gpep77

First off, I have searched and searched, but cannot find the answer to my question. Please do not flame me for posting this.

Okay so I bought the car (2004 S2k) in July of 2014. I just did my first aftermarket mod on the car - K&N FIPK. The car is otherwise bone stock. While installing the intake I noticed the fan on the right side (passenger side) had the plug disconnected. I reconnected the plug and proceeded with my install. After finishing the intake install I checked my radiator fluid and overflow tank. The radiator fluid was filled to the top as it should be. The overflow tank was very low (like slightly below the minimum line), but there was still fluid left in there. After driving to test the intake, I wanted to check to see if the fans came on as they should. I let the car idle for a long time after driving it and neither fan came on. Upon turning on the A/C both fans came on. If the A/C is turned off, both fans turn off. I realize it is the middle of winter right now (about 40ish degrees F in Seattle), but thinking back, I could not remember my fan turning on during the summer while sitting at a stop or in stop and go traffic. The engine has NEVER overheated and I have taken the car on long drives when it has been hot out. The heater works perfectly fine inside the car. The radiator is OEM.

My questions are:
1) Which fan is the A/C fan and which is the radiator fan?
2) How long does the car have to idle for the fan to turn on? And which fan(s) should turn on?
3) Is it dangerous for the fluid in the overflow tank to be that low?
4) Is it normal for the fans to always be on when the A/C is on?
5) Where should I start in diagnosing this? Or what should I replace first? The fuse relay?

A little about the car:
2004 S2000 with 60K miles and clean title
Bought off an elderly retired guy who owned it for 8 years and bout it around 17.5K miles
He was the third owner
The first owner did have a "minor" front end collision in the car. Any further details about the accident I was unable to obtain, because the previous owner did not know. Although I'm guessing repair work was not done professionally.


Thanks for the help in advance!

Slowcrash_101

AC fan is the passenger side fan, Radiator fan is driver side fan. If you do mostly highway driving and cruising, you'll rarely if ever drive the coolant temperature to the point of running the fans. The driver side fan kicks on first, but both will kick on if it gets hot enough, or if the AC is on. They will usually cut on if you do a lot of stop and go. Car can sit for 15 minutes idling before the fans even think of kicking on. As long as the radiator has coolant you're good, some coolant will evaporate on its own over time, just keep it at the max line and you should be ok.

gpep77

so basically...don't worry about it unless the car overheats? I don't drive very hard EVER. So maybe that is why I don't notice the fan kicking on? Is the s2000 pretty efficient at cooling without the fan?

And I will be sure to add some fluid to the overflow tank so its above the minimum line.

Slowcrash_101

The engine itself radiates plenty of heat, coolant won't even flow to the radiator until it reaches 160F I believe, and in the mean time it's just circulating in the engine and radiating it's heat into the engine bay, even then most of the time just passing the coolant through the radiator is enough to get it below 180F, which is when I believe the fans kick on. VTEC it a couple of times going under 60 mph and I guarantee you'll hear both fans cut on when you come to a dead stop after you've let the car warm up to operating temp.

gpep77

Okay thanks for your input!