Coolant concern

Q I’m worried that my daughter’s Vauxhall Corsa 1.2 petrol with 28,000 miles is showing traces of oil emulsion in the coolant expansion tank. The engine oil dipstick is of good appearance and there is no loss or gain of oil or water. The coolant is clean and clear, but the presence of emulsion inside the cap and on the underside of the tank top is of concern. I first noticed this a few

months ago and used a clean rag to reach in with a bent finger to remove as much of the emulsion as possible. Some remains, but it has not changed in appearance or quantity since then. The immediate thought is of head gasket failure, but am I correct in thinking that on this engine there is also a possibility of oil/water communication through the timing case? Martin Keating

A As there is no loss of coolant or rising of the oil level, it is unlikely that the head gasket is allowing coolant to mix with the oil. If this was the case, I would expect to see evidence of emulsification on the dipstick and the coolant level would be dropping.

The emulsified oil may be seeping into the cooling system via either the head gasket or the water pump to timing cover seal, but there would be more evidence of this in the coolant if it was the case.

If your daughter bought the vehicle only recently, there is a possibility that a gasket has failed previously and the emulsion you found in the header tank is purely the residue of a previous problem. It may even be due to somebody inadvertently pouring oil into the header tank – I have come across this in the past! If this is the case, I would remove the header tank and clean it out using warm water and washing-up liquid, then refit it and continue to monitor the situation.