Diagnosing a blown head gasket

[ianess]

What are the classic tell-tale signs of a blown cylinder head gasket?
I recently had to top up the coolant when the heater output started to fluctuate without any advance warning. It's been back in and checked out under guarantee but I'm still not 100% happy. Also noticing the famous sludge in the oil filler cap, and a fair amount of steam out of the exhaust.
Am I being paranoid?

[tigga]

How is the engine running ? I'd have thought that if the head gasket was blown from a cylinder to both water and oil, it would be running like a bag of spanners.

Have a look at your spark plugs, ideally they should be dry and a tan colour, there is a series of pictures in all haynes manuals to compare them to to aid diagnosis.

To be absolutely 100% though, the best bet would be to call out a diagnostics guy, he will do compression tests, use a probe in the exhaust to test for water and/or unburnt fuel and test your coolant for traces of hydrocarbons too for about �35, at least then if there is a problem, you will have it in black and white for your warranty.

[homer75]

You are right to be paranoid. The mayonnaise type sludge and losing water would worry me. Tigga is right, cylinder compression test and pressure test on cooling system will confirm one way or another.

[Narolines]

Sounds to me like you've just described the classic signs! I'd put my money (well, perhaps someone else's money!) on it being the head gasket, but in accordance with everyone esle, get it checked properly to be sure.

[Fresh121]

Has anyone used Steel Seal ot repair a head gaskit?