Coolant in oil problem source?

Took my 2000 Sunfire (2.4 L not GT) to a mechanic for a routine oil change and was shown that the oil contained coolant and was very milky. Was quoted an excessive amount of money for a head gasket repair. I had the oil changed and took the car to the GM dealer for a second opinion. They did a pressure test on the cooling system (17 psi) and shampooed the engine but said they could not find any problem or breach of the cooling system. Their advice was to drive for a couple hundred kms and return so they could see the state of the oil for themsleves.

Since then I have driven for almost a hundred kms and the oil has become very milky again. Did they do all the tests necessary to check the source of the problem? Based on the info I have, what other causes of this problem could there be?

Thanks for your help.

It sounds to me like you have a bad head gasket. If the oil is milky like you said then there must be coolant leaking into the oil from the head. Due to the fact that the engine is a 4 cylinder and there is no actual way that coolant can get into the oil from the intake manifold then the problem has to be coming from the head or the head gasket. I don't know how they tested the engine but it sounds like when the engine gets warm the coolant is leaking. The only other test they could do is a pressure test when the engine is hot. If the head is warped or the gasket blown then the pressure should drop. If the water has been getting into the oil for an extended period of time you can do damage to the bearings and you may have to have the entire engine rebuilt or replaced. I would not continue to drive the vehicle. Cost to repair between $1200 and $1500 US. Head gasket with resurfacing of the head.