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Unread 09-18-2011, 05:17 PM   #16
lucdog
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1980 CJ5 
 
Join Date: Jul 2006
Location: , Il.
Posts: 8,085
Quote:
Originally Posted by foggybottombob

I'm not buying this at all.

When you are driving at speed, the fan can be not turning at all, turning slow, turning 2 times slow or turning really fast and the air flow change through the radiator will be negligible. I have an electric 2 speed fan that I can turn on hi, low or off and it makes no difference in coolant temp when you are driving fast. The no clutch fan will add a little more drag on your engine at high rpm but I would guess that factor is less than 5 horsepower.

Now if you are getting detonation (pinging) your engine will definitely heat up really fast at high speed. You might try some higher octane gas for a tank.
I agree with Foggy on this. Back in the day (60's) IIRC most cars had fixed fans. I don't ever remember my father complaining or having to slow down because of overheating.
I dought if every CJ with a fixed fan, went back to the dealership, for overheating at hiway speeds.
In fact my DD 1983,258,2.72 gears, 31" tires, fixed 4 blade fan, and 2 core old radiator, will run all day at 70 mph without the temp rising



Bill

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1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac trail Jeep.
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Unread 09-18-2011, 05:21 PM   #17
jumbojeepman
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1976 CJ7 
 
Join Date: Sep 2008
Location: Greenville, NC
Posts: 1,099
Quote:
Originally Posted by foggybottombob View Post
I'm not buying this at all.

When you are driving at speed, the fan can be not turning at all, turning slow, turning 2 times slow or turning really fast and the air flow change through the radiator will be negligible. I have an electric 2 speed fan that I can turn on hi, low or off and it makes no difference in coolant temp when you are driving fast. The no clutch fan will add a little more drag on your engine at high rpm but I would guess that factor is less than 5 horsepower.

Now if you are getting detonation (pinging) your engine will definitely heat up really fast at high speed. You might try some higher octane gas for a tank.
I'm not buying this either. Slow fan speed is causing air to back up, so making the fan turn even slower will help out?

The reason for my doubt: I have a Mercedes 300E. It has 2 pusher electric fans in front of the radiator, and 1 mechanical fan behind the radiator. I was having a problem overheating at stop and low speeds. Once you got over 45 the engine cooled just fine. The eventual problem I discovered: One of the electric fans was spinning backwards! That's right, it was pushing air away from the radiator. In spite of this, once you got moving over 45 the air rushing through the grille was enough to overcome this and cool the engine sufficiently, even in the summer with the AC on.

My guess as to the actual problem is a bad radiator.
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Unread 09-18-2011, 06:33 PM   #18
Foundrydude
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1995 ZJ 
 
Join Date: Jan 2011
Location: Flatsville, IA
Posts: 2,692
Quote:
Originally Posted by foggybottombob View Post
I'm not buying this at all.

When you are driving at speed, the fan can be not turning at all, turning slow, turning 2 times slow or turning really fast and the air flow change through the radiator will be negligible. I have an electric 2 speed fan that I can turn on hi, low or off and it makes no difference in coolant temp when you are driving fast. The no clutch fan will add a little more drag on your engine at high rpm but I would guess that factor is less than 5 horsepower.

Now if you are getting detonation (pinging) your engine will definitely heat up really fast at high speed. You might try some higher octane gas for a tank.
You don't have to buy it, but I didn't make it up. It's a known phenomenon with fixed mechanical fans. When you have a 60s style blade with only four tiny airfoils the effect is less but if you have a more agressive truck fan it's very real.

good luck to the OP
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Unread 09-18-2011, 07:04 PM   #19
brownbagg
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1930 MK Compass 
 
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but the air is going through the radiator before it hits the fan. the fan is no different from the front of the engine itself.
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Unread 09-18-2011, 10:27 PM   #20
foggybottombob
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1984 CJ7 
 
Join Date: May 2008
Location: Monument Colorado
Posts: 5,830
It's a "fluid dynamics" physics phenomena. But I still say the effect of the fan on blocking air flow through the radiator is negligible at high speed regardless of the fan speed.
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