#1  
Old 09-24-2019, 02:47 PM
alanmay0 alanmay0 is offline
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Default diameter of cooling fan??

Hello again, I have a 1967 GTO with factory AC. I am confused as to what size diameter the cooling fan should be. Ames shows a 17.5" for 64-67 and they also show a 18" fan for 64-76. I currently have a 19 1/2 in 7 blade in my car.

I am having an issue with the clutch fan coming on when driving on the highway above 60 mph with the AC on. I have changed out the clutch but it still does it. The water temp. gauge shows the water temp to be around 180-190, not hot for a 90 degree day with the AC on. I have put a 160 degree thermostat in the car but no changes.

I am wondering if maybe the fan diameter is too big. I read where you should have 1" space between the end of the fan blade and the shroud, is this correct? Mine have about a 3/8" clearance.

My fan blades are about have way inside the shroud and half way outside, this I have been told is correct.

So any suggestion as to why my clutch fan comes on while driving on the highway??

ps I have also changed out the water pump just to be sure that was not the problem.

This problem started when I was told that my ac condenser should be within 1/2 " from my radiator. wHEN i MOVED IT THIS CLOSE IS WHEN this problem started. Now the ac temp is much cooler with the condenser closer but the clutch fan engages on the highway.

thanks
alan


Last edited by alanmay0; 09-24-2019 at 03:04 PM.
  #2  
Old 09-24-2019, 02:55 PM
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Tom Vaught Tom Vaught is offline
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If you have the factory a/c system you should also have the 4 core radiator and the deeper square bottom Horse Collar that the radiator fits inside.

The 17.5 and 18" fans were for the 3 core non A/c radiators.

The fan shroud you are using, is it plastic or metal? Original I would think.

Tom V.

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  #3  
Old 09-24-2019, 03:08 PM
alanmay0 alanmay0 is offline
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I have replaced the original radiator years ago with an aluminum one that is much better the the original. The shroud is the plastic one. Just spoke to Ame's as was told that the blade should be 17.5" for an AC car. Seems small to me. I now have a 19.5". Don't know if this would make a difference in cooling but should have no effect on the cooling at highway speeds as the fan is more or less free wheeling when the clutch is not engaged. I could be wrong about this. Do you know what distance the ac condenser should be from the radiator??
thanks

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Old 09-24-2019, 03:09 PM
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Could be you have a really steep pitch 19.5" fan and a standard duty fan clutch. Given the small space you currently have between the fan tips and the shroud I'd say your fan is a bit big in diameter also.

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  #5  
Old 09-24-2019, 03:50 PM
alanmay0 alanmay0 is offline
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Default thermal vs not thermal clutch fan

I currently have a thermal clutch fan and am thinking of changing to a non thermal to see if that solves the problem of the clutch fan coming on when driving at highway speeds. Any thoughts on this??

  #6  
Old 09-25-2019, 08:46 PM
TedRamAirII TedRamAirII is offline
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Quote:
Originally Posted by alanmay0 View Post
I currently have a thermal clutch fan and am thinking of changing to a non thermal to see if that solves the problem of the clutch fan coming on when driving at highway speeds. Any thoughts on this??
If you do, it will be roaring.......All The Time.

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  #7  
Old 09-25-2019, 09:23 PM
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BLUE TA BLUE TA is offline
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hi, 1974 TA stock fan with a/c 19.5 with clutch. hope this helps. BLUE TA

  #8  
Old 09-26-2019, 10:18 AM
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FWIW, this is a clip from the Paul Zazarine Restoration Guide about the various sizes of fans and shrouds for 66-67 GTO's.
Mike Pearson
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  #9  
Old 09-27-2019, 11:56 AM
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It might be due to the clutch. Here's an article about how to change the lock up temp of the clutch.

http://midamericachevelles.com/tech/...tch_adjust.pdf

  #10  
Old 09-27-2019, 02:33 PM
Schurkey Schurkey is offline
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Fan clutch engages based on the temperture of the air surrounding it. NOT based on engine coolant temperature.

If the engine coolant temperature is low, but the clutch engages...and it does it with the A/C turned on...I have to think the A/C condenser is getting too hot. What are your A/C high-side pressures when the clutch engages?

For fukk sakes, do not install a piece-of-crap non-thermostatic fan clutch.

A fan with the blade tips close to the shroud is more efficient when it's powered than one with extra clearance. Downside is that it may block air flow when it's not powered. This is why electric fan shrouds have flapper-doors on them, that open when the fan(s) are off and the vehicle is moving, but close when the fan(s) engage.

  #11  
Old 09-27-2019, 03:24 PM
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Formulajones Formulajones is offline
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I was going to say something similar Schurkey.

It's not uncommon for the clutch fan to kick on at highway speeds if the air coming through the radiator is hot enough to engage it. Some of my cars will do that, perfectly normal. Since you mention it does this when you turn on the AC it makes sense.

What you didn't mention is whether or not is shuts back off after a period of time or if it cycles.

That's what mine will do on a really hot day, cycle on and off. No big deal.

You did mention you're only running 180-190 with the AC going on a 90 degree day. Doesn't sound like anything is wrong to me, I wouldn't mess with it.

  #12  
Old 09-27-2019, 05:49 PM
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Hikin Mike Hikin Mike is offline
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Not to hijack, but how can you tell if the clutch fan is engaged at highway speeds?

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  #13  
Old 09-27-2019, 07:32 PM
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I don't know about the op but I can hear mine roar to life, especially since I'm typically buzzing along at 2800 rpm or so.

  #14  
Old 09-29-2019, 01:51 PM
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Your system is working exactly as it should. As said above, fan clutch responds to air temperature, and both fan clutches you installed are detecting temps high enough to engage. A properly working radiator is extracting heat from the coolant to the fins and the hot air needs to be pulled away from the fins by air flow. Having owned four 67 GTO's, one thing I noticed is there is definitely a high pressure area under the engine at freeway speeds and it kills much of the air flow through the radiator. Some properly designed cars – and especially ones with good front air dams – will allow excellent air flow through the radiator and a fan becomes unnecessary at speed. Unfortunately this isn’t the case with our 67 A-bodies, and the fan needs to continue to run to pull air through. The addition of a fabricated front air dam could solve the problem by creating a low pressure area allowing more airflow without the fan, but right now it is the fan coming on at cruising speeds and keeping the air flow moving and the coolant temperatures at a good level.

So your system is working perfectly and keeping the observed engine temps at comfortable levels. Only thing I might explore is checking engine timing at cruising RPM because if engine is generating unnecessary heat by incorrect timing, then the cooling system has a bigger job to do. Less heat put into the radiator is less heat triggering the fan clutch.

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