As Ed mentioned in a recent post, He gave
me his spare radiator cap when mine was found to be defective. It had
been bad since day one when I installed it on the Renesis
installation. I had noticed that the coolant pressure was low
(almost zero) after the engine cooled down after initial climb out but had
written it off as normal for the new system since it was cooling
adequately.
I've been flying with good pressure after replacing the
cap and noticed that the cooling system performance was generally
better. What really interested me was the change in temp differential
between the water temp at the combustion chamber side and the intake/exhaust
port side (I measure it in both locations). Previously, there
was an 8 - 10 degree rise in coolant temp as it went through the port
side and I had assumed this was due to the increased exhaust port heat
transfer to the coolant on the Renesis. This really bugged me since it
represents a LOT of BTU into the coolant. Now that the coolant pressure
is normal (~10 psi at cruise) the port side temp increase is down to 1 - 3
degrees. The question is, why?
So far, the leading theory is water pump
cavitation. The low coolant pressure allowed the pump to cavitate which
reduces coolant flow rate which in turn caused the temp rise to be
higher. As a side note, the Renesis uses the same pump design as the 3rd
gen, a cheap stamped sheet metal impeller instead of the nicely scrolled cast
impeller of the 2nd gen. I think the stamped impeller is more likely to
cavitate.
Anyway, this almost eliminates what I considered to be
the only down side to the Renesis vs the earlier 13B.
Tracy