Help Sizing Trailer to purchase

[HammerWerf]

Hi Everybody,

New guy here. Next summer we are planning a lengthly trip pulling a travel trailer.

The tow vehicle is a 1999 GMC Suburban LS 4X4 6.5TD w/ 4L80E and 4.10, 8600 gvw. We made sure to order the trailering package to get the heavy duty everything.

The truck is stock. We are looking at reliability, so any ideas here will be helpful.

The original Load range E Firestones were replaced with load range D Goodyears. We can change back to load range E tires.

We have looked at the local RV dealers, and have seen that the trailers GVW tend to cluster around 7800 lbs and 10000 lbs. The owners manual lists a towable weight of 7500 lbs over base vehicle. I weighed the suburban with my family and a full tank of fuel, and came in at 7400 lbs. Base vehicle is far less than this, but how much less?

What weight range trailers should we be looking at for this truck? From the signature tags, ya'll know an awfull lot about towing with the 6.5TD. We are looking up in the 24 - 32 foot range. I know that being conservative can be a good thing, but a trailer in the 4500 lb range sounds pretty small. I've also seen 32 footers being towed by Tahoe type vehicles.

This trip will take us through mountain passes and towns. Without an intercooler, what type of performance can we expect at mountain elevation?

Any ideas are appreciated. Thanks for your help.

HammerWerf

[tanker]

Hammerwerf, welcome to The Diesel Page. A few things to consider is #1 safety, #2 reliability. Your suburban should weigh in at about 6500 lbs, and GM would want you to stay around a 6000lb trailer with the K-2500 6.5TD W/3:73 axle. Going over this and you are pushing the envelope somewhat. You said you do not have an intercooler, so you do need gauges, (pyrometer-boost) at the very least. Towing in the mountains, with summer heat is hard on any rig, and the heavier the combination, plus the elevation, and the % grades all add to these issues. If you want to tow heavy, and through the mountains in the summer, you should look at several modifications to keep things cool. #1 would be an exhaust system that is free flowing, a free flowing airfilter, an intercooler, an additional transmission cooler, a 12-V fan type cooler works best. Transmission heat is generated when the torque converter is unlocked and pulling a heavy load up a mountain. This heat is then transfered to the radiator, which adds to engine heat, and heat can and will kill almost anything. My last trailer was a 30' Jayco, and I had a GCW of just under 14000lbs (truck & trailer) and I did real well with this combination here on the East Coast as well as making several trips across the Rockies. Keeping an eye on my gauges for any excessive EGT's, coolant temps, and transmission temps. I have done many modifications to help eliminate heat, and I still have to watch the gauges.
We now purchased a new Holiday Rambler 32FKD with 2 slides and a 11,500lb gross weight rating, and now my GCW is 18,220lbs (truck & trailer). I have not had it out into the higher elevations of the Rockies yet, but the 6.5 knows something heavy is back there. I am way over what GM would want, but with the many modifications that I have done, from engine to rear hitch, it does a decent job.
Plan what you are going to do, and plan on modifications if you are going over what GM has rated your truck. For stability go with the E-rated tires with proper inflation for the load. Wish you well with your new rig, and use caution. ;)

[rjschoolcraft]

Hi, welcome aboard.

I tow a 31' (32' in actual measurement) 1999 Wilderness 31G travel trailer with my Suburban. Over the last year I have made several incremental modifications to improve performance; however, I towed in stock form for more than two years prior to that, including a trip to Yellowstone National Park. My trailer weighs in at a little over 8,000 lb. loaded for a combined, loaded weight of a little over 16,300 lb. My Suburban has 4.10 gears, as does yours. In stock form, the Suburban did a pretty good job towing anywhere east of the Mississippi River. The only problem I had here was running hot...but yours already has all of the cooling upgrades that I added built right in.

