Hot Rods New engine build overheating help

My dad told me he used to crank a new one up and drive it without any water in the motor to seat the rings. I guess it’s the hot/cold/hot/cold thing and it seemed to work well for him. Me on the other hand I build mine with a little slop because for the most part it’s going to be run hard and put up wet right from the get go.
The last 347 I built I punched it out to match each piston with a torque plate attached, gapped all the rings to fit each cylinder, miked everything basically I went overboard with the assembly. That was one of the most reliable motors I’ve built, no issues (not that any of my other motors had any) but I knew that I could send it to the outer limits ever so often and not worry about picking up parts on the street.

I kinda miss those days

 

Try disconnecting your fan and drive a short distance to see if it runs cooler. Wondering if the fan might be wired backwards if it runs cool at idle but heats at speed.

 

The 350 probably wants more carb and it sounds like the distributor is shorting with the advance

 

If its HEI, the small green and yellow wires do go bad from the pickup coil to the module. The vacuum advance is always pulling on them, that could be why it acts erratic when hooked up.

 

What about improper ring gap? If I messed those up and did either too much or too little, could that cause this style of overheating without any other adverse effects? (

 

Doubtful
Cracked block , cracked head(s) bad head gasket , plugged water jackets ....

 

Sure, too little can cause trouble.
Any result of running it with MMO.?

 

Does the car have a heater in it? If so, have tried running it on high to see if the motor temp comes down?
Have you tried pure water or a water wetter type of additive?

 

Why do you think you messed up the gap ?

 

fair question… I don’t really know. It’s been a year at this point since I set them and I don’t really remember details, and like I said it’s my first time doing it. So probably just overthinking it at this point.

 

Nothing anyone has said has changed MY mind.
Next time you climb the driveway and she geys hot, grab the garden hose and spray, lightly, the radiator. Does it dry evenl

 

Ok, I’ll try to reply to as many questions/suggestions as I can. (Again, thanks for so many replies. This is really boggling me so I’m thankful for all the input).

I have run it both with and without a thermostat. I’ve run with the heater on, off, and AC on on multiple occasions. All with the same results… still heats up real nice and slow til 180 (especially without a tstat), then will idle just fine. Once I start driving, it will start heating up slowly and not want to come back down. Creep up and up and up to 230/240 but tops out at like 245. It’s like the cooling system is working but the engine is building heat too fast.

I’ve blasted water through the block, through the intake, through the hoses. Nothing kinking, blocking, or restricted that I can tell. I can see water flowing aggressively through the upper hose at idle. Electric 3000cfm fan, pulls hard. 3 row aluminum radiator rated for a v8. Aluminum aftermarket water pump that seems to do good. I can’t fathom at this point how any part of the cooling system can’t handle a plain Jane 350, even if it is bigger than the 305. Hell, the 70yo 6cyl copper radiator worked just fine for cooling thr 305, I just swapped it because it leaked and I knew I would be adding AC eventually.

I have not yet tried Marvel Mystery Oil, but willing to give it a shot.

Wiring is all BRAND NEW, so no issues there. Did it all myself and it’s done right.

I did a leak test for combustion gasses suspecting a cracked block/head or bad gasket/heat bolts torque. No gasses, compression good.

Checked, double checked, and triple checked the timing. It’s perfect. Purrs like a kitten.

I’m 100 mi out from fresh build now so about to do my second oil change. It sounds good and feels great, all except for the overheating.

I pulled the intake to make sure gasket was not blocked or weird in any way: nothing remarkable.

on recommendation of Lostone, today I took it out and heated it up to 220-245, then used a pressure washer to cool it to 140 (as cool as I could get it while idling). Did that 3 cycles. Flushed the radiator (cuz it was rusty yucky), added Water Wetter to new fluid. I’ll change the oil tonight and see how it does tomorrow… ‍♂️ that’s about all I can think of left to try. If that doesn’t work I’ll have to pull it out and tear it back down.

 

Does it dry evenly?? I’m not exactly sure what you mean. But I did use a pressure washer and it cooled right down. Again… even while I fired the pressure washer up and before spraying anything, I let it sit idling from 245 deg and it started slowing cooling down on its own. At idle it acts just like it should. Just heats up when driving. ????? Weird to me

 

It’s the radiator. The water pump doesn’t push the water fast when the motor is at idle. Hence the water stays in the radiator longer and has time to cool. At speed the water pump is pushing the water a lot faster and doesn’t have time to stick around in the radiator to cool off before it’s in the motor again. Try a 195* t stat before you swap the radiator out just to see. The longer the water stays in the motor the longer the water is in the radiator to cool down

 

So what’s the solution to “it’s the radiator”? It’s already a nice aluminum 3 row…. 4 row??

 

I agree with lostn51. I think it’s radiator flow as well. Disconnect both radiator hoses, put your had over the lower hose connection, fill it to the top and release your hand. Water should flow out about 18 inches if it’s flowing good.

 

An electric fan blocks more air than it pulls at highway speeds. It may have been adequate with the old, loose engine, but not any more.

Gary

 

Post some pictures of the set up, radiator front and back, water pump and drive belts, fan, anything related to cooling. Could be something you are not seeing.
What about fan a shroud? I've seen a bunch of them that block a lot of air, could be why it only heats up when moving.

 

I was surprised it took this many posts before Shroud was mentioned .I'd start there.

 

sorry - old setup cooled just fine with fan zip tied to the rad. I made an aluminum shroud. Now I’ve tried both ways, had it in and off. Makes not a lick of difference. Cools/heats up with the exact same profile with shroud on and with no shroud. Even swapped fans once last week - no change.

also I’ve pulled the hoses and checked rad flow a few times, no restrictions during any checks. Ran flush through there anyhow just to be sure. Radiator flows just fine. This one’s really got me scratching my head.

 

It’s obvious that the radiator isn’t doing its job at speed. Just go buy/build a good radiator for “X” number of horsepower or cubic inches and you’ll see the difference trust me on this. I be been in this rodeo several times. If you build enough nitrous motors this becomes second nature.

 

99% of the time when this situation occurs it ends up being the radiator. Been there, done it, seen many others do it too. Far easier to try a different radiator than to pull and tear down a fresh good running engine looking for a possibly non-existent problem. Not trying to be argumentative, just passing along what 55 years of wrenching for a living has taught me.

 

Oh yeah while I’m thinking about it, the amount of rows in the radiator do not matter. The last radiator I had built for my car was a 2 row (aluminum 1” cores) and it worked well with 900+ horsepower spraying the house down with nitrous at the track daily driver. Remember hot rodding isn’t cheap and sometimes what works with one thing is useless for others.

 

You could try a smaller pulley on the water pump to spin it faster and move more water.

 

Pull the shop rag out of the inside of the radiator.