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Oil in Coolant

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I have recently bought a 5 year old XK5.0 from a private trader with less than 20,000 miles on the clock. I found Oil mixed/floating in the header tank. The local J dealer  did some tests and said they could find nothing wrong so they removed the header tank and cleaned it out and flushed the coolant.  All semed well for 100 miles so concluded someone had put Oil in  the header by mistake. Now after a few  hundred miles of motorway driving, the first signs of Oil are reappearing, some emulsification and maybe  a teaspoonful floating in the surface of the water.



What is the next step in getting to the bottom of the problem?


Any help much appreciated.



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Hi Jo, and welcome to the club.


I have seen this before in a Rover Sterling, about 20 years ago which was eventually diagnosed as a failing cylinder head gasket.


There could well be another reason, and hopefully it will not be an expensive one.





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Hi joe,

Iwould say Peter is correct in his diagnosis. There is an Oil gallery seal in all engines on the cylinder head and it sounds like yours has failed between the Oil gallery and the water jacket.

Hope its not too expensive to fix.



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Thanks for your responses guys, I also wondered if it could be this but I understand that both the engine Oil and the gearbox Oil pass through the radiator to be cooled so it could be a leak in the radiator somewhere. I wondered if anyone had experienced the problem specifically with the XK with its complex cooling system.


I would like to know if it is common and how the cause of the problem was diagnosed. 


Thanks again,



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  • 5 years later...

Just a tip to help.

Check if you have water or coolant in the Oil, since Oil systems work at higher pressure oil will be going from a higher pressurized side into the coolant which is at lower pressure, the top pressure for cooling system is  15 or 16 psi, Oil runs at a higher pressure, this will indicate oil getting into the coolant at heat exchanger, the xkr has one under the supercharger in the v of the block, on the other hand the head gasket side will be different way since oil is just dripping from valve train down to the sump, water or coolant will be in the oil if head gasket is blown and coolant excaping (usually this happen with compression blowing from the pressurized cylinder 150 psi into the cooling 15 psi or oil drain back under atmospheric pressure at idle due to pcv vacum), when the engine is shut off hot pressure will remain in  the coolant side and will try to go in the oil heat exchanger side with minimal possibilities because the oil in the galleries does not drain back and has minimal space to accept the coolant and if a little coolant gets in it will evaporate and be discarded by the pcv system when the engine gets hot again, base on the pressures explained here I would check the engine oil and if there is no emulsified traces of oil and coolant in the oil, then for sure I would look into the heat exchanger or engine oil coolers, check the one in the v of the block for a bad seals, on the other hand if a head gasket would be blown, when the hot engine is shot off, high pressure will not be in the cylinders anymore, this will permit low of coolant to the cylinder and could cause hydrolock when trying to crank it the next day after cool down, and definitely will get a burnt coolant smell in the exhaust. my 2 cents

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