Towing in drive - turning 2400 rpm @ 55 mph

[m-keith]

Apologies in advance as I know that this has been a much discussed topic. However, I'm having trouble finding info in the archives.

I towed with my Suburban for the first time this past weekend. I brought home a boat that I just bought. I towed in drive, as GM recommends, but I was disappointed to find that it turned about 2400 rpm's at 55 mph. I'm in the Houston/Galveston area, & the terrain is flat. I figure the boat/motor/trailer combo weighs about 5500 lbs. The boat's trailer needs work; so I had planned to take it slow that day. Once I start trailering the boat regularly, I'd like to be able to maintain a 65 mph freeway speed. However, I'm afraid that I'd be revving the motor too high; 2400 rpm's already seems a bit on the high side.

The vehicle is a '95 Suburban C2500, 6.5TD, 4L80E, 4:10, & stock size tires. I bought it wholesale back in Feb, & I don't know its history. According to the RPO codes, it originally came with a 3.73. However, according to the speeds vs. rpm's that I see in unloaded driving, it seems to have a 4.10 per the gearing spreadsheet. I know that I have the correct alternator pulley, & the speedo seems accurate relative to the pace of traffic. Also, I've verified that my torque converter locks in unloaded driving.

Are the engine speeds I'm seeing considered acceptable? Any suggestions would be appreciated. I've thought about going to a 3.43, but I'm concerned that it may not be able to pull my boat with that ratio. I'm leery of towing in OD, but I just might have to try it.

I'm also wondering if I'm getting some slippage from the torque converter when I'm towing. I haven't had a chance to put it to the gearing chart, but 2400 rpm's at 55 seems a bit high, even for a 4.10 towing in drive. Is drive a 1 to 1 gear?

Thanks,

[WAPATI]

I have a 96 C2500 HO with the 97 upgrades 4L80E and 4:10.

The owners manual says to tow with over drive selected.

I tow a 30' fifth wheel in overdrive. It has the standard tires. Can't remember size numbers.

At 2500 and cruise controll on in overdrive it runs little over 65.

I have found that if I'm pulling in over drive and start to pull a hill that is fairley steep the transmission will shift down one gear and the torgue convertor will stay locked up.

If you don't have the 97 upgrades you probably should install them and if you don't have gauges you need them to make sure the tranmission oil doesn't over heat.

Hope this helps.

[jspringator]

Are you sure it is going into lockup?

[jeffreydmet]

I have a '99 K3500 4x4 Dually Crew Cab 4E80L trans. I have changed my gearing and tires to give about 20% over stock. I also pull in OD at least the speed limit (75 in most western states). I run almost 2100rpm at 70mph. My payload is 4000lb trailer and about 3000lb in the truck. It has no problem on flat ground. In the mountains I have to shift down. Sometimes I have heat problems if I push it to hard but I think that may be another problem. I haven't however seen any significant mileage increases after changing the gearing.

[Johnny B.]

I towed my travel trailer to western Wyoming twice in the past two years. I use OD except when pulling on a grade I usually shift down to keep my rpm's up and then settle to about 2200 in 3rd at about 52 mph. I have found that I pull grades best at about 2200 rpm's. I used to watch my trans. temp gauge and engine temp religiously. I rarely get my trans temp above 200F in the pan. My engine did get to about 265F two years ago I80 east bound east of Laramie Wy. This past year I managed to keep the engine at no higher than 245. My trans temp maxed at 230 near the summit.

A couple of weeks ago I added the 97 cooling mods and can't wait to tow with it. Today I just got my new trans cooler on Ebay $25 GM OEM plus $9 shipping. I plan on adding it in line with my current trans cooler, it can't hurt for $35.

I use OD al the time while towing or I would pretty much be limited to 55 mph while towing. Some people say that your trans. temp runs hotter in OD, I beg to differ. I usually run 65-70 mph on interstates around 2800-2900 rpm's and get just over 8 mpg towing a 7000 lb. 30' travel trailer. I get just over 9 mpg towing at 55 mph.

The only difference that I've notice between towing 55 mph in OD and 65 mph in OD is higher engine temps and decreased mgg at 65.

I use Meijer store brand trans fluid when I vhange it once a year. I thought about synthetic, but I keep thinking about it.

You should be fine with the rpm's you mentioned.

[moondoggie]

Good Day!

