engine cooling questions

J

John

My 1995 Subaru Legacy L has two engine cooling fans. Should both of the
fans continually cycle on and off together very frequently?

Thanks,
John
 
My 2000 Forester has two fans. One fan seems to cycle to keep the engine at
the good temperature. Both fans run when the AC compressor is running. ed
 
John said:
My 1995 Subaru Legacy L has two engine cooling fans. Should both of the
fans continually cycle on and off together very frequently?

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
 
My 2000 Forester has two fans. One fan seems to cycle to keep the engine at
the good temperature. Both fans run when the AC compressor is running. ed

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
 
John said:
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.

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 said:
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

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
 
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



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
 
busterb said:
That's just so a relay or something can fail and cost ya big bucks
when head gasket blows.

Ah, yes, Conspiracy Theory Engineering 101. I slept thru most of that
class!
With a longitudinal engine there is no excuse
not ti run a mechanical fan.

"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
 
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 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.
 
Rick Courtright said:
that
class!


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

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.
 

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