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Old 05-17-2009, 10:14 AM   #1
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GM transmission cooling upgrades

For a number of years now, I have read on this and other truck forums where folks have indicated that even with the towing packages GM offers that trans temps getting upward of 200 degrees. As most of us know, heat is the number one cause of transmission failures and finally, I decided to take peek as to how GM on trucks like mine deals with this. Much to my surprise, I found that on trucks and SUVs that have a tow package that includes a trans cooler that the trans cooler is extremely small. In some cases, depending on model year only about an inch of the cooler itself is exposed to airflow due to it being hidden behind the Chevy emblem on the grill. What was even more odd is that when I took a look at an older GM truck say from the mid to late 90s, they all had very beefy and extremely well positioned trans coolers. This stopped around late 99 with the 6.0L coming out as far as I can tell. This document covers a number of trucks built between 2000 and 2004. My dad has a 2500 (non HD as it was not avail in 2000) that is identical to my 2004 Suburban. Though other model 3/4 ton trucks with the 4l80e and either 6.0L or 8.1L have the same cooler, some front grills appear to have been redesigned to get the cooler more direct airflow. You will need to check yours to see if yours was like mine with only about 1" of exposed cooler at the bottom of the grille emblem. Allision transmissions require different coolers so this does not apply to folks who own trucks with the Allision tranny.

I looked at the problem two fold. First was heat dissipation and second flash heat when you tow up a good grade for a few miles. These two were addressed two ways.

First, the transmission cooler clearly could not have been more than a 10k (if that) cooler. Even the base model stacked plate coolers are 15k, however, most of the 15k BTU stacked plate coolers like B&M, TrueCool that fit dimensionally the same as the factory cooler (11" wide) and are just slightly taller than the factory cooler still only allow maybe an additional inch of direct airflow over stock. These same compaines make 11x11x1.5 coolers (29k BTU), but without significant modifications up front, that one was just too big. It could have worked if I wanted to modify the current piping significantly and mind you I'm not a huge fan of rubber hoses, so the connection to the cooler had to have metal lines. So this brought me to the 11x8x1.5 20,500BTU cooler. As you will see in the pics below, it is at least 2x the cooler that the factory installed as part of a package or when bought as a kit from your GM dealer.

Second area was the trans pan. I'm no physics major and heck, it took two passes for me for pre-algebra, but that aside, the info I realized is that with more volume, time to heat takes longer. Similar to putting two identical pots of water on a stove, one nearly half full and the other 3/4 full with the same heat applied, the nearly half full will boil sooner than the 3/4 full pot. With that in mind I added a deep trans pan to my 4L80e. Depending on who you talk to or which brand you go with, most add between a 1/2 gallon to a bit over a gallon of addtional trans fluid capacity. It is important however that you either get a deep pan filter or that the pan is designed to support the filter as the Mag-Hytec appears to do.

With the trans pan in, and mind you, it is not a simple two hour pan swap, cross beams have to be unbolted and you really have to squeeze it in, but with the pan in and an additional gallon or so of fluid I found that the truck's trans did take longer to creep up to it's normal operating temps. True the deep pan alone will not cool your oil very well alone as eventually even the 3/4 full pan of water described above will in fact boil too. So that lead me to the cooler.

I did find that if you go with the 15k cooler, you can simply fabricate brackets and swap out the GM quick connect to 3/8th fittings and reuse them, replacing only the clips (which BTW GM wants nearly $8 per clip and you need two). GM suggests not reusing these if removed and the GM part number is 24205103 As I said earlier it will dissipate about 5k more BTUs than the stock unit which may be great for some, but for me, with the Tim Allen complex, I wanted more of the cooler to be exposed to direct airflow and compromised by putting in the 11x8x1.5 20,500BTU unit. Going with this unit and still mounting conventionally, you will have to cut the metal trans lines, flare them and get a 3/8npt male to 3/8 inverted flare. There are several brands an models out there. Some that connect with rubber hose and some that are hard piped. I chose the hard piped (even though GM has some rubber connections along the pathway to the trans). In any way you go hard piped using the stock metal pipes, going with the hard piped trans coolers, you will need to do the following:

Trans coolers I looked at had 1/2"npt female. You will need to get a 1/2" male to 3/8" female adapter. I picked them up on eBay for about a buck or two a piece plus shipping. If you go with the 5 3/4" tall cooler from there you just install the GM quick connects from the old factory cooler to adapter, connect your lines and you are good to go (provided you've cut a few new brackets for mounting the cooler). If you go with the taller 8" cooler with 20,500btus of cooling, it will sit too far down, and as I said earlier you will need to cut, flare and attach to the 1/2 to 3/8 adpater.

