[DieselDrax]

I need to look into the various t-stat options as well as the best way to bypass the stock cooler. Knowing that someone here has experienced a stock cooler failure and strawberry milkshake recently has me a little paranoid now that I'm over 100k miles. A fall/cooler weather project will be to add the t-stat.

While overcooling the fluid isn't really an issue in terms of fluid/transmission performance, I do have some concerns about fluid contamination due to condensation build-up caused by the consistently-low trans temps, especially in the winter. The trans vent is nothing special and will pull in ambient, moist air when the fluid cools and then it doesn't get hot enough for it to easily evaporate. With how sensitive Dexron-VI (and HP) are to moisture, I feel like I'm solving one problem and creating another as I had a weird, slight shudder earlier this summer when towing our big travel trailer again. Never had any problems on our long trip to OR last year or when empty, but after another cold winter and consistently cool trans temps the shudder came back and was resolved with a fluid service. Fluid still looked great, and yes I've seen the other posts/videos about the TCC valve wear, but my trans has only been weird since towing heavy combined with being tuned. Absolutely fine and flawless the rest of the time. If I had issues even while empty or towing our smaller trailer then I'd start to be concerned, but considering the cost of removing the trans I'm not going to go down that road unless I absolutely have to and only if a replacement/updated valve body doesn't fix it (only considering that if problems come back more often).

So, at this point, my ideal setup would be:

• Aux trans cooler (Done)
• Bypass OEM cooler (To-Do)
• Install t-stat to allow the trans to get up to a better temp that will help reduce condensation contamination (To-Do)

Hopefully those last 2 things will be relatively easy to get done this fall.

 

[DieselDrax]

So, I think my plan is to install 6L, 8L & 10L Transmission Cooler Adapter with Thermostat (improvedracing.com) and order the hose/fitting kit like @ARCowboy linked above. I'll then remove the factory hard lines, insert the quick-connect barbs into the OEM cooler ports and cap them off so the OEM cooler doesn't get junk all up in it even though it'll probably never be used again, and then run new braided lines to connect directly to the AN lines in my pic that was linked above for Step 5.

 

[DieselDrax]

Yeah, that should be the only difference. You don't have to run ACDelco-labeled fluid (GM doesn't make their own fluid), often times big brand ATF like Valvoline is cheaper and just as good since the Dexron-VI spec is licensed and all fluids have to meet it in order to be licensed.

 

[DieselDrax]

From what I gathered the full syn 9423 was the hot ticket on our trucks tho and rock auto has it for 6 some a Quart but I'm doing 2 vehicles so if I can buy bulk I will. Wish it was sold in a 5 gallon bucket. I think I'm going light weight shockproof in the diffs

There really isn't anything special about the ACDelco-labeled Dexron-VI so don't spend more on fluid than you have to. $6/qt is actually cheaper than the Valvoline I use (linked below). The bigger deal is with the 8-speed trucks and getting clean Mobil 1 HP LV blue label fluid in. I've been running Valvoline since I started servicing my own trans (Lifted, tuned, larger tires, tow heavy at times, upgraded torque converter) a couple of years ago and I have no complaints.

Amazon.com

I would just make sure that you install a thermostat for the trans fluid since the aux cooler doesn't allow the fluid to get warm enough to evaporate/boil off the condensation and such that builds up and these fluids tend to be sensitive to moisture contamination, so making sure your trans fluid temp consistently runs 165-170F but < 200F is the sweet spot, IMO. Even with hot summer temps in the 90s my trans fluid basically never gets above 150F unless I'm towing or idling in traffic a lot. In the winter (Illinois) it's not uncommon for my trans temp to stay below 100F from like Nov-Mar which really accelerates condensation contamination, the fluid still has great color but starts to lose its frictional properties. I'm going to remedy that this fall by installing a thermostat.

 

[DieselDrax]

I ordered a derale thermo when I ordered my parts so that is already in the works.
I figure severe service intervals on it with the fluid of my choice. Now is the blue label an approved fluid for our 6 speeds?

Severe service intervals with the stock cooler would be like 45k miles max (fluid color tends to get pretty bad by this point). See pic below showing new vs old fluid with only the stock cooler. Oxidation from heat is what kills trans fluid, condensation from running too cool too often results in contamination. So, with a thermostat and proper cooler there should be no reason to service the fluid following any severe service intervals as the whole point of adding the cooler and t-stat is to keep the fluid condition in check which will extend transmission life and reduce maintenance costs by needing to rarely service the trans fluid.

With my aux trans cooler my fluid color really doesn't change since my trans temps never go over 200F and fluid color is how you can tell if your fluid is oxidizing due to excessive heat which would necessitate more frequent fluid changes.

 

[DieselDrax]

25k miles and my fluid is pretty disgusting I'm color

Yeah, doesn't look great. If you're going slow off-road (4H or 4L) often, especially crawling up hills and such, then that's what you can expect after not very many miles. With the stock cooler it would only take a few miles of off-road driving for my trans fluid to hit 240F and by the end of summer my fluid would be rusty brown due to heat oxidation so I'd be servicing my fluid at least once a year with that kind of driving/use. Just wait until you get the new cooler stuff installed, your fluid will never look like that again.

