Trouble and overheating trans while towing

aaserv

Original poster
Member
Dec 1, 2019
408
N of Baton Rouge, La.
Finally found a lightweight camper at a good price. Drove about 75 miles away to pick it up yesterday. Immediately upon pulling out on the road I noticed it felt like I was pulling the USS Kidd....thru gumbo mud! Yea maybe the 3.43 gears are not great for towing. 1st stretch of road I came to I layed on the gas hard and 1st and 2nd seemed ok but when it hit 3rd gear it felt like i was pushing against a wall. Topped out at 50mph and the RPM's kept rising..... My newly rebuilt (for towing) transmission was slipping like crazy and the temp gauge was climbing. I was thinking of turning around but slowed to 45 mph and toughed it out. All flat terrain , no climbing. It was 90 degs when I left with it but dropped to low 80's pretty quickly. Did better then topping out at about 60 mph.
This camper only weighs about 3400lbs so I should be pulling it with ease. Hopefully the transmission guy is cooperative and it doesnt take him a month to correct it like it did for the original rebuild. I still think my 220k miles worn out camshaft and valve springs are contributing to the lack of power but Ill prolly wait until I get the transmission problems cured before going into that and possibly shopping the u-pull-it for lower rear gears......
 

Mooseman

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Dec 4, 2011
25,257
Ottawa, ON
I can tow with my TB my equivalent weight sled trailer loaded and it has no issues except can't tow in 4th as usual. You were towing in 3rd right? And also have an aux cooler? A must. Maybe a clogged cat?
 

Reprise

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Finally found a lightweight camper at a good price. Drove about 75 miles away to pick it up yesterday. Immediately upon pulling out on the road I noticed it felt like I was pulling the USS Kidd....thru gumbo mud! Yea maybe the 3.43 gears are not great for towing. 1st stretch of road I came to I layed on the gas hard and 1st and 2nd seemed ok but when it hit 3rd gear it felt like i was pushing against a wall. Topped out at 50mph and the RPM's kept rising..... My newly rebuilt (for towing) transmission was slipping like crazy and the temp gauge was climbing. I was thinking of turning around but slowed to 45 mph and toughed it out. All flat terrain , no climbing. It was 90 degs when I left with it but dropped to low 80's pretty quickly. Did better then topping out at about 60 mph.
This camper only weighs about 3400lbs so I should be pulling it with ease. Hopefully the transmission guy is cooperative and it doesnt take him a month to correct it like it did for the original rebuild. I still think my 220k miles worn out camshaft and valve springs are contributing to the lack of power but Ill prolly wait until I get the transmission problems cured before going into that and possibly shopping the u-pull-it for lower rear gears......

Saw this, and naturally took an interest in it, since we have similar vehicles (both '03, both V8s)...

- Were you towing in 3rd, or 'D' ? (Although on very flat terrain, it really shouldn't matter)

- Guessing you don't have an external trans cooler, and you're using the factory one that's integral with the radiator. If so... 3400 of extra tow weight is really too much for the factory cooler.

Hearing that your new rebuilt trans is slipping... does not sound good. Definitely check the fluid (both capacity and quality). While I have a 3.73 gear, I definitely didn't experience slippage / flaring after my trans was rebuilt (which is when I actually started towing with it).

My first trailer weighed about 4000 lb; at 10ft tall, my Voy pulled it exceptionally well on flats. But when I hooked up the trailer that replaced it (1000 lb heavier and 11ft tall), I really felt it towing it home from PA. How tall is your trailer?

Finally, at 220k miles... I doubt your cam is worn, if you've had good oil pressure all this time and kept up on the oil changes. When I did the cam / head swap on my Sierra at about the same mileage, the cam lobes and journals looked great (and I can guarantee that at least one of the previous seven (!) owners probably skimped on the maintenance, given what I found in the oil pan). You can see the old cam in the pics on my build thread from a couple of years ago.

