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This Toyota Truck Common Problem Can Destroy Your Transmission!

A Toyota mechanic sees a new problem developing in these two models of Toyota truck that can destroy your transmission if not detected in time, and what you can do about it.

We’ve reported before about the importance of ensuring that your transmission fluid needs to be changed more often than recommended by car manufacturers. But aside from trans fluid being changed every 30,000 to 60,000 miles, is there something else you should be doing to prevent transmission damage in your Toyota truck?

You bet there is. And it’s all because of the sealed transmission many models carry.


This topic has been approached before; however, it is one that bears repeated reminding for car owners who are unsure what to believe when it comes to whether the fluid in a sealed transmission really does need to be changed…ever.

Call it what you will―a white lie, a scam, or a myth―but the fact of the matter is that transmission fluid (just like your engine oil) does break down over time with use, over-heating, and exposure to moisture.

However, there’s more to the hazards your sealed transmission could face.

What is a Sealed Transmission?

A sealed transmission, often referred to as a “sealed unit,” is a type of transmission that is designed to be maintenance-free, meaning it does not require periodic fluid checks or changes by the vehicle owner or service department dealership. Instead, the transmission is filled with transmission fluid at the factory, and the manufacturer typically states that it is a “lifetime” fluid that should not need to be changed under normal operating conditions.

Why Do Cars Have Sealed Transmissions?

Whether you may have noticed it or not, many modern car models today come with a sealed transmission, which is easily identified with the “missing transmission dipstick” confusion new car owners have reported online and asked about.

This missing transmission dipstick is due to a change in the automotive industry to install sealed automatic transmissions into new cars.

Automotive makers extoll the virtues of a sealed automatic transmission in that it:

  • Will no longer require the past 50,000-to-60,000-mile transmission fluid check and change requirement.
  • Will provide customers with what they want by making vehicles almost entirely maintenance-free.
  • Will save on the need for significant transmission fluid oil production.
  • Sealed transmissions help reduce the amount of “bad” transmission fluid being disposed of that they believe is totally unnecessary due to the advances made with synthetic oil.

Even today, we still hear service stories of service departments telling their customers that sealed transmissions do not require servicing because the transmission and fluid are engineered “to last the lifetime of the car” ―but you should think about what this really means.

Why Are the Problems of Owning a Car With a Sealed Transmission?

While sealed transmissions offer convenience to vehicle owners by eliminating the need for regular fluid changes, they can also present some potential problems:

1. Misinterpretation of "Lifetime" Fluid: Some vehicle owners may misunderstand the term "lifetime" fluid and assume that it means the transmission fluid will never need to be changed. However, "lifetime" typically refers to the expected lifespan of the transmission under normal driving conditions, rather than the longevity of the fluid itself.

2. Fluid Degradation: Despite being labeled as "lifetime" fluid, transmission fluid does still can degrade over time due to heat, contaminants, and normal wear and tear. This degradation can lead to decreased lubrication and cooling efficiency, potentially causing premature wear or failure of transmission components.

3. Limited DIY Servicing: Sealed transmissions are often more challenging to service compared to traditional transmissions with accessible dipsticks and fill tubes. Specialized tools and equipment may be required to check or refill the transmission fluid, making it difficult for owners to perform DIY maintenance.

4. Cost of Repairs: If a sealed transmission develops a problem that requires repair or fluid replacement, it often involves a trip to a dealership or a qualified mechanic with the necessary tools and expertise. This can result in higher maintenance costs compared to vehicles with serviceable transmissions.

5. And Most Important of All…Leaks: While sealed transmissions are designed to prevent fluid leaks, they are not immune to seal failures or other issues that could lead to fluid leaks. If a leak occurs and goes unnoticed, it can result in low fluid levels, which can cause transmission slippage, overheating, and ultimately, transmission failure if not addressed promptly.

Which is the genesis of today’s topic due to a recent Car Care Nut YouTube channel episode where the owner of a 2006 Toyota 4Runner comes into the host’s garage with a check engine light warning and complaint of difficulty with shifting his truck lately…at just under 100,000 miles.

Toyota 4Runner and Toyota FJ Cruiser Transmission Problem

According to the host of the Car Care Nut YouTube channel, he is beginning to see a common problem particularly endemic with Toyota 4Runners and FJ Cruisers when it comes to their vehicle’s transmissions―unnoticed loss of transmission fluid until it is too late to avoid damage.

The source of this fluid loss is not due to poor seals or other transmission design-related problems. Rather, it all has to do with undercarriage rust and the effect it has on the thin transmission coolant lines that cannot handle the level of exposure and rusting from road salt the rest of the truck is experiencing.

Related article: Used Toyota 4Runner Walk Around Demo

Follow along with the host as be:

  • Explains the three common engine codes signaling a problem with your Toyota transmission.
  • Explains how transmission solenoids work and the problems they can experience.
  • Shows multiple problems with rust damage on the underside of the truck and how he diagnosed the source of transmission fluid loss.
  • Demonstrates how to figure out how much transmission fluid was lost when there is no transmission fluid dipstick to check with.
  • What does it mean when fluid loss is between 3-4 quarts before being detected.
  • How to replace the coolant line on your Toyota.
  • The future of this truck.

This Problem Can Destroy Your Toyota Truck Transmission! Is it Too Late for This One?

For additional articles related to transmissions, here are three for your consideration:

Timothy Boyer is an automotive reporter based in Cincinnati. Experienced with early car restorations, he regularly restores older vehicles with engine modifications for improved performance. Follow Tim on  “Zen and the Art of DIY Car Repair” website, the Zen Mechanic blog and on Twitter at @TimBoyerWrites  and Facebook for daily news and topics related to new and used cars and trucks.

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Image source: Deposit Photos