Overheating issue with the old slant 6

scamp225 said

that is the new a radiator ! and how would water get in trans anyway through trans cooling lines and if so do i need to replace them?after flushing transmission should i put some stop leak

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Unfortunately, if that is the pix of your coolant in the bucket, the trannie cooler loop in the new rad is apparently defective; I would venture to guees it has a small pinhole in the loop. Hard to say exactly why until it is pulled out and taken apart. Do you have a local rad shop there? Or is this under warranty?

The trannie fluid is pumped under higher pressure than the coolant pressure so it is entering the coolant when running. But, once the car is not running and that trannie pump pressure is gone, there is nothing saying that some rad fluid won't seep back into the trannie cooling line and get carried into the trannie when it gets started again. You'll only know by puling the trannie pan and looking carefully. Once the rad is pulled and fixed for sure, then the flushing of the trannie ought to carry any coolant out of the lines. I would not put in any stop leak; it is not designed to fix a leak like you have in the trannie cooling loop in the radiator.

Thinking more about it, I would be doing the engine flushes and the trannie change/flush at the same time: i.e., put in the engine flush and fresh trannie fluid/filter and run for a bit at the same time. BTW the hose in the thremostat might help some to initially flush the engine, but that won't necessarily get into all the nooks and crannies. Like RRR said, your engine needs to have the he** cleaned out of it; any of that oil will block heat flow from the engine surfaces into the coolant and from the coolant into the radiator.