Over the last few years I've noticed more and more coolant (Evans) in
the overflow tank.

This is an open non-pressurized system -- a header tank on top of the
firewall -- bottom outlet goes to the pump inlet, and near top to the
thermostat (cap) filler neck.

I though the problem was that there was a small leak in the system
somewhere so coolant was not being sucked back into the header tank and
engine as the engine cooled down.

Now I'm beginning to think that it could be blown (or weak) o-rings
allowing compression/exhaust gasses to escape into the cooling passages,
forcing out the coolant.

In a normal pressurized system, one should be able to look at the
coolant pressure gauge (I don't have that -- no sensor) and see pressure
increase as RPM is increased if there were blowby, I guess.

But how do I do it in a non-pressurized system? Add a pressure gauge and
temporarily block the hose to the overflow tank and run the engine for a
few seconds?

I'd rather not do an engine rebuild if I don't have to. Any other ideas
(than coolant o-ring) of what could cause coolant to accumulate in the
overflow tank?

One more data point: on flight before last the water temp (sensor
mounted near top of pump housing -- filler neck) dropped to 60F (same as
with disconnected sensor), went back to land, and during and after
landing temp showed 185F. I figured it must have been a bad connector,
but was worried about lost coolant. Later I pulled the cowling and found
about 1/3 more in overflow tank that what I'd seen last time the cowling
was off.

Finn


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