I would guess there's a temperature threshold somewhat below operating temp at which the pressure is pretty close to operating pressure.  If that is so:
Have the temperature, as it rises above that threshold enable the pressure alarm which would activate when pressure dropped.
Overpressures (like firing into the water jacket) would activate the pressure alarm regardless of temperature.

Just a theory .... Jim S.

lonnwood wrote:

Tracy, this has got me to thinking about an alarm system that would be useful for the coolant pressure gauge.A simple pressure activated warning light would not be useful because the pressure starts out at zero andgradually builds, then during different modes of flight when your engine cools the pressure would go back down.Not having flown with a water cooled system yet I don't know how much it would fluctuate.Would it be worthwhile to have a small processor programmed to keep track of engine temps and comparethose to what the coolant pressure should be, then set the alarm off if they don't add up?Lonnie

The best advice I can give is to learn the behavior (not just the static reading) of your coolant pressure gauge and pay attention to any anomaly.  It tells the whole story IF you know how to interpret it. Tracy Crook