I have not completed the install of the lines to the cooler. You will see in the pics the cooler has been bypassed temporarily until I can complete it sometime next week. From there I will drive the truck exclusively for a few weeks before the midwest rally to test and shake out any bugs that come up. It is my hope that with these two items I can keep my trans temps well south of the 200 degree mark. Towing in 90 degree outdoor temps I could get to 195.

I started doing this with my first tow vehicle, my Impala SS. There I installed a deep pan and a second inline cooler. I did see temps drop significantly from the stock configs. I am hopeful that this will in fact do the same for the Suburban. I know a number of folks will say, hey yer in Chicago and it gets might cool out there. Very true, however when I replaced the pan, I put in Amsoil ATF which has flow down to -63F and I still have the oil to water connection still in service. This has been the case on my Impala for the past 5 years and I've had zero issues with the cold. Pics to follow....

Credit goes to Dave from the SilveradoSS forum for giving me the inspiration and help answering all my dumb questions (Dave installed the 11x11x1.5 cooler):

http://www.silveradoss.com/forums/in...mission+cooler
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Old 05-17-2009, 10:36 AM   #2
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In this pic you can see the stock cooler (right) to the B&M 70266 supercooler (left). The difference is pretty night and day. The B&M is 11" wide by 8"tall (not including the attached mounting brackets which add about 1.25 additional height)by 1.5" deep.

The factory unit is 11" wide by 4.5" tall by 3/4" deep.

Also you can see on my factory grille, the Chevy emblem all but can cover the cooler from airflow.
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Old 05-17-2009, 10:37 AM   #3
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Here is the 11x8x1.5 cooler mounted:
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Old 05-17-2009, 10:39 AM   #4
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Here are a few shots (sorry, I didn't think to take pics of the MagHytec before I installed it) of the deep trans pan and the factory 4L80e pan:
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Old 05-17-2009, 10:42 AM   #5
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I forgot to mention that the bottom factory bracket had to be flipped around. This required some slight cutting, and of course there is a sensor on the driver's side that has to be re-attached. Simple drill and pop back in type of thing. Also if you do install a larger cooler remember that the larger cooler will also add some capacity to the overall fluid requirements. Make sure you have the appropriate fluid level hot and cold. NEVER overfill!

One last thing, I used PTFE thread sealer on the adapter fittings. This is suppose to be better than teflon tape or plumber's putty. It is suppose to have a 10K psi rating and be able to withstand 500F temps, of which I hope my trans never ever sees. I think teflon tape is also rated for 500F, but hey, what's a few more bucks for some PTFE thread sealer?

Happy modding!
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Old 05-17-2009, 11:10 AM   #6
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Wow thanks for sharing. We have a 08 Tahoe that we use to tow a SOB and our trans cooler is about the same size as the one in your Suburban. I too wish it were bigger and good point on where GM installed it reletive to the front Bow Tie. That is dumb. I am concerned about doing anything to our Tahoe because of the 5 year 100K warranty. For now I'll have to live with it as is and just slow down to keep the temps incheck. Good luck with the project and keep us posted on your results.
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Old 05-17-2009, 01:19 PM   #7
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Hello

Today 200 degrees is not overheating. The new tranny coolers are desiened to flatten the fluid and twist it for increased cooling area, as opposed to the old round tube/fin type.

Auto Mfg. have to take into consideration over cooling. The balance is trying to acheive cooling, with out over cooling, which is just as bad. That is why tranny fluid also enters the radiator. Optimum temp is the same as the engine, since they are attached. Years ago, trannys where made from different material, now mostly alluminum, they dont want firm shifts, and they want to keep the tranny at consistent temps.

You need to becarefull when over cooling in the winter time. Unless your vehicle is stored. Just like the position of the cooler in relation to tranny. Is it before the lines going into the radiator, or after. After would further cool fluid, and a better bet for summer time, hot weather towing. After the radiator tranny cooler would be great for winter use, then the fluid would get preheated before going back to the tranny.

