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