TH350 cooler flow

I'm just finishing up putting a new Griffin cross flow aluminum radiator in my 66 Bel air. Now I know that the transmission fluid flows out the bottom fitting on the TH350 and back into the top fitting, but which way are they supposed to go into the cooler in a cross flow radiator?

I've been looking over a bunch of different forums and they all say different things. Some guys are saying that you have the fluid flow from the transmission to the bottom fitting on the radiator, then out the top of the cooler and back to the transmission. Some guys are saying that you route the fluid out of the transmission to the top fitting on the radiator, and back to the transmission from the bottom fitting on the radiator. The cheapo aluminum radiator I had in there before was a down flow, so the cooler just flowed side to side.

So what do you guys think is the correct way??

Since the cooler lines are vertical because it is a crossflow, usually the top line is the pressure side and the bottom is return.

i have a hang on aftermarket trans cooler on my pinto and it does`nt matter or know which way the fluid enters or exits ....it`s under pressure .. its` gotta go somewhere ...

While it probably really doesn't matter, I "theory" I would expect it to flow like the water - in the top and out the several degree somewhat cooler bottom fitting. Recall that radiator you are taking out - the entire cooler is in the cooler bottom tank

I agree it probably doesn't matter which way your flow goes, but just in case I'd probably give Griffin a call and ask them if they had anything in mind for the inlet/outlet fitting. Never hurts to talk to the guy who designed the product. From the Griffin website -

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For more information on our products please contact us at: 1-800-RACERAD or (864) 845-5000
(Griffin believes in customer service, your call will be answered promptly by a member of our staff located at our main production facility in Piedmont, SC)

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I'm of the opinion that,, since the engine coolant is hottest at the top and cooler at the bottom, I would also want the return of the tranny fluid to be from where the coolest temps are. Since the temperature transfer is due to contact with the engine coolant, go where it's lowest for the return...

I would say that since technically the counter-flow method is most efficient in all heat exchangers, the hot trans fluid should enter where the cooled engine coolant is coming out of the radiator. But unless the loads on the trans are only at about stock levels and stock stall speed, I would add an external tranny cooler.

There is no counter-flow/parallel-flow option on the tranny cooler as I understand how they're made. It's a simple finned tube heat exchanger running across (or across & back in) the bottom (vertical flow radiator) or vertically in the cooled fluid end (cross-flow) tank of the radiator where the engine coolant temperature is pretty well fixed once you're up to temp. The tranny fluid cooler doesn't "see" the top to bottom or side to side differential of the engine coolant, unless my understanding of how radiators are made is totally wrong. It runs side to side in the bottom tank, or up & down in the cross flow, and the engine coolant temp is relatively constant. If in doubt call Griffin - they can tell you how your's is built and eliminate all question, again IMO. If you call, let us know what they say - it's always good to learn.

Thanks for the replies you guys. I'll let you know if I get in touch with them!

I think I'm right on this, on any modern auto trans, the out line is the one closest to the pump. As far as plumbing to the radiator, I have no idea what is correct, but here's my thinking.....
1. I don't want to overcool the trans fluid. It has to be pretty hot to operate properly, so I would want to cool it to the hottest part of the radiator.
2. If you're pushing fluid vertically, it makes sense to me to introduce it into the bottom fitting and bring it out the top fitting to prevent air in the system.
Bottom line: call the radiator mfg.

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Originally Posted by rspears

There is no counter-flow/parallel-flow option on the tranny cooler as I understand how they're made....

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After reading your post and thinking about it I agree with you that the typical auto radiator and trans cooler don't fit the counter-flow/parallel-flow examples so my comment doesn't apply to this.

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Originally Posted by techinspector1

I think I'm right on this, on any modern auto trans, the out line is the one closest to the pump. As far as plumbing to the radiator, I have no idea what is correct, but here's my thinking.....
1. I don't want to overcool the trans fluid. It has to be pretty hot to operate properly, so I would want to cool it to the hottest part of the radiator.
2. If you're pushing fluid vertically, it makes sense to me to introduce it into the bottom fitting and bring it out the top fitting to prevent air in the system.
Bottom line: call the radiator mfg.

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See that's what I was thinking about. I don't want to get air in the system. Obviously I would fill the cooler up before I hook up the top line and start the car, but it seems like pushing the fluid up and out the top fitting would prevent any chance of air.

Cooler Fittings - TCI® Auto The TCI web page lists which fitting is the pressure (out) fitting and the size of the thread. Handy to know.

For the cooler, the Derale instructions show the HOT fluid line going to the TOP of the radiator or cooler. Same for an oil cooler, hot in top, cold is denser and is at bottom. Thermosiphon (no water pump) cooling works same way.

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Originally Posted by Dieselholic92

See that's what I was thinking about. I don't want to get air in the system. Obviously I would fill the cooler up before I hook up the top line and start the car, but it seems like pushing the fluid up and out the top fitting would prevent any chance of air.

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It cannot "get airbound".. above the fluid reservoir, it's all air other than the valve body. After the pump raises the fluid pressure it sends a portion of the fluid over to the cooler and then it's back to the reservoir. All the older trannies had vented to the atmosphere cases. Heat will kill an automatic. No matter how you plumb it, you gain some cooling, if you're that worried about it add an external cooler after the radiator cooler.

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Originally Posted by 34_40

It cannot "get airbound".. above the fluid reservoir, it's all air other than the valve body. After the pump raises the fluid pressure it sends a portion of the fluid over to the cooler and then it's back to the reservoir. All the older trannies had vented to the atmosphere cases. Heat will kill an automatic. No matter how you plumb it, you gain some cooling, if you're that worried about it add an external cooler after the radiator cooler.

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I'm not worried about cooling at all. I was just wondering if there was a "correct" way to run the lines.