Tranny Cooler Questions

Okay been on here reading for awhile about after market transmission coolers. I have a few questions hopefully someone will have answers for.

I plan on getting to using a Fin and plate cooler and adding a spin on filter in line on the line feeding the cooler. I also plan on running new lines and not using the original lines. From what I have read PTFE braided stainless lines seem to be a very good option so I will probably go with them.

The original lines are 5/16 OD. When you installed yours what size lines did you use?
What size cooler did you use?

Also maybe someone has some insight on this.
The original transmission cooler lines run from the passenger side of the transmission to the driver side of the radiator. The oil cooler lines run from the drive side of the engine to the passenger side of the radiator.
Why?

I used -6 or 3/8" PTFE braided stainless.

Ran from transmission to aftermarket cooler to radiator to transmission.

I don't recall what size cooler I used, but I wish I would have gone larger. On a hot day I can get the transmission above 240 in the highway mountain grades, some day I'll swap it with a larger one.

Never bypass the radiator transmission cooler. Water cools 1000 times better than air. If you heat a piece of steel up to red hot how does one cool it? By waving it in the air? NO! They dip it in water! Adding an auxiliary cooler in conjunction with the radiator cooler does help! Any trans temps over 200 degrees decreases trans life very rapidly.

Not sure why they put the trans cooler on the left and the oil cooler on the right side of radiator. All the gas chevy's put the trans cooler on the right side of radiator.

As for lines, steel or braided really doesn't matter. Braided are a lot easier to work with as far as routing them around the engine, frame rail, etc.

Trans temp failure:

175 degrees = unlimited miles
195 degrees = 100,000 miles
200 degrees = 80,000 miles
220 degrees = 50,000 miles Varnish starts to form
240 degrees = 20,000 miles Seals start to harden
260 degrees = 10,000 miles Plates start to slip
290 degrees = 5,000 miles Seals and Clutches burn out, Oil forms carbon
300 degrees = 500 miles Catastrophic failure (hard parts may have a tendency to brake)

The reason for the cooler locations is the engine oil needs to be cooler. At normal operating temps the "hot" side of the rad is 195 deg. So the fluid should be held to 195. This is no problem for a TH400. The easiest way to lower this temp is to install a 180 Thermostat on the engine. . You can drop the tranny temp 15 deg for less than $10.

Also you don't want to bypass the RAD cooler so it can heat up the trans fluid in the winter. Too cool trans fluid is bad as well.

ken said:

The reason for the cooler locations is the engine oil needs to be cooler. At normal operating temps the "hot" side of the rad is 195 deg. So the fluid should be held to 195. This is no problem for a TH400. The easiest way to lower this temp is to install a 180 Thermostat on the engine. . You can drop the tranny temp 15 deg for less than $10.

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Engine oil has the heat of combustion, transmission heat comes from converter slip and pumping losses. The indirect injected engine of the CUCV means less piston heat but it still gets a good blast of flame from the precombustion chamber. Gasoline engines have uniform heating of walls, head and piston.

How about using an additional cooler after the radiator together with a thermostatic bypass valve in the fluid lines close to the transmission? These valves are supposed to keep the transmission oil at 180 F even if the oil coming from the auxiliary cooler may be too cold.

PS: I am going to install a beefed-up 700R4 in my M1009 this weekend and would like to keep it around 180 F transmission oil temperature.
Since I would have to order the auxiliary cooler and thermostat valve, I may go with the 180 F coolant thermostat initially.

Great idea.

alpine44 said:

How about using an additional cooler after the radiator together with a thermostatic bypass valve in the fluid lines close to the transmission? These valves are supposed to keep the transmission oil at 180 F even if the oil coming from the auxiliary cooler may be too cold.

PS: I am going to install a beefed-up 700R4 in my M1009 this weekend and would like to keep it around 180 F transmission oil temperature.
Since I would have to order the auxiliary cooler and thermostat valve, I may go with the 180 F coolant thermostat initially.

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Alpine, please keep us updated with your progress with photos if possible. I'm planning on installing a Bowtie 700R4 in my M1028 and would like to keep my temps down as well. Your idea of an aux cooler with a thermostatic valve is Brilliant, Brilliant!

Sharecropper said:

Alpine, please keep us updated with your progress with photos if possible. I'm planning on installing a Bowtie 700R4 in my M1028 and would like to keep my temps down as well. Your idea of an aux cooler with a thermostatic valve is Brilliant, Brilliant!

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I changed to the 700R4 and NP241C with tall adapter yesterday. Did not take any photos but there is no mystery about replacing a transmission and T-case. Just a bunch of hard to get to bolts and the pain in the neck fluid line fittings that never want to line up and catch the thread.

Did a couple of test drives today and have to say that I should have converted to the 4 speed much earlier. I think the times of having to drive with earplugs are over.

I was a little too ambitious adding fluid and decided to take the top line off the radiator and route it into a catch bucket with a piece of hose. Unfortunately, the oil came squirting out the radiator instead of the line and created a mess. At least the fluid level is now correct.

If I understood some post on the various GM boards and a video of monster transmissions correctly, the transmission fluid is supposed to flow through the radiator top down. I had labeled the return line on the TH400 (top fitting) with a zip tie before taking the tranny out and put it back in the top position on the 700R4. So something must have gotten mixed up before or the designers of the CUCV were more concerned with keeping the TH400 warm enough. Since I am trying to get heat out of the 700R4 it would make sense if the return line to the transmission would emanate from the radiator at the cooler location, which is towards the bottom.

I am going to order a temperature gauge, a Derale thermostat valve, and auxiliary cooler tomorrow and will take photos of the installation once I have figured out the best line routing.