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When bypassing the radiator transmission cooler with an external trans cooler… Is it necessary to plug off the old trans cooler line holes in the radiator? Thanks
 

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Lighter-than-you
TrailblazerSS
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Not necessary
 

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Run the output FROM the transmission TO the new cooler and take the heat load off the engine and it's cooling system first ---- THEN run it through the radiator heat exchanger to make sure the fluid is running at least at 160°F degrees so the transmission gets to normal - but not overheated - temperatures.

NORMAL temps are necessary for the ATF to work and keep things supple (the seals, o-rings) and clean (the valves in the valve body) and generally of the correct viscosity for long life of the unit.

Really though --- the single best thing to do for these units is to remove the PWM valve and replace it with an analog unit that is either ON - or - OFF. This will lower the temperature so much that an external cooler may not even be necessary.
 

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I wouldn't (and wont) run the trans fluid through the radiator at all if I install an external cooler.
 

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That's your call and when I had my own transmission shops, people that made this same decision only heard me say; "You can't make me mad slapping me in the face with money".

Go for it ---

.... but seriously though --- read that last paragraph of mine if you REALLY want a transmission to last a long time.

Excessive heat kills them just as much as operating them cold does.
 

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I have the PCM brake duck kit on mine with their hoses and such, can't remember if it puts the cooler before or after the radiator Joe cool do you know what side of our radiator is in and out?

Sent from my SM-G991U using Tapatalk
 

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Not sure what a "duck kit" is .... and I'm not sure which way it flows but that's easy enough with a hand wrapped around one or the othe lines after a cold start up.

But seriously.... the PWM-Delete will drop the temps a lot all by itself and save the TCC at the same time.
 

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I live in Phoenix, Joe. No such thing as "too much" heat rejection here. And, I need to get as much as possible away from the engine cooling system.
 

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That's why you dump the heat from the transmission first by running through the add on cooler ... THEN send the fluid through the heat exchanger in the radiator ... and back to the transmission.

This takes the transmission induced heat out of the thermal load imposed on the engine's only way of cooling itself. Then if needed, the engine coolant can raise the ATF back up to the engineers designed-in operating temperature for the transmission of approximately 170-180°F.

This routing will actually decrease the thermal load imposed on the radiator/engine cooling system.

I lived in SoCal in Palm Desert, Hemet (yuck) and Anza ... while driving through the Salton and Chiriaco to Yuma and Showlow/Concho/Phoenix/Tucson and Albuquerque all the time ... so heat has always been a big concern for me too.

And ....... again ........ by installing the PWM DELETE you will definitely lower the heat generation of the TCC, which isconstantly never getting to 100% locked nor 100% released. That's a LOT of heat you can stop right now!
 

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Sorry I meant brake duct kit as opposed to in front of the radiator.

Sent from my SM-G991U using Tapatalk
 

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I'm going to have gauges set up to monitor post aftermarket cooler and sump temps. We'll see how it works out...
 

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I run dual gauges in my K5 with a greatly modified THM700R4 that is not electronic in any way.

The main line temp after 1 hour of running, no real load and generally highway speeds over 50MPH runs right around 140°F and the pan runs approx 175°F or so.

Pulling logs at 7500' altitude for an hour gets the trans cooler fan activated because I like to have it come on at 180°F line temps. The temps stay below 200°F at all times, although the pan temp can get right up there with hard work and lots of torque convertor work WOT, pulling three or four trees at the same time.

Without the extra cooling ability --- an external cooler on the hot side of the cooler lines and then going through the heat exchanger in the radiator to keep the temps normalized --- I would see 230-240°F working hard and 200°F at 55-65 MPH highway.

I'd say it works very well and yet it allows the transmission to work at those temps where it was designed to run under almost all driving conditions now.

My TB, my Astro and now my wife's K1500 Silverado (all very much the same related transmissions) run at 180°F almost all the time, and the K1500 just had the PWM-delete done to it --- so now has the temps dropped another 20-25°F. --- so I'll NOT install an external cooler --- yet somehow try to get it back up to 180°F at least.

I wanted that PWM-delete in the K1500 Silverado for the sake of the clutch in the TCC --- but now the trans is constantly too cool.

Ugggh!
 

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I'm not really following your logic of needing to heat the fluid.

