built in transmission cooler?

[desertrat]

Hi, I'm having my new/old 1988 Horizon ST gone through by a friend/mechanic. I was going to have him install an external transmission cooler on the beast, but he called today to say there was already one in the unit built in and utilizing the radiator to cool the engine and transmission. Can anyone explain how these units work. Wondering if the radiator has extra tubes carrying trans fluid to cool within the radiator fins?

Thanks in advance for any help or info

Steve

[WME]

The radiator has a plate cooler built in. It works OK for a Pickup. but not to good for a heavely loaded camper. It cools

from the water in the radiator NOT the air. So it adds heat to the radiator and MAKES IT RUN HOTTER.

An external wcooler helps keep the trannie much cooler

[Bodybagger]

The fluid passes through a series of plates in the bottom of the radiator, which is the cool end of the radiator. It leaves the radiator and enters a small (maybe 6"x6") transmission cooler in front of the AC condenser.

The system is sized adequately for a small pickup truck, but hopelessly inadequate for a motorhome.

I replaced the original pickup sized cooler with one about 75% of the area of the AC condenser. I think it's 12" by 17" or so. I have 175F-200F transmission fluid, and 175F is ideal. Before me, the tranny cooked it almost black.

The fluid must flow through the radiator FIRST, then through the cooler.

With all due respect to your friend/mechanic, I would think it's pretty obvious to a mechanic that the stock transmission cooling system for a compact pickup is way undersized for a motorhome. Thus, I'd be concerned that the aftermarket cooler is installed properly since it's being done by a person who doesn't understand why a motorhome needs a bigger cooler.

[turtle]

Your auto trans fluid needs to run between a set temp range to operate efficiently.

There is a dual purpose for using the water radiator to stabilize the trans temp. First is to heat the fluid up rapidly in cold start situations by using heat transfered from the water. Second is to keep the temp within the necessary temp range for proper operation.

When a vehicle is heavily loaded as in towing or carrying a heavy weight (like our RVs) the fluid becomes too hot even using the engine water to stabilize the temp. Thus the need for a secondary air exchange radiator to cool it down before it goes back into the trans.

You can replace the factory stock trans cooler with a larger one or you can add a "supplemental" cooler in conjunction with the stock one. Most people just cut one of the lines on the stock cooler and branch out to a second cooler as this "adds" cooling capacity. If you replace the stock cooler you may not end up with much more cooling ability since you are taking one out of service and replacing it with another one. I would suggest that you add a secondary cooler rather than replace the primary one (unless the primary cooler is damaged or clogged).

In ether case never remove the lines going to the water radiator as you need it to heat up the trans fluid on cold start situations.

Using a synthetic or synthetic blend ATF will help a lot as they can run at higher temperatures before breaking down.

[desertrat]

Thanks so much for the info. Guess I'll be looking for an auxillary cooler soon. This mechanic said one of the lines to or from that aux cooler was clogged (not sure which one) so he flushed the cooler lines out. Hopefully that wasn't much labor cost.

Any suggestions on aux cooler brands/models? Are these things easy to install? I'm not super knowledgable about mechanics.

Thanks in advance

Steve

[turtle]

Thanks so much for the info. Guess I'll be looking for an auxiliary cooler soon. This mechanic said one of the lines to or from that aux cooler was clogged (not sure which one) so he flushed the cooler lines out. Hopefully that wasn't much labor cost.

Any suggestions on aux cooler brands/models? Are these things easy to install? I'm not super knowledgeable about mechanics.

Thanks in advance

Steve

Putting another cooler on requires cutting and bending one of the cooler lines then sliding hose over the cut line, clamping it, and taking the hose to another cooler and back.

You will need some specialized tools to do this (pipe/tubing cutter deburer, tubing bending tool, and it is nice to have a flaring tool to put a rise at the end of the cut pipe so that the hose does not slip off easily.

I used this tubing bender to make the brake and clutch pipes for my Landrover: http://www.toymike.com/misc/brakePipeBender.jpg There are other types of benders but you must make a clean smooth bend in the pipe and NOT kink it. If you do not have pipe bending tools you can take the hose straight and let it bend. You will have to use more hose as it does not bend as sharply with out kinking as easily as metal piping does.

If you have not done this it might be best to let someone else do it for you, or at least let someone take a look at it and give you a price for doing it. The size and shape of an aux cooler will depend on where you have room. The types made are limitless as far as size and thickness.

You may also want to flush and refill the transmission to remove the burned fluid (if the cooler line was clogged the ATF is probably toast). There are different schools of thought about flushing older auto trans. Some people advise against it others say it is fine to replace all of the fluid (trans and torque converter). Either way replace your old fluid with synthetic or part synthetic ATF.

A trans oil temp gage is a helpful thing to have in the cab. When you have the pan removed the shop can cut in and put a temp gage sensor and run a line for the gage. The only way to know what the trans is doing is to monitor the temperature of the fluid in the transmission.

[desertrat]

Thanks again Turtle. I'll be getting on this cooler thing soon. I appreciate everyones input. It's a great learning experience and I am amazed at the varied levels of knowledge on this board. Howd you boys and girls git ta be so smart?