If you are towing a trailer for the first time, you might wonder whether to use overdrive or lock it out. The short answer: for most towing situations, you should lock out overdrive to prevent transmission damage and overheating. Overdrive is a fuel-saving gear that reduces engine RPM, but under the strain of towing, it can cause the transmission to constantly shift between gears, generating excessive heat and wear.
What Is Overdrive and How Does It Affect Towing?
Overdrive is the highest gear ratio in an automatic transmission, typically 0.70:1 to 0.85:1. It allows the engine to run at lower RPMs at highway speeds, improving fuel economy. When towing, the added weight increases load on the drivetrain. In overdrive, the engine may lack sufficient torque to maintain speed on inclines or against wind, causing the transmission to “hunt” or repeatedly downshift and upshift. This hunting generates heat, which is the leading cause of transmission failure in tow vehicles. For example, a typical truck towing 5,000 pounds might see transmission temperatures rise 30-50°F above normal when overdrive is engaged on a slight grade. Locking out overdrive keeps the transmission in a lower gear (usually 3rd or 4th), maintaining higher RPMs (around 2,500-3,000) where the torque converter can lock up and reduce heat buildup.
When Should You Lock Out Overdrive While Towing?
You should lock out overdrive in any of these conditions: towing on hills or mountains, in stop-and-go traffic, at speeds below 50 mph, or with a heavy load (over 75% of your vehicle’s towing capacity). Even on flat highways, if your transmission shifts frequently (more than once per minute), lock out overdrive. Many modern trucks have a tow/haul mode that automatically locks out overdrive and adjusts shift points. If your vehicle lacks this feature, use the “OD Off” button or manually select a lower gear. As a rule of thumb, keep the transmission in a gear that allows the engine to operate between 2,500 and 3,000 RPM at cruising speed. This range provides adequate torque and cooling. For example, a 2019 Ford F-150 towing a 6,000-pound travel trailer should lock out overdrive on any grade over 3%.
When Is It Safe to Use Overdrive While Towing?
Overdrive can be used safely only under ideal conditions: towing a very light load (under 2,000 pounds) on perfectly flat terrain with no wind, at steady highway speeds (60-65 mph). Even then, monitor your transmission temperature gauge (if equipped) and lock out overdrive if the temperature rises above 200°F. Some newer vehicles with 8-10 speed transmissions have a wide enough ratio spread that overdrive (8th, 9th, 10th) is usable with moderate loads, but only if the transmission stays locked up and does not hunt. For instance, a 2022 Ram 3500 towing 8,000 pounds on a flat interstate might hold 8th gear at 1,800 RPM without issues. However, the safest practice for first-time towers is to always lock out overdrive until you gain experience. You can experiment on a flat stretch: engage overdrive and see if the transmission shifts repeatedly. If it does, leave overdrive off for the rest of the trip.
Risks of Towing in Overdrive and How to Avoid Them
The primary risk is excessive heat, which degrades transmission fluid and leads to slipping, burnt clutches, and eventual failure. A 20°F increase above normal operating temperature (usually 175-200°F) can cut fluid life in half. Other risks include increased wear on the torque converter, premature brake wear from constant speed adjustments, and reduced fuel economy if the transmission constantly shifts out of overdrive. To avoid these risks: install an auxiliary transmission cooler if you tow regularly (especially with a heavy load), use a scan tool to monitor transmission temperature, and follow your owner’s manual recommendations. Many manuals explicitly state to lock out overdrive when towing. If you are unsure, always err on the side of caution and keep overdrive off. For more on towing safety, check out our towing resources.
Frequently Asked Questions
Does towing in overdrive damage the transmission?
Yes, towing in overdrive can damage the transmission over time due to excessive heat from constant shifting. The added load causes the transmission to hunt for gears, generating friction and heat that degrades fluid and wears components. Locking out overdrive reduces this risk by keeping the transmission in a lower, more stable gear.
Can I use overdrive when towing on flat ground?
You can use overdrive on flat ground only with a very light load (under 2,000 pounds) and if the transmission does not shift frequently. Even then, monitor your transmission temperature. For most loads, it is safer to lock out overdrive to prevent unexpected downshifts on slight grades.
How do I know if I should lock out overdrive while towing?
Watch for these signs: the transmission shifts up and down repeatedly (hunting), your RPMs fluctuate more than 200-300 RPM, or your transmission temperature exceeds 200°F. Also, if you are towing uphill, in wind, or at speeds below 50 mph, lock out overdrive. Your owner’s manual may also specify conditions.
The Bottom Line
For first-time towers, the safest rule is to lock out overdrive whenever you are towing anything heavier than a small utility trailer. The fuel savings from overdrive are minimal compared to the cost of a transmission repair. Always monitor your gauges, and when in doubt, keep the engine revving a bit higher in a lower gear. Your transmission will thank you. For more tips, read our guide on best synthetic oil to keep your engine healthy while towing.
