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Old 06-16-2013, 05:06 AM   #15
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Thank you, Bob.
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Old 06-16-2013, 05:15 AM   #16
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92- I am replacing the fan clutch as it runs constantly and the vehicle is at always low temps- even under a heavy load. The electric fan works as it should.
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Old 06-16-2013, 07:58 AM   #17
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when you start it cold, you should not see water circulating through the radiator until the thermostat opens. have your mechanic check to see if it has a missing thermostat or if it is stuck open. if you hold your hand on the upper hose, you should feel a rush of hot water circulate in about 5 minutes or less. if you have a thermometer that fit it would be even better. now you have an excuse to get an infrared thermometer :-)
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Old 06-16-2013, 08:18 AM   #18
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The mechanical fan will always be turning when the engine is running. When locked it will "bite and pull" the air but when not locked it will simply freewheel. It's not really an On/Off type of thing but more like a slow progression from free wheel to locked based on ambient temperature. Try turning the mechanical fan by hand when the engine is off. You should feel a little resistance but it shouldn't be hard to turn. Check for any side to side movement in the fan as well. There should be no noticeable movement. If it's hard to turn or has significant movement then replace the fan clutch. Warning, if the clutch is bad, then the water pump may not be far behind.

As Richinny stated, if it's running cold, check/replace the thermostat. Even if the fan was locked up it shouldn't be running cold. You would notice a pronounced, rather loud, whirling sound though. All the air in the world going through the radiator will not make an engine run cold. If the thermostat is working correctly it wont allow coolant to flow through the radiator until it reaches its set point.
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Old 06-16-2013, 11:20 AM   #19
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Chev fan clutches have an operation range between 165 and 180 degrees. Yes a wide range but that is as close as manufacturing can get them. Now that said the mechanical fan will turn as long as the engine is running. However that turning is just a COASTING turning do to the viscosity of the oil inside. If the clutch kicks in the fan goes to high speed and you will hear it roar. This will only happen if the air flow over the clutch goes above the set point of the clutch. I doubt very much you would ever see this type of cycling happen unless you were going up a steep hill.

Now if it is the auxiliary electric fan is cycling, and they will even while stopped, that is not uncommon. Walk by any foreign car that just pulled into a parking lot and you will hear the electric fan running foe 2 or 3 min. If an electric fan is cycling the relay that controls it is GOOD.

Now what do you mean by running cool? is this below 180 degrees, a common thermostat setting? If so check the thermostat for failed open.

Again I suggest you find another mechanic. All of this is first semester.
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Old 06-16-2013, 11:37 AM   #20
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Again I suggest you find another mechanic. All of this is first semester.
Same thing I suggested. ANY competent mechanic should be able to diagnose a fan cycling and engine running cold issue. I just hate when someone gets the run around from a "mechanic".

The truth is that there are too many contradictions in this thread. It started with "where is my relay because my fan is staying on" and ended with my electric fan is working just fine. Mechanical fan working correctly? Not sure what the true issue is here. Might be several issues related or not. Might even be normal.
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Old 06-17-2013, 06:50 AM   #21
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I am not a mechanic and enjoy my full time job. I asked an apparent "dumb" question which has resulted in several long posts. To those whom are confused by contradictions stemming from my lack knowledge on these posts- I apologize.

I mainly learned that I need a new mechanic because of ME confusing the electric fan and the mechanical fan. My mechanic has not dove into this yet and he is working on it next week. He was apparently asking about the relay for the electric fan and I need to inform him that the electric fan is working properly.

There IS an issue with the mechanical clutch. There is a new thermostat and temp sensor installed as I decided to replace them last year. The clutch fan and entire cooling system worked properly last year. I know and identify the "roar" turning on and off and certain temperatures. Now it "roars" with no regard to the engine temp and there is an obvious and brief "cycle" now and then. This sounds as if roaring stops briefly. That cycle has no affect on the RMPs. The temps stay well below 200. I know that the thermostat is fine and not stuck open. There is adequate airflow to the motor.
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Old 06-17-2013, 07:02 AM   #22
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And 92- I remember when you bought your RV and posted for the first time. How on EARTH do you have 460 posts ?!?!?! I have a suspicion .........
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Old 06-17-2013, 07:36 AM   #23
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And 92- I remember when you bought your RV and posted for the first time. How on EARTH do you have 460 posts ?!?!?! I have a suspicion .........
And what would that suspicion be?
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Old 06-17-2013, 09:30 AM   #24
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mcm9970

You comment that you replaced the clutch for the mechanical fan last year. If the problem started shortly after that I would have to restate my comment that the operating range on those clutches is from 160 to 180 degrees. If by chance you got one at the lower in of the range and it is the confined space of a motor home that may be the answer.

I had one on one of my trucks that would not come on till the coolant was over 220 degrees but have known other that had them to cycle frequently.

If you can find a electronic thermometer and place it behind the clutch fan in the air flow coming towards the engine you could see if the clutch is in fact responding to temperature. The air flow will fluctuate over a wider range than the coolant in the engine because the thermostat is controlling that, at 180 degrees, by dumping heat into the radiator and thus increasing the air temperature hitting the clutch.
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Old 06-17-2013, 11:48 AM   #25
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Thank you, Howie. When I had the fan clutch changed last year- on a summertime trip (90 F +/-) the fan turned on when the temp got to 200 and turned off at 180 or so- it did this for around 600 +/-. After that- on a winter time trip (50 F +/-) it turned on and stayed on keeping the temps at 180 +/- - it did this for 500 +/-. On our latest spring time (80 F +/-) trip it stayed on for the most part and began cycling on and off with no change in temperature or engine RPM. Could the outdoor temperature affect this?

I checked the fan and the fan has resistance when you turn it with the engine off- so it doesn't seem to be locked up.
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Old 06-17-2013, 12:05 PM   #26
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Yes

I can't find the GM specs on the clutch that states the wide possible operating range right now. But if you got one made to the low end of the range that may be the problem.

This should help you understand what is happening.

Fan Clutch Diagnosis - Engine Cooling System
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