tow mode/transmission question

I have been advised to keep my vehicle in 4th rather than overdrive when towing my trailer to protect the transmission.  Someone else has said that is what tow mode is for.

My question is, what does the tow mode do?  I thought it was for electrical things, like turn signals, and brakes.

It's very similar for both Ford and GM.  What is does is that it changes the shift points a little bit higher so that the engine is in the power band longer.  It will also downshift fster when going uphill or trying to pick up speed.  Going uphill, if it downshifts one gear, it will stay in that gear pretty much up to the top, due in part to the higher shift points.  Also, if you go downhill instead of coasting when you take your feet up the gas, it will use engine braking.  The shifting is also done quicker and harder to prevent/reduce transmission slippage.

The tow mode is totally independent from driving in overdrive or not.  You should always use the tow-mode when towing.  Driving with the overdrive on or off depends on how the transmission behaves when towing.  If I keep the OD on, my transmission keeps hunting between 4th and 3rd (I have 4 speed).  Also, when in 4th, I feel the torque converter locking and unlocking often.  That's a recipe for the transmission to overheat and also failure, so I always keep it off.

My friend has a Chevy Avalanche with the tow mode, his first trailer was small and light, so he always kept the OD on and used the tow mode.  Now he has a heavier trailer and turns off the OD while towing and still uses the tow mode.  Even in tow mode, the load is heavy enough that it always wants to hunt for gears, so he turns it off.

So there is not one definite answer on towing with the OD on or off, it depends on the setup and how the transmission behaves.  However, if in doubt, there is no harm with driving with the OD off.

Marc...

I found this document online that explains it better then me and with a lot more information:
Technical Training Tip of the Month, Ford Transmission Control Switches Overdrive Cancel and Tow/Haul Mode By Grant Wolter

So if the vehicle is in OD and is not changing gears when i'm on a level road going a constant speed then it's okay?

Absolutely! The only time you need to turn the OD off is if it is giving poor results, i.e. the frequent up/down shifting that Marc described.  "Frequent" means a minute or less between shifts - maybe even as much as 90 seconds. Of course you expect it to shift if you come to a hill, but if it is shifting at the drop of a hat, shut the OD off.

But shutting it off when it could and should be on will cost you fuel economy, so it is worth experimenting with.

56kz2slow said:

I found this document online that explains it better then me and with a lot more information:
Technical Training Tip of the Month, Ford Transmission Control Switches Overdrive Cancel and Tow/Haul Mode By Grant Wolter

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The way I've read this, it's best to engage Tow/Haul once you get into the truck for normal around town driving, not just trailer towing.  And that it will still seek OD once a higher speed is obtained.  Didn't know that :-\

Thanks 56kz2slow for the link

Tow/haul does NOT inhibit overdrive in either a Ford or a GM transmission.  However, tow/haul will yield slightly lower fuel economy if it is engaged in conditions where there is no benefit from the altered shift strategies and engine braking is not needed. So no, you should not use Tow/haul mode every time you drive.

The default set-up is designed to yield maximum fuel economy under "normal" driving conditions, where "normal" is defined by the EPA's CAFE fuel economy test procedure. The EPA CAFE laws pretty much force the deign to be that way, since there is a penalty for any reduction in mpg.

Okay, i'm going to see how it does in OD and then decide, on small hills i'm sure it will downshift accordingly.  However, going through the mountains, in PA, for example, it's probably best to downshift manually, right?  I think i read somewhere to go to 1st and then work my way up, is that right?

momma22smallbears said:

Okay, i'm going to see how it does in OD and then decide, on small hills i'm sure it will downshift accordingly.  However, going through the mountains, in PA, for example, it's probably best to downshift manually, right?  I think i read somewhere to go to 1st and then work my way up, is that right?

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For most hill operation, normal operation of the automatic with the OD locked out works just fine.  On long downgrades, if you find that you are having to go to your service brakes frequently, you should then shift down to a lower gear to gain more engine braking.  There are plenty of grades out here in the West that I go down in, locked into 2nd and a few bad boys I do in 1st.

As Carl say, let the auto do its thing on the upgrade but help it out (shift manually) on the downgrade.

I'm nt trying to disagree with the other people who has given their take on the issue, but I have a more technical version of it given to me by a transmission mechanic who I consider very knowledgeable in the subject. His explanation to that is that when your vehicle is in overdrive, the hydraulic pistons inside the tranny adjust in such way to increase hydraulic pressures at the converter so your engine don't have to rev as fast to produce the same speed on the vehicle, this causes the tranny to work harder and hotter. The more load you put on the tranny, the harder and hotter it works to produce the right amount of hydraulic pressures to make the vehicle move. That is the reason why the OD is only for coasting speeds where the vehicle had built enough momentum as to not put the tranny under much stress. He personally advised me to turn the overdrive off when in the city where speeds do not go over 45mph becuase is also stressful for the tranny to be in overdrive at those speeds. Also when the engine is reving at higher rpm's, the torque increases which makes it easier for the tranny to produce hydraulic pressures under less stress. Hence the recomendation to push the "tow" switch (turn overdrive off) when towing a vehicle.
I don't know if I explained it correctly. If confused, let me know to clarify more.

No RV is going to get into OD at 45 mph anyway.

RV Roamer said:

No RV is going to get into OD at 45 mph anyway.

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I believe she is talking about her vehicle and not a motorhome. Check OP.

Trailers are RVs also.  Honest. 

I was referring to towing situations. If not towing, I agree her vehicle very likely will get into OD by 45 mph.

RV Roamer said:

I was referring to towing situations. If not towing, I agree her vehicle very likely will get into OD by 45 mph.

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on my Allison tranny on my 2008 Chevy 2500HD, you only have a choice to put in TOW/Haul mode or not. There is no switch to turn off OD, unless you go into manual shift mode. The Allison will choose OD if it sees fit, but it will have to go a higher RPM to do so while in Tow/haul mode. On fairly level ground, I would go into high gear at 66MPH, I would then slow down to 62-63MPH to obtain my best fuel mileage. If a hill caused the tranny to downshift, I would have to increase the speed to get it to upshift and then slow down again. I regularly hauled 17,500# and routinely got over 10MPG, whith some slight modifications on the truck. I have never had a heating tranny problem and I monitor it closely.

The choice on my 2005 Dodge is also Tow/haul mode on or off.  There is no way to choose OD or not.

Lowell said:

The choice on my 2005 Dodge is also Tow/haul mode on or off.  There is no way to choose OD or not.

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Tow switch or OD switch is pretty much the same thing. My 2000 Dodge Dakota actually read "OD on/off" at the end of the shift lever. Some trucks read tow or haul on/off. It does the same thing. It keeps the OD to kick in when the motor is under load or under 45mph.

That makes a lot of sense. Even my old 1996 Ford Windstar Minivan 3.8l has the OD on'off button on the stick. I used it when towing a small pup tent trailer from FL to WA and back. Quite a trip. It was a bear.. enjoyed every minute though.

Almost wrecked my engine towing that little thing. That was before I joined the RVforum and learned a lot about towing.


carson Fl

They are not the same on the new trucks I have driven and that my friends have.  I've test driven several new and fairly new Fords and Chevy in the last few months.  The tow-haul mode, as explained in the owner's manual and by the brochure says it changes how the transmission shifts, but not what gear it is into.  The default D position is includes the Overdrive, sometimes shown with a D in a circle. The one below depending on the year and number of gears will be a D with no circle or 3rd, sometimes 4th on a transmission with more than 4 gears is with the Overdrive off.

If you re-read the post I put earlier, the guy does a good explanation of the difference between the two.