While I didn't test the spring pressures on the heads that came off, none were broken or showed signs of fatigue / collapsing, etc. I just recently removed the springs from the OEM heads in prep for rebuilding them, so I'd recall if they were broken or looked marginal (they certainly required a decent amount of pressure with the spring compressor to get the locks / keepers off).

IOW, I'd be more suspicious of your trans / cooling, than your cam / valve springs, tbh. Remember that the radiator is undersized, especially for towing anything heavy (and there really aren't any readily available improvement options). The hotter the coolant gets, the less it can cool the trans fluid, if you're still using the factory cooler. At +90F ambient, with 3400lb in tow, I can guarantee your cooling system was stressed (as I've been there, with my own Envoy).
 

aaserv

Original poster
Member
Dec 1, 2019
408
N of Baton Rouge, La.
Clogged cats was the 1st thing that crossed my mind when I felt the initial tug because thats exactly what it felt like. Ive driven 2 vehicles with clogs and that is what this felt like. I dont "think" thats the case here because 1 I have been driving it a lil harder since I had the tranny done and havent felt anything like that and 2 I definitely saw and felt the rpms soaring with no increase in speed. It was slipping no doubt about it. However Im not entirely ruling it out.
I couldnt use D had to run it in 3rd, Even when i did put it in D on extended distances if it ever shifted to D it within seconds went right back down into 3rd.
I drove it a short distance today to where im parking it for awhile and noticed it did much better if I manually shifted it and extended 2nd gear to 45 or so before shifting to 3rd. Still I dont think I should have to do this but that may just be the 3.43 gears not really set up for towing.
Im not sure of the height but it is 10ft or so Id say.
I dont have an AUX cooler and know now that I need to get 1 installed ASAP. Ive had overheating problems with this truck since the day I bought it anytime the temp is 90 degs or higher. I have no idea however where its going to go, the damn thing has so many coolers now it isnt funny. power steering, a/c and now a tranny cooler.......by the time the air hits the radiator on a 90 deg day its going to be egg frying temperature already!!
Im sure there are multiple threads on installing coolers here but if anyone knows a good 1 offhand Id appreciate the link..... I want to get the consensus best set up on order 1st thing Monday morning.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Ive had overheating problems with this truck since the day I bought it anytime the temp is 90 degs or higher.
Do you mean engine or still talking about the tranny? In either case, are you also still running the original fan clutch? Is it working properly? Test it out to make sure it works.

How to test the electro-viscous fan clutch
If it's defective, you have two options. If you want to stick with the same original electro-viscous type, then get the OEM one. It's the only one that operates as per specs.


If you want something a little more reliable, you could go with the 08-09 thermal type and get the PCM tuned to turn off the codes for the fan clutch. @limequat does the tuning by mail at a very reasonable price and can also enhance other engine and transmission parameters at the same time. Well worth it IMHO.

Again, the OEM clutch is the better choice here.


 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Moved these posts to their own thread.
 
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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
And just to confirm, you have the 3.42 gears? You said 3.43, which don't exist. The 5.3 versions of these trucks typically came with 3.73 gears. Maybe a typo?
 
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Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
I dont have an AUX cooler and know now that I need to get 1 installed ASAP. Ive had overheating problems with this truck since the day I bought it anytime the temp is 90 degs or higher. I have no idea however where its going to go, the damn thing has so many coolers now it isnt funny. power steering, a/c and now a tranny cooler.......by the time the air hits the radiator on a 90 deg day its going to be egg frying temperature already!!
Im sure there are multiple threads on installing coolers here but if anyone knows a good 1 offhand Id appreciate the link.....

I've run 2, that were similarly sized, and fit in the space behind the grille. First one was a Long Tru-Cool 4589. Installed in 2016, it has a built in thermal bypass, which I thought was a cool feature, but I believe ended up being its downfall. After my transmission ate itself in 2019, and needed a replacement, I noticed the extra cooling was non existent. I believe the bypass valve got clogged and I couldn't open it back up.

