I am installing an AOD trans into a previously manual trans truck. I took the radiator that was in it to a shop and had it tested. He said it was in great condition and would perform above the capabilities I require. The radiator has the reservoir in the bottom to cool an automatic transmission. My friend says NO BUENO to the radiator style cooler and says external cooler is the ONLY way to go. The radiator guy said the radiator style cooler would work fine. I don't know one way or the other. Pros & Cons? Many more questions to follow based on the answers...............Thanks

 

I always run both. But, I'm in Az and the heat is brutal.


Guys that run both will argue which one first in the flow path. I've run external first and radiator cooler first and both worked fine.


Torque converters make a lot of heat. Some prefer to dump as much of that heat as possible in the external cooler before going to rad. to keep engine temps down.


Others argue that you can over cool a trans. I personally doubt it unless in REALLY cold country.


I have tried large external cooler only and it wasn't enough in AZ temps pulling my boat over mountain grades. I even had the largest cooler I could find and mounted a shroud and it's own electric fan. I prefer both.


Heat is the auto trans worse enemy.

 

I always run both, first to the radiator cooler and then to an aux cooler. Never overheated one.

 

I always run both, a external cooler is a lot cheaper than a transmission.

 

Radiators run at temperatures in the range of 190 to 210 degrees, why do we run transmission fluid through them and call it a cooler? Ambient air, even on a hot day is less than half that temp, I never use a radiator cooler but opt for an external cooler instead. Talk to a transmission guy instead of a radiator guy, he'll tell what is bueno. Without a doubt, heat is the biggest enemy of an transmission.

 

Radiators are definitely hotter than ambient air. The bottom of the rad where the cooler is should be about 10 degrees cooler than top. Still hot but, with trans temp even hotter, there is still a differential and some heat transfer.


When I tried external cooler only it was a huge B&M racing cooler and I even added a shroud and fan. My trans still got too hot for me on long pulls on mountain grades in 100 degree temps. The radiator cooler did help in this case. It was also a huge aluminum Be Cool Radiator. I had 160-180 degree coolant temps.


If you're not towing in desert temps the external cooler only should be fine. Definitely better than rad cooler.


Another reason some like to use the rad cooler last in line is because they worry about over cooling in the winter.


Your climate and how you use the truck matters.

 

Don't run only an external "heat sink" style cooler as I did. I fried my AOD on the way to the 2013 Supernationals in Pigeon Forge, Tenn. Towing a 1954 F-100 behind a U-Haul for 500 miles getting back home is not much fun. I bought a new radiator that was plumbed for A/T after having the AOD re-built and kept the "heat sink" as a pre-cooler. No problems since. Hope this helps you make up your mind. Experience is an expensive teacher!! Steve

 

Back in the day I had a 75 3/4 ton with a C6. Did a lot of hauling and towing so I put an external cooler on. Had a 3 way valve to use both or just the rad cooler. In these northern climates both would be too much. The rad cooler acts as a heater too in the winter. I guess maybe more like a warmer. I think there are thermostats you can get to put inline that will open when the fluid gets too warm allowing the external to operate when needed. Certainly cheaper than a rebuild.

 

I always use a stack type external cooler with the stock radiator room permitting. On my '54 with a C6 I cant get to the radiator cooler ports and used 2 stack plate coolers as I figured 2 short ones next to each other would be the same as 1 tall one. A tall one would have been blocked by the grille. I also installed a trans temp gauge after the coolers, barely gets to 100° and 115° on hot days.

Weeker style cooler (OK for street non towing use)




Better stacked style cooler (must have for towing):



Mine:

 

Here is the unit I am using on my latest 40 Ford coupe, I got tired of looking for a location on the car that had some modicum of airflow to support a "passive" cooler so this Derale unit fit the bill. Mounted in front of the radiator, it provides the air "push" to compliment the radiator fan "pull". The beauty of this design is that it can be mounted most anywhere and still perform as designed.

 

Because it cools the ATF. Every time. Always, without fail.

I used to be a transmission cooling engineer at Ford. It measured the ATF temperature entering the radiator cooler and the temperature leaving the radiator cooler. In ambients from -40F to +115F, unloaded or loaded to max load, the ATF leaving the radiator cooler was ALWAYS cooler than the ATF entering the radiator cooler.
And I just did.
You would have a much more efficient (read:more cooling) system if you changed the direction. The most efficient way to cool the trans is from the trans to the radiator cooler, then to the external cooler, then back to the trans.

 

"Because it cools the ATF. Every time. Always, without fail.

I used to be a transmission cooling engineer at Ford. It measured the ATF temperature entering the radiator cooler and the temperature leaving the radiator cooler. In ambients from -40F to +115F, unloaded or loaded to max load, the ATF leaving the radiator cooler was ALWAYS cooler than the ATF entering the radiator cooler."


I would caution the use of words like "every time", "always", and "without fail"...being an engineer you should know better than anyone that these absolutes do not exist in the real world. While your assertion that the fluid was "ALWAYS" cooler may be true but it has little value when assessing the EFFICIENCY of this cooling. Using your measure even a 1 degree drop would qualify as "cooling". Any fluid run through a coil bathed in another fluid that is of higher temp will exit at a higher temp...are you telling us that at -40F that trans fluid will be better cooled by 200 degree radiator fluid than by ambient air?

 

I used the word "Always" very carefully.

Why would you think that at -40F the radiator is at 200F? It's very obvious that you've never tested this. I have.

Did you notice the part where I said I had a thermocouple inside the radiator near the transmission cooler? When the ambient was -40F the coolant near the trans cooler never warmed above -30F. The trans was warmer than -30F at that point, so the fluid around the cooler that was at -30F was certainly NOT warming the ATF. The ATF temp maxed out at about +100F.

And yes, even a one degree drop in ATF temperature is cooling. Do you consider that warming? You are absolutely correct that Any fluid run through a coil bathed in another fluid that is of higher temp will exit at a higher temp. I'm telling you that at -40F the radiator ALWAYS cools the ATF because that side of the radiator is NEVER near 200F.

Why is there a radiator in the truck? It's to cool the engine coolant. If the temperature coming into the radiator is 200F, and the temperature going out of the radiator is 200F, why even have a radiator? It isn't doing anything.

At very cold ambients the engine thermostat only opens for a short time. 200F coolant enters the radiator, and coolant at -30F enters the engine via the lower radiator hose. That 230F difference cools the engine down QUICKLY and the thermostat closes. Now the coolant sits in the radiator and quickly gets down to ambient temperature. Then the cycle happens again. This is why the coolant around the transmission cooler stays near ambient temperatures.

If we had wanted to use the radiator to heat the transmission we would have put the heat exchanger in the hot side of the radiator where your argument would be valid. But since it is in the cold side, you're mistaken.

 

I don't want to get into an academic argument with someone who is obviously too emotionally involved in the subject matter to remain objective. I don't agree with your use of absolute terms since nothing in this physical world is absolute. The internal combustion engine generates the thermal energy that raises temperatures to 200 degrees...that is unless you have a thermostat that opens sooner. In no portion of your post do I see the work "thermocouple". I live in the real world where radiators fail, coolants degrade, loads on systems vary greatly...absolutes don't exist. My vehicle will have the cooling components necessary to ensure safe operation under all driving conditions...without regard for OEM assertions to the contrary.

 

That's fine. Why we don't we leave it to everyone to decide which way they want to go? We've each laid out our positions and everyone can choose which one they believe.