Early warnings of head gasket trouble
QI had my Maestro 1.3’s head gasket replaced a while ago after a spectacular failure. The garage skimmed the head and flushed the coolant, but the expansion bottle still had a thick coating of primordial ooze. Now, I’m getting paranoid about a repeat failure – some mayonnaise around the oil filler cap, traces of oily froth in the water and occasionally running a little hotter than usual. How can I tell if it’s working up to another explosion? Philip James, New Brighton
AFirst, remove and clean the expansion bottle so you can see what’s going on. If oil is being deposited in it, you’ll want to know at what rate.
When the gasket initially failed, there will have been mixing of oil, intake mixture and exhaust gases in the coolant – and there’s likely to have been water in the oil, too. The garage should have also changed the oil, removing most of the water content with it. A little may remain, though, added to by the condensation that forms in the rocker cover during winter motoring. This can create a modest amount of mayonnaise around the oil filler cap, which is nothing to worry about. If it just needs an occasional wipe with a small rag, it’s probably fine.
In the cooling system, meanwhile, a coating of oily gloop may have been laid down on all the internal waterways. Regular flushing will eventually get rid of it. Do this in spring when the engine can be safely run on fresh water. Drain it hot after a good run. A flushing compound may assist removal, but it’s primarily designed to remove limescale and rust rather than oil. A slight deposition of fresh gunge in the expension tank is nothing to worry about – it’s just the old oily deposits travelling around.
The occasional hot running might be caused by oily clag in the radiator (cured by a couple of flushes). Or the thermostat might be lazy to open, not opening fully or specified to open at a higher temperature than the one it replaced. You did replace it along with the head gasket, right? A thermostat’s likely be to damaged by overheating – and it’s also one of the most likely causes of overheating and subsequent head gasket failure in the first place.
Having put your mind at rest, here are some danger signs to watch out for. Bubbles rising into the expansion tank are suspicious – but only if the (previously cleaned) tank smells heavily of petrol or exhaust fumes. It may just be air that’s got in courtesy of a loose hose, or similar.
Very heavy caking of mayonnaise in the rocker cover is a worry, especially if it reappears soon after cleaning the last lot away. Don’t forget to clean out the crankcase
breathing system too, or the problem will quickly repeat itself.
If it occasionally runs very hot, then expels coolant if you stop or drops harmlessly back to its normal temperature if you continue to drive, this indicates a buildup of gas beneath the thermostat. This is especially common if the thermostat lives high up in the cylinderhead. This implies a major leak. It’ll need to be sorted – but it can be temporarily overcome to get you home by removing the thermostat.
Don’t forget that the head bolts should be retorqued 500-or-so miles after fitting a new gasket. Go round them with a torque wrench if you haven’t already. They should be 55lb ft in your case.