2Gen radiator cap psi?

[BrianB]

I believe the stock cap is 13 psi. Mazdacomp recommends no higher than 17-18 psi. I have a Mazdacomp aluminum radiator that came with a 20 psi cap.
What is a safe upper limit?
Brian

[C. Ludwig]

I ran a 20lb cap last year without problems. I am concerned about seal life at that pressure though.

Chris

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Chris Ludwig
08 ITS RX7 CenDiv

[Silkworm]

I ran a 19lb cap for 4 events before I swapped radiators (old one was a kludge). Haven't gotten around to finding a bigger rated one for the new rad (it's a .9 bar so about 13lb)

PaulC

[BrianB]

Chris and Paul, thanks for your replies!

Did you guys notice any effect on water temps with the higher psi caps?

Right now I have 3 caps. A 20 psi on the radiator, a cap at the uppermost part of the water pump housing( has no marked pressure rating) and a cap/housing between the radiator and the overflow bottle connected by small hoses.It has a .9 bar rating.I'd like to eliminate this one. There's a tapping on the radiator filler neck for a hose to the overflow bottle.Havn't found a small cap with a higher than 20 psi rating for the water pump housing neck as yet.

Thanks
B

[Silkworm]

Well, I did notice a big temp increase with the rad switch, but not sure if it's the cap or the smaller radiator core, but I jumped 20* switching from my griffin to the Koyo. I'll try a higher pressure cap and do a compare/contrast at my next track day.

PauLC

[Festus E. Simkins]

In theory the only thing the pressure cap does is raise the temp at which the coolant will boil. If a 18lb cap raises the boiling temp to say 240 degrees F then a 20 lb cap will raise that temp to say 255 degrees F.

However, the higher pressure you run the more chance you have of causing a leak at a weak point. Case in point: While on a trip I once had a seal in my street car's water pump begin to leak. It turned out to be a pressure leak. I loosened the rad cap so no pressure would build. The temp gauge did not go any higher but guess what? The water pump leak stopped. Drove 275 miles and didn't loose a drop of coolant. P.S. I was towing a trailer with a D Production GT-6 on a 1100 lb trailer. The car was a 1974 Ford LTD. A long time ago.