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When should you change the coolant in an almost 30 year old car?

I have a 1990 Volkswagen Polo Estate that had one little old lady owner from new and has done 51000 miles. It has been serviced annually by the same local independent garage for 20 years. The garage owner doesn't believe in scheduled coolant changes, "because it's not necessary, they only say that to make you buy more antifreeze. I'm trying to keep her bills down, so I just check the antifreeze strength each year". It had a full coolant change (with new water pump) in 2003, one litre of antifreeze added in 2008 and nothing since.

The car is now having coolant trouble (two losses of about 700ml in the last 150 miles. Mayonnaise thick under oil cap before 10-mile run, still some present after the 10-mile run). Head gasket seems the obvious problem BUT a rapid drip-drip-drip leak was visible under engine after that run, which (annoyingly) had stopped by the time the car got round to his garage.Another oddity - the cooling system is retaining some pressure, even in a stone-cold engine - does that suggest there's a blocked water passage that might be cured by flushing? Of course flushing has its risks too, for a 27-year-old heater matrix. Any suggestions?

Asked on 28 March 2017 by CB Keymer

Answered by Honest John
There are two elements of coolant that deteriorate. One is its anti-freeze properties. The other is its anticorrosion properties. This garage owner hasn't taken account of the latter and the result is corrosion inside the engine. Any remedial work carries risk. The waterpump might be shot. I think all you can do is a twin pack Radflush, obviously with the heater set to max heat to get maximum flow through it. Polo 1.4 always suffered winter condensation inside the cam cover. Then pick a coolant with high anti-corrosion properties. Once the system is re-filled, leave the heater on full and run the engine from cold up to temperature with the expansion tank pressure cap off and that should gurgle through any airlocks. Put the cap back on when coolant starts geysering out.
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