Keep in mind tranny temp is meassured by sensors, and is a factor on shifting, on new vehicles. I would say the tranny cooler is positioned in the middle like that because it will not effect over heating when used in hjot hot temps with A/C running, and maybe in taffic, because it is in position with the rotating fan center and not edges.

Alot of time goes into design, from mfg.
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Old 05-17-2009, 02:46 PM   #8
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You could always do what some of the guys with big diesel duallys who use their trucks for nothing but towing have done. Large fan cooled trans coolers are available that mount underneath the truck close to the transmission itself. A little more complicated, but not a bad idea for those who are pushing the weight limits of their tow vehicles regularly.
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Old 05-17-2009, 02:52 PM   #9
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hey eric,

you forgot to mention poping the little plastic thingies out of the bumper to improve airflow.

john
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Old 05-17-2009, 03:13 PM   #10
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My trans temp is fine when going down the interstate, runs about 160-180. My problem is in stop and go traffic it goes over 200. I have asked several people about this and have been told 200 is not bad. I have a 1990 Suburban with a trans cooler, extra capacity pan, filter outside the transmission. So is 200 and over bad and what else can I do to get the temp down?
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Old 05-17-2009, 03:32 PM   #11
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Quote:
Originally Posted by john hd View Post
hey eric,

you forgot to mention poping the little plastic thingies out of the bumper to improve airflow.

john
John is absolutely right, in post #3, there is a front view of the truck. Under the grille opening are 6 slots (three on each side). JohnHD when over at Norby's told me of this neat cheap/free mod. GM places plastic knock outs on each side. I'm not sure why they put them in there, but I removed them as they pop right out, and if you wanted, they snap back in, though mine has been out since that day at Norby's. I believe this allows more airflow through the front of the radiator. I am guessing that GM uses similar front ends for trucks and those with the Allison trans have bigger trans coolers and perhaps this is why the slots are there...could also be for an intercooler, not really sure....either way, they are there to do with as you see fit.

I did consider the fact that the truck does get used in winter time and that it might get pretty cool, but I believe I can easily overcome this problem by two or more things, some I did with the test subject Impala that has run in this manner for about 5 years now in my climate.

First, I don't by pass the oil to water stop in the radiator and I have not downgraded the thermostat, still allowing the engine/coolant temps to be at the standard 210F.

Second, I have Amsoil ATF which flows down to -63F. In addition, unlike a car, the truck in winter typically gets used in 4wd. I have noticed that in 4x4 mode the trans does warm up, which didn't happen with the Impala test. The Imp would stay about 150, until it got to over 50 degrees outdoor ambient temp. Not so with the truck in 4x mode. In 10 degree outdoor temps, the trans would get to 170ish, which IMHO is more than warm enough, even if it got down to 150ish.

Third, like the diesel counterparts, they have grille block offs which I could get, but doubt I will given the first two items.

Here is my take being a Tim Allen type when it comes to cars. The warranty cannot be voided unless it can be determined that the mod was the cause. I think the Magnuson-Moss Warranty Act covers this issue.

Keeping Your Mod's Warranty Intact - For Dummies

I think engineering is one reason mfgs build them the way the do, but I am also keenly aware they build vehicles to a price point. Say the trans cooler that I put in cost GM $25 more to install..not much right? Until you put it on 20k trucks, plus if they built em as meaty as they should the cost of the vehicle would not be competitive, thus the HUGE aftermarket vendors out there. If I had a deep pan a cooler and still got above 200, I would look at the cooler specifically for size and upgrade, but that is just me (as if you couldn't tell by this big production). I personally feel 200 is as hot as any trans should get (worst case), I know some may not agree, but that is my opinion. I would prefer it to stay around 175-180 all the time if possible, but again that's just me.

Of course every person reading this must assess their situation and make a decision on what is best for them. This is my answer, which might not be good for you. No warranties are implied or expressed and the info on this thread is offered as is.
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Old 05-18-2009, 08:06 PM   #12
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Airflow management is also important. I make it a point to mount aftermarket heat exchangers in line with the main cooling fan (or fans); otherwise, a dedicated auxiliary fan is called for; for, as one poster noted, it is in stop-n-go traffic that the problems build. (As well, an air dam -- or extension of same -- under the radiator to "pull" the air thru).

I also add power steering coolers for the same reason: low speed manuevering horsing a trailer around can cook things even on a winter day.

I build the hoses as a harness, that the entire assembly can be removed as one. Of the highest quality hose, approved-type, from NAPA. And secured every 4-6" with padded ADEL clamps plus some nylon ty-loks. And keep bends to large, gentle curves. Etc.

