My 1980 TR7 (iron block/alloy head) has remained continent since new with Bluecol and latterly Comma super coldmaster blue coolant. The important thing is never to change it, as once any corrosion has used the suspended oxygen, it will cease. If you had a second failure, the head might need skimming?

Many thanks for comments and suggestions so far. The original head has been successfully welded and skimmed twice and each time the repair was good until corrosion occurred in another similar area adjacent to the fire rings....here the original casting has a wall thickness of just a few mm.

I have always used aftermarket Comma Coldmaster and changed it every couple of years, but still the corrosion continues, despite the product being marketed as suitable for cast iron and aluminium engines.

The engine is now on it's second head, and the recent failure is identical to the others, that's why I posed the original question. I'll wait for further comment and then ask HJ.

RAB.

I don't understand the basis for coolant anti-corrosion package selection, and, from very brief recent research with a different objective, it seemed that the readily available published information wasn't likely to be specific enough to answer the OP's question.

VERY naively, I might look at "hybrid" anticorrosion packages (HOAT) which allegedly combine inorganic and organic anticorrosion additives, but I believe they are boh acids

Re thinking of "an effective non-ionic inert coolant medium",I suppose that'd be ethylene glycol in water, not unfortunately an option for me without extensive re-design.

I'm stuck with seawater, which...er...isnt really very non-ionic at all.

I understand my engine accomodates this as a coolant without disintegrating almost immediately (to the extent that it does) by the use of zinc anodes in the cooling passages.

Perhaps they would be useful in the OP's engine, if he could find anywhere to put them.

In that application, magnesium might be more effective.

https://www.anodeoutlet.co.uk/01303-zinc-anode-for-1gm-6ly3-yanmar-engines-27210.html

Edited by edlithgow on 27/11/2024 at 23:05

The primary reason to use anti freeze is for the anti corrosion function, the secondary function is to stop freezing in cold conditions.

Er, no. To the (limited in the UK, since you need both) extent that primary and secondary function has meaning, other way around, pretty much by definition. Hence the name.

You can get anti-corrosion coolant, that I understand has no antifreeze function, and I considered buying some in Taiwan, where I had no need of antifreeze.

Didn't do it because I'd never heard of the stuff, (claimed to be German, suspicious in itself). I believe the genuine article does exist though,

<< 50/50 antifreeze / deionised water is the optimal mix you should be using.. Less than 50/50 concentration will result in long term dissimilar metals corrosion problems. >>

I suspect diluting concentrate with deionised water may be more important than you think, especially if the alternative is hard tap water. I'm not convinced that 50/50 strength is needed to prevent corrosion, and it certainly isn't to prevent freezing unless your car experiences arctic conditions.