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Old 12-31-2017, 11:21 AM   #1
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Transmission cooler upgrade

So I have a 2006 GMC 2500HD with the Allison transmission and the 8.1 V8. I am looking at upgrading my existing transmission cooler to a new Derale 51978. I have removed the existing rubber crimped lines and replaced them with braided steel lines and used AN fittings after I flaired the metal lines.
Now looking at getting a bigger cooler and removing the lines going to the radiator and run them straight from the transmission to the cooler. I know they say that the radiator is to warm the transmission fluid when it is cold. Is there any problems with doing this?
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Old 12-31-2017, 01:59 PM   #2
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The only issue i had was the engine temps are 195f. its really not good for a transmission to have that high a work temp. Mine is with its own trans cooler and not connected to the radiator. It runs around 140 pulling hard and 105 when not. My fluid is still pink and no smell of burn at all. Transmission shifts perfect cold or hot. No issues! This spring i will change the filter and fluid in the transmission. First time in three years!
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Old 12-31-2017, 02:14 PM   #3
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I know they say that the radiator is to warm the transmission fluid when it is cold. Is there any problems with doing this?
Yes.

In the bottom of the radiator is an oil-to-water (OTW) tranny cooler (heat exchanger). If you bypass that OTW heat exchanger, you will be decreasing the tranny cooling capacity of your tranny cooling system.

Way back when, the new 1999 SuperDuty pickups had only an oil-to-air (OTA) tranny cooler. That proved to be inadequate for heavy towing in the summertime desert, so Ford replaced my radiator with one that included an OTW cooler, thus significantly increasing my tranny cooling capacity. After that, I had no more problems with overheated tranny.

In hookup your new OTA cooler without bypassing the OTW cooler, determine which line coming out of the bottom of the radiator is the return line. Connect the line that goes into the OTA cooler to the bottom of the radiator where the old return line exited the radiator. Then connect the return line from the OTA cooler to the old return line that goes back to the tranny. You may need to visit a good hardware store and buy connections to get it done.

A secondary purpose of the OTW cooler is to warm the transmission fluid when it is cold. But the primary purpose is to increase tranny cooling capacity.
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Old 12-31-2017, 09:53 PM   #4
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Manufacturers cut costs where they can but try hard to make sure that their expensive components last a long time. The transmissions, oil and coolers are all part of a system that should perform well. Anything can be improved and if you travel in mountain passes a lot then the extra cost for an add on cooler could provide an extra level of protection. Most wont need it.
Most of my trips include one trip over a pass, some maybe several miles of 6-8%. Temperatures never go into the danger zone.
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Old 01-03-2018, 03:25 PM   #5
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Well I was using the wrong part number for the cooler I am looking at. The number is 52578 which is a 25 plate cooler not the 19 plate I listed in the first post. Now for the follow up question, how should the cooler be mounted, fittings at the top or fittings at the bottom? The existing cooler has the fittings at the bottom.
I will not be using the existing metal lines that go to the cooler as I will be replacing them with braided steel lines and AN fittings.
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Old 01-03-2018, 05:18 PM   #6
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Now for the follow up question, how should the cooler be mounted, fittings at the top or fittings at the bottom?
It doesn't matter. What matters is that the line coming from the radiator goes into the inlet, and the return line going from the cooler to the tranny comes out of the cooler outlet.

Also, the final step of your install should be a flow check to determine how much ATF is flowing back to the tranny after all your plumbing mods. I don't know the GM specs, but on a Ford 4R100 tranny the minimum flow returning to the tranny is 1GPM (one gallon per minute) at idle RPM. Less flow than spec results in an overheated tranny, regardless of how much ATF cooling capacity you have.
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Old 01-03-2018, 11:24 PM   #7
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Yup, Smokey has it right. Guys who rebuild trannys will tell you that too cool is also hard on them. And don't shut the engine off after towing without allowing a few minutes of idle time to cool the transmision parts down. Some components can reach temperatures of several hundred degrees and when you shut the engine off the fluid in those passages will be burned leading to contaminated fluid. A 3 or 4 minute cool down will help keep the fluid clean and remove some of that excess heat.
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Old 01-04-2018, 12:03 AM   #8
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The only issue i had was the engine temps are 195f. its really not good for a transmission to have that high a work temp. Mine is with its own trans cooler and not connected to the radiator. It runs around 140 pulling hard and 105 when not. My fluid is still pink and no smell of burn at all. Transmission shifts perfect cold or hot. No issues! This spring i will change the filter and fluid in the transmission. First time in three years!
195F is not too high of a temperature for a transmission, that's still within the normal working temp.

You don't need to worried until you get into the 210-220 and no sign of decreasing and under a heavy pull.

Using the factory heat exchanger in your line after the aux cooler you're installing is actually a better way to go, because it will bring your trans fluid up to proper operating temperature faster, and that's also important for proper lubrication of your trans, which helps to decrease friction, in turn providing you a little better fuel mileage.

The aux cooler first in the out put side of your trans will be very beneficial decreasing the hot fluid leaving your trans before the heat is transferred to your cooling system, giving you longer up hill pull time before the temps rise to an uncomfortable level, if they ever do.

But answering your question as to if taking the factory cooler out of the line completely will hurt anything, no it will not.

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