Check Your Semi Truck’s Transmission Fluid by Yourself (The Right Way)

man holding dipstick to check transmission fluid

When was the last time you checked your semi truck’s transmission fluid? If it’s been awhile or you rarely do, chances are your semi truck is in a bad shape.

It wouldn’t be much of a surprise if you don’t care a whole lot for your semi truck’s transmission fluid because you know next to nothing about it. Unlike engine oil, which you’re probably more familiar with since you most likely have it changed regularly, transmission fluid doesn’t really come up that often when discussing maintenance. 

But, with everything that makes up your semi truck being equally important, from the smallest part to the biggest, not only do you also need to know about its transmission fluid, you need to be able to check it by yourself if need be. Otherwise, your vehicle could suddenly break down any time, adversely affecting your productivity.

Ready to start learning all about your semi truck’s transmission fluid? Read on to find out not only how to properly check it by yourself but what it is and the specific adverse effects of having little or none of it.

What Is Transmission Fluid?

Although the way we mentioned engine oil and transmission fluid makes them seem connected, they’re not the same thing. They have pretty much the same composition, but each serve a different purpose.

Let’s start with engine oil. Made up of a base oil with various additives, like detergents, dispersants and viscosity index improvers, engine oil keeps the engine sufficiently lubricated.

Transmission fluid has a similar makeup but is used to make sure your semi truck’s transmission, also called the gearbox, works smoothly.

What Will Happen to Your Semi Truck if It’s Low on or Have No Transmission Fluid?

As we already mentioned, having little or no transmission fluid will cause your semi truck to sustain more than the usual wear and tear. But how bad will it be?

If there’s little or no transmission fluid to make sure your semi truck’s transmission keeps running smoothly, it won’t be long until the parts that make it up start grinding against each other and heat up. 

If you don’t handle that right away, the transmission will inevitably break, forcing you to pay for extensive repairs or even have the whole thing replaced, both of which could cost a lot. 

It doesn’t matter if your semi truck’s an automatic. In such a vehicle, transmission fluid provides coupling between the engine’s output and the transmission. Without it, there’s no way the vehicle will be able to move.

3-step Process of Checking Your Semi Truck’s Transmission Fluid


Step #1: Park your semi truck properly.

In the event you suddenly have to check your semi truck’s transmission fluid by yourself, you might just park anywhere to get it over with. We know you’re stressed out, but to make sure you get it right, you need to do it properly.

Instead of wherever it’s convenient, park your semi truck on the most level part of the road you find yourself on. That means you can’t park on the side of the road if it means placing your semi truck on an incline. Doing so will make checking the transmission fluid harder than it has to be.  

Step #2: Find and pull out the transmission fluid dipstick.

To find your semi truck’s transmission fluid dipstick, look behind the engine. It’s located near the fire wall. 

Fire walls are built pretty much the same way with every vehicle, so there’s no need to worry about having a hard time finding that of your semi truck. The same goes for its transmission fluid dipstick. But, just to be sure, it has a bright-colored (sometimes yellow) plastic ring sticking out. When you pull out the whole thing, it will resemble a thin, relatively long and slightly pointy piece of metal except with oil on the tip.   

Step #3: Check the transmission fluid level correctly.

Don’t worry, you don’t need specialized knowledge to do so. 

Transmission fluid level dipsticks have markings that show whether there’s too much or too little transmission fluid. Located near the tip, they’re simply grooves with either min and max or L (Low) and F (Full) on either end. If the fluid goes past max or F, there’s too much. If it only reaches up to min or L, there’s too little.

You should also take note of the fluid’s color. It can indicate other problems your semi truck might have. You’re good if it runs clear pink or red. But if it’s dark, that means there’s debris and a filter change is needed.

If your semi truck’s transmission fluid level is low, consult with a transmission specialist as soon as possible.

Last Takeaway

It’s a must for every truck driver, worth his or her salt, to know basic transmission maintenance and repair. Keeping your rig road-ready depends on it. If you know how to check your semi truck’s transmission fluid by yourself correctly and when to call a specialist or semi truck mechanic, rest assured it will keep running smoothly and on time for many more years to come.

Nevertheless, if you think it’s time to get a new truck, you will find the best semi trucks at

For more tips, specifically on how to check your truck’s tires, read this article about maintaining a semi truck’s proper tire pressure.