20161203_114548-jpg.90666


Many folks here recommend Hayden coolers, so in 2021 I made the switch, and got a Hayden 678 cooler. Slightly wider than the Tru Cool by an inch and a half, and I think needed a tiny bit of trimming on the plastic header panel where the hood latch is, and at the bottom as well. Both of them I ran in series, following the OEM cooler.

20220417_174003-jpg.105099



I chose to have my ports pointed up, so any air would be burped on its own. Requires longer runs of tubing though. With in town driving, the temp usually stays around 170-175. After extended highway driving, when I've run into traffic jams, or stop and go driving immediately after, the temps will climb and match the engine temp for a short time, then the fan will cool it back down. I have also made the switch from the EV clutch, to the thermal one. :twocents:
 
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Reprise

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Im sure there are multiple threads on installing coolers here but if anyone knows a good 1 offhand Id appreciate the link..... I want to get the consensus best set up on order 1st thing Monday morning.
There's three main types of coolers... stacked plate, plate and fin, and tube and fin.

The stacked plate is the most efficient (so you can run a smaller footprint, in addition to the extra cooling benefit). But they're the most expensive. I run a tiny 10,000 BTU Derale, and it works great. But if I were still towing with the Envoy, and had it to do over again, I'd get a slightly bigger one. Maybe 12-15K (or even 20K BTU for the really hot days, which I'm sure you have a lot of in Louisiana).

Mine is plumbed to bypass the in-radiator cooler (the guy who swapped in my rebuilt trans installed it). At first, I thought he was being stupid to entirely bypass the factory cooler, but knowing what I know now about the Envoy's OEM radiator being marginal (and that's being kind), I've come around to his line of thinking (which was based more on the factory coolers failing, tbh). If you plumb it in series with the factory cooler, send it through the external cooler LAST. Otherwise, you could actually be adding heat back in, if it goes through the radiator cooler last.

The tube and fin are the cheapest, but they're the least efficient. So one that's thermally equivalent (say, 10K BTU) will be larger. The way that the fluid goes through them (180" turns) makes them more susceptible to heat, and they tend to increase fluid pressure a little bit, as well.

Where / how you mount it matters. The best place is in front of everything else, including the A/C condenser, where it can get direct airflow. If you can mount the cooler to the front bulkhead, great. But even if you have to use those zip-tie type things they give you to connect it through the fins of the A/C condenser... that's OK, too.

If you're really worried about blocking airflow to what's there now, I know Derale makes a remote mount one that has its own fan. But that takes 12v power, of course. And I probably don't even need to say that it's $$$. Use the airflow through the grille -- it should work fine with a large enough cooler.

The 'biggest one' that I know of is made by Tru-Cool -- it's a 40,000 BTU cooler. But I don't know if it would fit in the front of the Envoy without some serious 'surgery', tbh. They're intended more for motorized RVs and such, but they'll fit in the front of a full-size pickup, too.

Whichever one you put in, make sure you put enough extra fluid in to compensate for the volume of the cooler. Some manufacturers will give you the specs on what each cooler holds, but if you can't find it, a few minutes with a quart or two of fluid, the new cooler, and a drain pan will let you know exactly how much more you'll need, prior to installing it.

Finally, the radiator fan -- I replaced my OEM with a traditional thermal fan clutch, since the OEMs always fail, and GM went back to the fan clutches at the end of the GMT360 run, anyway. But this does require the PCM to be modified, as Moose mentioned, so the truck doesn't throw a million fan codes, potentially put itself in 'reduced power mode' because it thinks it's overheating, etc.

The thermal clutches can fail, too -- but they're generally more robust than the OEM E-V type. And easier to replace (and easier to find, too).

