'98 S70 Overheating

[dcmatos]

My car has recently been running hot after driving for a prolonged period of time. I flushed my coolant system thinking it was the coolant, however it overheated a few days ago and my coolant was boiling. I'm thinking my thermostat has gone bad, however I'm still a novice when it comes to this car. Does anyone have an idea what it could be?

[scot850]

Does your engine cooling fan run at all? The relay can fail which prevents the engine fan running = overheating. Also the fan is controlled by the engine temperature sensor. If the sensor is bad the fan may not be getting the signal to run.

The engine temp sensor is mounted in the thermostat housing. The connector to that can be problematic and it is mounted to the back of the power steering pump. Check the connector is good. There is a set of resistance values you can check for the correct operation of the temp sensor. I had a thread on how to do the checks maybe a year ago. Check for IAT or ECT testing and you should find it.

Thermostat may have jammed closed. The local dealer advises changing it regularly. Maybe ever 2-3 years. The thermostat housing is sometimes reluctant to come loose and uses a T40 (?) Torx to undo it. Soak the 2 top bolts with PB Blaster or Deep Creep for a while, then gently tap the Torx socket/wrench with a hammer to break any stuck bolt threads. Don't hit too hard as you can break the housing. While the cover is off, and changing the thermostat (check for recommended brands other than Volvo) it is easy to change the temp sensor which is at the front of the housing below the thermostat.

Neil.

[dcmatos]

Does your engine cooling fan run at all? The relay can fail which prevents the engine fan running = overheating. Also the fan is controlled by the engine temperature sensor. If the sensor is bad the fan may not be getting the signal to run.

The engine temp sensor is mounted in the thermostat housing. The connector to that can be problematic and it is mounted to the back of the power steering pump. Check the connector is good. There is a set of resistance values you can check for the correct operation of the temp sensor. I had a thread on how to do the checks maybe a year ago. Check for IAT or ECT testing and you should find it.

Thermostat may have jammed closed. The local dealer advises changing it regularly. Maybe ever 2-3 years. The thermostat housing is sometimes reluctant to come loose and uses a T40 (?) Torx to undo it. Soak the 2 top bolts with PB Blaster or Deep Creep for a while, then gently tap the Torx socket/wrench with a hammer to break any stuck bolt threads. Don't hit too hard as you can break the housing. While the cover is off, and changing the thermostat (check for recommended brands other than Volvo) it is easy to change the temp sensor which is at the front of the housing below the thermostat.

Neil.

Yes the cooling fan is running. I will attempt to replace the thermostat and temp sensor and see how it runs after that.

[98v70dad]

I had this problem and I tried all of the things suggested here and nothing seemed to work. What was eventually determined to be the problem was a lack of a good ground for the fan. My problem was intermittent. Every time I checked the fan it was running but several times a week, in traffic, the engine would almost overheat. Tightening the ground connection fixed all of that. If you did the pcv upgrade lately you had that fastener off.

[rspi]

Sad to say, if the engine has overheated, fixing the problem will not fix the head gasket.