My 95 pickup: 4.10 gears, 4% taller tires (LT245/75R16 is std, I have LT235/85R16

[JCM5]

M-Keith

As a long time diesel owner, the cevy 6.5 reacts more like a gas engine then a diesel. Typical diesels have a strong low end pull. These 6.5 have a strong pull around 2600rpm.

I pull ~8000lbs and as the same as you, I was worried about the hi revs. I would love to have a consistent pull at 2000, but thats not the case with these 6.5. If you have the cooling upgrades, then you can run 2800 rpm all day long with no issues at this weight. If you do not, dont monitor your RPM but your coolant gauge, run as fast as you can with out going over ~ 240. Anything over this a power starts to drop fast.

Run in OD, the 4L80 - E or not has a higher torque rating then the 6.5, you cant hurt it, unless you over rev, then I think you would mosty likely damage the engine first.

Changing fluids? 1 time every year is more then enough, I change mine based on trip mileage and were I plan on traveling. All flat ground, then run for 50K - hills then I run 30K. Also it is important not to exceed 200F on trans temp for any maintaind lenghts. With the proper coolers you can run below 150F at 90 degree weather. I do except in city traffic then I will see 180-200.

Hope this helps, forget RPM and watch temperatures, this is a diesel.

[rjschoolcraft]

I regularly tow with a gross combined weight of over 16,300 lbs in OD with my 95 Suburban 6.5 and 4L80E. I have put over 120,000 miles on the truck with a total of 175,000. Roughly 60,000 of my miles are towing miles. I know that the previous owner towed with it too. As previously said, I wouldn't worry about the revs your reporting, but your fuel mileage will be much better in OD.

[Kidd]

I always tow in OD with my 98 K23500 dually. I have grossed as high as 41,000 lbs. The 6.5 seems happiest at about 1800 to 2200 rpm. Max torque is at 1800 for my truck. Don't have any mods, but so far everything seems fine as long as I keep the rpm in this range. Truck has been 100% reliable.
Now that I have stated that, it will probably fall apart tomorrow. smile.gif

K.D.

[m-keith]

Thanks for all the input. Assuming that drive is a direct drive gear, the rpm's I was seeing were correct; so I'm not getting any slippage. That's a relief.

Didn't have any overheating problems, & I kept a close eye on the temp gauge. I don't have the cooling system updates, but they're near the top of the very long to-do list.

I need to pull it again this Saturday to have the trailer looked at. I'll try towing in OD. I figured it'd be OK, but it's against my nature to go against the manufacturer's recommendations.

Based on some of the comments regarding the 6.5's powerband, I'm thinking I should go to a 3.73 instead of a 3.43 as I had originally planned.

[Phil Holmen]

My truck has 3.73 gears installed, factory it came with the 245/75r16s but I have 285/75r16 and recalibrated my speedo with the use of a gps and my vssb is now directly out of a 98 with 3.42 and 245/75 r16 so I feel that is what I would effectively have for a ratio. I tow a 25ft fifth wheel on occation and don't have any trouble towing in OD on flat or moderate hills, I slow on the hills slightly and once it gears down I downshift it manually to keep it from hunting till i reach the summit. My truck and trailer combined weight is 13,500lbs. Just use common sense, if you work it drop a gear and slow down a bit...and keep an eye on your gauges...just my $0.02 worth...if anyone disagrees please feel free to pick at my statements... smile.gif smile.gif

[GMCHORSHAM]

M-Keith, My truck pulls 4500lbs in O/D the MPH is
approx 60mph @2400rpm. The axel is 4:10, fuel ranges from 13-15 mpg while towing, however the
varience is dependant on the wind conditions and
how hard I accellerate. The one thing that I have
discovered when driving my truck loaded or unloaded, mpg is a consequence of how heavy your foot is, anyway the RPM you mentioned sound ok to me.
Have Fun, Safely.
Rod.

[moondoggie]

Good Day!

If your Owner's Manual says "don't tow in OD," it's probably because the previous tranny (700R4) was junk compared to the 4L80-E. A 700R4 can be built to take pretty heavy work, but this was never done by GM, only savvy rebuilders. I've been told your 4L80-E is essentially a T400 with OD & lockup added.

Blessings!