 

[DieselDrax]

Does anyone know specifically the factory trans temp sensor location. I'm getting ready to weld my pan plugs up and trying to decide if I want to throw in another bung for a temp sensor in the pan to use for a fan controller aswell.

It's part of the TEHCM (transmission control module) that is attached to the bottom of the valve body, the sensor is submerged in and reports pan fluid temperature.

 

[DieselDrax]

So welding in a extra bung to control my derale fan relay related to trans internal temp is probably a good idea

You could, however after having my stacked plate cooler with no fan installed for a couple of years now and subjecting it to high load, low speed operation (like towing a 3,000LB trailer up a dirt road to over 12k feet elevation in summer at under 20MPH in 4L) my trans temps never exceed 200F. I see no need to install a fan. It's your choice, but it's overkill and adding unnecessary complexity, IMO.

 

[DieselDrax]

My derale kit is equipped with a fan, and I'm removing the entire factory cooler from the equation. Aswell as switching factory rad and fan assemble in the future to a aftermarket unit with e fan. My current trans setup is being installed in the free space tucked up under the bed.

Ah, right, under the bed. Yeah, probably good to have a fan then since it won't be being force-fed air while you drive.

 

[DieselDrax]

I currently have my transmission out and being rebuilt. I’m installing the RevMax torque converter and am seriously considering this transmission cooler install. I have a few questions:
Do you all have the part number or a picture of what you use to plug the factory transmission cooler off with? Thanks

A box of these (only need 2) and some rubber caps of the appropriate size will do the trick. I'll be getting the stock cooler out of the picture sometime this fall, I have all the parts needed to complete this, I'm just waiting to have the time and consistently cool weather.

Amazon.com: Gopayia 397 Transmission Line Fitting Radiator Adaptor Fitting Trans Cooling Adapter for GMC for Chevy Chevrolet 1996 and Later Transmission Cooler Installation, 5 Pack : Automotive

Buy Gopayia 397 Transmission Line Fitting Radiator Adaptor Fitting Trans Cooling Adapter for GMC for Chevy Chevrolet 1996 and Later Transmission Cooler Installation, 5 Pack: Cooling Lines - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

[DieselDrax]

I got started on this project today and will have to wait until Tuesday to complete it. You know what they say about assumptions. Well, I assumed the Improved Racing thermostat block would have the outlets at the same position as the factory lines so I ordered the unit with 90-degree 6AN elbows. Turns out the thermostat outlets are actually facing forward and ~45-degrees from factory, so I ordered a straight 6AN flare to 6AN ORB union which will get here Tuesday. In the meantime, I got the factory lines out, the OEM cooler plugged off, and the Improved Racing thermostat installed. The rest shouldn't be too bad.

 

[DieselDrax]

Ok, I got this completed today and actually ended up using the 90-degree elbow out of the thermostat. Once I started running the hoses and getting things sorted out as to the best way to run them the 90-degree out of the thermostat plus a 45-degree on the lines provided really good clearance, then once I got the lines run and attached permanently the little bit of extra length I included in the lines is providing just the right mount of stress relief and curve to not put any leverage on the fittings at the thermostat. I re-used the line bracket from the factory lines with the new lines. I haven't taken any pics yet, I was beat and had family waiting to play a game but I'll take some pics tomorrow when I correct the fluid level. I put a little extra in than I got out and then had to get the trans fluid warm enough for the t-stat to open and purge the air from the lines and cooler. With that done, tomorrow I can do a normal level check and not have to worry about air in the cooler/lines.

So far so good, though! No leaks.

 

[DieselDrax]

Hard to get good pics under the truck when it's dark and the parts are also black. Hopefully this gives you an idea of how I ran things on the transmission end. Have the 90-degree elbows coming out of the thermostat block into 45-degree fittings on the ends of the lines in the first pic.

Second pic is showing the lines as they're routed forward, under the motor mount, through the OEM bracket where the hard lines went through, and tie into my original 8AN fittings going to the trans cooler. I don't have pics of the forward end currently, skid plates are back in place and I'm feeling lazy. The length and routing of the lines is resulting in no leverage being applied to the fittings, they threaded on no problem and are "relaxed." I was also able to get my hands on the lines along the entire run except for under the motor mount, which I could see from underneath, and confirmed no rubbing or contact that would lead to problems down the road. Regardless, I did wrap them in cable wrap for a little extra abrasion protection, the lines themselves are nylon and stainless braid.

Next time I'm under the front of the truck with the skids off I'll take some pics, though it's not very exciting. The lines come straight through the OEM bracket, then I use one of the separator clamps (You can see the other clamp in the 2nd pic), and run to my 8AN fittings with an adapter and 90-degree ends on the 6AN lines coming from the trans.

Overall not a bad job, just take your time. If you're feeling frustrated or not sure how best to go about it then step away for a bit. Make sure you do leave some slack in the lines so neither end is tugging on the fittings.

