Too hot 327

I have a 62 impala SS with a 327. It has the 300 hp heads (double camel hump) and intake manifold. I have replaced the water pump with a high flow unit, and put a high flow 180 t-stat in it, installed a new thermo fan clutch, and had the raditiator boiled and cored. I cannot get this to run under 220 on an 80 degree day. On warmer days, or with the factory AC running it really gets hot. The block's cooling jackets look very clean when veiwed from the water pump and t-stat removal. The only thing I can think of that does't seem right is that the exhaust manifolds may be off a 283. The diameter going into the exhaust pipe is 1 and 7/8 inch and I'm thinking that's to small for those heads. Could that cause overheating like this? It runs hotter at higher speeds 55-75 than slower speeds 30 to 50.

Your exhaust system is sufficient for street running.

Do you have a vacuum advance distributor?

Is it sourced to full time manifold vaccum?

If not, that's more than likely what the problem is.

The vacuum comes right off the base of the carb, so yes, it is full time. 15hg.

I should of said, right off the manifold at the base of the carb. The left rear carb hold-down bolt is hollowed and tubed directly into the manifold. Thanks for the thought C9x.

Is the vacuum advance working?

A simple test is to remove the vac advance hose while the engine is idling.
If the idle speed goes down that's an indication the vac advance is working.
Although, you should shoot the timing with a light to assure that it's working correctly.

Along those lines, when you timed the engine, was the vac advance line disconnected?
It should be otherwise you're giving away a lot of horsepower and it could be retarded enough that it overheats.

It might be running a bit lean, try one size bigger jets. More advance might fix it too.

I timed it with the vacuum line disconnected and plugged. I set it at 10 degrees BTDC. I suppose it could be lean, but I'm at 5280 feet and richness is usually more of an issue up here.
I guess it is possible for the vacuum advance unit to work partially (pinhole leak in the diaphram?). Maybe changing would be a good thing to try? Thanks for the ideas.

You don't have to swap the vac adv unit until you know for sure it's bad.

Shoot the timing with vac adv disconnected, note the amount of advance.
connect the vac adv and shoot the timing again to see if it's holding at where the manual says it should.

Another test is to put the vac advance hose in your mouth, suck on it, see if the timing plate moves.
While suction is applied put your tongue over the hose end and see if vacuum remains or bleeds off.
Kinda crude, but it works.
(Engine off when you do this one.)


Any chance you have a reverse flow pump?

Got a shroud?

Is the engine bay stock with all the air blocking devices in place so air will go through the radiator?
Air takes the path of least resistance and will go around the radiator if it can.

It was hot before I replaced the pump. I ordered a high flow from Summit...I doubt it is reverse flow or the temp diff would have been significant when I changed it. The engine bay is stock, there is a shroud - looks original - fan is about half in, half out of it. There is definitely room for the air to get around the shroud instead of all coming through the radiator. I would have to check the assembly manual to see about blocking devices.

I have a vacuum pump so I can apply the same amount of vacuum to the advance as the manifold is pulling and watch what happens. I did advance the timing this morning to get the vacuum up to 17hg. Runs better too, but still heats up.

I'll try some of your suggestions and see what happens. Thanks again.