Safely long-haul towing with a 2006 Z71 Tahoe

[Stev1e]

Hello all,

Did some searching and didn't find anything that seemed germane to my question in the last couple of years, so here's my situation:
I have a 2006 Tahoe Z71 2WD with 230k miles that I intend to tow a 20-foot-long heavy trailer with. When I say heavy, assume near, at, or slightly over vehicle tow capacity.
I have a weight-distributing hitch, and successfully towed my heavy trailer from outside Columbia, SC to the Big Bend area in FL using back highways. The trip went well, albeit slow, and was primarily flat with some gently rolling hills. I was anxious for most of the drive and didn't want to try pushing past about 57 MPH for fear of wearing out the engine or transmission. The move was made in July or August, and I had no temperature issues (sadly, I cannot say whether I have a transmission cooler installed; I just don't know right now).
It's nearly time to take my heavy trailer from Florida to Maine. I have a flattish route picked out, and intend to be rolling in the 50-60 MPH max range again, placing the trip at just over 3 10-12 hour days of driving. As a holiday gift, I was given a OBDII scanner, with the intention that I use my phone as a transmission temperature gauge to help ease my mind as I pull my heavy trailer to Maine.

The question is this: Is there a safe RPM range I can sustain over that distance? Are RPMs irrelevant and I should pay more attention to the temp gauges? What temp ranges should I be looking for for sustainable operation here? The intention is to take this trip in either August 2023 or May 2024, depending on weather and variables beyond my control.

As far as I'm concerned, if I pull up to my new home with my trailer and my Tahoe shakes apart into small pieces, I'll still be satisfied with the job well done. What I'm really trying to avoid is an on-the-road breakdown where I'm forced to do some absurd gymnastics to get the heavy trailer up to Maine.
I do have fairly extensive towing experience by distance, though it's traditionally been in this same Tahoe pulling a U-Haul car trailer with a 1965 Mercury Comet perched on it, so far from the slowest or most technical drive you can do.

 

[B-train]

Keep her in 3rd gear and don't be overly aggressive with the throttle. LS motors are rpm Champs and don't care running for extended hours like that. Fresh oil change and Trans service beforehand. Maybe even a diff service too if it's been awhile.

You'll have good airflow at 55-60 so temps won't be a problem. If you start creeping towards the 230 mark, you might want to slow down or give it a rest stop. Leave the truck running all the time for quick rest stops or fuel upside. Shutting off just heat soaks and cooks stuff.

 

[Scottydoggs]

i see or hear the word germane and this is all i can think of lol

 

[rockola1971]

LS based engines are built for high RPM longevity straight from the factory. Cruising 1800-2500 RPM...the engine wont care as long as its got enough oil and cooling system is working fine. Transmission.....dont even consider running in 4th with that kinda weight behind the tahoe. You'll burn the 2-4 band up in short order then you are screwed and will only have 1st and 3rd gear. Tranny fluid and filter service if it hasnt been done since last time you went on your long towing expedition. Grease your front end, ujoints if they arent sealed type and check coolant hoses for loose clamps and hose deterioration.

How much does the trailer and load weigh?

 

[Marky Dissod]

I have a 2006 Tahoe Z71 2WD with 230k miles that I intend to tow a 20-foot-long heavy trailer with.
When I say heavy, assume near, at, or slightly over vehicle tow capacity.

Since you did not say that your Z71 has 4.10 or 4.30,

Keep her in 3rd ...

... don't even consider running in 4th with that kinda weight ...

Stay out of 4th, AND stay in Tow / Haul mode.
Even if Dexron 6 can handle 239°F, I'd still be concerned if ATF temp got up that high.

A supplemental ATF cooler fan never hurts.
If you can have your pcm reprogrammed to improve towing durability, that can't hurt either.

As for engine RpM, above 2000RpM, which should not be too hard in Tow / Haul mode while avoiding 4th.

