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2005 ESV
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Perform at your own risk. However, i would use a Dexron VI transmission fluid with increase additives for older transmissions to hopefully replace some of the friction material that will be lost over time from old clutch wear.

I only went full synthetic Dexron VI because I assumed that full synthetic transmission fluid would be better and plus it was from AC/Delco so it was OEM. I should have stuck with the Castrol fluid it seems.
Wow, I feel like everything that I've ever known is a lie! :)
 

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Perform at your own risk. However, i would use a Dexron VI transmission fluid with increase additives for older transmissions to hopefully replace some of the friction material that will be lost over time from old clutch wear.

Castrol older Dexron VI fluid was a blend which worked well in my transmission for years due to having a great additive pack that improved shifting, now it seems that Castrol have gone full synthetic Dexron VI fluid with an improved additive pack. I may still use it for my drain and fills since the old additive pack worked great in my transmission.

I only went full synthetic Dexron VI because I assumed that full synthetic transmission fluid would be better and plus it was from AC/Delco so it was OEM. I should have stuck with the Castrol fluid it seems.
I'm faced with this dilemma myself. In my eye if you don't flush/drain&refill every 20-30k maybe it's not a good idea to do at all. My Honda has 260k w/ original trans. Family member owned before me and did a drain and refill every 10k, sounds crazy I know. But is it if the trans lasted this long? Since I've owned I've done the same.

Now that I was suggested a good way to diagnose the radiator flow (trans overheating) that basically flushes all the fluid I'm stuck on what to do. I'd have to run 2-3qrts each through the rad and aux cooler. I can diagnose the problem for $65 and risk doing something bad to an old transmission or throw parts at it one at a time. New rad, trans lines and coolant $265, new aux cooler about $225.
 

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2006 Escalade AWD w/DiabloSport tuner,Jet Performance throttle body/MAF,Airaid MIT
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Discussion Starter #44 (Edited)
Wow, I feel like everything that I've ever known is a lie! :)
Well, I was told before that you should not completely flush an old transmission with over 100k miles due to removing the old fluid filled with clutch material, since it may start slipping soon after which will progressively break it and then you will need a rebuild.

However, some aftermarket transmission fluids like Castrol have additives that helps to prevent clutch slippage and keep seals plump which give some extra life to an older transmission.

The 4l65E was originally designed for Dexron III fluid which is a thicker fluid than Dexron VI fluid I believe. The original Dexron VI fluid was a blended fluid for the six speed automatics, while later version became full synthetic for the 8-10 speed automatics to my understanding.

On a new 4l65e the blended transmission fluid works fine, but I am not certain about using the lower viscosity full synthetic fluid in the old 4 speed since it was design with less tolerances than the 8-10 automatics, so the 4l65e may slip more with the fully synthetic fluid especially with an older unit with weak clutches. Just speculation.

My transmission is new internally, so using full synthetic should not be an issue for me but I will go with Castrol due to the additive pack that hopefully reduce slippage.
 

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Discussion Starter #45
I'm faced with this dilemma myself. In my eye if you don't flush/drain&refill every 20-30k maybe it's not a good idea to do at all. My Honda has 260k w/ original trans. Family member owned before me and did a drain and refill every 10k, sounds crazy I know. But is it if the trans lasted this long? Since I've owned I've done the same.

Now that I was suggested a good way to diagnose the radiator flow (trans overheating) that basically flushes all the fluid I'm stuck on what to do. I'd have to run 2-3qrts each through the rad and aux cooler. I can diagnose the problem for $65 and risk doing something bad to an old transmission or throw parts at it one at a time. New rad, trans lines and coolant $265, new aux cooler about $225.
I was told the same. If the transmission has been maintained then removing the old fluid by draining it is fine and is recommended. However, if the transmission has not been properly maintained and have very dark dirty fluid; leave it alone until it have issues and plan to rebuild it. Changing the dirty fluid may just accelerate it demise if the dirty fluid is the only way the clutches will engage.
 

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Has there ever been a 100% confirmed case of a transmission failing solely because of a transmission flush, and not because it was worn out/damaged internals? Mostly sounds like a bunch of old wive's tales. Most likely scenario is the transmission was having issues, someone tried a fluid flush, and it died shortly after. It was going to die soon anyway.
 

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But the question is... Is that gunk in the trans holding the damaged internals together? or Does it damage seals but gunk them so no issue until a flush?... Either way, flush or drain and fill every 30k and you can thank me later!
 

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Discussion Starter #49
Has there ever been a 100% confirmed case of a transmission failing solely because of a transmission flush, and not because it was worn out/damaged internals? Mostly sounds like a bunch of old wive's tales. Most likely scenario is the transmission was having issues, someone tried a fluid flush, and it died shortly after. It was going to die soon anyway.
The guy in the video explained why a transmission may fail after a flush. The flush itself was not the cause of failure, it was the old crude that can be dislodged and clog up the small passages in the valve body or the old friction material suspended in the dirty fluid has being removed in place of fresh fluid which cause the old clutch plates to slip and fail.

