My 2002 Volvo S60 has a coolant leak which I cannot find. The system stays pressurized - I can leave the car sit overnight, the next day take of the resevoir cap and there is lots of pressure released. After adding coolant the car will go 200-300 miles before the coolant low warning comes on. Today I filled it and after warming up fully the level went up to the overflow return. I went for a drive and after a couple full-throttle accelerations the coolant low light came on. When I got home the level was down to the MIN level. Just prior to buying the car the timing belt and water pump was replaced. It has been several months and I just keep adding coolant. Engine oil looks fine. Cannot find any exterior leaks. Any ideas about were the coolant is going and what the fix is?

Some are hard to find. had the same issue with my 850 especially when it's very cold. Check the heater hoses and radiator hose connections on the drivers side. Tighten all the clamps. Check the turbo water line connections. Remove the timing belt top cover and check the water pump. check for drips under the car after sitting all night. Another place to check is the thermostat housing. the paper gasket between the head and housing are known to leak. Lift up the coolant bottle and check for cracks. They get brittle with age. Any dried yellow looking crust usually indicates a leak.

I guess what really has me stumped is that the system holds pressure - overnight or even longer, so a hose leak, etc., doesn't sound likely. Seems to point to the turbo...?

mine held pressure also. a small drip may stop when the pressure drops some. I doubt it's the turbo. Could be a head gasket issue. Has the car been overheated? ARE YOU THE ORIGINAL OWNER? It may only leak when it's hot when the pressure is up. You will just have to go around checking everything. Heater core? Check under the carpets to see if any coolant is under there.

I have looked and looked and cannot find any leaks. I was thinking about using dye and a florescent light - anyone had any luck with that?

replace the radiator/or overflow cap and that should solve your problem if you don't see a leak or signs of a leak.

It turned out to be a bad head gasket - a test confirmed exhaust gases in the coolant. Typically there is white smoke out of the exhaust with a blown head gasket, but for some reason even though I was going through a lot of coolant it didn't puff white smoke.

Big tip off - if the car is cold, and you have lots of pressure when you take off the reservoir cap its probably because of exhaust gases pressurizing the system. Also, with the car cold, take off the reservoir cap to release any pressure, start the car and run for 60 seconds, then screw the cap off - should not have a pressure build up.

Total job cost $4,400!!!!!!! and it wasn't at a dealer. There were a bunch of, "its your option, but as long as we are in there we should replace x". Also had the valves/head gone through $900 (part of the $4,400).

These cars are ridiculously expensive to fix, and not as reliable as some will lead you to believe. The car has a common 3rd to 2nd gear downshift issue. When the trans goes out it will be $3,000+.

I would not have spent the money to do the head gasket except the angle gear and rear differential had recently been replaced.

I am going back to GM.