It appears that because of the check valve in the coolant line that leads to the bottom of the radiator you cannot reverse flush the transmission lines and cooler. If you flush it in the right direction you end up with a cooler full of cleaning solvent. I disconnected the lines at the transmission to the cooler intending to first blow them out, flush them, then blow them dry, all in reverse. There is a check valve that prevents that. If you pull the bottom line to the radiator to get the check valve out of the way first drain out your antifreeze. You can then put a solvent cleaner in the top and have it drain at the bottom. I blew it out with compressed air. Did the lines individually. You may have to make a tool to tighten the bottom line to the cooler, then secure the cooler to the water tank. Better would be a 1'' crows foot.

My question is why doesn't the trans line go to the top of the tank, then drain down to the bottom, and return?

 

All the cooler is is brass tubing that runs in the middle of the plastic side housing. It's purpose is to shed it's heat onto the coolant. It's under pressure so doesn't really "drain" it just gets pushed threw it.

 

Not to mention a flushing a transmission is bad

 

If you do the cooler and lines with air first, an approved solvent flush for cleaning the line and cooler, then blow it clean what harm have you possibly done in preparation for a newly rebuilt transmission? I am ten dollars and 2 hours into getting a build really clean. Cleanlinesss is the only religion when it comes to hydraulics. Anything else is heresy and cause to be throw into boiling burnt old transmission fluid.

Dealers use a flush when doing remanned transmissions under warranty I have read.

It would be better to replace the lines and radiator with internal cooler , but this is a budget, way over budget rebuild.

Now back to why the cooling tank seems backward.

 

If you are preparing for a new transmission absolutely flush the cooler and lines! As said it's not really backwards as it's under pressure. The way the factory does it, it allows the coolant to get up to temp quicker to allow you to use overdrive.

 

Does the temperature switch in the transmission control flow to the cooler? Or only decide that it is warm enough to kick in the overdrive?

 

Temp sensor doesn't do anything at all with fluid flow to the cooler, and I would dispute that on most of the trucks, it really doesn't inhibit O/D either. Both my 96, and my 98, will hit overdrive within half a mile of leaving home, regardless of outside temp. When it is -5 outside, I highly doubt my trans fluid hits 108 degrees in half a mile. I don't warm the truck up at all, I start it up, and drive it away.