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Thermostat sticks after changing H20[850/1995] posted by Craig on
Tuesday, 10 March 1998, at 8:26 p.m.
Why will the thermostat not open after changing the coolant or lowering the level and re-topping off? The thermostat works fine all year, then I change the water pump, re fill the coolant and start the car. The thermostat sticks shut and temperature continues to rise until it hits red. I shut off the car for fear of blowing it up, tap on thermostat housing (which gurgles), and restart car. Temperature climbs again and I (clenching my teeth) let it TOP OUT where the thermostat finally opens and temperature goes down. I don't know what else to do to get the thermostat to open after changing coolant. Now, just as before it works just fine and opens when it should every morning. Any reasons and remedies? Thank's -Craig
Re: Thermostat sticks after changing H20[850/1995] posted by Roy on
Wednesday, 11 March 1998, at 10:06 a.m.
Thermostats are cheap, just replace it.
I had a problem similar with an american car after replacing the anti-freeze. Replacing the thermo fixed it. I have had thermostats stick open or closed intermittently and replacing them fixed it.
Such a little part so much trouble.
Roy
Re: Thermostat sticks after changing H20[850/1995] posted by Rex on
Wednesday, 11 March 1998, at 11:49 a.m.
I'm a tech at a Volvo dealer, and have this happen to me about one out of every five times I replace a water pump.
I have no idea why it happens, but it's hard to explain to a customer why their car now overheats, and requires a new thermostat, after replacing a leaking pump. Now we almost always include a new thermostat when replacing an h2o pump.
Good luck Craig.
Re: Thermostat sticks after changing H20[850/1995] posted by Randy on
Wednesday, 11 March 1998, at 3:00 p.m.
>I'm a tech at a Volvo dealer, and have this happen to me about one out of >every five times I replace a water pump.
I respect the fact that you are a trained professional technician- having said that, however, do you think that it is possible that some of those bad thermostats may have just been a cooling system that needed "burped"? I too experience overheating after draining and refilling the cooling system on my Volvos. Sometimes I have to heat the system up and let it cool down two or three times before the air is finally purged and I can replace the full amount of coolant. Just recently on this board someone suggested loosening the thermostat housing just enough to allow the air to escape before tightening it back up and adding the remaining coolant. Seems like a reasonable fix and I believe I'll try it. I had a '67 Saab 96 that had small petcock on the heater (which was very high up in the cooling system curcuit) which allowed the air to escape after servicing the cooling system. My understanding is that the Saab 900's are well known for giving people problems with air locked cooling systems.
Re: Thermostat sticks after changing H20[850/1995] posted by Glenn Goodspeed on
Wednesday, 11 March 1998, at 9:21 p.m.
Hmmm.... Nobody mentioned Murphy's Law. More often than you might expect, repairs on one part of a system seem to cause trouble in another part of the system, when it is really just a coincidence of two parts failing at the same time.
However, in this case, I would suspect that the thermostat had been oriented in a way to prevent the efficient passage of air. When refilling a cooling system, air is trapped in some of the high points. A thermostat should always be fitted with the air bleed hole in the highest position relative to the ground to aid the escape of trapped air.
The bleed hole is a small hole in the flange of the thermostat. Volvo original thermostats always have a bleed hole, but I've noticed some aftermarket parts do not. If you have one of these, I highly recommend drilling a 1/16" hole in the flange to serve as a bleed hole.
You can make things worse by allowing a large quantity of air to become trapped in the heater core. To avoid this problem, always turn the heater on full blast when draining and filling the cooling system. -Glenn.
Goodspeed's Volvo 1800 Newsletter
Re: Thermostat sticks after changing H20[850/1995] posted by Craig on
Thursday, 12 March 1998, at 8:36 a.m.
I think Glenn and Randy are both right on this one. I never looked for the air bleeder hole in the thermostat when I installed it new, and come to think of it, I had the same sticking problem when I first installed it! Secondly, I loosened the thermostat housing bolts to see what was going on the other day when it wouldn't open. Air did burp out, and shortly after, the thermostat opened and is now doing fine. -Craig
Re: Thermostat sticks after changing H20[850/1995] posted by Ed Lipe on
Thursday, 12 March 1998, at 9:29 a.m.
Nailed that one squarely on the head. ED7