hotpepperkid
Chino Hills CA
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Joined: 03/29/2002
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You ever notice when this question comes up its the gasers that cant or dont use OD and all the diesel truck use OD at all time except if the tranny hunts which mine never hunts.
hpk
2000 Ford F-350 SRW 4X4 PSD Jayco Super Lite 29.5RKS (31') 5th wheel 50 gal X-ferflow in the bed tank. Banks big exhaust and Stinger kit.
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K3WE
Missouri
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Joined: 05/24/2005
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1) Hot pepper kid- You ever notice the RPM range that a gas and diesel engine have? Think that has anything to do with it?
2) The answer to this is OP is BOTH the owners manual AND common sense. There was a time that "tow-haul mode" WAS to lock out high gear...and if you didn't, plan on a shorter transmission life. So you better know what the manual says.
Now, if it says OD is ok, I will kick, scream and yell that there are weight, speed and topogophy combinations where it is in the best intrest of comfort AND the transmission to lock out high gear- even if you have a wonderful automatic and the ok from the manual. Our two suburbans (one with a 3.42 and the other with a 4.10 would cycle back and forth between 3rd and 4th all day long through the perfectly flat Arkansas delta/ I-55 while pulling our 27 ft, 7000 lb trailer. It was in the best interest to lock it in 3rd on the flat lands and low hills. On some moderate hills, I could go downhill a while- it could stay in 4th and going up hill, it knew good and well it needed to be in 3rd....wonderful- but the flat highway and highway speeds- that was a sour spot, not a sweet spot. Then it made sense to lock in 3rd, and I'm sure there are other vehicles, trailers, speeds and topographies where you might want to do this!
So, I cast dispuraging comments for any comment here that does not acknowledge that there are two sides to the story.
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345jeep
Fort Worth, TX
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Joined: 09/10/2009
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A a gasser driver, I think there is a certain "feel" that one develops for when the computer's gear selection (in tow / haul mode) needs to be tweaked. With the Hemi 545RFE combo, the tranny will tend to want to lug the engine in high gear and I often intervene to prevent that lugging. I also intervene when in rolling hills to reduce shifting. In those situations, I will hold back a gear and turn 2,700 rpm @ 62 mph.
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MitchF150
NW
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How many gears does your tranny have?? If it's a 5 or 6 speed, I'd say that you can just let the trans/computer decide what gear it wants to be in, as there are some extras there!
If it's just a standard 4 speed, then you might find that running with OD off eliminates a lot of shifts during a 'normal' hwy run...
I don't believe that you will necessarily 'save' more fuel by using OD compared to only running in 1:1. In my case, when my truck goes into OD, I find I have to give it a tad bit more pedal to maintain speed (60-65 mph). If the road is flat and no head wind, it'll usually hold OD and speed okay, but that little bit of extra pedal to hold that speed basically nullifies any 'savings' in gas.... Why, because I'm simply dumping more fuel into the cylinders as opposed to running less pedal, and higher rpms, which the engine likes anyway (2500 rpms gets me about 62 mph in 1:1).. My engine has very little torque at the 1500 rpms it turns in OD going that speed....
I seem to get 9-10 mpgs no matter using OD or 100% in 1:1... Wear and tear on the engine?? Well, I've got over 200,000 miles on my rig now and will tow it anywhere and not feel the least bit concerned about it!
Just my thoughts on it...
Mitch
1997 F150 XLT, 4x4, SuperCab, ShortBox, 5.4, 3.55 gears, Prodigy, EAZ-Lift WD hitch, Autometer Water/Trans temp gauges, 200,000 miles (GVWR #6250 GCWR #12500)
2003 Prowler Lynx 722F (GVWR #5000)
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SoCalDesertRider
SanDiego, CA, USA
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In the F350 351/C6, I never use overdrive at all, towing or not towing, on road or off, good weather or bad.
On the E350 6.0L/Torqshift, we use overdrive when not towing and turn it of when towing in the grades. On the flat we use the overdrive.
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RCMAN46
NorthWest
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colochoclab wrote:I really believe it depends greatly on the mfg and the specific tranny you have in the vehicle.
Nowadays we have 4, 5, and 6 speed automatic transmissions. some with an OD switch, and/or tow haul buttons, some without. It's not realistic to compare an Allison 6 speed against a "typical" 4 speed auto of yore. What may be appropriate for one system is harmfull to another.
I guess what I am trying to say, is first: Follow what your particular manufacturer recommends, and sencond, do what works best for you.
In my particular situation, I tow my 5 speed auto tranny in 4th with the tow/haul "on". I accidently left it in 5th once and my tranny temps went up dramaically!
Good luck!
-Lab It sounds like your transmission does not lock the torque converter in OD. I beleive the GM's do lock if Tow Haul is selected. That is what Tow Haul was all about with the GM's.
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92DakotaHD
Indiana
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In my Tahoe Tow/Haul only moves the shift points. It holds out 2nd for a long time (up to 55-60 mph at times). I chose to run it in 3rd, no OD. It's not revving out really there either.
1992 Dakota 2WD 5.9L V8 (NOT Stock)
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Steveo35
Ohio
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Joined: 06/16/2009
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07 Tundra Crewmax, 5.7L V8, towing a 5600# HTT.
I use tow/haul and OD, just listen to the engine and watch the tach. I've had no problems but lock the cruse at 60.
My BIL towed a 25" fiver with a GMC 1500 and Ford F250 V10 Triton. He always used the CC.
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LIKE2BUILD
Mt. Zion, IL
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Lonnie wrote:I have a '07 GMC Sierra with the 5.3L engine and 3.42 axle and tow package......The trailer we got weights in around 6800-6900 loaded so I am at the upper end of weight for truck.....My question is it ok to drive in overdrive or will that burn up the transmission.
Towing in OD will not necessarily burn up the transmission. Towing with the torque converter unlocked for extended periods, or frequent shifting will reduce the life of the tranny.
With 3.42 gears and towing nearly 7,000#, I'll bet your tranny will probably spend a fair amount of time in 3 (direct) regardless if you have D (overdrive) selected. I believe GM says you're okay to tow in OD, but if you experience frequent shifting (gear hunting) you need to manually shift into Drive (3) to keep the torque converter locked up and reduce heat.
You might consider getting a Scan Gauge II and set it up to monitor your transmission temperature since GM does not include a trans temp indicator in the gauge cluster. With the Scan Gauge II you'll be able to watch the tranny temps and if they begin creeping too high you can down shift and attempt to lower it.
KJ
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Jerome B.
Madison, SD
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I am not a GM driver. It would seem with that relatively small engine, an OD trans with 3:42 gears, you would be lugging the engine causing the transmission to "hunt" between OD and direct. This would cause undo wear on the trans. Those 3:42 gears would be ideal for solo cruising.
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