4L80 Transmission Temporarily Overheating

[Westieterrier]

Two questions, the first I know will lead to some deserved scolding. Apologies if this is too long a post.



My somewhat-new-to-me truck is a 1999 Chevy C2500 Classic, 2wd, Longbed 350, 10.5 Corp Axle, 4L80 trans with its stock cooler hauling a heavy Lance truck camper.



I’ve put 3,000 miles now on my truck with 152K total on the clock and it has performed beautifully, both with the occasional truck camper haul and as an occassional daily. I’ve done some recent work like a water pump; new HD springs, brakes, etc. My entire rig fully loaded with the camper and all gear/water is right at the 8,600 GVW as measured on the scales.



I’ve put 500 miles on it with the camper and it has performed really well on all manner of roads. I typically keep it at 65mph on the highway in direct drive, no. 3 on the gearshift selector. The other day, however, I did something imprudent to try to save gas and put it in overdrive while I was going over the Oregon Coastal Mountain pass (not the steepest mountains we have here). About halfway through the trip, the tranny stopped shifting and the truck was sputtering, unable to power over upgrades. I pulled over and smelled that smell we all hate, burning tranny fluid, though it was faint. I waited 30 minutes and restarted my journey in drive no. 3 and it did fine for the rest of the trip and several more.



All seems fine with the tranny now, and there was no loss of fluid from the incident above. The dipstick and fluid on it does not have that burnt tranny smell at all. The tranny and truck are operating as before, beautifully (such a well-made machine, really!!)



First question, what do you gentlemen think happened on that mountain pass? I know I shouldn’t have tried to use overdrive for such a trip, and probably should never use overdrive again whenever hauling a 3,800 lb. camper.



Second question, I went under the truck to inspect and plan for an eventual filter/fluid change, and, behold!, the tranny pan has a drain plug. Is this factory? If not, what brand does it appear to be? Super curious.

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Any insights would be greatly appreciated.

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[1998_K1500_Sub]

I put it in overdrive while I was going over the Oregon Coastal Mountain pass (not the steepest mountains we have here). About halfway through the trip, the tranny stopped shifting and the truck was sputtering, unable to power over upgrades.

There are more knowledgeable people on this topic, but here I go...

In later years (1996+) the ECUs were more capable, "they got smarter" [note 1], and I see yours is a 1999. The trans temp is monitored and if it's above a threshold (250F?), remedial action is taken. One remedial action is to lock up TCC, so as to keep heat from building in the fluid due to TC slippage. I might assume there are other remedial actions, e.g.,

- turn on an idiot light (Toyota does this, for one)
- restrict the transmission to certain "gears", e.g., disable OD
- lock-up the TCC (as I mentioned)
- attempt to operate at lower line pressures, e.g., to minimize heating of the oil
- impose certain limitations on the engine, e.g., such as torque management so as to allow the transmission to be operated at lower line pressures (see prior bullet)

Too, some of these transmissions (the 700R4/4L60 for instance) are unable to lock-up the TCC in other than certain gears (2,3,4 for the 4L60E). I'm not sure if the 4L80E has the same restriction (my 4L80E Technician's Guide is upstairs; in time I'll look into it) but, assuming it does, then in your situation the powertrain control algorithm(s) may have been (a) locking TCC in an attempt to keep the fluid temps low and consequently (b) using only gears which allow the TCC to remain locked-up, while (c) operating at lower line pressures to mitigate oil heating and (d) managing engine torque to enable (c).

I could research this more but I haven't time now, so let's see what others say. You may wish to access the service manuals for 1999 and investigate for yourself. Find them here:

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

Notes:

[1] Many years' controllers embodied some form of transmission-saving remedial action, but the methods they used became more sophisticated over time. The relative complexity of OBD II required the use of more capable processors in 1996 and, in turn, other functions (such as powertrain control / transmission control) were able to become more complex.

 

[1998_K1500_Sub]

Update: Attached is the description of the temperature sensor and related functions for the 4L80E from the 1990 4L80E Technician's Guide. The functions listed apply to 1990 and may (likely) be more extensive in 1999 as the functions aren't inherent in the transmission itself but rather its controller(s) (ECU / TCU / PCM / ECM / etc.)

See the first image below. In the 2nd paragraph, the high-temp remedial actions are explained.

The second image is simply the front cover, for reference.

Finally, that drain plug is OE. It's shown in various illustrations I've seen in the manuals.

 

[stutaeng]

The drain plug is factory.

That weight should be fine for OD. Unfortunately, those trucks didn't come with a transmission temp. guage, so you can't tell what the temperature was in those passes. Do you know for a fact the trans. fluid was not burn before?

What does the truck do now that it cooled down?

BTW, direct drive would be 3 on the gear selector. I didn't follow you on what you said there...

 

[1998_K1500_Sub]

...the truck was sputtering, unable to power over upgrades. I pulled over and smelled that smell we all hate, burning tranny fluid, though it was faint. I waited 30 minutes and restarted my journey in drive no. 3 and it did fine for the rest of the trip and several more.

I'm wondering if you've actually got some other problem and not a transmission problem. The 5.7L, to me, doesn't seem like it would be a challenge for a 4L80E.

The engine was "sputtering" you said... if it was running poorly, your nose might have picked up some scent... a hot cat, for instance.

DO THIS: Put a scan tool on it ASAP and see it if stored any codes or freeze-frame data (regardless of whether the SES light is on). If so, log the codes / data and start investigating. Post the information here if you need help.

 

[mr_josh]

Hey there- I have a '97 with 5.7L, 4L80E, and spent about a month on the road last year with my truck camper that is a little smaller than yours (I have 3.73 diff gears- don't know what you have).