Hence why many people just leave an old transmissions with unknown service histories alone if they are running well, because changing/flushing the fluid may cause it fail since the old fluid is probably the only reason why it is working at all.
 

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Discussion Starter #50 (Edited)
But the question is... Is that gunk in the trans holding the damaged internals together? or Does it damage seals but gunk them so no issue until a flush?... Either way, flush or drain and fill every 30k and you can thank me later!
I will change(drain from pan) my transmission fluid every year and the filter every other year to keep this transmission going. I am glad that my old one lasted as long as it did.
 

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Discussion Starter #51 (Edited)
He bought a stock replacement. Not an OEM part. I'd call it an OEM-minus part.
Exactly. The stock replacement OEM cooler cost about $136 online. The aftermarket cooler I purchased cost about $40. I was thinking that I was saving money and maybe getting an better designed cooler, however I did not.

Hopefully, the 2500 aftermarket cooler I just purchased would be a better performing cooler. It cost a bit more at $65, so hopefully I still save some money over not buying the stock cooler.

The stock cooler price and new design which seems not to fit my 2006.
 

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Discussion Starter #52
Is the stock transmission cooler not enough? I ask because I may be changing one out soon.
No, the stock cooler works fine. My stock cooler cracked and leaked so I decided to replace it with an cheaper aftermarket unit. I picked the wrong cooler it seems. The cooling fins are too small to keep the temps under 200F with aggressive driving and i assume it would perform poorly when towing as well.

I bought a hopefully better performing cooler to replace the one i have now.
 

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Discussion Starter #53
Today I order my Corvette servo made by Cyclone Transmission. It is suppose to be a drop-in unit. I will give feedback. My 1-2 shifts are pretty soft and could be firmed up.
 

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Discussion Starter #54
I just received my larger aftermarket 2500 cooler. Good news is that it fits the stock Caddy mounting holes and would really keep the fluid cool due to it size. Bad news is that the 5 speed Allison transmission cooler lines are twice the size as the 4L65E cooler lines. So I cannot use it and will return it.

So I am stuck with buying a stock sized cooler from a 1500 pickup it seems.
Hopefully this cooler I just bought will do the job as good as the stock one. It looks the same as the stock cooler.
 

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2005 ESV
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Well, I was told before that you should not completely flush an old transmission with over 100k miles due to removing the old fluid filled with clutch material, since it may start slipping soon after which will progressively break it and then you will need a rebuild.
Yep, your comments prompted me to do a bit of frantic research on this topic, just to make sure this wasn't a "blinker fluid" type of scenario. :) Indeed that makes a lot of sense in regards to the existing friction material making the fluid thicker and that weighty fluid can in some instances be the only thing that allows the torque converter to continue to function.

While there seems to be some debate as to whether or not this applies only to transmissions that have foregone regular maintenance or any transmission of considerable mileage, in the end, I've decided that I'll only do the 5 quarts in the pan and allow it to mingle with the remaining 10 quarts in the cooler.

The 4l65E was originally designed for Dexron III fluid which is a thicker fluid than Dexron VI fluid I believe. The original Dexron VI fluid was a blended fluid for the six speed automatics, while later version became full synthetic for the 8-10 speed automatics to my understanding.
Yep, that has me a little concerned and second-guessing my decision to go with Dexron VI as opposed to Dexron III. There's some thought that the Dexron III breaks down and gets to a lower viscosity than the Dexron VI quicker, which would imply that Dexron VI retains a higher viscosity over the long-run. Honestly, I don't really know whether or not this is accurate or to what extent the difference is, but in both instances, I figure that it'll more than likely be a bit safer to replace the fluid in smaller amounts over the course of the next 100,000 miles rather than trying to replace it all now.

Hopefully, regular faithful maintenance as opposed to drastic sporadic maintenance will help this transmission last another 100K miles. If not, my wife's going to be a pro at driving stick by the time we get to where we're going.

On a new 4l65e the blended transmission fluid works fine, but I am not certain about using the lower viscosity full synthetic fluid in the old 4 speed since it was design with less tolerances than the 8-10 automatics, so the 4l65e may slip more with the fully synthetic fluid especially with an older unit with weak clutches. Just speculation.
The idea of a 10-speed automatic still just floors me. I couldn't believe it when I saw a recent ad for the 2021 Escalade with a 10-speed auto...I was like, "Huh?" And here I thought a 6-speed was darn fancy... At least it was when I got to take a newer GTO with a manual 6-speed for a spin. :cool:
 

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Discussion Starter #56
Man. I just received my new trans cooler and it look just like the black cooler I already have. Not what the seller posted on the page.

