[stoveboltgeek]

Okay, I know hot-running engines are a perennial topic with Pontiac guys, so bear with me. I'm an experienced classic car guy, but new to Pontiacs. I'm trying to gain as much knowledge as possible before making a purchase. (I'm specifically looking for a stock 1968-72 A-body with a 350 or 400.)

In https://forums.maxperformanceinc.com...d.php?t=881949 the OP described what appears to be a common problem - a 400 running too warm on the highway but cooling off to normal when idling.

I know about the usual suspects for overheating - stuck thermostat, clogged radiator or water jacket, collapsed inlet hose, lean mixture, retarded timing, etc. I've also read about the Pontiac water pump impeller issues. So, I'd like to ask a few Pontiac-specific questions that go beyond these issues.

First - is this problem unique to 400s and 455s, or does the 350 have the same problem? The 350's smaller displacement/combustion chamber plus thicker cylinder walls are what makes me ask the question.

Are cars with factory A/C more prone to running hot? Does the factory A/C interfere with air exiting the engine compartment? (A big radiator is great, but the air has to exit the engine compartment after being pulled through the radiator.) Are there any baffles/shields/other sheet metal that interfere with airflow that should be removed?

Do any of you still have the air pump (aka AIR system) connected and operating? (Air pumps increase the under hood temperature due to additional combustion in the exhaust manifolds.)

Based on my reading on the Butler web site, Pontiac switched from the 8 to the 11 bolt water pump in 1969. Then, in mid-1969, the 11 bolt pump went from 4" to 4.5". Does the 4.5" pump have a physically larger internal capacity, and therefore move more gallons per minute of coolant? Or, is it simply a matter of shaft and body offset, and the internal volume of the 11 bolt pumps are identical?

Are there different sizes of water pump pulleys? If so, are the smaller ones used on 350s and 2 barrel 400s?

Any other unique quirks of these engines I missed?

Back in the day, I had a friend with a '70 Catalina with a 400 who had heat issues (he'd installed aftermarket gauges, so he knew that). I remember he went to the Pontiac dealer and told them he wanted the biggest radiator that would fit his car. I think that helped, but I don't remember all the details (that was almost 50 years ago!).

[RocktimusPryme]

I think you are over complicating it a bit.

I’m going to give you some generalities here but by and large they will be correct.

I don’t think Pontiacs are notably worse than any other major muscle car brands as far as cooling.

This has been talked about here before but the BIG caveat to cooling is radiator surface area. 60s cars tend to be undersized in the radiator department. I’ll post a picture I have from a video I’m editing for an electric fan swap on my 67 talking about how much bigger radiators started getting in the 70s and going forward. So a 60s car is almost certainly going to be harder to keep cool if you have a big engine in it. Not impossible, you just have to work harder with the radiator in a first gen bird compared to a second gen.

Related, yes different models were offered with smaller/larger rads depending on if they were AC or by engine size. I think often people swap big engines and aftermarket AC into cars that came with an 326 and no AC, then are shocked when it won’t stay cool. Other tricks too, extra baffling, bigger fans, smaller water pump pulleys etc. All the makes did that though. Not Pontiac specific.

If you want a Pontiac specific problem it’s that there is sometimes too big of a gap between the WP blade and the backing plate. Easy fix though. Some have reported that can make a giant difference. Going to the “ac” pulley setup did help me. Some people say there is a difference between the stamped and cast WP impellers. But others say there isn’t. So I wouldn’t put that one high up in the pecking order.

In short later cars are going to be easier to keep cool than early cars especially if you have a powerful big engine. Other than that, if you want to keep it simple, big clutch fan and a shroud and you will be fine most of the time. There is also a huge flex fan that some people swear by. I’m sure it works, just can’t stomach the power is sure it eats.

Electric fans are great, there is a reason the OEMS use them now. But there are always tons of pitfalls and ways to do it wrong. I would try the simple and cheap answer first with a big mechanical fan.

[Goatracer1]

I think a lot of the "problems" people have with "over heating" don't really exist. Someone installs a water temperature gauge and suddenly their car is running too hot. It may be hotter than they like but it is not over heating. People don't take into account that the original temp light did not come on until 240 degrees on non AC cars and 246 on AC cars. If you run the recommended 15 psi radiator cap then PLAIN water does not boil until 250 degrees F. If you have a 50/50 mix of antifreeze and water it raises the boiling point about another 14 degrees F. I drove these cares when they were almost new and never had a temp light come on unless there was a leak or something similar.

[Squidward]

Goatracer1, you speak truth. Back in the day when these were just used cars, a replacement 400 was a dime a dozen. Now that there is significant comparative rarity, we get all tweaked up about our investment. And me personally? The thought of motor replacement makes my neck and back hurt just thinking about it!