Take-aways: with the large frontal area of the camper and added weight, the 5.7L was really working hard. I tried OD a couple of times in different conditions and it just wasn't happy. I could maintain 60 - 65 but the slightest (and I mean slighted) rise in the road would put it back down to third. I figured in the long run, it was probably better to be in third the whole time than have it shifting back and forth from 3rd to 4th when it was hot and had a big load on it.

If your transmission fluid doesn't smell burnt or look burnt, then that is obviously a good sign. I am pretty sure that your sputtering, as was said, is a powertrain issue and not a drivetrain issue.

I do wonder- when you say "stopped shifting"... can you elaborate on that?

As for the smell, knowing what I know about the area you were in and the weather as of late, I doubt you were overheating the trans. Is it possible you leaked a little fluid out of the converter seal under heavy load and it hit the exhaust?

 

[L31MaxExpress]

The fluid might have expanded a bit, the level rose into the gear train, aerated it and pucked out of the vent on the top of the case. My van was missing the vent tube at the time and it puked on to the exhaust.

With that much weight and frontal area a 350 is not going to want to be in overdrive unless it has a 4.10 gear. With a 3.73 gear 3rd is where I would run. Mileage will be better there and the torque converter can lock up and keep the trans cool. I use a larger M7B Trucool on the stock bracket after the in-radiator cooler on my Van. Trans will stay under 170°F. I also have a deep pan that holds ~10.5 quarts of fluid.

I will say my 383 could care less if its lugging this slightly uphill in overdrive with a 3.73 gear. The added stroke and torque really changed the character of the engine. I was running a 5.13 prior. I think I am going to a 4.10 in the future and call it good. Less than WOT I have my Tow/Haul settings on my 4L85E to lockup just after the 1-2 shift and remain locked through all the shifts both up and down.

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The pan on my 4L85E and the custom moded 4L60E crossmember to fit it into place. The way the crossmember mounts on the van you cannot slide it back and redrill the frame. The 4L80E factory crossmember also does not work because the RH mount is 6" farther back on the frame. I am sure I could get a little cooler trans temps if I wraped the exhaust as it sits close to the pan but has yet to be a noticeable problem.

EDIT-One other thing. Moroso has the wrong part number listed as the filter for that pan kit. They list a 4L60E short filter, which absolutely does not fit. The 97+ 4L80/85E uses a long filter that also does not fit. Ended up using the shorter 91-96 4L80E filter that fit perfectly. I stuck the magnet to the steel on the bottom of the filter. Works perfectly as a spacer to keep the filter 1/4" off the pan floor and filter pickup tube securely into the pump as well as keeps the magnet in one place. The filter issue caused me several hours worth of frustration and ended up costing me paying for 3 different transmission filters. But it is all good now and that pan does not seep a drop using an OEM style gasket. Also has a nice port for a future transmission temp gauge and a magnetic drain plug on the side at the very bottom of the pan. On the list of things to do someday is a rollerized output housing but thats for another day.

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[Westieterrier]

Thank you gentlemen for all of your considered thoughts. Several of you have put significant time into your responses, which is really astounding. I owe each of you an Oregon IPA if you're drinking guys!

To expand and clarify a bit: I have the 3.73 gears, and yes, I was talking about gear 3 direct drive vs. little 'D' overdrive.

I probably misused the term 'engine was sputtering' and instead meant to say 'the truck itself was staggering' to get over those hills of the Oregon coastal mountains. The engine was revving fine, even over-revving, it's just that the truck wasn't getting over the hills because the tranny stopped downshifting. I couldn't maintain a speed over 40 mph anymore. So I pulled over and waited a bit. That's when I smelled a faint burnt tranny fluid odor (we all know what that is!). Again, fluid level, smell, and taste (yes, someone showed me at 16 this trick) are all fine now.

The Rt. 6 pass is a troublesome road of tight narrow turns, which was built for meandering to the coast from the valley at 55 mph, not the 75 mph commuter corridor it has become. Whether on my little 200cc dirt bike or in the camper rig, I always get some moron in a BMW or an overstressed logging truck-driver in a rush tailgating me at an already uncomfortable 65 mph. So, this time I had put the truck in overdrive and just kept mashing the pedal at every steep hill to maintain speed. It was constantly downshifting for the first 30 mins as I pushed and pushed her. After your responses I am sure this is what caused my tranny incident. Yes, I know, stupid! But after a 35 minute cool-off period it drove perfectly in drive 3 the rest of the day, and two more trips: another 90 minute drive to the coast from Portland, and a two-hour 65 mph round-trip on twisty I84 to Hood River, OR. The engine still runs great from idle to 65-85 mph (without camper) and has done so since last year when I bought her.

As an aside, I am super impressed with this truck, even as old as it is. I'm left wondering 'where've you been all my life?' Lol. I bought a brand-new S-10 in 1989 and a new 1999 Wrangler soft-top back in the day, and each time had considered a short-bed C1500 4X4 because I always liked how they looked. But in each instance I went with the other choices. Oh, the girl that got away!

In any event, I think 19881500 and L31's insights above are spot on at this point. I can't tell you guys how grateful I am to you for taking the time to post this awesome information. The advice from the other gents was very helpful as well. I know what to do now. Thank you all so much!

Here's another fun photo of my rig, this time loaded with said trail bike and tipping the scales at 8,900 lbs:

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[HotWheelsBurban]

Very cool rig! What's the story on the Chevy tanker rig and the power wagon, is that a Mule cargo mover too? Lotsa cool old trucks!

 

[Caman96]

and each time had considered a short-bed C1500 4X4

Of course you meant a K1500….right?