Head gasket gone?

[Decepticons]

Ok thought I would change the Thermostat and voila! Things seems better! The mayo may be the short journey thingy so going to check in the morning what its like. This morning there was mayo again so :/ No froth though no loss of coolant. Though once I was topping the coolant up I did panic as it took a while to settle

[Chris.]

What engine?  AJM 115 diesels are common for gaskets going.

Compression test wont always indicate a headgasket failure.  Only way a compression test would show a drop in readings would be if the gasket had blown between the cylinders, or you had a cracked head somewhere...but then you would probably have a very lumpy idle and a misfire.

[rockmonkey69]

A compression test is readily available at most garages and will suffice, so long as the operator is competent in diagnosing headgasket failure. In the past I've had to make do with some 3/8" long extensions as my only diagnostic equipment in diagnosing headgasket problems for a while  now there are a whole array of instruments available.

[Chris.]

How does a compression test find a fault between the oil galleries and water ones?

[rockmonkey69]

It doesn't any more than a sniff test if that's what you're asking. When the headgasket's integrity is compromised it will get worse and start leaking elsewhere with each heat cycle, making it's way into the bore. The best method of ascertaining with absolute certainty whether the headgasket has failed is by removing it. Leak down test, sniff test, compression test and water vapour test are only methods of diagnosis and not full proof.

For the purpose of general motorists a compression test, sniff test or leak down test will suffice. While none of them are 100% they have been used successfully in the industry with great success. A competent mechanic would be able to eliminate probable causes to derive at an ultimate probable cause.

[Chris.]

What im trying to say is a compression test wouldnt show anything as being 'wrong' if the gasket had gone between the cylinders.
A sniff test would indicate oil/water contaminiation, however that is clearly visible by the mayo thats been said in the coolant or dipstick.

[rockmonkey69]

You have been misinformed, a sniff test detects the presence of combustion gases in the coolant, not oil.

[rockmonkey69]

A simple test for oil in the coolant would be to look for separation in a sample mixture obtained from the cooling system. Oil and water are immiscible, the organic solvent will be ontop of the aqueous layer. It reminds me of an old secondary school science demonstration I used to show year 7 pupils, only with the addition of a suspension agent like methylcarboxycellulose or tragacanth.

For completeness the above does not conclusively indicate the presence of 'engine oil' but it will suffice for most, but if you was concerned with absolute certainty I would suggest the use of high performance liquid chromatography.

[Chris.]

BUt theres oil water contamination.  Not combustion gas/oil contimation.

I think its fair to say his headgasket has gone. You dont need any special tests to work out why there is oil in the waterways.

[rockmonkey69]

BUt theres oil water contamination.  Not combustion gas/oil contimation.

I think its fair to say his headgasket has gone. You dont need any special tests to work out why there is oil in the waterways.

Oil and water contamination are often found with combustion gas in the coolant. The latter case would be something a sniff test would be able to detect. As previously mentioned a sniff test does not detect oil in coolant as you suggested.

Oil and coolant contamination doesn't always mean headgasket failure, it is quite possible for this to be the result of a leaking oil cooler. It's crucial not to jump to conclusions with costly expenses so soon. All the tests mentioned are used in the industry with proven success, it provides the technician with a means of diagnostics and I would advise the OP to get it diagnosed before scrapping the car or paying for the engine to be taken apart. These tests are readily available, quick and cheap to perform.

The OP may or may not have a headgasket problem, it's important that the OP is able to make a well informed decision.