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I always tow in 3rd on my 4 speed automatic but with better gas milage available in overdrive I was wondering if anyone uses this 4th gear under tow with no long term problems?

Remember that overdrive is 1/1 or greater and unless the load is light or you are going downhill it could kill your gas mileage or overheat your trans.

BK, I think you should tow in overdrive with an automatic transmission. My reasoning is that your Mac trailer has surge brakes and in lower gears when you let off the gas your engine works as a break to slow your vehicle down and that braking action in turn causes your surge brakes to engage and you've in effect created a vicious circle of unnecessary braking action. When towing with surge brakes, the surge brakes stop the boat and your vehicle stops with its own brakes. When the motor in the tow vehicle lugs down due to load, the automatic trans will do its thing. I've always towed in overdrive with no problem! Terry

GMC recommends to tow in 3 not drive due to overheating the transmission. We've alway towed in 3rd and never had any complaints. Mileage isn't bad.

Jesse

The manuals for both my expedition and the tahoe before that, said not to tow in OD. I always just turn it off.

fwiw.. My chevy truck recommends non-OD for trailer pulling or large loads. I did install a transmission cooler.

That said...96% of the time I do not use OD. But if the road is dead flat or slightly downhill, I may put it in OD to keep the revs down a bit, but have to be careful that my speed doesn't get too high.

I think you are safer overall not using OD. The minor gas savings is insignificant compared to the cost of a transmission

Paul

My Dodge RAM 1500 book also says to diable overdrive when towing. Heck, I disable overdrive when going up or down hills when I'm NOT towing.

Looks like the consensus is, "Don't use overdrive when towing."

--Mark

Hello:
Another thing to remember is, when in overdrive, you are using the planetary gearset. This gear set is not able to withstand thousands of miles of extreme torque. It creates lots of heat and significant wear. In drive the entire cluster of gears and clutches is locked together rotating as a single mass which is very strong with only the input and output bearings loaded. In other words, drive has a significantly higher torque handling capacity than overdrive. Another consideration is the torque converter clutch may spend a lot of time disengaged because of the amount of throttle that has to be applied so the trans oil may overheat and breakdown. Trans failure follows soon after.
For those of you who have had success towing in overdrive, maybe your load was light enough but I suggest you smell the trans oil on the dipstick. If it smells any different than fresh trans oil, change it soon and discontinue the practice.

I agree with Don. While towing I have on a few occasions dropped it into overdrive. This was on smooth level pavement while already up to speed. If I needed to accelerate I manually shift to 3rd. I have also forgotten to run in 3rd and traveled as much as 10 miles or so before noticing.
My chevy truck manual says tow in 3rd not OD, but I'm pretty certain the Mac is right near the limit of safely being towed in overdrive. Especially at 55 mph on level ground.
I plan on installing a trans cooler, I already have it. My hope is once that is part of the system, I'll keep a close eye on trans temp, perhaps I'll even install a temp gage. Like Don says, keep a watch and a nose on the dip stick.
On a short drive, it's not worth worrying about gas mileage wise, on a long haul, it could add up.

On the half ton GMC I have D 3 2 1. I push a button on the end of the signal/wiper/dimmer stalk and a green light comes on indicating haul/tow. The motor revs up about the same as dropping down into 3rd.

I tow in D which is I assume overdrive. This is on flat Florida pavement. I travel just under 60mph, and with 4 lanes, it doesn't drive the truckers too buggy. On an overpass, the transmission will kick down into third unless I kick off the cruise and ease my speed on the incline.

I have never sensed any strain in this mode.

Don T's planetary explanation has me alarmed. I would think less revs, less heat. However, I'll check for the 'burnt cork' smell with the fluid.

All I know about transmissions is operating a 12 speed bicycle. If I don't change down on a hill my thighs begin to ache real bad.

Don T has it right - read your owner's manual and follow the instructions! You may not "see" or "hear" anything, and you may think lower revs = less stress, but few (if any) cars/trucks actually have the right instruments to thoroughly monitor the automatic transmission and tell you what is really going on down there.

A key point to remember is that the RPM you see on your dashboard is the speed of your engine, not your torque converter or transmission. Also, in some torque converters, overdrive means the torque converter is physically locked into a 1:1 metal-metal configuration, which means your engine has lost the "cushion" normally created by the fluid coupling in the torque converter - meaning any change in speed/load is immediately dumped on your engine and directly bears on this linkage in the converter. This system is designed to bear the weight of the vehicle but not necessarily a trailer or other large load - hence the manufacturers warning not to tow in overdrive. Not only is it hard on the relatively small planetary gear set(s) in the transmission, but it can be adding direct stress to the torque converter and via that, the engine's driveshaft and main bearings, etc.

For those who are interested or confused by Don's remarks, a good intro explanation of automatic transmissions is available at the link below. Incidentally, howstuffworks.com is great for all kinds of stuff that many of us don't actually understand

http://auto.howstuffworks.com/automatic ... ission.htm

- AndyS

The minor gas savings is insignificant compared to the cost of a transmission

I wouldn't be too fast in assuming you get better gas mileage in OD when towing. Certainly it is true when not towing, but once a greater load is put on the engine, you may actually get better mileage with the engine revving a bit higher.

I learned a hard lesson about towing in OD...
I used to trail a travel trailer with my F150. I just left the E4OD in overdrive. After a few hundred miles of this, I had to have the heads rebuilt because lugging the engine burned the valves bad, or so the dealer told me...

Dik...

For the record, my Toyota Sienna manual very clearly states *not* to tow anything in overdrive. I followed that advice when I towed my from New Mexico to Philadelphia and the car still runs nicely... and mileage was decent, considering I was towing +3400lbs.

I have a Tahoe. The Tahoe dealer said tow it in overdrive if the tranny does not hunt. I use overdrive until we hit a long grade and then take it out if it seems it might lug. I also have a transmission cooler.