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Volvo 850 R Thermostat Replacement

I recently replaced my thermostat and I thought I'd share what worked well and what didn't to help others. The pictures are all from the top of the car. Descriptions under the pictures.


The thermostat housing bolts can be a real problem to remove. Starting 1 week before I planned on doing the job I began treating the bolts with PB Blaster. Rather than spray it from the can I sprayed PB Blaster into a glass jar and used an eyedropper to apply the solution to the bolts. I treated the bolts before I left for work when the engine was cold and then again when I got home and the engine was hot. Just a few drops around each bolt.


I purchased a 5" long bit torx 3/8 socket from McMaster-Carr item # 6939A87. You really need the long bit due to the angle of the back bolt and the fuel rail position. If you try to use a short bit you stand a good chance of stripping the head of the bolt making for a much more difficult job. As you can see from the image above the angle still isn't ideal due to the fuel line. I decided to disconnect the line to get better access to the back bolt.


On the right side of the fuel rail is a schrader valve remove the valve cover and depress the pin to release the gas. I put a paper towel under it to catch the gas that came out.


Back on the left side of the rail above the thermostat housing I disconnected the fuel line again using a paper towel to catch the gas as it drained.


With the fuel line disconnected I had a much better angle at the back bolt and using a break bar was able to easily free the bolts. The picture above shows the coolant line already removed from the thermostat housing. I chose to break the bolts free before I drained the coolant, I wanted to be sure I could remove them.

To drain the coolant level I elected to use the drain cock on the bottom of the radiator. Having just replaced my radiator in the fall I wasn't looking to drain all the coolant just enough to bring the level down to avoid a mess when I took the housing off the thermostat. Draining wasn't difficult, getting the drain cock to stop leaking was a problem for me as I'll describe later.


Remove the thermostat cover and replace the thermostat.


Make sure you install a new gasket on your replacement thermostat. Be sure to put the gasket on the thermostat and not over or under it or else you'll have leaks and laughs from the board members. When you replace it make sure the bleeder valve is positioned to the front. The picture of the old thermostat shows the bleeder valve in the front. Replace the thermostat housing using NEW BOLTS. Volvo has a replacement part that is made of a harder material that is superior to the soft metal screws that were originally used. Part number 986228.

Reconnect the fuel line and refill the coolant you you're all set.


As I mentioned the drain cock was a real problem for me. When I tightened it back down the O-ring ripped causing a leak that left me no choice but to drain the coolant and get a replacement O-ring. Not quite sure why I had 2 O-rings, I suspect there should have been 1 and the extra one fouled the needed O-ring. I replaced it with 1 O-ring and so far no leaks.
After reviewing many threads detailing drain cock problems my recommendation would be to remove the bottom radiator hose to lower the coolant level.