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Q: I'm losing radiator coolant but find no leaks and the motor runs smooth on 1991 Cadillac Eldorado

Motor runs very quiet, very smooth, 82,000 miles. Have looked and checked everything but find no leaks. Parked there is no fluid loss only after being driven. Water temp is always in normal range in town or on hiway, never goes above 230 in town and hiway is normally about 200. Radiator doesn't appear to be rusty. Keep Prestone 50/50 filled to the top always.
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Thank you. I'm 82 and have driven the wheels off of a lot of cars so have already checked the oil and it is not milky. Thank you, I will have the system pressure checked. This is a GREAT site, wish I had found it years ago.
I believe I can tell you what the problem is: My friend has a 98 Eldo 4.6L and he had the same problem and he took the car to a raditor shop. I told them that no fluid was leaking on the ground, ever, but he put about a quart of coolant a week in the car and the info center would not show low coolant. The mechanic put a radiator and water pump on the car at a cost of 900.oo dollars. Car ran fine, except at idle it would have a ever so sliog it had a ever so slight miss, the problem is not any of the ones fixed, but a head gasket blown in a very small area between cylinders, put stop leak in car and it stopped the loss of coolant, but in time that could stop up the radiator so I found a guy in California that has a two part solution the works wonders. It cost 275.00 I have his e-mail address if you would like. It fixed the car and has been fine for over a year. It will cost over $2000.00 to have the engine pulled, if you can find someone to do it. The problem is greater than just a head gasket because the Northstar engine has an aluminum block and re-torqueing the head bolts pulls the threads out of the block, helicoils will not stay in under that much torque. So the fix that this guy in calif has works and will allow you to drive the car for quite few more years.
Mine had the same issue. It was the heater core. Look under the floor mats on the passenger floor. My brother was burned on his foot from the coolant leaking on that area. It was a $350 fix for me at my mechanic.
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