I am the proud adopted father of a 90 780, a couple of days ago as i was passing a lesser automobile on the highway i felt a change and noticed that the car was nearly overheating, after pulling over i could see smoke coming from under the hood after a quick check of all roses and clamps i found my Heater control valve cracked in two, being pressed for time i replaced it with an HCV from the auto parts store down the street, the car holds coolant now but will slowly over heat over the course of a few minutes (i have yet to let it get into the red on the temp gauge) , whne i pull over and pop the hood the reservoir appears to be empty, but when I remove the coolant reservoir cap with the engine hot all the coolant bubbles up into the reservoir and when i restart the car after only a matter of a minute or two the temp levels out as i drive away then slowly begins to build again. I am a bit of a rookie here sorry for the long post any help would be greatly appreciated.



-runnin hot in chicago

I really hate to say it, but something very similar is happening to me....
In my case, It's definitely a bad head gasket.

You can supposedly buy a test kit at Napa for ~10$ that checks for combustion gases in your coolant.
How long after starting your car (from cold) does pressure appear in the upper radiator hose? If there's pressure appearing within a few minutes of starting, it's a bad sign. It'll be combustion gas pressurizing the coolant system.

Try adding pure antifreeze. My car initially had no white smoke because I was using nearly pure water after many aparent "overheats" while driving only a few miles. After adding antifreeze and burping the system, everything seemed fine - until I started it up later that day, it blew coolant out the reservoir, and started blowing white smoke (not with every engine pulse) out the tailpipe.

I sincerely hope it's NOT your head gasket, but I encourage you to get a test kit for exhaust gas in your coolant.

Best of Luck,
Will
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1990 740 Turbo, on its way to stock specs, maybe beyond

Oh, how I hate to be the bearer of bad news, but . . .

Similar thing happened to my car, 1991 745 turbo, summer of 2008. Wife left house, HCV cracked, and she pulled over and shut down within a mile of home. Told her to start it up, watch temp gauge and drive carefully home. It did not go into overheat. HCV was spewing steam/coolant. I let it cool off and removed the HCV and hoses and capped off the connections. Car seemed to run fine, but something was wrong, hard to put finger on. She started drinking coolant, a little at first, then more and more. There was also something else that was just not right, but hard to put a finger on. Slowly, over the course of a couple of weeks, she began to show signs of overheating, the temp gauge would creep higher and higher. One day she just fully overheated and that was it. Time for a new cylinder head.

Short version: She, like your car probably did, warped her head during the short episode of loosing coolant. Symptoms were the same - drinking coolant and starting to show signs of over heating. It will probably get worse and worse.

Take it to a reputable mechanic (oxymoron?) and have them take a look at it. If you catch it soon enough, you might be able to save the head that is on the engine. If it overheats again and warps more, it might wind up needing to be machined way beyond the Volvo specs, which I advise against. But the situation is not going to get any better if you keep driving it. And, I strongly doubt that the problem is your water pump or thermostat.
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Scott Cook - 1991 745T, 1986 Toyota Tercel (Don't laugh, it is reliable, faithful AND gets 41 mpg!)

Sudden failure of the heater control valve cost me a head-gasket job once in a 745 turbo. The engine then quickly overheated, and cold tap water was put into the cooling system to limp home (won't make that mistake again). In that case, the head gasket failed into the combustion chamber and the car began emitting a nice hue of white smoke. Car had about 150K miles when HCV blew. Since then, changing that failure-prone valve is a first order of business after purchasing a wagon with the red-block engine. Chris in VT, '94 945, 153K.

Possible partially stuck thermostat?
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than for the reply

how would i test thermostats' opertability?

i just realized the vacum hose isnt conected to the valve gonna grab the keys and see if that was the problem.

thanx again

just replce the Thermo, for the cost it just never hurts to replace them espically since they are so easy to get to! if it turnes out not to be the thermo then your most likley looking at a failing water pump.

The vacuum line just opens/closes the valve to allow the water/antifreeze flow into the heater core area. That won't causes overheating if the valve won't work. The only real way to test thermostat is to pull it and put it in boiling water. They are relatively cheap.
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as dumb as this sounds where is the thermostat?

The hose that leads from the top of the radiator connects to the thermostat housing.

If you remove the hose and then the two 10mm nuts at the housing it will pull away from the head to reveal the thermostat.

Install the new thermostat (make sure you get it in the same way the old one was installed) with a new rubber gasket and replace the housing and hose.

Air in the cooling system can cause a problem like you describe. After fitting the new thermostat watch for a rise in temperature like you are experiencing now. If it goes beyond normal just shut off the engine and let it cool completely. Then when you check the coolant resevoir you may find the level has fallen and needs to be topped up. Repeat the process if needed.

Randy

themostat replaced, seems like problem is solved, drove for a bout 10 minutes in city stop and go and engine maintained a temp just left of center on the temp gauge it appears all good, the only time the car has been in the red was for about 10 seconds as i exited highway and immediately shut car off and found busted HCV the car was not started again until the HCV was replaced. the slow overheating showed its face on the highway drive home, when the car began to overheat (3/4 to red on qauge) i stopped and loosened drain cap forcing coolant through part of the systems this brought the car back down to operating temperature, this happened a few times on the 7-8 mi in stopandgo traffic, in other words it hasn't been driven in the red. fingers crossed my head is ok the car has about 215,000 on it now and it would be nice to see 3


thanx to all

-W

http://www.brickboard.com/FAQ/700-900/Cooling.htm
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Post Back. That's whats makes this forum work.

thank you for the link, i have read the faq, if you can find where it answers my question please enlighten me...

thanks

Which question? You have asked several.

Have you put the new thermostat in yet? If not, don't worry about the air bubbles now because you can get more in it when you replace the thermostat. Overheating can ruin a thermostat, so you have to put one in before you can do any more diagnosis or ask any more relavent questions.

Charley

To replace the thermostat you don't really even need to even disconnect the radiator hose. Just take off the two housing nuts.

is there any way i could have an air bubble in there somewhere?