Time to Get Serious With 4L60e/4L65e Cooling...

[alpinecrick]

From my very limited research it seems like Dex 6 is a better fluid... Except when it isn't. Clear as mud right?

To clarify a little I think it's a much better option than Dex 3 for what it was actually designed for, an automatic transmission fluid. But things get tricky when you start talking other applications like transfer cases. There's a GM service bulletin that states to use GM 88861800 (ACDelco 10-4033) manual transmission fluid instead of Dexron 6 in any transfer case which originally called for Dexron 3.

df,
Does that mean we shouldn’t use Dex 3 in the transfer case anymore?

 

[Pinger]

From my very limited research it seems like Dex 6 is a better fluid... Except when it isn't. Clear as mud right?

To clarify a little I think it's a much better option than Dex 3 for what it was actually designed for, an automatic transmission fluid. But things get tricky when you start talking other applications like transfer cases. There's a GM service bulletin that states to use GM 88861800 (ACDelco 10-4033) manual transmission fluid instead of Dexron 6 in any transfer case which originally called for Dexron 3.

Transfer cases hadn't crossed my mind and as my Burb is a C not a concern - though I do have a car here with an automated sequential (manual) gearbox that runs with ATF. Is Dexron IV less suited to it? What about the other application I will want it for - PAS and HydraBoost?

 

[df2x4]

df,
Does that mean we shouldn’t use Dex 3 in the transfer case anymore?

No, not necessarily. But you have no option to do so if you want OEM GM recommended fluids. GM stopped licensing/producing Dexron 3 so it's either Dexron 6 or approved alternatives like I mentioned if you want to stick to GM approved/licensed stuff. Store brand or other Dexron 3 should be OK, but personally I like to stick with GM fluids.

Transfer cases hadn't crossed my mind and as my Burb is a C not a concern - though I do have a car here with an automated sequential (manual) gearbox that runs with ATF. Is Dexron IV less suited to it? What about the other application I will want it for - PAS and HydraBoost?

I honestly couldn't tell you as I've never really looked into either of those. I do recall that the transfer case issue was something to do with the viscosity of Dexron 6 being different than Dexron 3.

 

[df2x4]

I just went out in the garage and had a look at one of my Dexron 6 bottles. The way that last bit in blue is worded, I'd say using it as power steering/hydroboost fluid might be risky.

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Also in the interest of full disclosure regarding the "Do not put Dex 6 in transfer cases originally designed for Dex 3" TSB that I mentioned earlier... I found out about that around three months after I had my mechanic fill the transfer case in my Suburban with Dexron 6. I bought some of that GM recommended manual trans fluid with the intention of draining the Dex 6 and swapping over, but that hasn't made it to the top of the priority list yet. It's been over a year at this point. 4WD still works fine, nothing is leaking, and nothing has exploded.

 

[Pinger]

I honestly couldn't tell you as I've never really looked into either of those. I do recall that the transfer case issue was something to do with the viscosity of Dexron 6 being different than Dexron 3.

Looking at the two I have in mind (from the same manufacturer) the viscosities are different and the Dexron IV is the thinner. As follows:

Dexron III VG @40C = 36.46cSt, @100C = 7.66cSt. GM appros: IID, IIE, IIIG, IIIH, Type A Suffix A.

Dexron IV VG @40C = 29.00cSt, @100C = 5.95cSt. GM appros: Dexron IV (J60347)

 

[L31MaxExpress]

I personally would not put Dex VI in any older automatic. It is known to cause $$$$ issues with them.

 

[Curt]

Is Dexron VI a significant upgrade over Dexron III?
Between a fully synthetic DexronIII and a 'synthetic based' Dexron VI - which would likely be better?

Dex III licensing expired in 2006. GM stopped enforcing the licensing then too, so any company that claims that they're compatible with Dex III is purely a guess. Personally, I wouldn't trust any Dex III fluid that simply states it's compatible with Dex III cars when no one certifies that statement as true.

From my very limited research it seems like Dex 6 is a better fluid... Except when it isn't. Clear as mud right?

To clarify a little I think it's a much better option than Dex 3 for what it was actually designed for, an automatic transmission fluid. But things get tricky when you start talking other applications like transfer cases. There's a GM service bulletin that states to use GM 88861800 (ACDelco 10-4033) manual transmission fluid instead of Dexron 6 in any transfer case which originally called for Dexron 3.

