On 6/24/05 3:18 PM, "Ed Anderson" <eanderson@carolina.rr.com> wrote:

Hi John,

A couple of things.  Tracy and I both discovered that one ALL the air is out of the coolant system, the coolant pressure may jump to 21 psi almost immediately upon start up - long before the heat would cause it to build to that point.  At first, I thought "coolant Leak", however, I could never find any evidence of coolant in the chambers nor loss of coolant in the system.  Talking to Tracy Crook, he reported the same thing.  We came to the conclusion that without a small cushion of air that the pressure sensor was seeing hydraulic pressure caused by the pump.  With no air cushion even a small disturbance would likely cause the pressure sensor to indicate high pressure. As the block and components heated up the coolant volume got a tiny bit larger due to expansion of parts and the hydraulic pressure quickly decreased.   At least that was the best theory we could come up with at the time.

During flight the pressure would quickly decrease until it was below 10 psi and on cool days would got to zero.

On my flight back home (some air still in system), the coolant pressure never got above 12 psi (right after take off when hottest) and most of the time ran at 8 psi.   So if you are seeing a nominal 10 psi and only seeing the 25 psi on startup, I don't think you have any problem especially if no evidence of coolant in exhaust stacks.  

Ed A

Ed, I think that maybe it takes few moments for the pump to accelerate the mass of coolant inside the cooling system. That’s why the pressure at the pump outlet is high for a while?
Buly