I bought a 1996 volvo 850 Turbo, hoping to find a good car for my wife. I replaced the spark plugs and wires, dist. cap, thermostat and flushed the radiator, fuel pump, and did an oil change. The 850 Turbo has 183,000 miles on her, and overheats after driving or idealing for just a little while. I can stand there, with the engine on, and the hood up, and watch the resevior for the coolant level rise up and up, until it blows the cap off. What could this be?
I had a friend tell me it was the head gasket, and he said it isn't worth it. I'm a mechanical guy, and I could do a difficult job, if that is what it is. Any help would be greatly appreciated.

Thanks

 

Does it blow steam out the tailpipe? If you or the previous owner been driving it like that it could be a cracked head in addition to head gasket job. And at that mileage you may as well do a top end OH while you're at it.

What do you mean it blows the cap off? Is it screwed on? Have you pressure tested the cooling system (cold) and the cap?

 

no, no steam out the tail pipe, what is a top end OH?
The cap is screwed on, and the pressure it seems just build, and the resevior gets to the top, and then blows off the cap. Maybe it slowly unscrews it, i dont know, but after it happens, the cap is somewhere by the engine if not on the ground, and the hood is covered with coolant, as well as the ground.
I haven't pressure tested the system or the cap, how would I go about doing that?

 

Top End OH = top end overhaul, removing the head and replacing the head gasket. The head gasket is the most likely cause of your problem.
Some of the auto parts stores will loan out a pressure tester for the cooling system. Make sure they have the screw on adapter so it fits your reservoir.
You can have a cracked head, cracked block or bad head gasket. The head gasket is the weak link and the most common but stop running the engine until you get it fixed or you will ruin the engine. You can also pull the spark plugs and compare them. One, two or three should look "cleaner" than the others. These would be the cylinders that are getting coolant. To get enough pressure to blow that screwed on cap off you'd have to have coolant leaking into the cylinder(s) and the cylinder blowing it into the cooling system. Funny you haven't blown the radiator or heater core.

 

When my head gasket blew it did the exact same thing. Each compression stroke blew into the water jacket, the pressure built and built and would blow the cap off. Just a word of advice...I waited 6 days before I pulled the head off my car. This is what it looked like. Dont wait.

 

Thanks for all the tips guys! I can't say how much I appreciate you all responding so fast, I have gotten better information from ya'll then from the three mechanics I talked to in town.
I am going to get a pressure tester and see what it says, but am also looking into head gaskets and head gasket sets. Do you have any advice on which one to get? I have been looking for a tutorial on how to replace the head gasket (knowing it will be quite a job) and thought somebody might know of a good one online, or a book would be ok too.

 

Two post above your's is a great head gasket tutorial. LOL
https://volvoforums.com/forum/volvo-...ts-pics-44879/

 

The head gasket is just that. It is one gasket that goes between the head and the block. In the picture above where you can see the pistons that is where you'd clean the surface and lay the gasket down before setting the head on. You need the set. The set will include most, sometimes all the gaskets you will need to reassemble the top of the engine. Anything you take apart to get down to that head gasket like intake manifold, exhaust manifold, distributor, etc will usually have a gasket in the kit. Replace gaskets you touch if they aren't in the kit and also think about doing maintenance. Now will be the perfect time to replace the "PCV" box or at least remove it and check to make sure it isn't clogged with sludge. That PVC box hides under the intake which is that black plastic box with the two nipples (one with a hose attached) on it in the picture in the lower left. AND, if you have any doubt about the quality of the heater hoses now is the time to do them as they are a chore to do with the head in place. If you have and doubt check to see IF you can see where the one by the distributor goes. As you have a turbo, also replace the 1 or 2 inch cooling hose that goes to the turbo. It's about a 3/8" line on the left rear corner of the engine. Better to put a new one in there now than run yours till it pops. I use fuel injector clamps as they are easier on the hose than the standard worm screw stainless steel. It's a buck or two more expensive but they seal better and will allow the hose to last longer. The hose and clamps about 5 bucks and it's so much easier doing it now compared to on the road with it hot and steaming and your 12 dollar a gallon antifreeze peeing out all over the place.