The other thing I did when I was towing with the Envoy was to run Torque Pro on my phone, so I could display the trans fluid temp in real-time (the trans has a temp sensor, and the PCM will report the output via the OBD-II port). Even though I had bypassed the stock cooler, you could see that as the engine coolant rose in temp, so did the trans fluid temp (the lesson here is that high ambient temps and high load conditions on a driveline do take their toll.) I have a thread from a few years ago that describes the experience (towing +95F @ 6800ft, with full black / grey tanks, at 40mph, in Montana). I had to eventually pull the truck over on a grade and let her cool off for 20-30min. But I did make it up the grade without blowing a head gasket or grenading the transmission.

Even before you get a cooler, a fan clutch mod, etc. -- I'd hook up Torque Pro and see what your trans temps are normally running. That gives you a baseline to work from. With no trailer, your temps should be on the low side of 200F. If they're higher (remembering the ambient temps you get out there), size up your cooler accordingly.

For fluid, you should run Dexron VI, which will be stable to about 265F. I use Valvoline's version, but the GM is fine, too. Try not to use the 'universal' type fluids that are 'Dexron compatible'. If your trans temp gets as hot as 230F, pull over. You can monitor the temps with the engine running, which should allow them to drop. If they don't, then shut off the engine and sit for awhile. You can still monitor the temps through OBD-II, without having to start the engine (but it'll take longer to drop; they may even rise slightly at the outset, with the engine off). What you want to avoid is 'thermal runaway' (yes, it's a thing).

Finally... you might want to have a conversation with your trans builder about the slippage / flaring, before installing all of these new 'toys', and get his input. NGL -- I read your description of it, and I do have some concern (but I'm the 'worrying type', too). Keep the trans in 3rd, even on flats, in hot climates.

For some 'emergency' help with the radiator coolant temps... turn off the A/C, open the windows, and set the climate control to full heat. You'll bake... but it could mean saving the trouble of a blown head gasket or a warped head (or block, since your engine is all-aluminum). I had to do this once when I first got the Envoy and I was in a construction zone with freshly laid asphalt (no towing, still had the OEM EV clutch). It saved the day.
 

aaserv

Original poster
Member
Dec 1, 2019
408
N of Baton Rouge, La.
Ok , Getting started on the project. Yesterday I noticed the battery light was on so I replaced both the battery and alternator. The battery I put it in 2019 and the alternator I had gotten from the u-pull yard maybe 2 years ago. Im not positive which one was causing the problem but it was time to replace them both anyway. I did step up the alternator to the 150 amp that came on the full size trucks and vans and naturally it takes a different pigtail connector so Im off to u-pull now to try to find the right connector.
I took the entire front off yesterday since Im going to repaint the front bumper cover also. I had already been sanding the bad spots and after hanging it up outside I began applying a light spray coat every few hours while I was out there. Its not in the direct light but so far it looks ok. There is also some light damage on the passenger side fender. I had mostly popped out the dents on the fender itself but I can see now the brackets that mount the fender to the frame are bent also so Im going to try to straighten that out also while Im in here.
I bought the Hayden trans cooler. Its the 3 turn all aluminum model. I do A/C work as some may remember and Im just not a fan of the micro tube coils in any way shape or form. Just a personal preference.
I also installed some time ago a 10" electric fan in front of the radiator. I would like to have that fan blowing thru the Trans cooler. So far I dont see a way to make that happen but Im going to work on it some more today.
Im thinking right now Im going to by pass the radiator cooler completely but Im still researching and watching YT videos so thats subject to change.
Im not going to consult the guy who rebuilt the tranny. Im going to wager that the slipping was caused by overheating and that it will be ok when Im done. He will probably not honor the warranty after Ive installed a cooler myself But i know he would charge me a several hundred to do it there and probably take a few weeks to do it so Im going to gamble the tranny will hold up.
Hopefully have some pics this evening.........
 

