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Discussion Starter #1
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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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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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.
 

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Discussion Starter #4 (Edited)
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-24452955-flowkooler-pontiac-8-bolt-1964-68-hi-volume-cast-iron-water-pump-w-billet-aluminum-impeller-brw-1622.html?ref=category:1234740

https://butlerperformance.com/i-24452826-butler-performance-water-pump-divider-plates-for-1964-68-timing-covers-stainless-set-aau-n140pf.html
 

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Discussion Starter #5
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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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.
 

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Discussion Starter #7
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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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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Discussion Starter #9
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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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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Discussion Starter #11
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.
Thanks GTG, the fan is a seven blade flex fan, pretty new looking with of course a spacer so its about half in (and half out!) Nice shroud, seems to fit fairly close. What I can't vouch for is the quality of this flex fan - it sure seems "thin" to me, and very easily flexed by hand. So my debate is now if I make the jump to a clutch fan or not, or focus on the pump. Still not sure if that would solve my problem though, kinda' agreeing with what you said.... But its true, all I have to do is move a little, and the temp comes down quickly, BUT I cant say for sure if that was due to more air coming through the radiator, or the pump benefiting from getting some more rpm on it....
 

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Ebartone, those thin flex fans move enough air, generally. When it's idling, see if it will hold a sheet of typing paper to the radiator (front side). If it does, it's pulling air. You MIGHT have a waterpump/divider plate clearance issue. A common problem with today's water pumps on yesterday's Pontiacs.
 

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Discussion Starter #13
So let me be the descending voice here, and probably draw some flack. I remember back in the day, when I bought a new water pump for my old Le Mans, I never went through the drama of the clearance issue. We just put the pump in, bolted it up, hope it didn’t leak, and called it good! Generally speaking it worked. I wonder what happened were now it’s a necessity to bang a spacer into position for “proper” clearance? Take a look at this link. If you scroll down to the bottom, they even comment basically saying as I read it, not to smash this gap so much, or it voids the warranty. Admittedly it’s all getting to be a bit confusing! :)

https://butlerperformance.com/i-24452955-flowkooler-pontiac-8-bolt-1964-68-hi-volume-cast-iron-water-pump-w-billet-aluminum-impeller-brw-1622.html?ref=search:https://butlerperformance.com/search.html?q=Water+pump

As always I super appreciate the feedback, and will try the paper idea for sure. I wa s just taught a long time ago “question everything”. :)
 

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It is not the water pump. (You should verify and calibrate your temperature sending unit and gauge.)

If you can drive the car hard and it doesn't overheat, but does overheat when sitting in traffic or idling, then you know the issue is air flow and/or heat transfer. The old cars have crappy radiators and shrouding by todays standards. When just idling, it is really important to have a great shroud (to force the air across the radiator and it is also very important to have a super efficient and effective radiator - without both and a built motor, you will most likely have issues.

Buy a great AL radiator and have a nicely fabricated shroud made and call it a day. I'm having these guys make a shroud and powder coated black to look OEM-like. Mahaffey Motorsports - Drag Racer, Chassis Builder, Fireman, and EMT
 

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Discussion Starter #15 (Edited)
It is not the water pump. (You should verify and calibrate your temperature sending unit and gauge.)

If you can drive the car hard and it doesn't overheat, but does overheat when sitting in traffic or idling, then you know the issue is air flow and/or heat transfer. The old cars have crappy radiators and shrouding by todays standards. When just idling, it is really important to have a great shroud (to force the air across the radiator and it is also very important to have a super efficient and effective radiator - without both and a built motor, you will most likely have issues.

Buy a great AL radiator and have a nicely fabricated shroud made and call it a day. I'm having these guys make a shroud and powder coated black to look OEM-like. Mahaffey Motorsports - Drag Racer, Chassis Builder, Fireman, and EMT
Thanks Cj911, that is exactly the case, when I run it hard and moving, I have absolutely no heat issue at all, in fact surprisingly cool at 180 or so with a 160 stat. In my mind I was asking the question "If I have no heat problem running hard, only sitting still, could it still be the pump?" Logic-ing it through, it seems like a pump problem would be a pump problem at any circumstance (?)

I'm just trying to understand where to focus my efforts (and money!). I do have a great shroud, and as mentioned decent 7 blade flex fan, BUT I cannot vouch for the radiator at all. After all the discussion I feel like I'm right back to the beginning and original post, suspicious of the radiator! Thanks! (PS, for giggles Ill borrow a flir from work as you suggested to verify my sensor is close, but it was new with a Dakoda Digital dash, so I suspect its good).

So I think I'm I'm back to my question, any recommendations on a radiator?? :)

My first thought is this guy, wih the "more rows=better" thinking...

https://www.summitracing.com/parts/sum-384001/reviews/year/1968/make/pontiac/model/gto/submodel/base?prefilter=1

But I hear a lot about Cold Case, even though they seem to be two row, but they say:


https://www.jegs.com/i/Cold-Case-Radiators/359/GMA42A/10002/-1?ymm=4294829710+4294829274+4294829241

https://www.coldcaseradiators.com/product/68-77-gm-body-auto-aluminum-performance-radiator

"Cold Case high-quality replacement radiators for GM vehicles are engineered with two oversized rows that perform as well as traditional 3- or 4-row radiators"

Thanks....
 
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