Replace your Thermostat on a 850/S70/V70/C70

By Matt

Overview

The thermostat is located between the engine and the radiator. The thermostat acts as a valve that stays closed during engine warm-up. When the thermostat is closed, it prevents coolant from leaving the engine and circulating through the radiator. When the engine gets warm, the thermostat's spring valve opens, allowing coolant to circulate through the radiator to be cooled.

If your Volvo is overheating (it failed closed) or the temperature needle is no longer reaching 3 o'clock (it failed open like mine), you need a new thermostat.

Tools

ratchet and 10mm socket
ramps or jack and jackstands to get the front of the car off the ground
blocks for the rear wheels
torx bit size T40, long
WD-40
bucket to collect coolant
funnel

Procedure

Raise the front of the car using a jack and jackstands, or if you have ramps like me, with ramps. Put the transmission in Park, activate the parking brake, turn off the ignition, and block the rear wheels. If the temperature needle is anywhere but 'cold,' wait an hour so that the coolant is cools. Remove the big black plastic radiator splash guard (one bolt on each side, 10mm I believe) under the radiator. Remove the cap on the coolant reservoir, then place the bucket under the plastic radiator drain valve. This can be found on the driver's side, bottom edge of the radiator. Drain about two liters of coolant into the bucket, then tighten the valve back up. Be very careful with this valve... it's plastic and they have been known to break easily.

The next step is to loosen the two torx bolts that hold the thermostat housing together. Two things to note: spray some WD-40 or other loosening agent on the bolts, and, you may want to take off the aluminum fuel injector rail guard to get a better look at the hidden torx bolt. Ok, on to the details...

One torx bolt is easy to get two... the other is, well, difficult. I got a torx bit and used that on an extender with a ratchet, but the bit was forced to contact the bolt at an angle that almost caused the bolt to get stipped. I'd strongly recommend getting a long torx bit like this. You don't need to remove either of the hoses that connect the housing to the radiator and coolant reservior. With the torx bolts off, the top of the housing comes right off, as does the thermostat inside.

Take it out and put the new one in. Put the top back on, tighten the torx bolts, and pour the coolant back into the coolant reservoir. Don't forget to make sure the reservoir cap is put back on and the drain valve is tight. Put the splash guard back on and you're ready to go.

Conclusion

Like I mentioned above, you can try to use a short bit to get the difficult torx bolt out, but my strong recommendation is to use a long one, or if you have the grip of Arnold Schwarzenegger, a T40 torxdriver. While you're replacing the thermostat, you might as well replace the coolant also, flushing the system in between. I didn't because I didn't have any Volvo antifreeze with me, but I'm going to pick some up in a week or two. Why Volvo brand? Because it's not that much more than name-brand stuff, and it's what my owners' manual says to use, and it's what a very experienced independent Volvo mechanic said to use.

Reader Comment Author: Nick I. The long T40 bit (a $15 investment) is a must! Definitely use some W-D40 on the bolts wait about 4 min (get a beer). Pop off the fuel rail. Loosen the easy access bolt first then the harder to reach one. Pull out old thermostat....replace with new. (replace bolts) then attach fuel rail Fill the reserve and go. Est. time 11 min. It's that easy! Reader Comment Author: Robert I had I similar problem but I found siphoning the coolant out to be very useful, very little mess and if you use a clean bucket the coolant can be reused (my coolant was only put in two days before so was worth saving), no jacking needed. Siphon out the expansion tank, so you can release the top radiator hose then stuff the pipe down the inside of the rad to the bottom, and then drain the rad. Pulling the coolant up a clear pipe (fish tank hose or wine making hose), till near the top, and then pinch off the pipe, and releasing when low down in a bucket saves getting a mouth full, best do this when the coolant is cold (obviously). Reader Comment Author: cameron I also replaced my thermastat on an emergency basis. The t-stat stuck in the closed position and my car overheated. Here is my two bits: 1) I agree with the LONG torx driver bit. Otherwise there is a good chance of stripping the head. 2) Try a hand-held impact driver to loosen the two stubborn bolts. 3) It is possibe to drain the coolant without a ramp or a jack stand. Simply detach the lower radiator hose from the radiator. That way, no need to crawl under the car, no need to remove splash guard. No fear of damaging the plastic drain plug. Reader Comment Author: Matthew R. Agreed that you must use the long T40 bit, but you must also watch out for the following. I have also heard of the hidden torx getting seized and snapping making for a very very expensive thermostat change. Do the easy one first, and gage the force required to loosen it, if the hidden one requires significantly more force before it moves you may want to do the following procedure to avoid snapping the bolt. Get a very long and thin high speed drill bit, now this may sound crazy, but you need to actually drill a hole into the thermostat housing/cover just below the head of the hidden bolt to gain access to the shaft of the bolt so that you can introduce lubricant or penetrant to the area that is actually seized. This area is solid aluminum and you wont cause any damage as long as you are very careful not to drill into the actual bolt. Once the hole is done all you need is one of those red straw adapters to your choice of spay to lube the seized area before trying to loosen the bolt. Good Luck!