However, it is unpainted aluminum so it may work just fine. The one i have now is painted black and to be honest the paint seems a bit thick so it is probably what is reducing the cooler performance since the fins does look to be a bit blocked with paint hence the small passages and reduced airflow.

The new cooler seems to be the same size, but the fins has more space due to not having paint on it. I would guess that this cooler will perform better.

I will post some pics when I install it and give some feedback.

After watching this video I learned that black painted coolers are not good to buy. I believe the stock cooler uses a very thin coat of black paint and larger fins which allows it to cool as good as it does, but a unpainted one would performance better I bet.
 

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Discussion Starter #57 (Edited)
Man, this cooler issue is crazy. Tonight on my way to work the black cooler I have actually kept my transmission cool tonight at about 170-180F after an hour of driving even with some hard acceleration from a stop a few times. Darn, it seems that I wasted money buying the replacement cooler.

I assume that my current cooler must have had some type of obstruction in the cooler that reduced the fluid flow and I guess it got dislodged and the cooler is working as designed. I will see how it goes this morning and if the temps stay below 200F after the hour drive home; if the current cooler works fine then I will just keep the new cooler as an back-up.

I also thinking that the shop did not properly flush the cooler after installing the transmission since a proper flush would have cleared out any debris. Hence why I hate relying on shops to do the job right, rarely happens in my experience. Even my transmission pan drain bolt was a bit loose and was weeping a bit so I had to snug it down, however in their defense I did use a aftermarket pan and and washer; so the factory torque specs may not have been enough if the shop went by the factory transmission pan specs.

I will also tighten down my transmission bolts on the bell housing and check the chassis support bolts as well as check the flywheel bolts.

I am beginning to think that some crud/debris from my failing transmission got stuck in the new cooler or the cooler may have had some debris left over from when it was made that caused it reduce the flow of fluid in my transmission which may have let it overheat and fail. Since my old clutches were 16 years old; the new fluid change probably did not help since most of the grippy old fluid was removed when I last drained the transmission.

I have drained the transmisson pan twice before the last drain, so most of the old transmission fluid should have been removed the last time I drained it. So it may have been a couple of issues that caused my old transmission to fail. Clogged cooler and slipping clutches.
 

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Glad to hear you got her fixed!... I was thinking the cooler or radiator is the cause of my overheat issue with trans but I'm hesitant to throw parts at it, maybe I should consider a new cooler?
 

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Discussion Starter #59 (Edited)
Glad to hear you got her fixed!... I was thinking the cooler or radiator is the cause of my overheat issue with trans but I'm hesitant to throw parts at it, maybe I should consider a new cooler?
Throwing parts at it could be waste of time. What is your tranny temps?

I read that Dexron VI fluid is good for 270F, so any transmission with Dexron VI fluid do not have to worry about keeping the fluid below 200F. When my transmission overheated and failed; the "transmission hot" message did not happen until over 260F in my Dexron VI factory-filled 2006 model.

To be honest, I never really paid attention to the transmission temp before my transmission failed since I tuned the engine. I noticed before the tune that my transmission temps usually was about 190-200F in the summer in heavy traffic. With the tune, the temps were about 190-200F on some long drives, but I never really paid attention to the transmission temperature gauge enough to really know what it was on average. Hell, it could have been the same temps as today after an hour drive. I never really paid attention.

Therefore, I will leave it be. 190-200F seem to be a good temperature since the newer GM transmissions run that by design as well as some other makes. I think it helps burn away moisture in the fluid like with engine oil.

The Diablo Sport tune i have is probably pushing the transmission to the limits, hence the additional heat. Using good fluid is probably why the transmission lasted as long as it did with the tune before it failed; which is pretty good since it lasted 3 years even though it had 206k miles on it when it got tuned. So my old transmission ran for about 23k miles on a 93 octane performance tune on stock internal parts. Not bad to be honest.

I will just swap coolers and keep the black one as my spare cooler, since the unpainted one should be a little better. A good cooler should help keep the fluid below 200F or a tad over when pushing the engine by towing and/or with a performance tune.

Note: The temps on my way home today was about 200-210F with some hard acceleration(I had to put some newer trucks in their place) and more stop-and-go traffic going to the early voting center. So, the current cooler is probably doing a decent job I guess based on my driving style and increased tuned engine output which is like towing i guess as it does put more stress on the transmission.
 

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Mine will creep up as far as I let it go. 20-30min drive and it's at 260deg or so but never got a light. Doesn't matter if I crank heat or turn on a/c to get the fans going, temp still creeps up. I kinda ruled out the torque converter as there is no shudder but I'm used to Honda's.
 
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