Got a mild 512 based on a 400 big block in a dodge 4x4 and it gets hot in just a few miles. fresh engine, good compression and leakdown. New high volume water pump and 4 core aluminum radiator, twin electric fans and 7 blade clutch fan as well. Tried 180,160, and no thermostat. Gets to 240 in about five miles just driving. I has MLR gaskets on it and I pulled the engine out of desperation and pulled the heads off to try and find something. No cracks or signs of coolant in the heads or oil. holes in the head gaskets are normal. I have an old set of Clark copper gaskets from a race engine laying around and they have a couple extra holes in them for more water ports. I read the slits at the top are to vent steam and air as the water runs across the head. Most stock gaskets have no holes open along the bottom. The copper gaskets do. Has anybody had experience opening these holes up to improve cooling?

Cant tell by your photo. Is the pump turning in the right direction? Did you verify the gauge is accurate?

Those 2 Electric fans could be restricting air, is the clutch fan engaging when it’s hot?

That serpentine belt have a tensioner?

yes drill the holes, you can see the "rust" spot on the cometics in your pic, but lay the copper on top for reference.

The fans were not on their when I started the project, it got hot without them. The water pump I used is a FlowCooler 12 vane and it is not dependent on rotation like a stock pump. Serpentine belt is tight. it is kind of driving me crazy because their is just not reason I can see.

when I 1st built my 400/512 I had the block hot tanked & then I flushed the cooling passages out with the freeze plugs out, put it all together , 1st test drive all was good, 185ish temp, then it started running hot, turns out that my new Champion 4 row radiator got plugged up from rusty scale breaking loose , replaced the radiator with a ECP 2 row & installed an Gano screen in the upper hose, at 1st it caught a lot of metal scale & I would clean it out when I did an oil change, now when I check the screen it stays clean. the 4 row Champion had very small tubes, a small chunk would plug the tube.

Are you saying the pump spins in the opposite direction of “normal”?

If so, the first thing I would have tried is a set of stock pulleys to see if the direction made any difference.

I’m guessing it is the flowkooler 1679, which “looks” like it could work either direction…..

What part number are you running? I only see one and it is #1679 and rotation is clockwise. Pump

I drill out a a couple extra holes. But now I just have Cometic do it for me. I also add extra material in the corners . They will custom build them pretty fast.

what diameter is the pulley on the water pump?
what diameter is the pulley on the crankshaft?

edit: How much clearance between the back side of the blades on the water pump and the surface on the housing?

direction of pully rotation is clockwise. I got the engine torn down completely now. I washed the block in my parts washer, without freeze plugs, but in looking down in the block I still see come crap that I did not get out. Going to wash again and back wash the radiator, drill extra cooling holes in head gasket. And see what happens. The engine is the original one in the truck, and it had some expanding freeze plugs installed sometime in the past, and in looking at the crap in the bottom of the block, I am wondering if someone had dumped a bunch of stop leak in it, and it is breaking loose with the new rebuild and fresh antifreeze.

Do you have them drilled similar to the copper ones in my pictures? And where exactly is material added in the corners?

i have been thinking about one of those, "just because", as a precaution.

Its made like a minnow trap, I also put a little magnet in the trap area, it caught LOTS of rusty metal chunks., the 1st one I got was see through, I now have the aluminum one.

What brand of radiator are you running? I hope it's not a Champion Ebay special. Actually, I do because they are garbage. Those things can't cool a lawn mower.