Info for Overheating S40/V40: Check this part

[drvolvo]

My 2001 S40 would only overheat when I would run the AC. The dealer replaced 3 relays but the problem continued, particularly in traffic. The weird thing was that both fans would work; however the real issue was that one of the cooling fans no longer worked at the low speed. (Apparently this fan has a low and a high speed). Since the fan would not come on at the lower speed (and lower temperature threshold) the car's temperature would rise to cause the high speed fan to kick on, but by that time, the engine thermometer on the dash was well above the 3 o'clock position. The issue was not the fan itself, but the blower resistor that controlled the low and high speeds.

I found this write up online that perfectly describes my situation: "On 1998 to 2000 Volvo S40 models with the 1.9L turbo engine, the engine cooling fan resistor may fail, preventing the cooling fan from working. This may cause the engine to overheat at low vehicle speeds, resulting in head gasket damage if the engine gets really hot. Replacing the head gasket will fix the coolant leak, but it’s important to make sure the cooling fan is working correctly and comes on when needed so the engine does not overheat again. The fan resistor is located under the front engine splashguard, just below the fan motor. A new resistor (P/N 30644121) can be spliced into the wiring if the original resistor is defective."
From: http://www.import-car.com/Article/61817 ... _fail.aspx

I found a few Volvo threads where people discussed this phenomenon but did not know what the true cause was. Therefore I wanted to share my findings. The resistor number is 30644121.

Stay cool!