Chris;

 

More pressure doesn’t translate to more cooling, but it does increase the temp at which it will boil, and reduce the probability of cavitation in the pump.  And recognizing that pressure caps are differential pressure valves (the absolute pressure on the coolant decreases with altitude), it’s good to use a cap with a relatively high pressure, maybe about 25 psi. I’d also suggest that the plumbing should be such that the pressure cap is on the inlet side of the water pump.

 

Probably the first thing affected by higher pressure would be coolant system hoses. If you use good quality hoses, and change them every few years or 100 hours, pressures up to 30 psi should not be an issue.

 

Al

 

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Chris and Terria
Sent: Monday, September 13, 2010 2:56 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Radiator cap - system pressure

 

Gents,

 

What pressure caps are you running with?  What maximum should be used?  I currently have a 16 lb cap, but have found ones up to 29 – 31 lbs.  I know more pressure means more cooling, but is there a maximum limit before hurting the engine?

 

Chris