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RE: 85 528e corrosion in thermostat housing

henri baccouche asks:

>I am looking to buy an automatic 528e and while I was looking at a 
>1985 528e with 120k miles,the manifold preheater hose broke off the 
>thermostat housing.
>The alloy inlet was completely corroded.....Is this the ominous sign 
>of cancerous corrosion throughout the cylinder head ? or a small issue 
>of replacing the thermostat housing ? There are visible signs of 
>corrosion at all the hose connections. Is cooling system corrosion 
>anywhere indicative of corrosion through out the system? 

I had a very similar problem on my '86 535i. Crusty green stuff was visable
around the ends of the coolant hoses. Underneath the hoses, the cast aluminum
thermostat housing and the other fitting that bolts to it were deeply corroded
and pitted on the hose sealing area, so much so that grinding them smooth
was out of the question. However, the inside surface where the coolant flows
looked brand new. Same with inside the head. It was not a serious problem.

The cast fittings did require replacement but the cost (discount mail order)
was much less than I had expected, $20-30 apiece I think.

It's all because of a poor hose clamp seal letting coolant seap out slowly
and corroding on contact with air.

Mark Mir
'86 535i
Austin, TX