 

[Fless]

Look through your grill and if you have one it'll be between the grill and the A/C condenser:

 

[nonickatall]

From my humble view, It is not the towing, that is the problem, for the automatic teansmission, but the shifting. Each time when there is a shift, greater forces act on the clutches than usual. Therefore, drive as evenly as possible on the highway, and prevent strong acceleration, then the automatic does not care.

 

[Mudsport96]

As all have said, keep it in third gear and let 'er sing. My 06 Z71 has 3.42 gears in it. So ASSUMING yours has them too.

55 in 3rd is 2060ish rpms
75 in OD is 1966ish rpms.

So if you ever have done Interstate driving at 75 you have already driven your rig at RPMS you will be doing towing. You will just be moving slower.

1. Fresh oil change
2. CHECK ALL fluids
3. If the atf is anything but pretty red, i would probably flush it.
4. Book on tape ( Jurassic Park is about 13 hours lol) as it will be a long drive, 26ish hours at 55 from big bend to Biddeford maine( dont know where you are going, but i picked Biddeford as i know where that is lol. )

 

[Stev1e]

...Fresh oil change and Trans service beforehand. Maybe even a diff service too if it's been awhile...

Good point on the differential. I'm sure it's been a time and a half, so I'll make sure that's taken care of. Had planned on the oil change and the transmission service, particularly since "the truck" (growing up, my folks had a '99 Tahoe and a series of sportier cars. Ergo, "the car," and "the truck." The '06 replaced the '99, but the '99 is still in the family, ticking away after 330k.) does a lot of sitting lately.

i see or hear the word germane and this is all i can think of lol...

Thank you.

...dont even consider running in 4th with that kinda weight behind the tahoe. You'll burn the 2-4 band up in short order then you are screwed and will only have 1st and 3rd gear...
...Grease your front end, ujoints if they arent sealed type and check coolant hoses for loose clamps and hose deterioration...

Well noted on the 2/4 band. I'm a glutton for good fuel economy, but I'll grit my teeth and keep it to 3rd rather than burning up a transmission for no point.
Will add those items to my list of services prior to heading out. May not end up passing the coolant inspection, but we'll find out in a few months, I suppose.

...Even if Dexron 6 can handle 239°F, I'd still be concerned if ATF temp got up that high...
...If you can have your pcm reprogrammed to improve towing durability, that can't hurt either...

Nice to have a number to 100% avoid, thank you.
In this case, I think "can" and "understands who to ask to do that" are different factors. Any recommendations where to start on that?

Look through your grill...

An excellent single-sentence tutorial; I do have a transmission cooler!

From my humble view, It is not the towing, that is the problem, for the automatic teansmission, but the shifting. Each time when there is a shift, greater forces act on the clutches than usual. Therefore, drive as evenly as possible on the highway, and prevent strong acceleration, then the automatic does not care.

Sometimes the most obvious information is the hardest to come up with on your own. 1. duh. 2. of course. 3. DUH. 4. Thank you, I honestly hadn't considered that. Than again, I've driven a lot of C4 transmissions (65 Ford 3-speed automatic), so I'm used to breathing wrong and the thing blowing up.

As all have said, keep it in third gear and let 'er sing. My 06 Z71 has 3.42 gears in it. So ASSUMING yours has them too...
...So if you ever have done Interstate driving at 75 you have already driven your rig at RPMS you will be doing towing. You will just be moving slower....
...4. Book on tape ( Jurassic Park is about 13 hours lol) as it will be a long drive, 26ish hours at 55 from big bend to Biddeford maine( dont know where you are going, but i picked Biddeford as i know where that is lol. )

I just did a 30-minute scramble trying to figure out what my gearing is, but unfortunately, with the glovebox having been replaced and today not being the day I'm going to jack my rear end up and watch the driveshaft rotate to calculate it, I can't advise what the gearing is... for now.
Another duh moment that is incredibly helpful to have said out loud by somebody else. Thank you.
I laughed a lot at #4. (Oakfield, which is 20 miles shy of Houlton. Basically I-95 from Portland to Canada lol)

 

[Marky Dissod]

Nice to have a number to 100% avoid, thank you.

Welcome.

In this case, I think "can" and "understands who to ask to do that" are different factors.
Any recommendations where to start on that?

