Radiator Selection - Pontiac GTO Forum
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post #1 of 15 (permalink) Unread 09-27-2019, 07:44 AM Thread Starter
 
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Radiator Selection

I apologize in advance if the answer to my question is on another thread - I've searched but not found it.

So simply my 68' GTO runs very hot when there is no air moving through the radiator - but when I'm moving (like at all) the temp drops right back down to under 180 (160 thermostat). Like many, I am trying to figure out what best to do. I know the possible culprits - fan selection, shroud, water pump clearance, idle mixture, and other possibilities. With that said, I've decided that I first want to replace the radiator. This is a non-AC car, and I think the original radiator (that was replaced I'm sure with an exact duplicate) was not up sized for a/c obviously - and frankly it looks thin; I've not seen any numbers on it to identify it though. On top of that, it keeps springing occasional leaks, another reason to replace it! I think it may have some years on it. I run 50/50 with Water Wetter. Terrified of the idea of sitting in a bumper to bumper cruise!!!

If this doesn't work I'd like to add a pusher and keep the flex fan in place (and shroud) - I really would like to keep the vehicle looking "kinda" original, and it seems I could hide the pusher easily up front under the cowl. If that doesn't work, time to dig into the pump.

The engine was rebuilt a few years ago and runs fine, Doug's headers, and a Ram Air III cam, so it does have some umph....

My question is what radiator to replace it with? I've heard simply "4 core is best" but then I hear Cold Case wide tube while not 4 core transfers more heat - so I was just looking for recommendations. Also, with a new aluminum radiator, is it normal to paint it to make it look more stock? Will that reduce heat transfer?

Thanks!

Ed
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post #2 of 15 (permalink) Unread 09-27-2019, 07:54 AM
 
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I’d advise tackling the pump first, specifically the correct spacing on the plates. If these aren’t correctly gapped you probably won’t gain much from another radiator. As the fluid is still not flowing through properly.
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post #3 of 15 (permalink) Unread 09-27-2019, 08:38 AM
 
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Sounds like your radiator is actually fine and you just need the correct fan and shroud to fix the "sitting in traffic" problem.

I have a 4 core aluminum radiator and it works fine when the car is moving, but without the proper fan and shrouding it will run hot when just sitting in traffic.

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #4 of 15 (permalink) Unread 09-27-2019, 08:59 AM Thread Starter
 
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Originally Posted by Dukes67 View Post
I’d advise tackling the pump first, specifically the correct spacing on the plates. If these aren’t correctly gapped you probably won’t gain much from another radiator. As the fluid is still not flowing through properly.
Thanks Dukes67 - any thought on this guy?

https://butlerperformance.com/i-2445...tegory:1234740

https://butlerperformance.com/i-2445...au-n140pf.html

Last edited by Ebartone; 09-27-2019 at 09:13 AM. Reason: Added Divider Plates
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post #5 of 15 (permalink) Unread 09-27-2019, 09:05 AM Thread Starter
 
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Originally Posted by cij911 View Post
Sounds like your radiator is actually fine and you just need the correct fan and shroud to fix the "sitting in traffic" problem.

I have a 4 core aluminum radiator and it works fine when the car is moving, but without the proper fan and shrouding it will run hot when just sitting in traffic.
Thanks 911, its a pretty decent quality shroud, fan half in, and a flex blade fan. That part seems fairly solid - I'm at work or I'd post a picture...
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post #6 of 15 (permalink) Unread 09-27-2019, 09:39 AM
 
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Thanks 911, its a pretty decent quality shroud, fan half in, and a flex blade fan. That part seems fairly solid - I'm at work or I'd post a picture...
Flexfans are not the best for what it is worth.....IMHO since it works fine when you are driving, I would leave the radiator and try an original clutch style fan.

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #7 of 15 (permalink) Unread 09-27-2019, 10:00 AM Thread Starter
 
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Flexfans are not the best for what it is worth.....IMHO since it works fine when you are driving, I would leave the radiator and try an original clutch style fan.
Thanks CJ911 - I can see your point. That seems to be key, that when I'm moving I have absolutely no temperature problem, BUT one could argue that its not the motion and airflow that's helping, but rather its the higher rpm of the water pump, overcoming a clearance or efficiency issue - it just so happens that when i'm moving, engine speed tends to be higher (obviously).

So I really can't tell if I have an airflow through the radiator at idle problem, or a pumping at low rpm problem. Any idea how to tell the difference? If its an airflow at low speed I could go down the new fan path, or additional pusher, or bigger radiator. Pump problem is obviously deal with that - just not sure how to tell which it is.

In truth its not a showstopper right now because I don't normally sit still long enough for it to get out of control, BUT I'd like to fix it...

Thanks!
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post #8 of 15 (permalink) Unread 09-27-2019, 11:25 AM
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Not a fan of pusher fans. (pun not intended). They're just a band aid masking the real problem. Plus you'll need to upgrade your electrical system with a larger alternator and assorted relays, sensors and wiring.

I too would concentrate on the water pump and the radiator. 68 GTOs had a three row radiator at a minimum. Five blade flex fan was stock with non-A/C cars. By installing crank and water pump pulleys from an A/C car you can speed up the water pump at idle speeds. A seven blade clutch fan will also help

Better cooling efficiency is obtained with just water. In my area I don't have to worry about freezing temperatures and run a 70/30 mix of distilled water/antifreeze in my El Camino. No water wetter required.
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Ed


68 GTO (Thanks Mom)
70 El Camino SS
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post #9 of 15 (permalink) Unread 09-27-2019, 02:28 PM Thread Starter
 
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Thanks everyone very much for the feedback and ideas! I know this seems like I'm going in multiple directions, but does anyone have a specific part number / recommendation or link for a 7 blade clutch fan? Again, a '68 with 8 bolt pump. Maybe I'll just replace the pump, plates, fan, radiator, add an electric fan, replace the hoses, and never drive it under 30 mph!

Thanks everyone, this forum is AWESOME!

Ed
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post #10 of 15 (permalink) Unread 10-02-2019, 02:53 PM
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Agree with the others that the radiator is not the issue here. If it was, you would be running even hotter going down the road. The problem is lack of air flow through the radiator when at slow speeds. You need an effective fan to move air through the core to remove heat. Replacing the fan clutch with a known good one is a start, or simply installing a QUALITY flex fan can be a huge help. I installed a factory GM flex fan off of a '69 Cadillac onto my '67 GTO almost 30 years ago and it made a huge difference at low speed. It's as quiet as a clutch fan at all speeds, as well. Not like those Flex-A-Lite fans, which make your car sound like a Mercedes or a Garbage truck.
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