I have 1997 850 NA with 134K. For the past 1000 miles it has been using about 1 cup of coolant per 100 miles. I can find no coolant leaks however there is a gray foam on the dipstick when I remove it. The oil appears normal when I changed the oil, no milkyness. The oil filler cap and oil fill area look completely normal. The car runs perfectly, no white smoke from the exhaust. As far as I know the car has not been overheated although I am the 3rd owner. I assume this is a head gasket leak allowing coolant in tiny amouts to enter the crankcase. Has anyone had a similiar experience and how much risk am I putting the engine in by continuing to run it if it doesn't worsen. Thanks much.

Pull your timing belt inspection cover and observe your water pump after the engine gets good and hot (radiator fan should be going on and off) The pump may be dripping antifreeze from the weephole indicating it's about to fail.

Don't assume headgasket until you checked out everything else first. Inspect the sides of the radiator, the coolant lines from the block to firewall, the bottom of the overflow tank, the cap for the overflow, and the heater core. Do this after the car is up to operating temperature and engine off, use a paper towel to look for color.

If it is a headgasket, a compression test will help. Removing the head and replacing the gasket is a costly procedure, usually more than finding a replacement engine.

A leakdown test can also be done. So can an oil contamination test, to check for antifreeze. Froth on the dipstick can be the result of the engine oil not getting hot enough to burn off condensation.

Klaus
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Proud owner of a 220S. If I had more room, I would have more Volvos.

One cup every 100 miles is a pretty slow leak and it just may be hard to spot until it gets worse. The stuff on the dip stick may be just from doing alot of short trips. Try tightening up all the hose clamps. You may not have a head gasket problem.

A warped head is usually a drastic, noticeable problem. Leaks around the plastic sides of the radiators are easy to get if you have had any fender-bender or very rough roads.
The leak will more than likely get worse and finding the culprit will more than likely get easier...
I had a leak on the tiny fuel line on the back side of the motor that feeds through the block. It was difficult to get to, but definitely easier than replacing the radiator.