Transmission cooling lines, inlet vs outlet

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G_RIDE_81

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Oct 30, 2019
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Hope this question belongs here (since its about cooling) and not the Transmission thread.

On the radiator, is the top or bottom line the outlet? Getting ready to add an auxiliary trans cooler and plan to feed it from the radiator outlet. Thanks in advance!

Car: 1981 Chevy MC, TH350, V8, original other than a 350ci upgrade.
 
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Top line on the transmission to the top line on the radiator is cooler in.

Bottom line of the radiator goes to bottom line on the transmission is lube (cooler out).

This oil lubes the planetary gears and bearings and cools the internal parts. The temperature can be too cool for proper lubrication a thermostatic bypass is recommended for the auxiliary cooler.
 
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I work in the food processing industry. Every heat-exchanger I've come across in our plants (tube-in-plate/tube-in-tube variety) are usually set-up to be 'flooded' @ all times for proper efficiency. Some of these units are the size of an entire g-body. 'In' is @ the bottom & 'out' is @ the top. I'd be curious if & why the arrangement in an automotive app would be engineered any different?
 
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Top line on the transmission to the top line on the radiator is cooler in.

Bottom line of the radiator goes to bottom line on the transmission is lube (cooler out).

This oil lubes the planetary gears and bearings and cools the internal parts. The temperature can be too cool for proper lubrication a thermostatic bypass is recommended for the auxiliary cooler.
Thanks for responding. Forgot to mention I did add a shift kit when the trans was rebuilt and added 3.42 gears in the rear when it crapped out. I'm certain these upgrades have added some heat when I'm at higher speeds. Haven't pushed the car passed 55mph since the gear swap since the rpm's are quite high at that speed.
 
I work in the food processing industry. Every heat-exchanger I've come across in our plants (tube-in-plate/tube-in-tube variety) are usually set-up to be 'flooded' @ all times for proper efficiency. Some of these units are the size of an entire g-body. 'In' is @ the bottom & 'out' is @ the top. I'd be curious if & why the arrangement in an automotive app would be engineered any different?
I've seen several videos of Chevy pickups from mid 70's up through 2000's where the tap into to top line at the radiator.

Can anyone else confirm that its the same on gbody's?
 
Trace the lines from the transmission to the radiator and see which is which. From GM drawings it is top to top and bottom to bottom.

TH200, 200c cooler line.jpg


200-4R cooler lines.jpg

350 cooler lines.jpg
 
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I thought we were talking TH350 here, not 200 series. 200 series has the return line exactly as described above. I always thought the TH350 was opposite of that, as shown below.

Hell, now I'm getting corn-fused.

1639163044413-png.429512
 
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This does not look like my trans per the images. To the best of my knowledge I have a TH350, with the governor on the DRIVER side. Certain of this as I had to use a governor calibration kit to adjust shift points after the gear swap.
Sure, the governor is on the driver side, but the round accumulator cap on the passenger side should look like yours too. The 200C and 200-4R, I believe, are the only "backwards" flow transmissions GM has with the pressure port on top and the return line on the bottom.

As far as the heat exchanger goes, it kinda doesn't make much difference which line goes where, although generally the return line comes out of the top line, although not always. The radiator is a cross-flow design on a G-body which means the coolant should be about the same temperature coming from the cross tubes entering into the tank whether top or bottom. But, since the coolant flow is down, it makes sense to run the transmission fluid upward against the coolant flow to maximize heat transfer between the two fluids.

As far as mounting an aux cooler, you would disconnect the return line to the transmission from the radiator. Connect one port of the aux cooler to the radiator port, and the other connection to the line going back to the transmission. You're effectively putting that aux cooler in series on the return line from the radiator to transmission. You're done. Theoretically, most aux coolers don't care which way fluid passes through them as it's a cross-flow air to fluid transfer anyway.

4l60e-cooler-line-flow-direction.gif
 
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I work in the food processing industry. Every heat-exchanger I've come across in our plants (tube-in-plate/tube-in-tube variety) are usually set-up to be 'flooded' @ all times for proper efficiency. Some of these units are the size of an entire g-body. 'In' is @ the bottom & 'out' is @ the top. I'd be curious if & why the arrangement in an automotive app would be engineered any different?
And in heat exchanger land, counter flow heat exchangers are more efficient. So I would think setting up the car would be the same idea.
 
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