Would my motor hack 210, 220? Sure. But part of my fun is engineering a solution so that it doesn't have to run 210-220.

[Squidward]

To the OP: the 11 bolt pumps are the same except for snout length. Pulley alignment would be different for early vs later water pumps. And in 1970, there were long snout pumps with deeper pulley grooves that aligned with earlier accessory setups.

Water pump pulley diameters are also different. HD cooling systems and AC got you a smaller diameter water pump. Smaller diameter gave you higher water pump rpm, which meant 2 things: more coolant flow, and higher fan speed.

[srmmmm]

I strongly recommend a cast impeller over a stamped one. The stamped impeller units I have used in the past (only the first time by choice), always induced cavitation within the pump housing and caused the increased highway driving temperatures.

[RocktimusPryme]

slight devils advocate on the running hotter conversation.

1. I agree, its always been a strange flex to me when someone says "Car wont get over 150 degrees", and most OEMs set the thermostats between 195-205. So if you car runs comfortably in that zone its fine.

2. Caveat here though, in the world of hot rodding, where maybe we have some extra compression, etc....... there can be some safety benefits to keeping it below 200 on the regular. My car will start to audibly ping once its good and heat soaked at 190 or above. For the most part, its just pulling away from stop lights and light load, which I dont overly care much about. My C6 did the same thing. But its gets worse as it gets hotter, and starts to concern me more.

[stoveboltgeek]

A few more thoughts:

Perhaps the better question is to ask: is it typical for the 350/400/455 to run more than 5-10 degrees above the thermostat's rated temperature? And if so, why?

Coming from the world of '55-57 Chevys with first-generation small blocks (265 and 283), if it's running over 190 degrees with a 180 thermostat, something's wrong. (My experience was more like 180-185, even on 90+ degree days.) And, these cars didn't even come with a fan shroud or fan clutch. So, I'm trying to understand the differences here.

Digging around, I found a copy of the 1969 Pontiac owner's manual online. The scans included the emissions equipment folder as well. See:
https://oldcarbrochures.com/static/N.../dirindex.html and
https://oldcarbrochures.com/static/N...nsert%20a.html

Here is a summary of the exhaust emissions changes to control HC and CO (NOx control was not yet a requirement in 1969)
https://oldcarbrochures.com/static/N...nsert%20c.html

Based on this page (and some independent checking) the '69 Pontiac came with a 195 degree thermostat.

So, with a 195 degree thermostat, I would expect 195-205 degrees. OTOH, if you used a 180 degree thermostat, I would expect 180-190. But, I'm gathering that often isn't the case?

A random thought - I wonder if folks have problems with the fan clutch not properly freewheeling when you're at speed? A fan clutch that properly locks up at idle but won't freewheel at 30-40 mph can actually interfere with proper airflow through the radiator. (This would be one advantage to an electric fan - it won't interfere with airflow at speed.)

[RocktimusPryme]

Originally Posted by stoveboltgeek

Coming from the world of '55-57 Chevys with first-generation small blocks (265 and 283), if it's running over 190 degrees with a 180 thermostat, something's wrong. (My experience was more like 180-185, even on 90+ degree days.) And, these cars didn't even come with a fan shroud or fan clutch. So, I'm trying to understand the differences here.


So, with a 195 degree thermostat, I would expect 195-205 degrees. OTOH, if you used a 180 degree thermostat, I would expect 180-190. But, I'm gathering that often isn't the case?

(This would be one advantage to an electric fan - it won't interfere with airflow at speed.)

Unpacking a couple of things with your statement there, you may have answered your own question about what the difference is when you are talking about early SBC tri-five cars vs some pontiacs.

A V8 tri-five radiator from cold case in 374 SQin of surface area for a 265 or 283. A non AC 65 GTO radiator is 399 SQin. for a 389. So you have 7% more radiator for 27% more engine.

Now say someone yanks out the 389 and installs a hot 462 in a car behind a radiator that was probably barely enough for the 389. You can see where I am going with this. But I think the same would apply to the tri-five when someone stuffs a 540 in there. Its not brand specific. 90% of this battle is simply available radiator surface area vs powerplant its being asked to cool. I just dont think the perception that a 55 chevy cools better than a Pontiac is accurate. Because its rarely an apples to apples comparison.

On a normal, not scalding hot ambient day I would agree if you engine is running way hotter than the thermostat rating there is an issue with your cooling system. Thats no different on a pontiac than a chevy.

And electric fans can be restrictions at highway speed, but its most common with dual fan setups that just block too much of the back of the radiator to flow.

FWIW the basic cheap aluminum radiator in my 62 cools the olds 455 in it just fine with a clutch fan and no shroud. But that smogger era probably doesnt generate enough power to make any real heat.