Coolant, motor oil, brake fluid, gear fluid, hydraulic fluid, and transmission fluid: these are just a small sample of the many fluids that keep trucks running. While most motor oil requires a change every few thousand miles, transmission fluid change intervals aren’t always as clear. How often should you replace transmission fluid, anyway?
The answer is every 30,000 to 100,000 miles, with some trucks not needing an oil change until 250,000 miles or more. But the devil is in the details.
If you tow heavy loads often, you may need an oil change sooner. Not sure when to replace your transmission fluid?
We’re here to help.
In this article, our diesel truck repair technicians will walk you through how often to replace your transmission fluid, as well as how to replace your transmission fluid.
Ready? Let’s dive in.
Table: Key diesel truck transmission fluid change intervals
|
Truck category |
Transmission fluid change interval |
| Light-duty trucks | 30,000 to 60,000 miles |
| Mid-duty trucks | 40,000 to about 80,000 miles |
| Heavy-duty trucks | 80,000 to about 125,000 miles |
| Semi-trucks | 250,000 to 500,000 miles (or every 5 years) |
*Note: These numbers are estimates and are used for informational purposes only. Always consult your local diesel truck repair technician for up-to-date, accurate truck maintenance support.
When to change transmission fluid for your diesel vehicle
If you need to change your transmission fluid, most truck repair shops will recommend replacing transmission fluid every 30,000 miles up to 125,000 miles for light- to heavy-duty vehicles. For semi-trucks, fluid levels and fluid replacements often occur at 250,000 miles or more.
With that being said, you should still take care of your transmission by bringing your truck in for planned preventive maintenance and regular service throughout each year, regardless of how many miles are logged on your rig.
Doing so will ensure optimal performance out of your engine, fewer breakdowns, and a longer life for your truck.
Also, trucks that use manual versus automatic transmission may need to be serviced at different intervals. The time period for replacing transmission fluid depends on the transmission type, make, model, and how you operate your vehicle.
What’s more, if you’re the type of driver who often logs many miles on the road in extreme environments and with heavy loads, you may need to schedule a transmission fluid change sooner.
If in doubt about when to replace the transmission fluid of your truck, you can always schedule an appointment at a service center with a certified diesel truck repair technician. They’ll be able to identify the warning signs regarding when to change your transmission fluid.
How to service and change your transmission fluid
Now, let’s say you’re the type of person who likes to tinker with your truck. If you’re curious to learn how often to change your transmission fluid and how to keep your transmission in great shape, you might consider changing your transmission fluid yourself.
If you’re thinking of changing your transmission fluid, follow these six steps:
- Allow your truck to idle for a few minutes, turn off the ignition, raise and secure your truck, loosen the bolts, tilt the pan, and drain out the old fluid.
- Clean the surface of the pan and gasket, and inspect the pan for any signs of low transmission fluid or damage to the transmission itself.
- If you notice the transmission is low on fluid, remove the transmission filter and O-ring. Lace a new filter inside.
- Lower the vehicle and fill the transmission with the right amount of transmission fluid. If you’re unsure, check your truck’s owner’s manual, as it will spell out the manufacturer’s recommendations for your transmission.
- Start your truck, warm it up, and then turn it off. You should check for leaks during this time.
- If you don’t see any leaks, consider shifting gears to ensure everything sounds and looks normal (meaning no grinding noises or slipping gears). If everything operates smoothly, your truck should be road-ready.
If you’re wondering where to buy transmission fluid, you can purchase fresh transmission fluid at local retail stores, truck supply, and truck repair shops.
Time for a fluid change: Certified fact or fiction?
Speaking of fluid, let’s play fact or fiction.
Fact or Fiction: Running your diesel truck low on fuel won’t hurt anything… 🚫🤔
Fiction!
The truth?
Running low can let air in the fuel system, overheat your injectors, and cause major damage.
Remember: your injectors rely on diesel for lubrication. Keep that tank up to keep your truck alive. ⛽💥
To watch our co-founder, Steve Conner, explain this concept in detail, check out this Instagram piece.
Unsure whether your transmission fluid needs a top-up? Schedule service with certified experts.
The bottom line is that if you don’t change your transmission fluid according to manufacturer recommendations, you can experience transmission failure or worse.
Drivers: make sure your transmission stays in tip-top shape by adhering to a regular maintenance schedule. To keep your truck in tip-top shape, your transmission needs regular tender loving care and quality service.
If you’re in the Florida area, we’re here to help. Feel free to bring your vehicle in for service at one of our three convenient locations in Sarasota, Fort Myers, or Tampa.
Our diesel truck repair technicians have more than 25 years of experience servicing trucks of all different shapes and sizes.
Whether you operate an automatic or manual transmission truck, our team of certified truck technicians can give you the reboot your transmission needs. Contact us today to schedule no-hassle, reliable truck service.
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