Vernon Klukas wrote in message .. .
5. Galvanic corrosion .. magnesium is at -1.6 V and alumnium at -0.75 V on
the galvanic table. That is a big different. You definitely need something
to separate the two or the magnesium is going to get gobbled up !!

Hmm, perhaps. I get that aluminum alloy is about -1.05. But look at
the difference between Cast Iron (-.5) and aluminum (-1.05). Lots of
cars, with WATER running through their engines, have cast iron blocks
and aluminum heads. In this situation, there is no ready source of
electrolyte. I don't see this as a huge concern. I'm more bothered
by oil leaks.

Auto engines have head gaskets between the electro different metals,
plus if you don't run an inhibitor is a mutli-metal water cooled engine
you will corrode the aluminum away, period.

Yours
Vern

Vern is 100% correct. I have repaired several automotive engines where
this has been a problem. I used Belzona Super Metal (1111) to repair
the problem. Also have used it to fix a multitude of diesel engines.
These were do to electroylisis and cavitation. This is caused because
the owners did not change or maintain the proper chemical balance of
the antifreeze.
Toyota engines require the Toyota antifreeze. Dexcool is not approved
and according to a Toyota engineer, it will eventually damage the
engine. He also told me not to mix Dexcool with glycol antifreeze.
To make a long story short, follow the engine manufactures
recommendations.