"97" 350 engine overheating

I put an industrial 350 engine in a 78 GMC 4x4. Had steel rods, 194 heads, windage tray and roller cam. Seemed to be a good choice as a replacement motor. Has headers, aluminum manifold and a stock roller cam. Block had cylinder wall damage which required it to be bored out .060". Problem is when the weather gets up in the 80s it overheats or when pulling a car hauler. I have a new radiator core which I bumped up from 2 to 3. I installed a high flow thermostat and put bigger jets in carter carb. It did help but not completely. I had installed an early dual plane manifold, flat top pistons and rebuilt engine with "95" engine gaskets. I did talk to a performance engine shop about problem. They felt the over bore was not the problem. Any ideas.

First thing I would do is to make sure the bottom radiator hose has a spring inside to prevent collapse. I've had this happen to me with a cheap hose. Then I'd install a Flowcooler water pump or modify my pump with a Flowcooler disc and run Redline water wetter.

If you read Smokey Yunick's book on the small block Chevy, you'll find that the thin cylinder walls could be the problem. When the walls get thinner than about 0.130", there is insufficient mass to cancel harmonics which are generated by the sliding of the piston rings up and down the bore. They don't actually slide, it's more like a continuous skidding which generates the harmonics. These harmonics of course transfer to the water coolant side of the cylinder, forming air bubbles which cling to the cylinder and prevent cooling water from contacting the wall to carry away heat. The water wetter should help.

Just sharing my similar experience, and results:

I have a 4 bolt 350 in a 56 convertible. It was stock bore, but with a B&M 144 blower. I used the original radiator on it for 15 years, and no heating problems.

I rebuilt it in 1999, and due to a head gasket failure a few years earlier, I had pitted cylindars. I bored it 30; I also changed the cam to one 'designed' to work with the blower. And, I put a new alumin, larger, Walker radiator in the car. (I only did that to get the polished aluminum look.)

After all that, this engine had heating problems.

I finally fixed it with: Aluminum flex fan on motor AND high RPM Spal elec fan on front of radiator (on all the time). I also put on a high volume water pump. Oh, and a fan shroud.

Engine runs very cool now. I tried early this summer to have the electric fan off (I'd like to take it off...for looks). But I found I need that fan running too.

I'm presuming my heat problem was more due to the bore than the cam...but who knows?