Brian Johnson, #5044

[Kollin Syverson]

Not to raise any feathers, but out of curiosity, I went and checked my owners manual in my truck, which has a 5 speed manual. Want to know what it says? DO NOT TOW in OD. and this is with a manual tranny. Keep in mind mine is a 1994, they may have changed their minds in later years. Of course, like the rest of you, I do tow in OD. Go figure.

[GMCHORSHAM]

M.Keith, Kollin Syverson.
I have read similar articles about towing, they
appear to be an older style O/D gearbox.
My theory is that the older style O/D's were designed as a fuel misser gear, and as such were not strong enough to consistently handle the additional loads placed on them, by towing.
The O/D's in Manual gearboxes as well as Autos seem to be made adiquate enough to handle towing stresses, these days.
This isn't qualified info, just my theory, which could be possibly dumped by some more knowledgable
subscriber on TDP.
Have Fun, Safely.
Rod.

[Kidd]

GMCHORSHAM.. you got it, the older gearboxes couldn't handle the torque.. my brother took the box out of his truck towing a 24 foot trailer.

I wish GM had stuck with their policy of using the manual boxes out of the bigger trucks in their pickups.. no way you could hurt those babies.

K.D.

[pgoldstein]

For what it's worth, I tow a 6000# trailer behind my 97 K3500 crew cab with a 4L80E. My total gross is about 13500#. I have 4:10 gears and tires that are 2" taller than stock. This combo gives me about 70 mph @ 2300 rpm in OD. I am towing in Kentucky where no roads are flat. My truck frequently downshifts on hills but then pulls fine. My converter will stay locked down to about 40 mph. On 90 degree days my water temp never gets over about 210.
Happy towing in OD.

[richard7]

On my 2001 owner's manual, it says:

" You should use third (3) (or, as you need to, a lower gear) when towing a trailer. Operating your vehicule in third (3) when towing a trailer will minimize heat buildup and extend the life of your transmission."

But the reality is that heat buildup will happen if the transmission is frequently going from 4 to 3 and 3 to 4 (hunting), and, when the lock-up is not engaged. If it happens, to prevent the down-shifting and up-shifting situation, it is a must to leave it in 3rd.

Driving in 4th (OD) with the lock-up engaged in a stable situation does not make your transmission to overheat at all. In fact, it keeps it from getting hot, and the engine and your fuel bills like it too.

[britannic]

285/75R16 tires, 700R4 in OD with 4.56 diff gives me 1960rpm (approx.) @ 60mph, but the best rpm for me to tow is at 2500rpm and above, so I wired my 700R4 to lock up in 3rd (2nd as well, just in case :D ), 'coz the CHP don't like nasty looking military CUCV Chevy trucks hauling 7000lbs at 75mph plus with the turbo in full scream :D :cool: .

As soon as the transmission locks, the temps fall from 160F to 110F (I have 2 tranny cooler radiators in series totaling 43,000lbs worth of heat exchange).

Engine coolant temps have risen on heavy grades, but never above the middle of the temp. gauge, it's usually pegged at 1/4.

The Allison in my Duramax runs hotter @ 200F under the same loads and unloaded up grades, but out on the freeway, it drops to 130-160F.

[matts]

2400RPM's seem alittle high for 55mph,get that thing into OD, 4th gear.

My truck routinely pulls a complete drag race operation gross combined weight of 24000lbs. We pull mostly highway in the northeast, never over 210 on the coolant, and never over 1000 on the EGT. Always in OD, (real men are confident that their transmissons will select the proper gear! LOL)I'll shift it to 3rd on a long downhill to prevent riding the brakes. I run mostly around 65mph, up to 75mph where permissable. Engine RPM is generally around 2350, up to 2800 on a hard pull.

Good luck to ya...

[SFD]

I am towing about 7500lbs. I have done the exhaust upgrades, K&N filter and Bigger fan and fan clutch. I notice black exhaust smoke when towing. Mostly happens if truck seems to be lugging up a grade and the like. Is this normal?

[britannic]

Originally posted by SFD:
I am towing about 7500lbs. I have done the exhaust upgrades, K&N filter and Bigger fan and fan clutch. I notice black exhaust smoke when towing. Mostly happens if truck seems to be lugging up a grade and the like. Is this normal? How much boost are you making?

If the engine's lugging, it probably can't make enough boost for the amount of fuel injected, change down to the next gear and get the revs up, which should clean up the smoke.

[rjschoolcraft]

Mine used to smoke like that too. The injection pump was replaced under warranty and the problem was cured.