I know the cheapass ones from autobone and kragen leak a lot. I am about to order a new cap from mazda for the coolant filler neck.. but I have an aftermarket AST. I know it's either 13lbs or 16lbs but my concern is more in getting a quality cap that won't leak. Appears to be a greddy aluminum AST but there isn't a logo on the ast itself. The mouth is about a 1.5" opening. Those cheap caps from autozone fit, but I want one that isn't going to leak.

You can see the AST in the bottom right hand corner of the pic.

 

The AST appears to be a Pettit or something similar.

The cap that fits the Pettit is a Stant 11329/11330 (13lb/16lb). It is also availabe from Napa as part# BK7032461/BK7032462 (13lb/16lb) for $4/$5.

The 13lb cap corresponds to the Mazda recommended pressure after the collant system recall.

To confirm this is the correct cap, measure the depth of the pressure cap mount. If it is 16mm, you need a Stant 11327. If it is .75 in, then the previously posted part numbers are correct.

I had the Stant cap for 4 years over which time it worked fine. After letting it sit for 2 months while I replaced the cooling system, the cap went bad. I replaced it with a Napa cap and it has worked great so far.

Hope this information helps.

 

Found my old AST, had the cap with the "S" on it. I believe it's Stant! I threw it on, but I am going to pickup a new one. Thanks for the info bro!

-Darren-

 

The safetly pressure release (with the red lever) are known to leak, get one without the red lever. I just replaced one that was brand new.