1997 850 wagon disappearing coolant

[Tobers]

I cranked it up with the a/c running and let it run for at least 45 minutes in my driveway. It was at least 85 degrees outside. For about 30 minutes the coolant level stayed the same. Then it slowly began to rise. Over 15 minutes (or longer) it slowly rose to the top of the reservoir. It seemed to hit a static condition, where nothing seem to be changing. I did not see any bubbles this time, though yesterday I saw some bubbles coming out of the small overfill hose. I'm guessing this scenario is max stress on the system, as the car isn't moving down the road. The car never ran hot -- always at midpoint on the meter.

After 45 minutes I cut the car off. When I did the coolant pressure cap began to leak coolant. Dang. I didn't expect that it would begin to leak when I cut the car off! I'm guessing the pressure increased when I cut the car off? Go figure.

Would a new pressure cap fix this? Should the reservoir stay at the same level when a car runs, or is it normal for it the level to increase as it gets most stress?

The amount leaking out of the pressure cap, if this occurs each time the car is run, would account for losing a reservoir of coolant every 2-3 weeks.

thanks. Rick

[scot850]

The pressure caps are designed to 'leak' if the pressure gets too high. The pressure does 'peak' when the engine is switched off as the fan stops and you get heat soak into the fluid as the pump isn't working. This could be the reason you don't see leaks. As the guys say, if the leak is small enough you may not get fluid hitting the ground before it evaporates. I would suggest having the system checked for over pressurising for starters and replace the coolant cap which do fail eventually.

Also check the header tank for cracks, the small pipe from the tank to the thermostat housing as suggested, and the pipe and unions from the pipe under the header tank that runs to the hard line at the back of the block. IF this one is leaking, you may see green residue on the hard line.

Finally, check the top radiator hose and the area around it for dampness. The radiators I've had fail do so in this area, or crack at the bottom RH side of the radiator.

Neil.

[abscate]

A radiator leak can evaporate but will leave white or green residue

It is hard to inspect the radiators on these cars without removing them, though.