A very effective method for checking for cooling system leaks
is to pressurize the cooling system BEFORE you start the engine.
Once you start the engine you can be fooled by the system
pressure as the coolant expands as it heats up. You could be
losing coolant at such a low rate that the pressure remains normal for
quite some time. The leak could be internal within the engine through
a water O-ring failure.

Pressurizing the system when its cold on the other hand will immediately
show you if there are any leaks.  Here is the guts of the little 12 volt
electric compressor Perry and I used to trouble shoot his cooling system failure.
Available in any auto parts store as an emergency tire pump.

I am going to mount one of these permanently under the cowl (without
the black plastic case) with a switch on the instrument panel. It only
takes a few seconds of operation to get the system up to 30 psi.

Paul Lamar

Rino Lacombe wrote:

Hi Paul,

Super idea.
I drilled a hole on the thermostat housing, taped it to 1/4" NPT, installed an all
metal valve (brass) with a metal cap.
I am getting the engine ready to start on the test stand.  Put the pressure ON, had a
few leaks, fixed that.  Now I know that the cooling system has NO leaks.  I do not
have to wait until the engine has run for a while before finding about a cooling
system leak.  If I wait for the engine to build the pressure, by that time the engine
is HOT and it is much harder for example to change the thermostat housing gasket --
like I had to do in this case.

Presurising the cooling system will be on my preflight check list.
I will probably not install the air compressor permanentally in the plane, (weight
considerations)  I will carry it in the car.

Rino

 
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