[many birds]

Problem solved!!!
I put in the flex fan from my ‘75 t/a and everything is perfect! Even on 93 degree day, in stop and go traffic, up a slope, the temp never went over 180 degrees. This is without a shroud. I am just amazed. The cooler running is helping with oil pressure too. And no more slow cranking on a hot engine.

My plan is to buy an OER shroud and a clutch type fan set up—since that should be a little more efficient. I hoping I can go back to ported vacuum and maintain these temps.

Who would have figure the stock setup from 50 yrs ago was/is cheaper and way better than the modern aftermarket crap.

[dataway]

I think people totally underestimate the OEM cooling systems. They were designed to be able to sit in an Arizona parking lot idling with the AC on for hours.

But ... the parts have to be right, and working, which usually means a new core on a 40 year old radiator, and a properly operating clutch on the fan etc.

[steve25]

Good news and a easy fix, it's a beautiful thing!

[TAQuest]

Lots of junk aftermarket radiators being sold.

Here's a local (to me) success story, a quality oriented aluminum radiator company. Buy American made and be proud of it!
https://becool.com/

[78w72]

Originally Posted by many birds

Problem solved!!!
I put in the flex fan from my ‘75 t/a and everything is perfect! Even on 93 degree day, in stop and go traffic, up a slope, the temp never went over 180 degrees. This is without a shroud. I am just amazed. The cooler running is helping with oil pressure too. And no more slow cranking on a hot engine.

My plan is to buy an OER shroud and a clutch type fan set up—since that should be a little more efficient. I hoping I can go back to ported vacuum and maintain these temps.

Who would have figure the stock setup from 50 yrs ago was/is cheaper and way better than the modern aftermarket crap.

thats great a simple stock clutch fan fixed your problem. so much for all the "you need a huge aluminum radiator to cool a pontiac" or "only this brand or that brand will work"... you just showed that an old stock radiator & clutch fan will cool a common build pontiac that was overheating with an electric fan.

imagine if you just went out & bought a $300-$500 radiator to fix this? im betting many of those using electric fans could solve overheating problems with a clutch fan & factory shroud as well.

hope it stays running cool for ya!

[TAQuest]

Originally Posted by 78w72

thats great a simple stock clutch fan fixed your problem. so much for all the "you need a huge aluminum radiator to cool a pontiac" or "only this brand or that brand will work"... you just showed that an old stock radiator & clutch fan will cool a common build pontiac that was overheating with an electric fan.

imagine if you just went out & bought a $300-$500 radiator to fix this? im betting many of those using electric fans could solve overheating problems with a clutch fan & factory shroud as well.

hope it stays running cool for ya!

Yup, they worked before and they work now too. The world didn't change the rads just got older and dirty. People forget to put their shroud on, ignore their fans, etc.

An aluminum rad can be a great choice for a budget.

You can get one for around what it would cost to have your old one recored, many times less. Can be much quicker to buy a new one. They fit nice(if you buy a good one) and are light. One of things that 'to each their own' applies well.

[STEELCITYFIREBIRD]

It was a flex fan used for the test/ diagnosis.

The problem was vehicle low speed air flow across the rad core.

Shame that the electric fan “upgrade” was apparently the causeusual part in the head gasket failure.

Nice job testing and diagnosing!

[78w72]

he said it was the "stock" fan from his 75 t/a.. i assumed it was a clutch fan since most mid 70's firebirds used clutch fans.

[moontower69]

They work! Funny how the old stuff still works. I've seen a stock clutch fan solve overheating issue several times. I know it was a stock flex fan in this instance, but point is stock stuff works. Folks get too crazy with aftermarket stuff and once I spent a fortune on a Griffin alum radiator and my issue was just clearance of the water pump plate.

[many birds]

Just to clear up any confusion:
Yes it is a flex fan. I’m using it for testing only. I took it off my ‘75 t/a. It’s the fan the car came with when I bought it 25 yrs ago. I thought it was original to the car since most everything else was original. It is a 7 blade 19 inch fan. So far, I have been running it without a shroud. I intend to purchase a shroud and am currently debating whether I should go clutch or flex. Flex is definitely cheaper.

I’m not really sure which clutch (their prices seem to vary quite a bit on summit) I need or what I’m gaining by going the clutch route over the flex fan.

Lastly, I did try going to ported vacuum advance with the initial timing at 10 degrees. Temperature started rising back into the 210 territory when idling. And cooled down once the car was moving—that’s probably topic for another thread.

[389]

-160 Stant Super stat thermostat..
-Stock clutch fan, don't worry about the shroud, use it if you have one.
-If you use an open element air cleaner, pick up one of these diverters like I have on my car (photo), they really work!

There is no way those two electric fans can over come the build up temps from that 180 stat (yes, I'm one of them). Frankly I see no advantage to electric fans period, unless the engine is transverse. The engine compartment in these cars was designed to have continuous air flow..

If you want to make things better, get rid of parts under the hood that no longer do anything, they act as heat sinks. Those HVAC plenums really choke the under hood air flow. For a fair weather car, a heater isn't needed. Or just run a small heater core in the air vent with a ball valve to control it (photo).
Maybe I'm wrong but wouldn't headers on a street car act as two giant radiators, even coated? Pontiacs have some beautiful exhaust manifolds...

[389]

Ported seems to idle better and the power just off idle seems more crisp and smooth, you know "right there"..
When on full vacuum, the idle jumped around because the engines vacuum jumped around because the timing jumped around because the vacuum advance jumped around, haha.. I use ported.. The factories went to it when they needed every little bit of power and smoothness after the 1975 emission mess hit..

[TAQuest]

Originally Posted by many birds

Just to clear up any confusion:
Yes it is a flex fan. I’m using it for testing only. I took it off my ‘75 t/a. It’s the fan the car came with when I bought it 25 yrs ago. I thought it was original to the car since most everything else was original. It is a 7 blade 19 inch fan. So far, I have been running it without a shroud. I intend to purchase a shroud and am currently debating whether I should go clutch or flex. Flex is definitely cheaper.

I’m not really sure which clutch (their prices seem to vary quite a bit on summit) I need or what I’m gaining by going the clutch route over the flex fan.

Lastly, I did try going to ported vacuum advance with the initial timing at 10 degrees. Temperature started rising back into the 210 territory when idling. And cooled down once the car was moving—that’s probably topic for another thread.

The only advantage a clutch fan has is when it's cold out. It doesn't help in cooling better than a good flex fan.

[ta man]

Seen a few comments about not needing a shroud? This makes zero sense, you absolutely need a shroud.

[many birds]

Yes, I definitely plan to go with a shroud. If nothing else, it will keep me from losing a finger.