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Old 01-06-2010, 01:12 PM   #1
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Why shouldn't I use overdrive?

It's been a while since my last dumb beginner's question, so here goes. My tow vehicle is a 2005 Ford F-150 with a 5.4L V-8, with a tow rating or 8000 pounds. My trailer has an empty weight of 5300 and max weight of 7300 pounds. (I know this is not the optimum tow vehicle for this size trailer, but when I bought the truck, I had no idea I would someday be needing it to tow a travel trailer.) I have read that I should disable overdrive when towing a trailer, and Ford has even put a handy little button on the console to accomplish this. My owner's manual just has a brief mention that I should do it, but doesn't give any further explanation. What I'm wondering though is why is this necessary? Would it damage the transmission otherwise, or what?
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Old 01-06-2010, 01:19 PM   #2
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I have a F250 and a 5.4 Triton. My trailer weighs 4500#. I use overdrive for towing 95% of the time, occassionally switching off the overdrive on long steep hills when I don't want the tranny frequently switching in and out of the high gear. It feels like the most efficient use of the drive train to me. Somebody correct me if I am wrong.
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Old 01-06-2010, 01:25 PM   #3
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We have a 2008 Tundra that has a "tow/haul mode" switch for the same purpose. However, like you guys, we leave it turned off on the flats; and only turn it on in the mountains when we need engine braking, or the transmissions starts hunting (can't seem to find a good gear and stay in it).

It is supposed to reduce engine lugging, but I think with the new electronic controlled engines and transmissions, that it is best to just let the electronics do their thing, and ignore what the engine and transmission is doing (in most cases).
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Old 01-06-2010, 01:56 PM   #4
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Background:

1990 Ford F-150 (Overhauled) 302 cu. in. engine, stock transmission (very high speed 4th gear), 06 Bambi 16 (3460 lbs. loaded), full timing (except this winter), just the 2 of us. I only use 4th gear down wind or down hill, 3rd gear 99% of the time.

We also only drive 60ish on busy roads (where others can pass easily), faster on roads where passing is harder, if we can (retired, what's the hurry?).

Someone on this forum had what was a great idea in my mind to determine which gear to use. Get the rig up to a steady highway speed while on the level. Note the position of your foot on the gas pedal. Now, change to the other gear and carefully keep the speed the same and note if you need to push down or let up on the pedal. The position of the pedal is a rough indication of the power needed and gas being used to keep the rig going at that speed. Use the furthest "up" position. Also, usually the further down the pedal is, the harder it is on the engine and gas mileage.

Our bottom line? Slow down, use 3rd gear mostly, use 4th when light. I also keep the RPM at or above 2500; seems like less than that and the engine is struggling too much. Also, slow down, or did I mention that?

Using this method we get around 11.5 MPG (with the trailer), and about 18 without; plus, I expect the engine to last longer.

Happy trails!
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Old 01-06-2010, 02:03 PM   #5
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I use overdrive unless we're pulling up a long hill. Haven't had any problems that way yet. 1995 E-150 with 351 V8.
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Old 01-06-2010, 02:08 PM   #6
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I have always wondered this myself. A certain retired professional truck driver of this forum can explain it better, but I believe he never uses overdrive.

To me, the engine just sounds like its running easier in overdrive. But, consider the cost. If the engine is running easier, the tranny is working harder. Especially in hills. Going flat, I still don't see a problem. (Rumor has it a certain Durango was spotted doing 90 with trailer in tow.)

In the hills, You can almost feel the tranny getting kicked when it shifts in and out of gear if you are using overdrive. I now understand that it is safer (and less expensive) to tax the engine. I was told "the overdrive gear is the weakest gear".

Just my non-mechanical knowing opinion!
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Old 01-06-2010, 02:14 PM   #7
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Quote:
Originally Posted by mddsmith View Post
My tow vehicle is a 2005 Ford F-150 with a 5.4L V-8, with a tow rating or 8000 pounds. My trailer has an empty weight of 5300 and max weight of 7300 pounds. (I know this is not the optimum tow vehicle for this size trailer, but when I bought the truck, I had no idea I would someday be needing it to tow a travel trailer.)
I have the same truck, same engine and almost the same trailer. The truck is actually a really good match for that size trailer and controls the trailer better than my Excursion diesel did. If you install extra gauges you'll see that even though the engine and transmission are spinning faster, the transmission and exhaust temperatures run cooler with the overdrive off. That's all the convincing I needed.
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Old 01-06-2010, 02:41 PM   #8
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The reason for not using overdrive when towing, is that usually when towing, you are driving slower. Slower equals lower RPM, which can equal lower oil pressure in the transmission. If you have a heavy load, and low transmission oil pressure, that combination can cause clutch slippage, which will certainly result in premature transmission failure.

My Silverado owner's manual says to tow in overdrive. That would indicate to me that even at low RPM, that transmission has sufficient oil pressure to not allow clutch slippage. That said, I still shift out of overdrive when the speed drops, and/or the load increases such as going up hill.

That may be "old school", but it works for me, as the truck now has 154K miles and is still doing a good job.
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Old 01-06-2010, 02:57 PM   #9
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Tow-haul mode will keep the trans fluid pumping more efficiently...my truck will downshift in or up shift as it deems necessary by the electronics...if your TV has a Tow-Haul mode, I suggest you use it whenever you are pulling something to keep the trans from overheating...its there for the safety of the transmission, not your comfort.......if you are towing with your 1/2 ton truck, use the overdrive off mode for the same reason...to keep the juice flowing and keep the trans cool.

at least this is how I understand how mine works
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Old 01-06-2010, 03:09 PM   #10
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It is my understanding that towing in overdrive is ok on level ground, but in hills or mountains, the transmission will continuously be shifting back and forth in and out of overdrive. I have talked to a number of people who have towed in overdrive and some who have locked out overdrive. The common result I have been told is that those who use overdrive in hilly country have all had transmission failures much sooner than those who stay out of overdrive in those conditions.

Dennis
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Old 01-06-2010, 03:14 PM   #11
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AMEN, Dennis
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Old 01-06-2010, 03:23 PM   #12
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Towing in overdrive, puts a heavier load on the engine, and raises the cylinder head temperature, that could lead to engine problems.

Also, if a vacuum gauge was hooked up the the intake manifold, or vacuum system of the engine, that when towing in overdrive, the vacuum gauge reading will show a lower reading, confirming a heavier load on the engine.

The heavier the load, the lower the vascuum, the higher the manifold temperature.

Towing a small Airstream, probably no problem. Towing a larger Airstream, total different story.

Andy
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Old 01-06-2010, 03:43 PM   #13
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Andy, I always tow in "Tow/haul" mode until I get to highway speeds then I would turn it off to be in overdrive. So that I understand this right, you are saying that I should stay in "Tow/haul"? I tow with a 2001 Yukon XL. I am glad this question came up because I thought I might be doing it wrong.
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Old 01-06-2010, 03:58 PM   #14
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Vacuum gauge is invaluable.
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