QQ to all: Does the S40 use a gasket between the thermostat housing cover and the thermostat housing? I see there's an o-ring that comes with most replacement parts but nothing online about a gasket for the cover...

Backstory: Driving my s40 on the first 40 degree day since Jan 5th when the cooling fan kicks on when I parked after a 10 mile drive. On the way home I notice the temp gauge fluctuating between mid gauge then slowly creeps to 2 clicks short of red where the fan comes on (while driving at 30 mph) only to have the temp go back to normal and the fan kicks off. I suspect it could be low coolant (not even sure if the s40 has a coolant level sensor like my 850) or the thermostat is wonky or the coolant temp sensor.

Since I don't recall when the thermostat was last changed, I figured its time then I can top off any low coolant.

QQ#2: Is it necessary to drain the radiator to do both the stat and the sensor? I don't mind losing a cup or two of fluid in the process if that's all it will be...(better than getting under the car to remove shrouds to get at the radiator drain)

QQ#3: Any consideration for Volvo vs replacement brands? Don't see the need for a 3x price jack by Volvo if aftermarket parts last...

Thanks

MT

 

There should only be the ring between the housing cover and the housing. There is a gasket on the lower part of the housing where it actually meets the block but you're not replacing that. You could try to get fancy and use something like "Permatex Water Pump & Thermostat RTV Silicone Gasket" if you wanted to go overboard but shouldn't need to.

I would ask do you have coolant in the tank right now? Redline is worrisome indeed. Temp sensor should be sitting straight up in the middle at operating temperature.

You do not need to drain it. Make sure you use the appropriately sized torx (it strips easily) on the two screws on the cover and have some towels around it, you will lose whatever is in the upper hose as it will spill out and you'll want to replace back. I think the sensor itself is a 19mm. You'll want to just cut the wire and use a long socket to remove it. Putting it back on there should be a crush washer with it and I personally put Teflon tape on the threads. Putting it back on you'll need an open end wrench unless you have some sorta crows foot to get into the small space.

Stant stat - you can get it with the rubber ring for ~20 (got mine at advance) and for the sensor I wouldn't cheap out and would get Volvo branded oe)

 

So I got around to changing the coolant temp sensor today. A few lessons learned... As usual Volvo over-engineered the connector to the temp sensor. There's a two step process to disconnect. First you press the catch button on the ride side and slide the opposite end towards the firewall. Then you can rocker the temp sensor's connector (clockwise) and also slide that to the firewall. I popped off the thermostat cap and snipped the wires to get easy socket access to pull the old part out. I just let the top coolant drop into a catch pan - a couple cup fulls vs draining the radiator. Tightening up the sensor is a real hassle. I used a combination of a 19mm open end and a crow foot wrench to tighten. The trick here was to unsnap the fuel rail cover (not the rail) and slid it over half an inch to the right. That gave me just enough room to flip the wrenches. I used a new crush washer but if I did it again, I'd use some teflon tape on the threads (couldn't find my roll). So tools required: 30 torx for the valve cover, 40 torx for the thermostat cap, 19 mm open end (thinner the better) and if you have one a 19 mm crows foot open end, and some teflon pipe tape. Total time - less than an hour. Just refilled the coolant and checked for leaks...

 

Just FYI, car companies don't engineer every single thing on a car, like connectors. And just because it's a little tricky doesn't mean it's over engineered.

Teflon tape is not used for the sensor, so you'll be fine.

 

I had recommended teflon on the sensor. I would like to take that back. Don't do it. I changed my thermostat last weekend and saw bits of the sensor teflon tape around it.