My personal recommendation, from personal experience, is
pcmperformance.com
As mail order tuners go, he's among the best.
That said, fairly sure there are other talented pcm / ecm / tcm tuners to whom you can physically bring your vehicle so it can be more personally tuned.
I'm sure this or other forums will give you a few local suggestions.
You let your tuner know that you're towing a wee bit more than GM's suggested limit, and that you want Tow / Haul mode to be programmed to avoid 4th under, at least, 74MpH - a road speed you must never achieve while towing - and you're golden.

If you have electrical fans, the tuner will program them with heavy towing in mind.

 

[Mudsport96]

I laughed a lot at #4. (Oakfield, which is 20 miles shy of Houlton. Basically I-95 from Portland to Canada lol)

So a good bit further north. That's cool. Ive haven't been out there in a very long time. Got family in Biddeford so that's how I have an idea of where you are traveling. Long drive and massive weather change, going to the ice box zone, or you going back to Florida for the winter?

 

[JCODOHERTY]

Keep her in 3rd gear and don't be overly aggressive with the throttle. LS motors are rpm Champs and don't care running for extended hours like that. Fresh oil change and Trans service beforehand. Maybe even a diff service too if it's been awhile.

You'll have good airflow at 55-60 so temps won't be a problem. If you start creeping towards the 230 mark, you might want to slow down or give it a rest stop. Leave the truck running all the time for quick rest stops or fuel upside. Shutting off just heat soaks and cooks stuff.

Excellent answer

 

[SnowDrifter]

Excellent answer

If you need to park it for cooling, flip the a/c on

That will kick your efans on and pull air through the radiator. Else they will only activate based on coolant temp. Which flows through the radiator, and across the transmission's radiator-located heat-exchanger.

Hot coolant through rad (tstat open, cooling fan off) does a better job of warming transmission fluid than cooling it. Pull some cool air across both the external cooler, and the radiator (and in turn, cool fluid across the heat exchanger)

 

[Marky Dissod]

The distinction is crucial. SnowDrifter is absolutely right. Radiator sidetanks are NOT coolers.

Radiator sidetanks are Heat Exchangers.

 

[nonickatall]

The distinction is crucial. SnowDrifter is absolutely right. Radiator sidetanks are NOT coolers.

Radiator sidetanks are Heat Exchangers.

That is correct, in case of the automatic transmission, it should help to get the transmission fast on operating temperature, by exchange Temperatur with the engine coolant. There is not much cooling, except the temperature ist above water temperature. But the cooling surface is far too small to cool efficiently.

 

[03yukXL]

if you don’t have a trans cooler install one as others have suggested.

Obd2 scanner can read your trans temp from the internal sensor. May be worth the 15-20 bucks to get one. Mind works great!

Brakes. I would give them a once over.

 

[RobH]

My transmission went south on me during a trip from Texas to Florida to Pennsylvania and back to Texas in April. It became very apparent in South Carolina. I got a fluid flush which helped for a little while. I changed to driving at 2000 RPM at about 60 MPH on the interstates and nursed it home. I would have skipped Pennsylvania and come straight home except that my brother-in-law was going in for surgery and I wanted to see him.

Heat probably killed my stock 6L80E tranny's torque converter lockup clutch, known 6L80E failure mode. It began slipping, with engine RPM rising and falling as I went up and down hills on I-95. It probably sloughed off material which contaminated the rest of the tranny. Shifts became delayed and very abrupt. I would back off on the gas pedal going up hills to try to minimize slipping. This was with just me in the Tahoe and no trailer.

I'd try to keep the transmission temp below 200°. Pulling into a rest area and shutting down the engine and raising the hood allowed me to get the trans temp down from 195° to 155° in about thirty minutes while I ate lunch or walked around. When I got gas, I did the same thing. Raising the hood assisted convection cooling of the radiator, transmission oil cooler, engine, and tranny.

