A gasket
 

Well I went to top up the windshield washer tank today and when I flipped open the yellow snap on lid, I noticed that the gasket under the lid had fallen into the tank. Fished it out and it looked rough and shrunken. Too small for the cap. Went to the shop and found a silicone rubber mat that is used on stove tops between the burners to protect the glass. Perfect I thought, for such a gasket. Nothing sticks to this stuff. Hope it does the job.

Re: A gasket
 

There's a gasket on there? mine don't have one.

Re: A gasket
 

Ya, I checked the yellow cap of the coolant overflow tank and it had no gasket under the cap, but the windshield washer tank had a strange foam rubber gasket with a strange plastic backing. This had shrunk smaller than the cap diameter curled a bit and fallen into the reservoir. God only knows what's going on when someone else can get in under the hood eh?

Re: A gasket
 

Weird, no traces of a gasket or washer on the two XJs I have. I thought it was supposed to be open for venting purposes.

What model Jeep?

Re: A gasket
 

An '08 Sahara 2 dr. It's odd too, now that I think on it, because the cap just snaps on and off - no threads to indicate it must be an air tight seal. Hmmm? Now I'm wondering if I should remove the gasket I built for it. What you said makes sense now. Otherwise the pump would start to pull a vacuum as the fluid level goes down.

Thanks oldfart & salad! Your feedback has me convinced that I should have no gasket at all under that cap. Of course I'd failed to mention the previous owner who abandoned this vehicle at 1300 Km on the odometer in 2009. That's why I got it for a song.