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?