How To Tow Without Damaging Your Transmission

Unless you’re that guy hauling a semi trailer with a regular Chevy Silverado, towing shouldn’t damage your vehicle when done correctly and within proper weight limitations. That said, pulling a heavy load is an additional strain on your vehicle’s components, and in particular, the transmission. Getting a new transmission, or having one rebuilt, can easily come with a multi-thousand dollar price tag, so you’ll want to take precautions to protect that pricey gearbox from premature wear while towing. 

For the purposes of this article, we’ll stick to discussing automatic transmissions. To be sure, manuals are great for towing and can outperform their automatic counterparts in certain situations, but the reality is that manual transmissions are just so scarce in new cars and trucks sold in the United States. 

Our first step toward transmission longevity is a bit of a controversial one: whether or not you should use overdrive gear(s) when towing. When I was younger, towing in overdrive was widely accepted as a no-go, both anecdotally and in vehicles’ owner’s manuals. Nowadays, using overdrive while towing to lower engine RPM and improve fuel economy on the highway is more widely accepted – though you’ll still want to use it cautiously. For example, disable overdrive when in traffic, climbing hills, or in other circumstances where your transmission excessively hunts between gears. Ditto for downhill scenarios where engine braking is helpful. Better still, some trucks and SUVs come equipped with a tow/haul mode that will optimize transmission settings for you automatically. 

As far as specific equipment that you can install to protect the longevity of your automatic transmission, a transmission cooler is definitely at the top of that list. Think of a transmission cooler like a mini radiator. Metal or rubber lines carry hot automatic transmission fluid away from the transmission and through the cooler, which should be mounted in an area with good ventilation, like behind your grill. Temperature now reduced, that fluid is then sent back to the transmission.

If your vehicle doesn’t have a transmission cooler and you tow frequently, it’s a must-have accessory. Note that some vehicles like pick-up trucks and SUVs are equipped with a factory-installed transmission cooler. That’s particularly likely if an optional towing package or factory trailer hitch is present. Still, some OEM transmission coolers are something of a cheap affair. It may be worthwhile to upgrade to a heavier-duty transmission cooler, even if you already have a wimpy one from the factory. 

Drivers frequently keep an eye on their engine temperatures, but transmission fluid temperature? Not so much. Transmission temperature isn’t one of the gauges that’s apt to be displayed by default on your dashboard, like fuel level or battery voltage. On modern vehicles, you’ll likely have to scroll through your digital display’s menu to locate this readout, and some vehicles may not display the transmission temperature at all. Instead, there could just be an “idiot light” to warn of high temperatures. Significantly older vehicles without a computer-controlled transmission may have no temperature monitoring at all. 

Much like adding a transmission cooler, adding an aftermarket transmission fluid temperature gauge can be a worthwhile mod if you find yourself regularly towing heavy trailers. For the record, a normal transmission operating temperature is typically between 170 and 225 degrees Fahrenheit. And speaking of transmission fluid, be sure to keep up with necessary fluid and filter maintenance. Although some manufacturers now allow up to 100,000 miles or more between transmission fluid and filter changes in normal use, regularly towing heavy trailers is considered a “severe service” condition and will shorten that recommended interval.

So far, we’ve focused on ways to protect your car or truck’s transmission while actually underway on your work or leisure adventure, but an automatic transmission can be damaged while the vehicle is parked, too. Specifically, we’re talking about the parking pawl, which is a pin or lock that engages with notches in a transmission’s output shaft when the unit is shifted into park. This effectively locks the output shaft and prevents the vehicle from moving.

As you might imagine, parking on any kind of incline or loading vehicles or equipment on or off a trailer will put additional stress on the parking pawl that’s locking the transmission’s output shaft in place. In extreme cases, the parking pawl can fail or break entirely, which will require tearing into the transmission to fix, if you’re lucky. A worst case scenario would be tiny fragments of the parking pawl circulating around inside the trans. For these reasons, it’s good practice to always use your parking brake when parking with a trailer attached, but especially on non-level terrain or when the trailer may be jostled.

Of course, before you rely on your braking brake to hold the vehicle at a standstill — with the parking pawl acting as a second line of defense — you’ll want to verify that the parking brake works and is properly adjusted. Parking brakes in automatic vehicles don’t get exercised as much as their manual counterparts, but you can test their holding power on a slight incline with the vehicle in neutral. It’s better if you don’t accidentally roll into any cars while testing, so pick a secluded spot.

Finally, destruction-free towing involves not only the vehicle doing the hauling, but the trailer itself. You might be safely observing your car or truck’s weight limit for towing, but poor maintenance or improper loading can create extra work for your faithful transmission. One of the easiest and cheapest places to start is to check your trailer’s tire pressure. An under-inflated tire is prone to dangerous blowouts, and it’s harder to rotate, which creates a ton of unnecessary drag. Not only will your transmission be cooler and happier with free-rolling, properly aired-up tires, you’ll save on fuel, too.

Equally important to proper trailer tire pressure is making sure that a trailer is loaded properly. Too much weight placed toward the front of the trailer will increase the weight on the trailer’s tongue — the part that connects to the hitch ball. Alternatively, if the bulk of your load is at the very back of a trailer, the tongue weight will be overly light. In a recent study by Weight Safe Trailer Hitches, a 15% too-heavy and 10% too-light tongue weight resulted in an approximately 8% and 13% drop in fuel economy, respectively, versus a properly balanced load.

Reading between the lines, burning that extra fuel means that the whole drivetrain is working harder, including the transmission. As a reference, tongue weight should be 10% to 15% of the total weight of the trailer and load combined. And yes, special scales to measure tongue weight are available for as little as $100, which is a tiny fraction of a new transmission.