I previously posted about having oil in my water resevoir, and have had the same thing told to me.... Head gasket.... However, could an oil cooler line in the radiator be leaking and causing the problem since there is no water in my oil and the oil pressure is higher than the coolant pressure? Also, is it normal for the top radiator hose to the thermostat to be very hard (from pressure?) after getting to normal operating temperature? One more..... How can I best find out which type of system I have in my car, a REX or other? Where do I find that info? Thanks for all your help for this very novice mechanic/Volvo owner.