Transmission cooler options

[tim1973]

Hi all, this is a good forum been following it for years as anonymous. This is a lil long, but hopefully yall dont mind. Anyway, looking for some thoughts from other RV'ers. I have a 2011 Denali Yukon 6.2, recently purchased a TT with 6400 dry weight and about 7200 loaded(checked weight on a scale) with about 650 tongue weight. When i first bought it, we brought it home which was about a 90 mile ride, some small hills etc. Noticed the engine temp got up to about 230ish and the transmission also got up to 225-230. I decided to update the cooling system and add a larger transmission cooler. Put the 40K cooler in place of the factory one, and replaced the water pump(AC delco), aluminum aftermarket radiator(With internal transmission and oil cooler, as the OE one had), new ac delco radiator hoses and tsat.

Took TT on a 4 hr trip, pretty much flat ground, and ambient about 80F. This time, transmission got up to about 140F, engine though, still was getting up to about 230 at times..then going back down to 215ish. So, I didnt like the trans not getting up to proper operating temp(With no trailer, its barely getting over 110F), so I decided to install a transmission thermostat/bypass. Got the tru-cool one. Heres where i wasnt sure what to do. I decided on installing the tstat before both of the coolers, allowing bypass until up to proper temp. i decided to have the fluid go to the external cooler first, then on to the radiator internal cooler, then back to transmission. Vs going to the radiator first, as the OE had. Ideas? Thanks!

My thinking is, this allows full advantage of the 40K external cooler, and will reduce the amount of heat being given to the radiator coolant...hopefully allowing engine to run a little cooler? So far ive driven vehicle about 45 minutes, with no trailer on it. Tranny fluid gets to 185 and so far stays perfect.

[hotpepperkid]

My old 7.3 air to oil would get to 230 going light to light no trailer in Bullhead City AZ in July outside temp 118+. I put an oil cooler from the 6.0's dropped the temp to around 140

[C_Schomer]

180 will sure do it. Craig

[Grit_dog]

What’s “power mode?”

[tim1973]

BenK wrote:
Know that 'power mode' has several levels and each has engine/tranny temps as the basis to either turn on power mode, or drop down into a lower power mode


Right down to the various limp modes


All of those decisions are made based on engine/tranny temps

Not sure who you’re talking to. Are you referring to the tow mode feature?

Also my transmission gets up to 180 all the time now that I’ve installed the bypass thermostat. Before I installed it, I’d be lucky to get up to 130, pulling the trailer. No trailer, maybe 105. As far as a minimum, I was always of the train of thought, it needs to get warm enough to work out the moisture.

[C_Schomer]

tim, what minimum temp does your trans get. Does GM have a minimum?

[BenK]

Know that 'power mode' has several levels and each has engine/tranny temps as the basis to either turn on power mode, or drop down into a lower power mode


Right down to the various limp modes


All of those decisions are made based on engine/tranny temps

[tim1973]

Not sure…I think it’ll be ok. But we don’t camp much in the summer. Seems like this is normal gm behavior…running warm, and they say it’s ok. Kinda like they say it’s normal for them to burn oil(every gm truck I’ve ever owned has). Back on topic though, I just figure I’d try and reengineer the cooling system a bit, try and get those temps more “normal” or what is normal in my mind.

[Huntindog]

tim1973 wrote:
So, did the drive today. About a 3 hr ride. For the most part I’m happy. Transmission was at 185-190, whole trip. Hills, stop&go highway. Engine, got up to 226, going over the Dames Point bridge, which is pretty steep. Other than that, ran about 219-222. I can live with that. Agree maybe should’ve gotten the two row radiator vs the thicker than OE single row. Also, transmission cooler, with a fan bypassing the oe radiator cooler sounds like a good idea. I assume it has a tstat for the fan and a bypass? I ask, because when I first hooked up my 40k without the bypass, in non towing driving, transmission wouldn’t warm up enough.

What do think it will do in the summer?

[C_Schomer]

Sorry my sig is only in one of my posts. It's a 12 Dodge diesel. Mine had the optional Max Tow which is a liquid/liquid or coolant/trans fluid xchanger plus a thermostatic fluid bypass block in the trans lines and it also has an air cooler up front. Your liq/liq xchanger is in your radiator. Mine was on the engine side. That system was more of a trans heater than anything.
I deleted the stat block and replaced the xchanger with a BIG Derale fan/cooler, under the truck, and the fluid lastly goes thru the front air cooler. All the xchanger did was to make sure the engine and trans heated each other! Separating them and using the fan/cooler, instead, made the engine and trans, both, run much cooler... especially the trans.
The Derale cooler has a stat on the fan. Going down the hiway, even towing my 15K 5er in the summer, the trans stays in the low 150s and the Derale fan doesn't need to come on. On mtn. passes or slower traffic the fan cycles on and keeps trans temp below ~160. Even in summer city traffic when the tq. convertor is unlocked, I've only seen a high of 181.
My 68rfe needs at least 110* for it to shift properly so I'm in good shape.
Now, when I'm screaming up mtn. passes, if the engine gets to 218, the electronic engine fan cranks up and it will actually bring the temp back down... it wouldn't do that before! Craig

[tim1973]

So, you run your transmission fluid at 140? During non towing driving? If I read that correct. Do you drive a gm? If so, what about engine cooling temp? Did separating the two bring down coolant temp when towing?

[C_Schomer]

My trans was hitting 219 and the bypass valve, TBV, was the first thing I removed. Then I figured out the coolant was still heating the trans to high temps so I got rid of that exchanger and put on the fan/cooler, under the truck, with a fan stat. Fan comes on at ~153 and shuts off ~140. Then the fluid goes thru the front air cooler. When I'm on the hiway, towing or not, the front cooler keep the trans temp down so the fan on the Derale doesn't even come on. My trans still gets to ~140 w/o the TBV. I got lucky, the Derale fan/cooler and the front air cooler work GREAT together. Craig

[tim1973]

So, did the drive today. About a 3 hr ride. For the most part I’m happy. Transmission was at 185-190, whole trip. Hills, stop&go highway. Engine, got up to 226, going over the Dames Point bridge, which is pretty steep. Other than that, ran about 219-222. I can live with that. Agree maybe should’ve gotten the two row radiator vs the thicker than OE single row. Also, transmission cooler, with a fan bypassing the oe radiator cooler sounds like a good idea. I assume it has a tstat for the fan and a bypass? I ask, because when I first hooked up my 40k without the bypass, in non towing driving, transmission wouldn’t warm up enough.

[hornet28]

When a vehicle is used for towing bigger is always better. IMHO you should have opted for the larger radiator.

[C_Schomer]

Do you have room somewhere for a big fan cooled remote cooler? I put a 67kbtuh Derale with a fan stat on my truck and removed the liquid/liquid exchanger and all is great... 140-160 degrees trans temp and The engine and trans can no longer heat each other. Craig