I tow trailers and car haulers all over the country, and I am always concerned about keeping my vehicle protected the best I can when towing or hauling heavy loads. In all our trailer towing online courses I discuss a feature on your tow vehicle called the tow/haul mode. It seems like lots of people have questions about this topic, so I wanted to offer some information. I am not writing about how you turn the tow/haul mode on, or how to use it, you can find that information in the vehicle’s owner manual. I am writing today about how the tow/haul mode on your vehicle works. After you understand how it works, you will understand more about how and when to use it.
When you purchase a vehicle, the transmission has shift points or shift cycles designed specifically for the vehicle’s size, weight ratings, engine, and rear differential. In today’s world of vehicle manufacturers more shift points or gears are added to the automatic transmission mostly to meet EPA standards on fuel economy, but it can improve the ride as well. The problem is, when you add or tow additional weight, having 8 or 10 gears is not ideal for towing. Even older vehicles with 4 or 5 speed automatic transmissions with overdrive are not ideal for towing. The best way I can explain this is; if you tow or haul a heavy load without the tow/haul mode engaged the transmission does what I refer to as hunting for gears. It will shift in and out of overdrive based on the amount of weight you are towing or hauling and the terrain you are towing in.
It’s important to understand that towing and hauling heavy loads is not good for any vehicle. It increases heat to all the components and it adds wear and tear to the engine, transmission, rear differential, suspension, brakes, and other components on the vehicle. And if you do not understand when or why to use vehicle features like tow/haul, exhaust or auxiliary braking, and cruise control, you can permanently damage the components I just mentioned.
So, what does the tow/haul feature do?
Your vehicle does not recognize when you add weight in, on or behind the vehicle, so it can’t properly adapt to hauling or towing additional weight. To compensate, manufacturers add features like tow/haul to help prevent damage to the vehicle. For starters, the vehicle requires more torque to handle heavier loads. This helps when accelerating from a dead stop, and when building speed through the transmission’s gears. This is why lots of experienced people choose diesel over gasoline for towing. For torque, or raw pulling power. The torque produced is ideal for moving heavy loads.
When a vehicle starts driving from a dead stop in a low gear, the drive wheels rotate at lower Revolutions Per Minute (RPM’s) than the engine. About midway through the transmission’s gears the drive wheels will rotate at the same RPM’s as the engine. When the transmission is in a higher gear, like overdrive, the drive wheels rotate at higher RPM’s than the engine. So, driving in a higher gear allows you to travel faster, but it lowers the torque at the vehicle’s drive wheels. In essence, your tow/haul mode adjusts and reduces the transmission shift points based on hauling heavier loads, and it extends and raises the shift points in RPM’s. This combination results in better towing & handling capabilities, and reduced wear and tear on the transmission.
When you haul or tow heavy loads, the tow/haul mode is designed to make the engine’s performance more efficient with the added weight. The way it does this is, it reduces the number of shift points or shift cycles by eliminating some of the lower gears and by eliminating overdrive. It also increases the amount of time between shift points in lower gears for better acceleration. This increases the RPM range too, not only to help protect the transmission, but to increase torque and provide the peak RPM range for optimal performance with the additional weight. The tow/haul mode also limits the number of shift points on steep uphill grades, and as an added benefit you get a type of auxiliary braking from the engine/transmission to assist with controlling the speed on downgrades and require less braking. These shift point adjustments help prevent damage like overheating the transmission or damaging other components in the vehicle’s drive-train.
On the negative side, your fuel economy will decrease using the tow/haul mode, but this decrease in fuel economy is worth the trade-off to increase the life of your vehicle’s major components.
So, with that said some recommendations I make are:
- Use the tow/haul anytime you are towing or hauling heavy loads.
- If you are hauling lighter loads, and the transmission continues hunting for gears, use the tow/haul mode.
- If you use cruise control with the tow/haul mode and the transmission keeps shifting gears turn the cruise control off.
- When using the tow/haul mode take advantage of the engine/transmission braking to prevent overusing the vehicle brakes, especially on steep downgrades.
- If you are traveling on a flat even road surface it may no be necessary to use tow/haul, but if the transmission starts shifting in and out of overdrive I recommend using it.
- If you tow often and your vehicle does not have a gauge for transmission and differential temperature, consider adding them.
The bottom line is towing and hauling heavy loads is not good for any vehicle, but using the tow/haul mode will assist in peak performance by adjusting the transmission shift points and raising the engine’s RPM’s to better handle the load, while protecting the transmission by limiting the otherwise constant shifting.
Here is a link to another article I wrote on how to maximize the life of your tow vehicle.
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