And, finally, a MAGNEFINE or RACOR auxiliary transmission filter. With one installed (and a reasonable run on the first batch of ATF or PSF), one need not again replace the pan filter. It isn't much more than mesh anyway.

OilGuard Online Shopping: Automatic transmission filter kit, 6 micron, w/ mounting bracket and fittings, hose not included

Magnefine--Your Source For Magnefine Inline Filters

On another note, the industry standard is to measure transmission temperatures at the sump. I have seen confusion going back years when someone mounts one elsewhere (for comparative purposes). The OEM dash "gages" aren't worth a hill of beans compared to a good aftermarket gauge (AUTOMETER and other).
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Old 05-23-2009, 10:40 AM   #13
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Ok, trans cooler is now connected. Drove about 5-10 miles in 4x4(since the tranny gets warmer when in 4x4).

Trans temps about 110 degrees @ 70 degree outdoor temps. This has not been the case since I got the truck new. It typically shoot up to about 150F in 4x4 mode at 70F outdoor temps and even in the dead of winter it gets to about 125F in 4x4.

Oddly, I have had my pops 2000 Silverado 2500 these past few days doing transfer case and trans oil changes among other things so I've been driving it too and even though it's the same engine, trans, trans cooler, etc, his trans temps stay fairly low most of the time with the stock cooler and pan. About 10-15 degrees cooler and it takes far longer to heat up to about 150F (not towing just drivng around town in 2wd). I don't know if it's because I have 4.10s compared to 3.73s on his truck, but only now since adding the deep pan and the larger trans cooler do I find that my Suburban now runs closely to what me pops truck runs stock. Maybe the Burb weighs a bit more with that whole back end (glass, seats, roof, along with the 4.10s). Not sure, but so far my initial findings (though I admit are early) seem to indicate about a 20 degree drop over stock. What I also noticed was that the trans would drop 10F fairly quickly when on open road (not driving like I stole it). This was not the case on the stock setup. If the temps did go down while in operation, it took a lot longer. Additionally, 10F increases were slow to happen, which was also not the case. It could in the past, in stock form, shoot up 10 degrees fairly rapidly.

Anyway, that's where I'm at right now and will be switching to the Burb as my daily driver these next few weeks before the midwest rally to shake out any issues that come up and to do observations. As long as the next few weeks go well, I'll proceed to towing and see in fact if all this time, effort and $$$ was worth it. All initial indications seem to point to some benefit, but the real test is towing in a few weeks.
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Old 06-17-2009, 08:26 AM   #14
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Ok, I have now towed about 300 miles with these mods and have found overall I have shaved between 10 and 20 degrees off the stock cooler and pan temps (depending on outdoor ambient temps). The deep pan does NOT appear to keep the heat as was suggested, but it does take the trans longer, even under load to get up over 140. It is a very slow climb at 70 degrees outside and a bit quicker climb in 80 degrees, but still slower in both cases than stock.

In about 70 degree outdoor temps, towing a fully loaded trailer, my peak heat was 165F (stop and go) and once on the Interstate I hovered around 145F.

On the trip home (less roughly 300lbs of water), the outdoor temp was 81F. My peak temp was 170F (stop and go) and once on the Interstate, I stayed pretty much around 155F.

Average speed with Tow/Haul enabled was between 59 and 62mph.

As a comparison, towing in similar situations, the trans temps with stock equipment would range anywhere from 165 to about 195 with the temps hovering on the Interstate around 170F.

I have however noticed something odd that I am still not sure is the cause of the cooler being installed. My A/C in the truck is not working very well. At first I had thought the heat from the cooler which takes up 2x the size of the old cooler was pre-heating the condenser. This was my only thought since the trans cooler is about 3" to 4" from the condenser as was the case with the factory cooler and that air flow from the fan should still produce enough flow over the condenser so maybe the heat from 2x the size prior was causing the issue. So, the next day, I had tried the A/C around town as the trucks operating temps were still cold. The A/C still didn't operate normally. I had blown out the radiator and condenser with air from my compressor then followed up with water from the front of the engine out and perhaps something happened when I did that, or the cooler could still be the culprit (though I can't see how given the massive amount of open and exposed condenser).

Will check on the A/C unit and report back, but for now, the cooler is staying put and has worked as expected in reducing trans temps.
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