73-87 Chevy _ GMC Trucks > Engine/Drivetrain

Transmission cooling lines in new aluminum radiator

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In replacing my radiator, I noticed the tank fittings were 1/2 inch instead of 5/8, looking inside, the opening was roughly 1/4 inch diameter.

I called the distributor, was told not to worry, aluminum is more efficient at cooling. So much for a 'factory fit' replacement.

The transmission is a '66 GM THD 425, and the cooling lines are definitely a higher capacity.

I thought I could laser measure the temp after a run to see if the trans is running hotter then the engine by a significant percentage.

Being ignorant of transmission design, I don't know if this obvious restriction is severe, or if the 'flow volume' of oil is not that great.

It's not that there are load issues.

The question is: should I worry? and/or add an outboard cooler, bypassing the wimpy one?

As always, thanks in advance for you help!


A lot of folks will say "run both!" plumb from one to another...I don't subscribe to that theory.  I much prefer the solo cooler, as big as you can fit.  JMHO.

Thanks Shifty..need to see how much real estate I have that's accessible. Pretty packed in there.

Thought about calling manufacturer again to ask if they have a volume rating.

I have always run from the transmission, to the external cooler, back into the radiator cooler, then back into the transmission. I have this on all of my automatic vehicles and have never had an issue in 30 years. I do think however, that it might matter in what climates you are running your vehicles. If you run in cold climates it might help to warm the fluid up a bit before you dump it back into your transmission. That is the theory anyways. I have never tested it with actual transmission temp gauges. There are aftermarket thermostatic control valves that will bypass the cooler until the fluid reaches a certain temperature. Derale and Improved Racing make them, I know.

Being in AZ, that's never been a consideration for me...I get a choice, hot, or hotter.


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