February 17, 2009

Replace Thermostat Volvo 850, S70, V70, C70 or XC70

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 antifreeze with me, but I’m going to pick some up in a week or two.

Tags replace thermostat, thermostat replacement tutorial
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