Need help with my overheating S40
 

My 2002 S40 is overheating. The fluid level is fine. No apparent coolant leaks. But the temp gauge has been riding high lately - going steadily to 1/2 to 2/3 towards red. Before this problem, the fan comes on long before it gets that warm. There is a small fan running continuously. But now, the large fan only comes on when the temperature is rapidly increasing from 2/3 to red. At this point, I turn the car off. The fans turns off when I've turned the engine off. Of course the fans should be on, running on battery.

I'm not sure why the fan is only running when the car is in an advanced state of overheating - and why it does not stay on when the car motor is off. The temperature gauge on the dash is working, so does that mean the temperature sensor is all right? I suppose I could change the thermostat and temperature sensor. But it seems it might be chasing a phantom problem. The insulated hose that runs coolant from the engine to the radiator is definitely warm. So it doesn't seem the thermostat is stuck closed. Perhaps its just partially closed? Because I can hear the fan (only when the car's temp is in the red), does that mean the fan is not the source of the problem?

Any ideas or suggestions welcome. If I took it to a Volvo dealer, what might I get stuck with? Parts & hours . . . ? Thanks!

Have you had the coolant system flushed out recently?
Does the heater generally function properly between hot and cold.
Possible air lock or maybe a blockage if your system is overdue for a flushout?

Any trouble codes set?

Has the engine overheated to the point of puking fluid out the overflow tank?

The heater function seems to work. I've been using the heater once the temp gauge on the dash rises above 1/3.

No fluid puking out. Fluid reservoir is fine.

I've been meaning to borrow my neighbor's computer. But two issues . . . I'm not sure where the computer connects and not sure if I will need an adapter. Is the connection under the dash or under the hood?

I do have a check engine light. I'm figuring that the engine temp sensor, near the thermostat, is an input to the car's computer, helping determine when the fan kicks on. This is not the same sensor/input as the signal going to the temp gauge on the dash. Just guessing . . .

I have a thermostat (180 degree) and cheapo coolant temp sensor coming in the mail tomorrow's mail. Hopefully that will help things. Should know by the weekend.

Thanks.

If anyone can help vector me to the car's computer connection, I'd appreciate.

My 2002 V40. Right hand drive model has the OBD11 plug located on the right side of the centre console. (where the carpet finishes and the bottom edge of the plastic console side panel starts.)
It is fairly hard to see it. You have to get down low in the footwell area and peer back upwards under the lip of the plastic a little.
It's a 16 pin plug from memory.
LHD models may be opposed???? not sure.

Yes, the left hand drive models have the OBD2 plug about at the drivers right knee just where the plastic center console ends.

T-stat change and new coolant temp sensor will hopefully fix you up.