How do I know if my head gasket is going? Advice pls..

 

there are many signs sometimes 1 or a few,
why do you suspect this, more opinions will follow , I`m sure

 

oil in your water or steam out of exhaust or water in your oil with mayo round filler cap are a few of the obvious ones

 

Full loss of coolant from expansion tank (unclear what caused the loss) - believed to occur over a couple of days.

Car drives normally at all times.

Temperature gauge reads normal. After a short spell of driving with boost (high rev range) the temperature gauge drops quickly - below the scale. Coolant appears to be boiling in the expansion tank.

Have checked for air in system. Doesn't appear to be any air (have checked bleed point and run for a while with expansion tank cap removed). Thanks for advice

 

some garages can pressurise the system and test for leaks,
some can analyse the water for noxious gasses, I;e inpending gasket failure.
others just hit and hope, water could vapourise as steam, if boiling up yes,
is cooling fan working,
could be leaky rad leaky heater matrix, pinhole in a water pipe thermostat housing rubber ring letting go, my guess its a zetec that's why I say rubber ring, loose hose clip,, what car would help , water pump gasket or failing pump seal ,
cream under oil cap as per 1-PD would indicate water in oil or dipstick tube or in breather pipes

 

Sometimes you can get misfires too.

 

Sapphire cosworth. Ok thanks will get them checked!

 

sniff test

 

Easy...

Step 1) Walk to the rear of the vehicle
Step 2) Look at the boot-lid just above the exhaust pipe

If it says "Cosworth" anywhere... the head gaskets gone.

 

On a more serious note - it sounds like you have indeed got a potential head gasket failure, but what your describing can be caused by other things too such as a stuck thermostat or sheered off water pump rotor. Both will cause localised boiling of the water which then creates pressure, air locks and water loss.

Does the system run the correct head pressure?
Once its up to temperature does loosening the cap release pressure or not? (It should and must)

Does water flow correctly around the system, has it been checked?

 

Hi there Anne27 not seen you on here befor.