[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!).