Bernie IMO if everything is normal at other than WOT your coolant temp must be rising as well, your cooling system is inadequate for constant WOT. Georges B.    -------Original Message-------   From: Rotary motors in aircraft Date: 06/27/05 09:02:09 To: Rotary motors in aircraft Subject: [FlyRotary] Re: Coolant Leak       On Mon, 27 Jun 2005 09:07:24 -0500 "Mark R Steitle" <mark.steitle@austin.utexas.edu> writes: Ed, Not to stir the swirl pot, but I thought that it was decided some time back that higher pressures were better than lower pressures.  The higher pressures are supposed provide more margin of safety before a boil-over occurs, permitting a thinner ethylene-glycol solution and enabling the engine to tolerate higher temps before experiencing catastrophic boiling.  So, I’m wondering where this leaves us.  Is it better to run at low (7-8 psi) pressures, or high (28-30psi) pressures?  Mark S. I agree, Al, inquiring minds at least like a plausible hypothesis and I think the discussion has led to that.  Perhaps I'll leave the "cup" of air, just for peace of mind {:>) Ed   =========================================== I thought higher pressures were good also because the higher boiling temp, but conversely more apt to leak. My volvo reservoir shows a max cool liquid level which leaves some air. Interesting my pressures look nothing like everyone else's. Where is everyone measuring the pressure. My sensor is connected to the small stem by the return inlet from radiator. I assumed this is one of the lowest pressures in the system. If I climb WOT, the pressure continues to climb steadily to 24 psi indicated and if the throttle is not reduced, coolant will be dumped by the cap. At 5500 rpm cruise, the pressure runs in the teens.   Bernie