Out west, I really had to watch the gages to keep things in check, especially coolant temp: but you shouldn't have a problem with the new cooling system. At the very least you should have boost and egt gages (as tanker said) or you could let combustion temperatures get out of control on a heavy climb. In stock form, mine performed well (aside from the coolant temperature issues) out west except on the steepest grades at the highest elevations. Two places that made me really slow down were climbing the Bighorn Mountains in northern Wyoming (west to east) and climbing out of Denver to the Continental Divide in Colorado. Most everywhere else, the truck did fine. Yours will actually probably do better because of the cooling features and better programming from the factory. Yours should be rated at 195 HP and 430 lb-ft while mine was rated at 190 HP and 385 lb-ft. That is more significant than it looks.

See my post on the 6.5 forum "Significant improvement in towing performance" for more information on how my rig does now with modifications. Again, I had to do significant changes to the cooling system on mine just to match what you bought new with yours.

Aside from the power issues that have now been corrected with mine, the Suburban is a wonderful tow vehicle. I have four children, so we need the seating capacity. The Suburban handles the trailer well in all weather conditions... including a lake effect snow storm south of Buffalo, NY last winter where six inches of snow was on the ground with more falling rapidly. Make sure you have a good weight distributing hitch that is set up properly and a good brake controller that applies effort proportionally to the truck brakes. I use a Hays-Lemmertz controller and really like it.

I would also recommend installing load range E tires as tanker did. The heavier sidewalls and inflation pressure give you better stability.

Good luck.

[Phil Holmen]

Hammerwerf, in addition to the posts from Tanker and Ronnijoe, I would recommend that you also take a good look at your cooling system, inside and out. First, with a cold engine, remove the rad-cap and see if anything has built up on the bottom of the cap, if so may need a flush. Next, stick your finger into the tank and feel as much of the tank as you can if your finger comes out clean you should be good but if it is dirty you also need a flush. Second, remove your upper fan shroud, and try to look through towards the front, if you can only see a little bit of light your radiator will need washed.

[Heartbeat Hauler]

I would add one more thing to consider. Towing is not just about pulling the trailer, it also includes stopping the trailer. Going over the recommended tow rating puts additional strain on the tow vehicle's brakes. There is some reserve capacity built in from the factory, but not something I'd wanna test rollin' down a 6% grade with loved ones aboard.
Back to durability enhancements: adding an aluminum deep pan to the tranny can go along way in extending tranny life. These pans have additional fluid capacity and the aluminum affords additinal fluid cooling.
Good Luck,
JP

[jspringator]

I think I have the same truck as you. As far as cooling goes, make sure the radiator is free from debris. You may have to loosen the oil and transmission coolers to clean behind them. Heath sells an improved fan clutch that I have. Mine has a build date of 8-99, and I had to use the post 99 fan clutch. I use synthetic transmission fluid and rear differential oil, and change it regularly. This may prevent you from having to add expensive finned covers to assist in cooling. I have an Amsoil dual bypass oil filter, which extends change intervals to 6000 miles, with synthetic oil. I have the Kennedy boost controller and love it. Of course, you need the boost and pyro guages to use it effectively. Don't forget about the trailer light draw across your headlight switch. I have relays from Kennedy (headlights) and Reece (trailer lights) to aid in headlight switch longevity. I did a poor mans exhaust, with a Heath downpipe, drilled cat, and flow through muffler. I had the shop cut off and remove the muffler behind the cat, then, someone magically drilled the guts out of it! I would love to have an intercooler, but my truck does pretty well without it. I am trailering to the Keys after christmas, and have confidence my truck with 150,000 miles will make it there and back!

[Turbine Doc]

On the stopping front you might want to take a look at slotted or drilled rotors and hi performance pads, has made a huge difference in my stopping and comfort when I have to move 12K of tractor, trailer and impliments.

[HammerWerf]

Folks,

Thanks for the replies and guidance. I am putting together a plan for the upgrades to help us have a successful trip.

RonnieJoe, The TorqLoc looks like a product that can help us out both when trailering and going up into the Sierra's. Thanks for the writeup.

James, enjoy your trip. Would like to hear how the mule pulled and handled. Thanks for the tip on using a trailer light relay for additional protection.

Hammerwerf