemore WD, keep working it until it losenes up and works right. Wipe off the filler tube and excess WD from the cap, have a good day.