If your sump temps are in the area you would like to run the trans at, then it seems you're good. That's the temp it's operating at, aside from the cooling/lube circuits. Using the cooler outlet temp to to gauge the trans temp is like taking your engine temp off the bottom tank of the radiator. It tells you how cool the fluid got down to, not how hot the system is operating at.
 

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That's why I measure at the pressure tap on the driver's side of the case for the ultimate temperature picture.

Yes --- pan temps can be obfuscating - and the best thermal gauge is coming out of the pump.

There was a "kit" that placed a thermistor inside the dipstick tube to give a reading of the transmission temps - and that was just wrong too.

Sensing points aside, the engineers decided to use a heat exchanger - not a transmission cooler - inside the radiator to keep a stabile temp in the transmission fluid and not make it rocket surgery. Any time that design is impeded, things can go sideways since a too-cool transmission is just as bad as a too hot one.
 

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The pressure port will typically be hotter than the pan...pressurizing fluid causes heat (you know this). But, you take temp readings on your K5 at the pan?

Many (I might go as far as to say most) real trucks have standalone trans coolers. The Allison in my DMAX is that way. And, was probably under sized for heavy towing. Running it through the radiator would've just compounded heating issues, potentially dragging the engine cooling down with it. I installed a much larger trans cooler, as well as an enormous engine oil cooler.

In a traditional truck cooling stack, the trans cooler is out front. It gets the coolest air to reject the maximum amount of heat, always. Then the a/c condenser, charge air system if equipped, and finally the radiator. Difference here, versus a trans cooler in the rad, is that the heat from the trans isn't directly put back into the cooled engine coolant. When designing the powertrain system, the engineers deemed it OK for the trans cooler to lead the way even when ambient temps could be sub zero, in rain, or snow. They didn't seem at all worried about a trans that is too cool.
 

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The pressure port will typically be hotter than the pan...pressurizing fluid causes heat (you know this). But, you take temp readings on your K5 at the pan?

Many (I might go as far as to say most) real trucks have standalone trans coolers. The Allison in my DMAX is that way. And, was probably under sized for heavy towing. Running it through the radiator would've just compounded heating issues, potentially dragging the engine cooling down with it. I installed a much larger trans cooler, as well as an enormous engine oil cooler.

In a traditional truck cooling stack, the trans cooler is out front. It gets the coolest air to reject the maximum amount of heat, always. Then the a/c condenser, charge air system if equipped, and finally the radiator. Difference here, versus a trans cooler in the rad, is that the heat from the trans isn't directly put back into the cooled engine coolant. When designing the powertrain system, the engineers deemed it OK for the trans cooler to lead the way even when ambient temps could be sub zero, in rain, or snow. They didn't seem at all worried about a trans that is too cool.
True dat... but I worked in a real radiator shop for a while and saw thermal bypass valves in a lot of those coolers too and you'd never know about it if you didn't take the header off the cores.
..... some shops just tried to flush them, others like the one I worked in, took them totally apart.
...... and I was always surprised by the amount of silicon RTV 'worms' were in the tank/header area from overly enthusiastic mechanics who thought "just one more tube of RTV will make it better".

But, those coolers with the thermal bypass devices would modulate the fluid flow through the cooling tubes or send it right back to the transmission without it losing any temperature .... if they weren't plugged up with excessive RTV.

When the transmission started showing either very hot or very cold, that's when we'd get to fix them because no-one could figure why it was cold. They'd understand hot, but cold had them flatfooted.

FWIW ..... Allison's don't like cold ... and remember that an Allison is really a THM400 inside with much of the same clutches, pistons and seals, governor and hard parts.

Some Allison transmissions ran on 30wt engine oil .... I'd rebuild garbage truck units for.Riverside County's various cities and they always ran cooler and more consistently on 30wt instead of ATF.

So there's a lot of discussion on this kinda oil v ATF, the best operating temp and clutch materials, etc.

However, I still know that the colder running units had prematurely hardened seals, excessive clutch fracturing from low and late apply pressure and generally a lot of inner case deposits, like varnish.

The 700s and 4Ls seem to get a lot of clutch/seal slush in the pan and filter when they are kept cold.

Go figger.
 

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An Allison and a TH series trans aren't even in the same ballpark.

Curious, what is the torque rating on the side mount PTO for a TH400? I don't recall what the 6th gear ratio on the TH400 is either..
 
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