Towing Mods

I just passed 238k miles on my 2002 Z-66. I've towed with it for 8-1/2 years beginning with my race car trailer (6800 lbs.) to my current travel trailer (5800  lbs.) I've towed tailors for over 40 years and my Avalanche has out performed any other tow vehicle I've used. With that said I have made several mods to the Avy for towing over the my ownership which greatly improved it's performance. By the way the truck is still far from being worn out. I plan on replacing the engine at 300k and to continue towing with it. It came from the factory with a 5.3 engine and 3.70 rear ratio and still has both. It was obvious up front that the factory cooling was marginal so I replaced the radiator with an all aluminum unit (end tanks are AL not plastic) I also installed a 26000 lb plate type trans cooler, dual electric fans with adjustable thermostatic switch and 180 thermostat. I put a switch on the fans and only use both when towing. Cooling problems solved. Next suspension mods: installed air lift airbags (run 20 psi when towing 8 empty), boxed in rear lower control arms with 1/8 thick 18 long steel flat (stop short of bushing), next I fabbed a new panhard bar for the rear using 1 inch ID schedule 40 round tubing with 3/4 rod ends at each end (huge difference even when not towing). Pretty much covers my mods for towing, none very expensive but worth the effort. I'm sure someone's gonna ask about trannys. The original was rebuilt 2 times (clutches only) before a thrust bearing failed recently. I didn't have time to rebuild so I bought a used trans out of a local yard, tranny came out of a 2007 Suburban and performs much better than the original ever did. Kinda curious about what GM did to the tranny (4L60E) over the years. Much better down shifts. Engine is untouched other than new O2 sensors every 100K and new knock sensors at 180K. Last summer I towed 6800 miles at 228K engine used one pint of oil. I've towed across the Rockies 4 times with this truck with no issues. The truck has only let me down once, a fuel pump failed on the road at 140k. One other key point when climbing mountains or big hills I make sure the rpm never drops below 3000, even if I have to manually downshift as the 5.3 in pretty anemic below 3000 rom. Hope this helps others. Oh by the way love this truck  Also forgot to mention that I changed the differential oil to 140 wt. synthetic.

Super stuff. Thanks for the Info 

Forgot: one more item. I've owned two trucks with 5.3 engines and both seemed to develope piston slap on startup at around 140k. I found that by added another pint of oil after the dip stick reads full pretty much eliminates the problem. I think the oil pump is slow to pick up prime at higher mileage. Never experienced a downside to this remedy.

Well put together towing bible. 

I tow with a lifted Av.  First off - the auxiliary trans cooler helps immensely. By the way, I tow in the mountains here in Colorado.  Anywhere from 6600 ft (home base) to 13,000 ft elevation.
Travel trailer is 30 ft; loaded it's not incredibly heavy at 6200 lbs.
I have a Derale  aux cooler with a 750 cfm fan on a dash switch.  Awesome mod. I've yet to exceed 214 degrees trans temp when towing after the mod...going up mountains (reading the diablosport trinity monitoring feature)

I currently run 4.10 gears, but I admit the tranny does hunt for gears when towing.  June 3rd begins the 4.88 gearing. That will help.  I don't push it too hard either. Never in a race when towing.

The rear control arm(s) upgrade to Spohn Performance helped too. I noticed stability right away with this mod.

Darn good topic here and honestly what pushed me to most of the mods after lifting the Av. I still needed to tow!!  Love the 5.3 as a tough little workhorse.  Mine gets forced induction soon with a Magnacharger Radix kit. 

Break upgrades and pitman/idler arm braces (on lifted Avs) for added safety/stability are good mods too.

My $0.02

The original trans seemed to hunt between over drive and drive when towing as you mentioned. For some reason the 2007 trans doesn't do this, not sure why since the computer is the original.

Junkyard- You seem to have done everything you can to make your Av into a tow beast. I think all of your mods are great except one: I would NOT run the oil one quart over spec. I think this may cause oil foaming on start up. However, the splashing of the oil has cured the piston slap by coating the cylinder walls, which in my opinion is no big deal any way.

You are correct in changing the radiator and putting a 180 tstat in. I did the latter on mine. GM specs on the low end for cooling, why i dont know.

I run Mobil 1 10-30 year round and this helps keep my temps from going over 200 when towing with the AC on. I also installed a Mag tech rear diff cover to cool my diff fluid.

The most important thing to do is to TOW AT SAFE SPEEDS. The poeple that fly by me at 80 with a camper behind them are the ones I see in the ditch 20 miles later.

Be safe out there everyone 

Avalon

Been running 1 pint over full for many years, no issues, very familiar with oil foaming I used to race cars and built many engines which ran up to 9000 rpm. In those cases I ran 1 quart under full, but of course also used windage trays, crank scrapers, and accumulators.

Well 1 quart may do it but not 2...

Avalon

Note I said 1 pint, agree with you on running a full quart over full.

avalonandl said:

Junkyard- You seem to have done everything you can to make your Av into a tow beast. I think all of your mods are great except one: I would NOT run the oil one quart over spec. I think this may cause oil foaming on start up. However, the splashing of the oil has cured the piston slap by coating the cylinder walls, which in my opinion is no big deal any way.

You are correct in changing the radiator and putting a 180 tstat in. I did the latter on mine. GM specs on the low end for cooling, why i dont know.

I run Mobil 1 10-30 year round and this helps keep my temps from going over 200 when towing with the AC on. I also installed a Mag tech rear diff cover to cool my diff fluid.

The most important thing to do is to TOW AT SAFE SPEEDS. The poeple that fly by me at 80 with a camper behind them are the ones I see in the ditch 20 miles later.

Be safe out there everyone 

Avalon

Click to expand...

  Is that 200 on the engine or tany? My standard engine temp is 100 C (212F). This is normal operation winter , summer or tow  - no matter what I tow, or external temp. It hasn't moved ever even 1 degree no matter what - that is with Factory tow package. Last 3 avy's all the same. Just trying to benchmark.

My engine temp typically runs about 195 except when towing long 6-8% grades. Have actually seen 230 when climbing Dead Mans Pass or Big Horn Mountains in Wyoming. Big Horn Mountains have been the toughest climb I've experienced, if I remember the climb was 40 + miles. My trans temp light actually came on 1/2 way up and had to pull over for about 10 mins only time it's ever happened.

I think you put out some great tips junkyarddog specially the tranny cooler with a fan on it.
The tranny is OK as long as it does not go over 230.

BTW avalonandl tows a weee bit more than most folks

Bassman Z71 yes he was talking about his engine temp not tranny.

Great info. My Av is just beginning it's towing career. I hope it lasts like yours has. My mods are just finally complete:

- Magnacharger with tune
- Corsa Touring
- New auto ride shocks all around
- EBC slotted and dimpled rotors
- EBC yellow stuff pads
- B&M Transmission cooler mounted behind license plate holder (no fan needed)
- Curt 14080 hitch
- Prodigy p2 brake controller
- wired in a trailer backup cam

So far it's a beast. I wish I had the 6 speed though

Towing about 11,000 lbs. Engine temp and Trans are remarkably consistent at about 200 and 210 resp.

Going to add another item. Putting on a new set of tires Monday. Third set of Hercules Terra Track, got 65k miles on the last 2 sets, no issues, have worked well for towing and very smooth ride.

Junkyarddog:
I'm interested in the panhard bar you fabbed.  I got a new rear differential cover but the clearance with the panhard bar is to close so I want to fab/buy one to clear.  Maybe post here a pic or two or do a writeup.
Appreciate it.
Mr.Jay