Something I did to help get the line onto the fittings was wrap where I was going to cut with electrical tape, then using these cable cutters or something similar - https://www.amazon.com/9-Inch-Leverage-Aluminum-Communication-63225/dp/B08HC6N4J9 - cut the line leaving roughly 1mm of electrical tape on the end of the line. Lightly oil the fitting inlet and then twist and push the line into the fitting. It won't be easy but doing it this way I was consistently able to get the line into the fittings without any drama. Additionally, the sliver of electrical tape would remain at the fitting opening and is easily removed once the line is fully seated.

If you haven't made AN lines before then it can be a rather frustrating process if you don't have the right tools and a couple of tricks up your sleeve.

 

[DieselDrax]

This evening I was able to go on a longer drive (we went to "the city" to try a new burger place), ambient temp was mid-60s. Country roads a few miles to the interstate and then about 15 minutes at 75MPH got the trans temp up to around 145F by the time I got off the freeway and then with some gentle city driving for another few miles the temp got up to around 160-162F.

Ate a tasty dinner and then about a mile down the road, still city driving, the temp got up to 170F and stayed there until I pulled into the garage ~25 minutes later. Excellent!

Curious to see how it'll do in the dead of winter.

 

[DieselDrax]

Great job! Could I ask what was the temperature rating of the thermostat you installed? They have 140F and 160F options

I went with the 160F version to help condensation evaporate better. The trans also shifts smoother when the fluid is properly warm.

The thermostat isn't a full bypass one, even when closed it does allow some fluid to flow to the cooler to help avoid thermal shock and large temp swings until the fluid reaches equilibrium. I'm honestly not sure why they recommend the 140F version over the 160F. The unit is also rebuildable and if you want to switch to the other temp then you can just swap out the thermostat inside and not the whole unit.

 

[DieselDrax]

Would you happen to have the part numbers of the 90 degree fittings from the thermostat on the transmission?

I ordered them as part of the thermostat "kit" but here's the page for just the elbow.

RaceFlux Low-Profile 90-degree -6AN Male Flare to -6AN Male O-Ring Fitting

RaceFlux Low-Profile 90-degree -6ANAN Male Flare to -6AN Male O-ring Boss Adapter

www.improvedracing.com

 

[DieselDrax]

What have your transmission temps been from this install? Towing vs normal driving?

For me, I have 3 different stages and different temps as a result.

Stock cooler: Towing up grades or going slow off-road would see trans temps of 220-240F, empty temps would run up to 180-195F or so, mainly 100F over ambient.

Aux cooler downstream from OEM cooler: Trans temps were usually 50F over ambient when empty and when towing never over 200F even if I tried (towing off-road in 4L at high elevation and 20MPH or less would hit 199F).

Aux cooler, OEM cooler no longer in the loop, 160F trans thermostat in place: On the freeway it'll creep up to 145-147F, in the city and such it'll get up to 165-170F but no higher, and then when back on the freeway it'll drop back down to the 140s. Haven't towed since the t-stat install but I'm not expecting any differences to peak temps.

 

[DieselDrax]

Ok, so tonight was the first time driving in cold weather since installing the trans t-stat and taking the stock cooler out of the loop. Basically drove 20 minutes on country roads at 60MPH for 90% of the drive, got fuel, parked for about 15 mins, drove back. Temp was 19F outside, truck parked in the garage and probably in the 50s in there. Anyway, after the first 20-minute drive the trans temp got up to 120F and then after the 20-minute drive back the trans temp was up to 154F as I pulled into the garage. Very light engine/trans load on this drive so not surprised at the slowness that the temp rose.

Anyway, huge improvement over stock + aux cooler without the t-stat, in temps like this my trans fluid would never break 100F even on the freeway at 70MPH and the increased wind resistance to put more load on the trans.

 

[DieselDrax]

I’m one of those who got bit,(badly),by a failed stock cooler. Not the fault of the part but inept shop tech. The design of the system leaves room for such mistakes in my opinion.
I may have to add an aux cooler to my rebuilt trans. It runs hotter than prior to wrecking it with engine coolant. The shop that did the rebuild,( who I really like), had to program the trans brain twice. The owner of the shop is comfortable with trans temps 120* over ambient. He does GM trans 5 days a week. Lots of 8 spds.

Hmm, not sure how the cooler could fail and be the fault of a shop. Can you provide more details on that?

 

[DieselDrax]

https://www.coloradofans.com/threads/6l50-saga.445691/

here is the thread from last summer

Ah, I remember that. So not a cooler failure but improper repair. Oof.

With my stock cooler it usually ran about 80F over ambient and when towing a fair amount it was 100-120F over ambient. What actual trans fluid temps are you seeing? Around town it wasn't hard for me to get up around 200F and when towing 215-220F was the norm. If you're seeing temps over 200F when empty and just cruising then something is definitely wonky, but if it's still staying under 200F then I wouldn't be too worried, especially during the winter. My winter trans fluid temps were still getting up around 160F when it was near freezing outside and running the stock cooler.