[pfilean]

Cooling the Pontiac seems to be a popular subject. I have always feels my 61 ran hot. The PO said he had some problems. He had put in a 4 row radiator and a flex fan to replace the factory 4 blade. Even a 195 thermostat which I can't understand. My 61 has green and red temp lights. Green out at 140 then red on at 240. So factory thought 240 was a temp to worry about. But I'm old school and like around 180.

Originally on real hot days I could get vapor lock but solved that with a GF98 vapor return fuel filter. Then over the years I changed to a 180 thermostat, added a factory fan shroud and seven blade declutching fan. Used a Hayden 2747 and have done the repositioning trick with the thermo spring. Still on a 90 degree day 195 to 210 depending on road situation. More in traffic.

So I have been close to hitting "add to cart" for a Cold Case radiator but decided to try a high flow thermostat first. I got a EMP Strewart (by RobertShaw) 180. Now on a 90 degree I see around 190 ( 195 at a light) depending on road conditions. May see higher in worse traffic but have not seen 200 yet.

I know there are differing theories on high flow or the need for the little bleed holes that this thermostat has . But without starting long discussions this was my experience. Somewhere around a 10 degree drop is what it is even if more would make me happier.

[JLMounce]

Important to note that most thermostats typically start to open at or just below their rated temp. That is the "minimum" temperature of the thermostat. So, depending on the thermostat and at what type or rate it opens, you can absolutely see that kind of change.

As coolant temperature increases above the rated temperature more flow occurs and the radiator cools more as a result.

The engine does need a bit of restriction in the system, at the engine, to keep from building steam pockets. I don't know whether or not a high flow thermostat could cause that situation. I do know that race cars that don't run thermostats at all usually have some sort of restricting pipe in the system that to me seems like it would still flow more coolant than the high flow stats I've had in the past.

[70GS455]

Were you able to put both thermostats in a pot of hot water to watch the opening temp? One may have been slightly off compared to the other

[SRGN]

I just swapped out the 4 bolt water pump and timing cover for an 8 bolt on my 62. Before it ran at 195-200 cruising with a 160 stat, hit 205-210 at idle. After the swap, I had to switch to a 180 stat because it wouldn't get over 170 at idle, with ambient temps in the pow 90s. I'm finishing my AC install, that will be the real test. I have an aluminum radiator already, and a 6 blade fan with clutch.

[Formulabruce]

High engine temp can wear your auto transmission pre-maturely .
I prefer to use a 170 T stat, and of course the 421 Mod virtually Ends "hot heads" .
https://www.summitracing.com/search/...-degrees-f/170

[Kenth]

Most people seem to think that all a cooling system needs to do is keep the engine from overheating.
But what is not realized is that if the engine runs too cool, thermal efficiency is lost and power is reduced.
Many will argue that an engine has more power when it is cold, but that is only due to the fact that the intake air is colder and denser, actual BSFC is higher.

Remember that an engines whole job is turn heat into mechanical energy.

Running the engine as hot as possible (limited by the detonation limit) will increase power and provide a lower BSFC.
If steam pockets will form, detonation will limit power.
Most of today's high output street motors using a water/ethylene glycol mixture will be limited to about 200° F before detonation becomes a problem (unless other steps are taken).

Another goal of modifying the cooling system is to even out the temperatures of the whole engine, which is not easy to do.
All it takes is one hotter cylinder to run into detonation to limit the engines power.
It only takes 1 cylinder to limit all of them.
Most high performance engines are close to detonation to begin with, so a good cooling system is a must.

[76TA462]

With the engine upgrade I had higher temps that haunted me foe a few years. Adding an A/C rad made the problem worse. Did a few things. On the topic of thermostats, I changed to a hi-flow 160 and had a noticeable but only incremental improvement. A Cold Case rad with their 12 inch e-fans helped some more but again, only incrementally. Last month after seeing a Fast Monty discussion on this site, I learned that this set-up was designed for an unmodified engine (I have the 455) so I picked up his Second Gen fan shroud designed for the Cold Case and swapped to 14 inch fans. Night and day improvement.

