John at Mazdatrix claims this is caused by a failed pressure
cap. Even in street cars. I am not so sure. It looks like
simple corrosion to me. In any event it would not hurt to
buy a pressure cap tester. Such a cheap device can be critical
to the cooling of your aircraft engine.

A pre flight cold cooling system pressure check using compressed air
would accomplish the same thing.

Paul Lamar


Paul,
Could this be caused by depleted corrosion-inhibitors in the coolant as a result of not changing the anti-freeze regularly, or possibly using the wrong type of coolant? I don't see how a defective pressure cap could cause this damage.

One more thing I've been wanting to ask for quite a while now, but never did.  Since we're discussing cooling system corrosion, this seems like an appropriate time to ask it.  It concerns electrolysis in the cooling system.  I have heard that the radiator needs to be electrically isolated from the engine in order to prevent electrolysis from eating your radiator.  Would using wiggins couplings, or braided SS hose, throughout the cooling system provide enough of a electrical path to set up an electrolysis situation?  If so, can I add some insulation gaskets in the wiggins couplings to interrupt the electrical circuit and thereby prevent electrolysis from starting?  Or, am I worrying about nothing?

Mark S.


No telling the history of that engine. The owner could have been using
tap water to cool it. As I understand it and not very well it takes
a voltage difference between objects to cause galvanic corrosion.
Use a digital voltmeter that can read down to milli or micro volts
and measure the voltage difference. If you have a voltage difference
you have galvanic corrosion... I think.  :)

Paul Lamar

We have an engine that is made up of aluminum and iron sandwiches. That in
itself is a recipe for galvanic corrosion. It can be controlled by proper
use of passivating layers provided by the additives in glycol coolant made
for aluminum/iron engines.

I don't know of a meaningful voltage drop test that can tell you that you
are 'safe' or not in such a system because of the intimate contact between
dissimilar metals in the Mazda engine.

Running with plain water, or with the wrong additives could be detrimental
to the health of your engine.

Bill Schertz
KIS Cruiser # 4045