how much lbs should the radiator cap be rated for? The reason I ask is because the one on the AST says that its a 13lbs cap. But the one that autozone gave me for the readiator was a 16lbs cap. Will that make a big difference on my coolant system? Or is that cap correct?

 

If your cooling system is in good shape the higher capacity rad cap will work for you by lowering the boiling point of your coolant. In other words, dont worry its a good thing!

 

I know you meant RAISING the boiling point, keeping it from boiling so easily... I get dislexic, too, sometimes.

 

ok just checking.

 

When the cars were built they had 16 pound caps. After the recall Mazda installed 14 pound caps if I recall correctly. I use a 14 pound cap.

Running the coolant at higher pressures will allow higher temps without boiling at the expense of additional stress to the hoses and internal coolant seals.

Increased system pressure does not make any change in coolant temps if the water is not boiling. There is no sense in using a higher pressure cap if you don't have to.

 

Orginal system was 1.3 bar (~19 lbs), and changed to 0.9 (~13 lbs) after a recall that included fan relay mods. Many aftermarket caps for R's are 1.1 bars (16 lbs) and some dealers amd Mazda North America itself did not change 1.3 cap in recall.

 

The orignal FD cooling system cap was 1.2 bar, or 17.4 PSI. The recall changed it to 0.9 bar, or 13 PSI. The pressure was reduced because some cooling system components - mostly hoses and the AST, I think, couldn't handle the pressure and temperature, resulting in engine fires and a safety recall. Mazda made production line changes as they built more cars, so later ones only needed a few new parts per the recall, while earler production cars needed more new parts, including even a new water pump for some, IIRC. You can find out if Mazda's records show whether your car had the recall performed on it by asking a dealer. Mine was supposedly done by the dealer prior to sale, but it had the 1.2 bar cap on it until I noticed it. So, the dealer probably lied, charged Mazda for the recall, and didn't do it.

 

lol, i knew it was something like that...

 

Good post. That explains a few things that are happening with my car.

 

Factory spec on cap was 1.15-1.45 Kg/cm2 (16.4-20.6 psi) per the FSM. Orginal caps were marked 1.3.

Read the TSB Recall 94V094000 .. items would be changed out IF sign of leakage.

 

Thanks Julain, I stand corrected - the original caps were 1.3 bar (not 1.2). That is about 18.85 PSI.

I saw a post years ago about some 1.1 bar Mazda radiator caps also being used on FDs.

 

Further, the hoses that failed causing the fires were the coolant hoses going to and from the turbos. Mine suffered that fault (happened to first owner at about 20,000 km). The car got new turbos and a new engine due to the fire. The fire is caused by glycol running onto the red hot turbo housing. Glycol burns well! Hey, it's cheaper than gas - maybe I can run the engine on it!

If you are going to use the higher pressure cap I'd reinforce the turbo coolant hoses with stainless mesh. Otherwise, I'd recommend the lower pressure caps as posted above.