Transmission Coolers 101
June 18th, 2009 kevin
Towing trailers, or saving your transmission while towing, I must confess I had a hard time naming this post. Transmission oil coolers are by far the most important addition when we set up our tow vehicle, but there are many upgrades involved in a good tow package. We will let other upgrades slide for later posts and focus on our transmission.
If you have followed this blog you know about my teardrop. To stay cool we have started traveling in the mountains. I felt it was time to add a transmission cooler to the 1.5 liter automatic Mazda I have been pulling it with. As you know small cars are not designed to tow trailers, and therefore cooling is less than what is needed for the demand I place on it. To save the transmission I installed an over the counter transmission cooler (Transmission coolers are not listed by vehicle brand). What brought on this post were the instructions shipped with the cooler. I must say I disagree with the supplied instructions. After years of towing trailers and working on cars and trucks, the thought of lowering the operating temperature of the fluids below operating temp going in to the transmission are of great concern to me. Granted the oil works to cool the transmission so it won’t burn up, but the transmission clearances are designed for a small temperature range and the instructions are clearly not taking this point into account.
A little about the original cooler and it’s job.
The cooler built into the radiator serves two masters. Not only is it designed to cool the oil from the transmission it also serves to maintain the oil at proper operating temperatures. On cold mornings and cold climates, the radiator heats the oil for better shifting, and reducing wear from running the transmission too cool, a fin cooler can’t do this. So you can see that the engine heat helps maintain proper oil temperature in the transmission when needed. The factory cooler is designed for standard loading, anything above that loading increases the oil temperature above what the factory cooler can cope with, so we add more cooler to keep up with the task at hand.
We don’t want to loose the original coolers ability to keep the oil at proper temperatures, so we put the after market cooler in the line with the oil flow coming out of the transmission, so the after market cooler cools the oil first. The oil then travels to the original factory cooler, that can now maintain the oil temperature keeping the oil temperature from fluctuating out of operating range. This issue is small in the south west, but becomes a big problem with autos used in colder climes.
The oil should flow into the lowest fitting on the cooler and out the top fitting. To keep the oil in the cooler I install the cooler with the lower hose looped above the cooler so gravity won’t drain the cooler when the vehicle is dormant. On my first tow vehicle, I didn’t do this trick and had transmission leaks as the fluid level in the transmission rose while the vehicle was not in use, you may not have this problem but I feel it is a good design idea. With the cooler filling from the bottom up, no air pockets can reduce the cooling effect of the cooler.
Recap:
- Transmission oil coolers need to be added to tow vehicles without tow packages, the original is just not big enough to handle additional loading.
- The after market cooler should be the first cooler in the oil flow. Disconnect one hose to find the fluid flow direction. Connect your cooler to the line that oil is being pumped out from the transmission.
- The lowest fitting on the cooler becomes the inlet on your added cooler, this arrangement reduces the chance of an air bubble reducing cooling.
- Loop the connection hose above the cooler on the cooler’s inlet side, this will work to stop a high oil level in the trans when vehicle is not being used. This may or may not avoid an oil leak but will help.
Warning:
My last cooler came with instructions to place the after market cooler after the factory cooler. From the standpoint of lowest temperature out maybe, but we are trying to maintain the proper operating temperature, our final stage should be the factory cooler. In first place, or last place, the same cooling capacity has been added, so our effort should be proper operating temperature, not lowest temperature.
Auto parts Warehouse has this model, the one I am using, Clicking on the picture, or the link below will give you more of the details about this cooler.
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4-seasons transmission oil cooler fs53000
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