From what I've heard and experienced with the fluid, it definitely seems like better stuff. Our supercharged H2 loved the Dex VI and it feels great. The added capabilities of the fluid just seem like it trumps Dex III tenfold. As for transfer cases and power steering fluid, not sure there. Haven't educated myself enough to talk about that.

I personally would not put Dex VI in any older automatic. It is known to cause $$$$ issues with them.

All licensing for Dex III permanently expired at the end of 2006 with no renewal. GM stopped enforcing the licensing then too, so any company that claims that they're compatible with Dex III is purely a guess. GM also stated in their specifications for transmission fluids that any company that claims their fluid is compatible with Dex III fluid should be avoided. FWIW, Dex VI is fully backwards compatible with other variants of the fluid. I'd choose a licensed and controlled Dex VI trans fluid over a competitor who states they're Dex III compatible. Also, I've thrown Dex VI in our towpig (03 H2 that states it needs Dex III) and it feels better with VI over III. Just my .02 though, YMMV.

 

[Curt]

On a side note, I just replaced the CFI with MPFI and found something shocking. @L31MaxExpress was onto something with the radiator. Granted, I always believe in the best in people but I found out some f**king idiot bypassed the radiator trans lines and used a piece of rubber hose to route the lines into each other. I was and still am blown away. The sad part is, it looked like it was done a while ago and unfortunately no one throughout the years caught it, myself included. Now educating myself on transmission cooling lines, the issue was a big slap in the face. I am not sure why the idiot bypassed the radiator but after talking to my dad it was probably done back in 2004-2005 when the second 60e died. We got stuck in a little town with a transmission shop and my dad told them that he just "needed to get home". I'm assuming I've been running cooler-less ever since. Without a gauge, I'm positive that's why the 3rd 60e did NOT last long. I admit to my naive-ness for sure. Don't know who's the bigger idiot here... me or the guy who bypassed the radiator. I really should've caught this earlier but nothing I can do now but fix it. New radiator will be on order and lines will be connected shortly after. Then I will decide if the 40k cooler is necessary.

 

[df2x4]

On a side note, I just replaced the CFI with MPFI and found something shocking. @L31MaxExpress was onto something with the radiator. Granted, I always believe in the best in people but I found out some f**king idiot bypassed the radiator trans lines and used a piece of rubber hose to route the lines into each other. I was and still am blown away. The sad part is, it looked like it was done a while ago and unfortunately no one throughout the years caught it, myself included. Now educating myself on transmission cooling lines, the issue was a big slap in the face. I am not sure why the idiot bypassed the radiator but after talking to my dad it was probably done back in 2004-2005 when the second 60e died. We got stuck in a little town with a transmission shop and my dad told them that he just "needed to get home". I'm assuming I've been running cooler-less ever since. Without a gauge, I'm positive that's why the 3rd 60e did NOT last long. I admit to my naive-ness for sure. Don't know who's the bigger idiot here... me or the guy who bypassed the radiator. I really should've caught this earlier but nothing I can do now but fix it. New radiator will be on order and lines will be connected shortly after. Then I will decide if the 40k cooler is necessary.

Considering this info, I bet a fresh radiator and an M7B would be plenty. Bypassing the internal transmission cooler in the radiator means you're giving up a bunch of cooling capacity. The M7B would be much easier to fit than the 40K, it even uses the factory AUX cooler mounting brackets with a little trimming.

 

[Curt]

Considering this info, I bet a fresh radiator and an M7B would be plenty. Bypassing the internal transmission cooler in the radiator means you're giving up a bunch of cooling capacity. The M7B would be much easier to fit than the 40K, it even uses the factory AUX cooler mounting brackets with a little trimming.

My thoughts exactly. Man, it seems like you're reading my mind haha. I was either thinking the M7B or the Tru-Cool Part# 20-4590 @Wheeler mentioned earlier. As an added thing, I'll throw in the transmission thermostat @alpinecrick mentioned as an added safety along with the deeper pan. With the winter Tahoe driving this truck sees, and even though it is an LPD cooler, I won't need to worry about the trans hitting optimal temp when it's 30*F out.