3.0 V6, oil in coolant reservoir bottle dilemma.
After noticing what appears to be oil in the coolant reservoir bottle, I
decide to perform a sniffer test on my V6. I'm using an American made Trident block tester, to perform the test. Got the car up to temperature and started the test after the radiator fan came on. Initially I could only manage to squeeze the aspirator bulb a few times before it remained squashed, and there was no more air that could be sucked through - it was air tight. That first air that came through did not have any effect on the colour of the test fluid. After a few minutes when the fan came on again, some bubbles started to rise up through the device, and it took a few more minutes till the aspirator bulb expanded a bit and I was able to squeeze it a little, sucking some air up. This time the fluid turned to a blue green. After fives more minutes and more air comming up, the colour of the test fluid turned to yellow. It took ten minutes for the test fluid to turn yellow and prove that combustion gases are getting into the cooling system.
My observation from the test above, is that there is a trickle of combustion gases that come up into the coolant reservoir bottle just after when the radiator fan comes on.
Next I perform a compression test on the engine, and the outcome is that I've got 190psi on cylinders 1, 2, 4, and 6, and 182psi on cylinders 3 and 5. I carried that out twice on each cylinder, engine hot, so the readings are reliable. The difference on two cylinders is less than 5%, and the spark plugs were all clean and in good condition.
Don't know what to make of this compression test, as I was expecting to find two adjacent cylinders a bit low on compression.
The car is running fine, and it has just past a mot so engine emissions are ok.
The only signs of a head geasket failure, is oil getting into the cooling system, and a build up of pressure due to combustion gases also getting in.
I fear that it's at the early stages of a head gasket failure, but I'm not an expert on these matters, what do you guys think?