[pfilean]

Were you able to put both thermostats in a pot of hot water to watch the opening temp? One may have been slightly off compared to the other

I tested the old 180 thermostat and it started to open at 180 as advertised. Also tested another old RobertShaw I had from somewhere. It was a 160 and opened at 160 but I didn't use it because I thought 180 was more appropriate. Did not test the new 180 .

SRGN - your experience is interesting. I'm still running the old 4 bolt but it does have a cast impeller. But it sounds like we are now at about the same result. When I ran my test route with the AC on I saw generally about + 7-10 degrees. I have the condenser and also an oil cooler in front. I run my oil through the radiator cooler before the remote oil cooler.

[73ta]

455-462, 570 HP. Factory shroud, factory 7 blade fan, AC pullies, 180 stat, severe duty fan clutch, flowkooler pump with clearanced back plate, Bekool aluminum radiator. No issues.

[vertigto]

Is your fan clutch operating properly? Mine was failing and puking out coolant, pegging the temp.

[Skip Fix]

My wife's 73 454 truck had a big radiator in it, winter time it was barely warm enough for the heater to keep you warm! But stayed cool pulling the horse trailer! Pulled it easy and I swear as fast as my 78 TA's 180 HP motor!

[pfilean]

Is your fan clutch operating properly? Mine was failing and puking out coolant, pegging the temp.

As far as I know. But a little hard to check without loosing fingers. But if hot enough it will shut down within one turn after turning ignition off. Which is supposed to be some kind of test.

[vertigto]

Originally Posted by pfilean

As far as I know. But a little hard to check without loosing fingers. But if hot enough it will shut down within one turn after turning ignition off. Which is supposed to be some kind of test.

IIRC...that seems similar to mine pre-fix. You might want to try a new heavy-duty or severe-duty...pretty cheap/easy install if that's the issue.

[JLMounce]

Originally Posted by 73ta

455-462, 570 HP. Factory shroud, factory 7 blade fan, AC pullies, 180 stat, severe duty fan clutch, flowkooler pump with clearanced back plate, Bekool aluminum radiator. No issues.

It's always a good idea to qualify these statements. It's not an apples to apples comparison. The 2nd Gen F-Body and later A bodies got big upgrades in cooling capacity from the factory.

The OP's full size 1961 would come with a radiator with a basic size of around 17.5 to 25" or there about. The Cold Case replacement is 17x25.5" for a total frontal area of 433.5"^2

The cold case radiator made for your 2nd gen is 18.4x27.5" for a total frontal area of 506"^2. There's 15% more surface area and that's before we start looking at total system capacity.

For reference the first gen F-body is 16.85x23" for a total frontal area of 387.55"^2. A whole 24% less surface area than the big radiator in the 2nd gen.

The non-ac early A-bodies come in just under 400"^2.

If you look at all of the cooling issues threads on this board over time, the vast majority of them come from people with early A-body and first gen F-Body cars. There's a reason for that and it's almost always because the radiators in these cars aren't as big as they need to be, especially when dealing with the amount of power we can extract from Pontiac engines these days.

[SRGN]

Originally Posted by pfilean

SRGN - your experience is interesting. I'm still running the old 4 bolt but it does have a cast impeller. But it sounds like we are now at about the same result. When I ran my test route with the AC on I saw generally about + 7-10 degrees. I have the condenser and also an oil cooler in front. I run my oil through the radiator cooler before the remote oil cooler.

I forgot to add, I changed the timing chain while it was apart. I wonder if the wear on the chain was causing retarded valve timing which likely would have contributed to running hot. The chain really wasn't that bad though. I reset the ignition timing afterwards to 34 degrees all in by 2800 without the vacuum advance connected. That's where I had it before as well. Mine is the 10.25:1 compression 389.