engine cooling questions

Are they both electric on your car?

On earlier models (like mine) where one was mechanical, one electric, the mechanical one runs all the time, the electric one kicks in intermittently if the temp reaches a certain point (there's a sensor in the radiator that tells it) or full time whenever the A/C compressor's on.

If they're both electric, IIRC the main electric fan cycles as needed, instead of running full time, and the secondary runs as described above (someone may need to correct me here--I haven't looked at a newer one for a while.) The primary may be wired thru the A/C compressor, too, which could produce the result you describe.

Rick

I am not sure what you mean by electric vs. mechanical fans. I should turn on the A/C to see what the fans do.

John

Mechanical would be driven by the engine as opposed to as electric motor.

Ed, the ECU will also call on the second fan to assist when conditions are such that the first is inadequate to keep the coolant temp in check. -Danny

Mechanical fans are usually driven off the water pump, either directly or thru a clutch. If you have a direct connection, the fan always turns at water pump speed. If you have a clutch, the fan speed can vary with temperature, acting kinda like a lock up torque converter in an automatic trans.

Many newer cars use only electric fans because of the lower power loss when they're not needed, and the added flexibility of determining operating condition via temp sensors, A/C operation and/or ECU inputs as someone mentioned.

Rick

Thanks Danny as I did not know that. ed

Yeah, there's a second, slightly higher coolant temperature threshold, that when reached will trigger the second fan. Then like you say, the second fan also comes on with the AC compressor.

I'd still like to know if there's a speed override on the fans. Meaning, that when I'm cruising on the freeway at 70 mph, are the fans still coming on with the AC compressor? I hope not. I've never been able to get a definitive answer to this question. It drives me crazy I tell ya. -Danny

Danny,

I can't speak for your car, but on mine, the secondary fan will still kick on climbing some hills during the summer or with the A/C, even at freeway speeds. I can see the voltage gauge drop a tiny bit when it kicks on. I suppose if you were REALLY curious and ingenious some weekend, you could wire in a coupla test warning lights to watch from inside the car?

Rick

That's just so a relay or something can fail and cost ya big bucks when head gasket blows. With a longitudinal engine there is no excuse not ti run a mechanical fan. If if the clutch fails the fan still turns.

John

Ah, yes, Conspiracy Theory Engineering 101. I slept thru most of that class!

"Longitudinal" engine? This terminology is used as opposed to a transverse mount? Regardless, there are many sound reasons to use other than a straight mechanical fan. Some, but not all, were mentioned in previous posts.

Rick

Rick, that's a way better idea than climbing out on the hood and checking, uhh... as was a suggestion given to me on USMB some time back. Actually I could extend some temporary wires into the cockpit to my Fluke meter in lieu of a lamp.

Probably. Good engineering means finding the simplest, durable solution to a problem. If a belt breaks there are a thousand available substitutes'

There is no valid reason not to use a mechanical fan for a non racing vehicle. Will you notice the 5??? hp it saps while off roading in the desert . not likely but your engine will not overheat.