aaserv

Original poster
Member
Dec 1, 2019
408
N of Baton Rouge, La.
Ok guys heres my 1st idea. It will definitely keep it well forward of the a/c condenser.. Im thinking some chicken wire and screen over the front face to stop road debris from puncturing it. Its 92 degs outside so the heat could be affecting my brain but Im not seeing why this wont work. (Thats where ya'll come in) Im probably missing something obvious so go easy on me..
Pic of the new alternator also......Capturealternator.JPGCapturecooler.JPG
 
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corky

Member
Jan 23, 2012
77
Portland OR
Finally found a lightweight camper at a good price. Drove about 75 miles away to pick it up yesterday. Immediately upon pulling out on the road I noticed it felt like I was pulling the USS Kidd....thru gumbo mud! Yea maybe the 3.43 gears are not great for towing. 1st stretch of road I came to I layed on the gas hard and 1st and 2nd seemed ok but when it hit 3rd gear it felt like i was pushing against a wall. Topped out at 50mph and the RPM's kept rising..... My newly rebuilt (for towing) transmission was slipping like crazy and the temp gauge was climbing. I was thinking of turning around but slowed to 45 mph and toughed it out. All flat terrain , no climbing. It was 90 degs when I left with it but dropped to low 80's pretty quickly. Did better then topping out at about 60 mph.
This camper only weighs about 3400lbs so I should be pulling it with ease. Hopefully the transmission guy is cooperative and it doesnt take him a month to correct it like it did for the original rebuild. I still think my 220k miles worn out camshaft and valve springs are contributing to the lack of power but Ill prolly wait until I get the transmission problems cured before going into that and possibly shopping the u-pull-it for lower rear gears......
Had the same issue turned out to be my cat clogged up and pvc hose one the left side of the engine plugged.
 

aaserv

Original poster
Member
Dec 1, 2019
408
N of Baton Rouge, La.
Hopefully someone can answer this. I have to pull my trailer on the 20th. I dont have time or money to replace the cats. If I take them off will I still be able to drive it? I guess Ill leave the O2 sensors where their at for the trip? Disconnect them? I dont have time to get the computer reprogrammed and from what Im reading I probably will end up having to replace the cats even with a tune because we have very strict emission testing here. I wont have to have it tested again until next March I think so I can buy a lil time. But I have to make this trip on the 20th. I can cancel pulling the trailer and just stay in a hotel but Id rather make that my last option.. HELP????
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Yes you can. The post cat sensors only tell the PCM is the cats are working, and obviously, they won't in your case.

If the CEL bothers you, you can cheat the system. People used to use spark plug defoulers (or spacers) however they seem to have become unobtainable in the US. If I search for them on Amazon US, they don't come up and I get results for shower extensions? But Amazon Canada, no problem.
 

Reprise

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Jul 22, 2015
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If I take them off will I still be able to drive it? I guess Ill leave the O2 sensors where their at for the trip? Disconnect them?

Are you taking the front set off, the rear set, or both? Assuming you're going to do something to cobble the exhaust back together (even if you use hand-tightened exhaust clamps)... you should be OK.

I wouldn't drive without at least a partial exhaust -- a good 18" minimum from where the front cats were (and a little longer would be better). If not connected to a muffler, it's gonna be really loud, but I'm sure you know this. If you go open exhaust from the front cats back... I remember the driver's side one (if not both) is nearly adjacent to the manifold. You don't want to be 'open' at that point, as you might have issues with flame, so close to the manifold exit.

If you're only doing the rear cats, you can decide if you want to reconnect to where the rear ones are removed. Again, it'll be loud, but at least you won't lose too much in the way of power (does this model have 4? I can't remember. My Sierra does, so if you only have the two up front, ignore this).

Yes, I would disconnect and remove at least the front O2 sensors. You don't want them 'free in the wind'; running them like that might (?) damage them. Wrap the harness plugs and tuck / zip tie them out of the way. You don't want water getting into the plugs, if it rains. Label which sensor went on which side, just to be safe.

Do those things, and I think you'll be OK pulling your trailer. Don't forget to keep it in 3rd!
 

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