I just purchased a 2002 Discovery II with 131K miles (my first Land Rover) for my son. I assumed the vehicle had a head gasket problem when I purchased. The previous owner said the car had sporadic problems with overheating and the last time it overheated she had parked it. I checked the oil and it was probably 2+quarts high and mixed with oil.

After I purchased, I read a few threads here where people replaced head gaskets and still had a leak into the oil. It appeared the problem was either the valley gasket or the gasket for the timing chain cover. I decided I better check compression before I tore into the heads. I ran a cold compression test and all cylinders were between 155-160 psi. I assume this means the water came from one of these other know sources and not the sleeve liner, block, heads, head gasket , etc. Is there a way to determine which gasket is bad. I am planning on pressure testing the cooling system to find any external leaks. If I pulled the oil pan would could I determine where the internal leak is coming from?

My current plan is to pressure test the cooling system and check for external (and possibly internal leak), drain the cooling system, change oil (is there a recommended way to flush the water out of the oil system?), and then start the engine for a very short time to make sure the main bearings were not damaged from the previous owner driving it with the problem. If that all checks out, I assume I have avoided an engine rebuild/replacement. I can then replace what ever gasket needs to be replaced for the internal leak and then flush the cooling system and chase down any cooling problems. Is this a reasonable approach? Does anyone have any further suggestions on how to diagnose the internal leak?

BTW, the car will start and runs fine, but I am obviously not going to run the engine until I resolve this problem. The check engine light is not on and I have not tried to pull any codes yet.

Thank you for reading.