Silverstone

I think I may need a new AST cap cause I have that coolant alarm going often after driving some good distance and then letting it cool. The next time I fire it up I get the low coolant buzzer. I check the coolant and sure enough it is about 2 inches low each time. Having no overheating whatsoever though.

Is the AST cap on the after-market metal ones the same size as the stock AST from Mazda? If so then I can just order one from Mazda. I've tried the local auto parts stores and all the metric numbers on the cap just baffle them. Here is the info on my cap:
R123
88 kPa
.9

I measured the diameter of the lip the cap fits over as 5.5 centimeters.

BTW the other smaller cap on the cooling system was easy to find at the auto parts store. They just plugged in year and model and handed it to me. I hope this solves my problem. It is cheap and if it does not work at least I'm not out much money and I will rule out the caps as the problem.

scotty305

iTrader: (2)

88kPa and 0.9 (bar) are pressure ratings. The AST cap (parts stores will be familar with the term "radiator cap") will vent and relieve pressure at about 13 psi. Just ask them for a 13 pound radiator cap that matches the one you have. If they can't find that, they shouldn't be working for an auto parts store.

-s-

bajaman

I can only vouch for the Tri-Point aftermarket AST here, but its opening is MUCH larger than the stock AST. The cap it takes is huge by comparison to the stock AST or the stock filler neck.
You simply need to do as scotty305 suggests, just take your (suspected leaking) cap to any autoparts store like AUTOZONE, O'REILLY'S, PEPBOYS, etc and tell them you want a 13 psi cap (they get ALL fucked up if you start talking 'bar', lol!) that matches what you've got. It needs to be the venting type.
And make sure you have a stock, non-venting type on your filler neck.

CantGoStraight

I have a Tri-point AST and my cap is the exact same one as the stock AST. My Pettit AST used the larger one found on most radiators. I have pictures. The cap with no label on it came off my original stock AST.

bajaman

CantGoStraight - Man...that is odd. My stock AST cap measures 1.150 on the inside diameter, whereas the Tri-Point measures 1.530....basically there is 3/8" difference! I wonder if Tri-Point made a few different sized necks?

CantGoStraight

That would be my guess (different suppliers/makers) for tri-point. I bought mine from them specifically because of the use of the stock caps. I used my original AST cap only I removed the sealing rubber to make it pressure less (I'm running Evans coolant) The tri-point was a stronger version of the Pettit AST . I found the Pettit AST would flex or distort if pressure was placed on the cap. Any way just thought I'd pass that info along. Jack

bajaman

Yes, it is good info to get out to the public, details like this are what make the Forum so worthwhile.