Your fans probably don't come on until 200°F or more engine temp. If you can get a tune to keep the fans running when engine coolant temps go above 180-190° that will help your engine and tranny survive. Their thermostats will use as much of the cooler coolant as needed to keep temps reasonable. Personally, I don't like to see engine temps higher than 200-210 and transmission temps higher than 180-190.

My replacement 6L80 has the factory service bulletin 158°F (70°C) thermal bypass valve. I don't know if your 4L60 has a thermal bypass valve/thermostat or not. An additional, bigger, inline transmission fluid cooler may help avoid a trip interruption, especially in August or May.

You might consider getting a Scan Gauge II. I've used the same one on three different vehicles. I always keep one of the four gauges on engine temp. One of the "XGauges" will display your transmission temp. It plugs into the OBDII diagnostic connecter under the dash.

www.scangauge.com Manual attached.

Good luck with your move.

 

[Marky Dissod]

MOST people think of some variant of 'more power' when they think of pcm / ecm & tcm tuning.
Power is NOT the most important thing addressed by a proper tune.
The most important things addressed by a tune improve the powertrain's longevity and durability.

1. Most obvious would be colder fan-on thresholds to lower the powertrain's operating temps.

GM prefers the motor oil and ATF hotter, for minimal friction possible, so you get 1 or 2MpG more.
If any underhood stuff needs servicing / replacing sooner / more often from the extra heat, oh well.
If you prefer it a bit cooler underhood, so you don't have to replace those coolant connections quite as often,
get tuned.

2. ...

 

[Marky Dissod]

2. Another thing more important than 'powah' is transmission tuning.
GM's OE 'Normal' shift table is written expressly to maximize a given vehicle's CAFE MpG score on a test that seldom resembles how even conservatively normal drivers drive in the real world.
Transmissions are commanded to upshift to top gear as soon as possible, and avoid downshifts unless the driver applies a whole lotta throttle, discouraging enthusiastic driving.
Since 1995, GM programs the torque converter clutch (TCC) to engage and disengage progressively, so that the driver and riders barely notice. The price is more TCC wear.

Proper transmission shift tuning reduces unnecessary upshifts and downshifts, which directly impacts transmission longevity and durability.
Locking and unlocking the TCC positively, extends the TCC's lifespan considerably, which ultimately delays rebuilds.

There's FAR much more to pcm / ecm & tcm tuning than the above.
Without going into more detail, hopefully the above will help the hesitant understand why a proper aftermarket tune will help a vehicle powertrain last longer and perform better than GM's OE calibration.

 

[Alex_M]

I've towed a lot with my high mileage Tahoe at and we'll above the rated tow capacity, albeit with a rebuilt trans. Here are a couple notes:

The advice to keep it in 3rd is paramount. Fuel is cheap compared to trans rebuild.

The factory engine temp gauge is not 100% accurate. Will still read ~200* until around 220* actual temp. Monitor engine temps on grades VIA OBD2. Otherwise, don't fear the RPM.

I just recommended against it in another thread, but for towing a TruCooler 40k is a nice tranny cooler that will replace your factory one with relative ease. For the cost of one on eBay, might be worth installing for the trip and going back to a smaller cooler for regular driving.

You should be fine at 70mph. I think my longest haul with a heavy load behind my Tahoe was Indianapolis to Bristol, VA with around 9,000-10,000#. My Tahoe has 3.73 gears and had 33" tires at the time, I maintained a happy 75 most of the trip. Remember, highway driving is what's easiest on a vehicle. Speed isn't the enemy, lots of shifting is (as mentioned).

Don't go overboard on maintenance before the trip. Oil change, grease the ball joints, make sure you've got gear oil in the rear end - sure. Tranny service is 50/50. Has it been done before? How long? If you have a filter/fluid change done, have them drop the valve body and make sure none of the check balls have beat their way into the separator plate, and put a shift kit in while you're in there and block off the PWM solenoid. Honestly though, if the trans was acting right I probably wouldn't touch it and just make sure it stays cool. Definitely do not have it flushed. Mostly make sure everything is working as it should and if it is don't mess with it just before a trip.

*If* you have a tune done, have them tune out the Torque Converter PWM. That's your #2 weak link that will take out the trans.