Big block running hot. Can’t figure out the issue

Slooptin said:

Not sure what was in it originally, it appears to be the original rad. I ordered a replacement off rockauto

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With only 2 rows and 1-9/16" core thickness, that looks pretty small.

nvrenuf said:

With only 2 rows and 1-9/16" core thickness, that looks pretty small.

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Interesting. I thought it said 4 row on the description. Oddly enough I just slapped a similar radiator in my suburban with a 2-1/4” thick core so if this one is thinner, I might just put it in my suburban and put the suburban radiator in the k30 since they both are 19” tall radiators

Slooptin said:

I believe so. When I burped the system initially it looked like there was fluid flowing once the t stat opened up.

I haven’t paid attention to the lower hose but I’ll check it out. I also don’t suspect the t stat since the new one didn’t change anything.

As far as the water pump, it should be a reverse rotation since the front accessory drive came from a gen 6 motor.

And yeah I made sure to use the right gaskets. Fel pro 508sd I believe.

Thinking I might order another rad cap and make sure the overflow line isn’t plugged too

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Yes, the incorrect cap will make it run hot with too much pressure for sure!

Adding to the discussion maybe it will help although I’m not well read on reg vs reverse rotation, but I have a Gen VI 454 bone stock in the 86. But it has old fashioned v belt system. Presuming the water pump was swapped for a v belt pump when the engine went in.
So do they cool the same reg or reverse rotation? I’d think so. IE it doesn’t matter which way you push the coolant through the engine.
But reverse cools the heads quicker (aka the 90s lt1 engines, early aluminum head 350s).
Not sure if this helps w your issue or just rambling.

Where is the sensor? if it's in the head it will read high unless it's pissing out the cap your probably fine

Hello there, I have built several big blocks, one thing on the stat, I drill 2 1/8" holes in the stat to bleed the air off if any is trapped that would insulate the stat from the water, also, make sure of your water pump rotation, last if those things are good, take the top hose off the rad hold over a bucket and see if its pumping, also if water moves too fast it can't change out the heat.
I hope this helps

Ajax19 said:

Where is the sensor? if it's in the head it will read high unless it's pissing out the cap your probably fine

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Sensor is in the head. It’s a new sensor too and I verified using my ir heat gun. The external head temp was reading around 235-245

Grinder60 said:

Hello there, I have built several big blocks, one thing on the stat, I drill 2 1/8" holes in the stat to bleed the air off if any is trapped that would insulate the stat from the water, also, make sure of your water pump rotation, last if those things are good, take the top hose off the rad hold over a bucket and see if its pumping, also if water moves too fast it can't change out the heat.
I hope this helps

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Thanks for the tip. I’ve got probably 5 or 6 t stats sitting around my garage so I’ll try that with one of them.

Radiator got delayed so hopefully one night this week I’ll have time to swap it all in

I may have missed that you already attempted this fix, but I had the same issue with overheating, the eventual fix was adding the bypass hose from the top of the water pump to the intake manifold, allowing coolant to circulate in the block before the tstat opens. Also I changed tstat to 180.

I have had an 85 3/4 ton since new has a 350 motor.Mine was runnning a little hot ,flushed the radiator twice and put a new GM Radiator cap and it helped a lot.