Blown head gasket diagnosis

Good tip nitros44. Done that a few times myself however some testers aren't happy with you using the sniffer in this way. Need to be very carefull not to get too close and start sucking up coolant.

I did not state it is a method davidg
Its a tip,do you here its a tip given to members if they want to use it as some kind of indication,or point them in the right direction,most common outcome after seeing HC"s in the cooling system is a blown head gasket,very rare its anything else,I know coz I do it on a regular bases.
I don't want to bore the members of the ins and out of trouble shooting head gaskets.
Put it this way, an engine overheating with HC"S reading is just ruled out a simple air lock or just a faulty thermostat ain't it,how much time has that saved you.

Last week;
Impreza booked in for overheating,flat 4 engine-two cylinder heads-hydro carbons found in coolant system-suspect head gasket

So which side has the leak? (V12,V8,V6)

Remove the plug leads one at a time which alters the hydro carbon reading.
In this case the left hand side HC readjng had the more significant movement, and was causing the problem,head has to be removed and hey presto!!
Head gasket burnt out across cylinders.

Customer pleased that we managed to fix the problem by removing one cylinder head and not both just to be on the safe side.
Saved the customer lot of money in parts and labour.

nitros. Your post on using the EGA to source possible head gasket failure might be just what i am looking for as i am working on a customers BMW 535i V8 this week with what looks like a blown H/ gasket. I will run it into one of my local VTS's and follow your advice.

Thanks for the tip.

Thats a differcult question for me to answer Gaz,as there is no lower or higher limits to go by.
Normally the HC fig on the screen will top out at so many parts per million,by introducing a misfire which results in more raw fuel produced,the previous fig will see a increase,by that i mean it will be a very significant increase,its worth pointing out that the misfire only needs to be forced for a couple of seconds,a couple of times so as to protect the catalytic converter etc.If you have a gas analyser with a graph similer to a scope its easier
Where coil on plugs(pencil coils)are concered on flat 4"s and vee"S just insert a spark tester bewteen plug and coil to extend on to the plug.

I will nitros, and thanks again.

A Diesel engine will produce similar amounts of hydro carbons as a petrol engine.
Never attempted to try on a diesel as we don't come across that problem much as its not a issue that happens as much like petrol engines.
Will try it when or if we get one in.
Good point David by the way.