1998 Cadillac Catera

Engine Cooling problem
1998 Cadillac Catera 6 cyl Two Wheel Drive Automatic

We have a 1998 Cadillac Catera, 3.0 L engine. There is a small coolant leak ( 2 litres per week with daily driving) that seems to be a little worse on extremely hot days. This coolant is showing up in the engine oil but not in the cylinders (no smoke) and not at the spark plugs as the car starts and runs very well. We have an appt. With the dealer to have it checked but I would like to be knowledgeable about the oil cooler/head gasket issue and cost beforehand as most dealers assume that women know very little mechanically, therefore they can charge us more ! This car has many little issues that I have dealt with so far but the could be (or not) very serious. Any input you could give me would be most helpful, Thank you in advance.
August 11, 2010.

I assume there is no indication of an external coolant leak. The cooler is in the center valley of the engine, and I would think you would have more chance of oil in the coolant as opposed to coolant in the oil. How did you determine there is coolant in the oil?

Aug 15, 2010.
Coolant keeps going down, oil increasing ! Dropped the oil out and had considerable coolant in it but not in the cylinders or spark plugs. No external leak that we can see.

Aug 16, 2010.
It is odd, but it sounds like you are on the right path. I woul think that if it was a problem with the oil cooler, you would have oil in the coolant. Reason being, is your cooling system is limited to building about 16 psi of pressure, the oil pressure can range from 4-10 psi at idle, and increases with engine speed up to 40-60 psi. There is no oil pressure when it is not running, and if hot, the cooling system can retain some pressure when it is shut down. This would be the only time cooling system pressure could force it's way into the lubrication system. The only exception, would be if there is a coolant leak in an area void of oil pressure. An example of this would be a possible leaking head gasket near an oil drain passage, or a crack in the cylinder head, or block where it could leak into the crankcase. Those can be challenging to diagnose.

Aug 17, 2010.