The cap on my coolant expansion tank is stuck (W209 M272 Engine). It doesn't budge even a tiny bit when I try to open it. If I try closing it more, it does have some give.

Has anyone else had this happen? I'm worried I'm just going to end up breaking the tank by squeezing and turning too hard on the cap.

 

do you have an oil filter wrench?

 

Yes, will that safely get it off? I think there's a tab on the bottom of it and maybe it got misaligned or wedged aginst the stop?

 

I dont think you really have any other choice. Either you get it off or you break it. One way or another you're going to need access eventually.

 

If it's that well stuck, it's probably time for a new cap, and maybe even a new tank. Both are prone to leaks with age. The gasket in the cap will leak, and the tank will leak at the overflow nipple or the seal between the top and bottom halves.