Overheating
 

I have done some searching on the site about overheating but have not found anything that clearly answers my problem.

I noticed as I stopped at work the other morning that the fan ran on after I killed the engine indicating that the engine was running hot. It was a cool morning and not much traffic so no reason for this. Not much I could do while at work so I drove home at the end of the day

The evening drive was warmer and a lot more traffic. The temperature gauge got up towards the red high temp line. I could hear the fans going. I stopped. When I kill the engine, the larger fan runs on. If I turn on the ignition, both fans run. The front of the radiator is cool (probably from air movement) and the back is hot.

On the advice of a colleague I replaced the thermostat and gasket. On a drive that night and the trip to work in the morning, everything was ok. No fan run on when I killed the engine so I assume everything is now working ok.

On the drive home, again when in stop and go traffic, the temp gauge goes up and gets scarily close to the redline. When I stop the fans are both running, and when I kill the engine, the larger fan stays on.

Running the heater seems to make the problem worse, not take temperature away from the engine (like it did on and old car of mine)

What I know:

Probably not thermostat as this has been changed
Seems to cool well when at highway peeds, but gets hot in traffic
Fans seem to be working as designed
The check engine light has not come on
If I kill the engine in traffic, when I turn on the ignition the temp gauge goes up to above normal. When I turn on the engine, it limbs back to very high

I m looking for advice on other things I an check before taking it in to a mechanic. I am short on cash so I would prefer not to take it in. I have a Haynes manual for the car.

I have read about people changing the temperature sensor, flushing the radiator etc. Can anyone suggest what I should check next? I bought the car (2000 v40) a year ago. I have read that the coolant fluid should be changed regularly - could it be just that?

Thanks,
Nick.

I would try changing the coolant temp. sensor. They are known to go bad.

+10,000 -- It's one of the most common issues on s40concepts.

I got the coolant temp code. I got away with just replacing the thermostat, but it looks like you're not getting off that easy!
Sorry.

Answer
 

Well, I couldn't figure out what was wrong and I needed my car so I took it in. The mechanic replaced the cooling fan resistor. The part number on the worksheet is 30644121.

Apparently the cooling fan resistor controls when the fan comes and the speed it runs at.

Thanks for the other suggestions.