If I convert my truck from manual transmission to automatic, I will need to cool the tranny fluid. Typically this is done through the radiator. However, the radiator I have does not have tranny cooling lines.

My original thought was to change out the radiator. My question is, can I keep my existing radiator, and go with an auxiliary tranny cooler like this instead? Would this provide enough cooling for the C4 auto I plan to use?

Auxiliary transmission cooler with hardware NEW IN BOX

 

Vinny, I've known of folks that use only the auxillary type cooler with good results but do not know if the one in the photo is of adequate size for the job. It also matters where you place the cooler and some guys use a small cooling fan mounted to it.

Steve

 

I use the largest cooler that napa had and mounted it up under the running boards,no fan.I have worries about it but never had a problem .I run a C6 auto.I pull my boat and 16 ft trailer with it. It was used when I bought a 1968 fairlane that I pulled home from about 80 miles away.Drove it to pigeon forge about 150 miles and up to Doc's last year about 6 hrs away.never had a problem.

 

I had asked my radiator guy that many years ago. I wanted a cooler built into a radiator I was having made for my 351c/FMX combo. He said the best thing to do was get the biggest aux. cooler I could from pep boys. Never had a problem with it mounted in front of the radiator. Since then I have gone to a 302/4r70w combo still with no problems. In fact, the temp gauge i have hooked to the trans never goes over 175.

 

Which do you think will cool your transmission best...running it into a cooler surrounded with 180+ degree water, or into a standalone cooler at ambient air temperatures? Obviously the standalone cooler will do a better job. Plus, if your engine cooling is marginal, you won't have the transmission adding to the load. The only reason Detroit hasn't used external coolers is cost. I have been using standalone air cooled transmission coolers since the 70s and have never had a transmission failure. The main reason for transmision failure is heat. The cooler you can keep the fluid the longer it will last...

 

Extruded finned aluminum, one for the trans and one for the power steering/hydroboost. I like the idea of having some metal between the road debris and my fluids...

 

Sorry, I respectfully disagree with only using an aux cooler, especially where you live. There is a reason they are called an AUXILIARY cooler. No cooler manufacturer, radiator manufacturer or auto transmission engineer would ever recommend using one a the primary cooler. First, the engineers designed the tranny to operate while being cooled by the radiator cooler at a near constant temperature. It reaches that temp shortly after starting and stays there. The ambient air temp can be from below zero to above 100, and doesn't stay constant or quickly bring up to or keep the oil at it's designed operating temp. A water to liquid intercooler transfers heat much more efficiently than air to liquid one (stand outside for an hour when the air is 72, then spend an hour in a lake or pool where the water is 72, which cools more efficiently?). It is near impossible to size an air/liquid intercooler properly, it will almost always be under or over cooling (over cooling a transmission can be as or more detrimental than overheating, the oil doesn't circulate or build to the right pressures so bands and clutches slip). Second, most people that install an aux cooler place it for convenience and/or appearance not efficiency, often mounting it horizontally tucked up near or against a surface where no air can possibly circulate thru it, not in the airstream. Put a sheet of cardboard behind your radiator and/or remove the fan and see how long it keeps the engine cool. Even if in the airstream there is little to no airflow at slow speeds.
Those of you using an aux cooler only, look at the climate where you live, and how much you drive your truck in inclement weather. Compare that to someone living in AZ like Vin man here.
Radiators aren't that expensive compared to auto trannys.

 

If the radiator is old or will need replaced in the near future this would be the time to make the move. Mid Fifty has a nice four row with built in trans cooler.

 

Ax, you always have great info and a wealth of knowledge. I was going to mention they do make a system where you can add a thermostat to your trans cooler if you wanted to keep it at a certain temp.
However I slightly disagree with desert temperatures idea. I live in the high desert of California where it can reach the 120 mark. I have never had a problem with my trans overheating, and it doesn't take too long to come up to temp when driving. I have driven in day to day temp with my cooler but to each their own.
Ax is whole heartily correct (I believe) on the subject. As with most things, how well things work and for how long depends on how you use them.

 

Overcooling a transmission? I have never in my life heard of a transmission that failed because it operated too cool! And, I haven't always lived in NH. I lived in Florida for 50 years before I moved here. I always used a standalone cooler in Florida where the summer temperatures run in the 90s daily.

Believe what you will but I repeat that I have never had a transmission failure using a separate cooler!

 

Ax racer is correct to a point, The information I have says that the transmission needs to be above 5o deg F to shift properly. We don't have that problem with an occasional use truck as we seldom drive it in inclement weather or abuse the thing with constant WOT shifts all day long as with a tow rig. The cooler is used as a pre-heater as well as a cooler. The radiator helps warm the transmission in the winter. Does anyone have any information as to the efficiency of an automatic transmission? From the efficiency information we could calculate the horsepower lost in the driveline and the heat that needs to be rejected by the cooler.
Sorry, I suffer from an extreme incurable case of overengineeringitis.

 

Whomever you got your information from must not live in a cold climate. The automatic transmissions in my PT Cruiser and Dodge pickup shift perfectly starting out in below zero weather. I don't know how long it takes to get to 50 degrees but it's not very quickly....maybe a few blocks, maybe a few miles. There is no difference in shifting after it heats up that I can feel...

 

There is a difference in the lubrication from the ATF though.