Diagnosing HGF - general

Honest John Back Room » Technical matters
What is life like with your car? Let us know and win £500 in John Lewis vouchers | No thanks
View Threaded
Mon 13 Dec 2004 12:13
Diagnosing HGF - general - GrahamF1
My girlfriend's Fiesta is starting to deposit mayo on the inside of the filler cap and neck.

Now I've always been told that this means the head gasket's going, but how do I make sure that it isn't just condensation forming in the rocker box on cold mornings? Any other tell-tale signs for HGF, possibly more cast iron that the old mayo one?

Really don't want to lift the head in the middle of winter, so someone please offer me some alternative explanations...!
Reply | Report as offensive | Link
Mon 13 Dec 2004 12:40
Diagnosing HGF - general - Number_Cruncher
If the head gasket has failed in a manner so as to produce creamy slime in your rocker box, you should find some coolant loss. If you do find coolant loss, then here are three checks (I'm sure there are more);

1) Using an exhaust gas analyser, 'sniff' the air above the coolant expansion tank with the engine running - if the head gasket has failed, no products of combustion should register on the analyzer's display

2) Using a coolant system pressure gauge, check the pressure in the collant system. As the engine warms up, you get a pressure increase, which is, of course expected. With a failed head gasket, the pressure rise is very high and fast - revving the engine also makes the gauge shoot up if you have HGF.

3) If the coolant is leaking into the cylinder, you can get hydraulic lock if the cylinder fills up. If it isn't that bad, the spark plug of the affected cylinder can sometimes be different in appearance to the others - as if it had been steam cleaned!

Hope that helps.

number_cruncher
Reply | Report as offensive | Link
Mon 13 Dec 2004 15:55
Diagnosing HGF - general - GrahamF1
Thanks for the advice.

No noticeable coolant loss. Breather hoses and cap filter all ok. Rocker box cover cleaned out completely last week when I serviced it, and the mayo was back within days.

Can only think it must be condensation...?
Reply | Report as offensive | Link
Mon 13 Dec 2004 12:58
Diagnosing HGF - general - mini, pug, landy, Andy
could just be a blocked breather hose

my mini (original not a BMW jobby) started doing it very badly (thick white sludge inside rocker cover)

i found that the breather hose going to the carb was perished and flattened and also the little filter inside the oil filler cap was bunged up,

replaced hose and filler cap lifted and cleaned out the rocker cover (in kitchen sink, girlfriend NOT happy) and the sludge never came back

andy
Reply | Report as offensive | Link
Mon 13 Dec 2004 18:01
Diagnosing HGF - general - Sprice
What is the actual temp guage registering? The mayo could just be from too many short runs where the engine is barely warm, then being switched off.
Reply | Report as offensive | Link
Mon 13 Dec 2004 18:14
Diagnosing HGF - general - Peter D
High detergent oils like GTx are prone to this at this time of year. If you are not loosing coolant then it would appear to be fine. Remove and clean all vent pipes. Is the mayo on the cap or inside the rocker cover as well. Come back with oil type. A gas check is ok but you cap hace a water to oilway leak thus no gasses. Regards Peter
Reply | Report as offensive | Link