Is it okay to change transmission fluid after 100k miles?

Yes. In most cars, changing transmission fluid after 100,000 miles is safe and can help maintain shifting and longevity, provided you use the correct fluid and follow the maker’s guidelines, though a full flush isn’t always advisable for older transmissions.

As cars age, transmission fluid breaks down under heat and stress, losing lubrication and cleaning properties. If your vehicle hasn’t had a fluid change around the 100k-mile mark, a careful drain-and-fill or a manufacturer-approved service can refresh this critical fluid. The decision depends on your model, transmission type, and service history.

What to check before changing

Before you commit to a fluid change, consider these factors to avoid surprises.

• Owner’s manual for recommended service interval and fluid specification


• Current fluid condition: color, smell, and level


• Whether the transmission is labeled "lifetime fill" or “sealed” and whether a service is recommended


• Any shifting issues, slipping, or unusual noises that may indicate broader problems

Checking these factors can help you decide whether to change now and what method to use.

Your options for changing the fluid

Two main approaches exist for replacing transmission fluid in a high-mileage car: a drain-and-fill and a flush, with a full fluid exchange offered by some shops. Each has pros and cons depending on the transmission design and current condition.

• Drain-and-fill: drain a portion of the old fluid and replace with fresh, typically 3-5 quarts; lower risk to seals and easier to perform at home or in a shop; can be repeated if needed


• Flush or fluid exchange: uses equipment to force old fluid out and replace with new; may remove more contaminants but can stress aging seals and push debris into delicate passages


• Full transmission replacement: rarely necessary; used in extreme cases where fluid has degraded or there is a known failure; not typical for normal service

Discuss your options with a qualified technician who can assess your specific model and its condition.

What to expect after the change

After performing a drain-and-fill or a flush, monitor how the transmission behaves and watch for leaks or new noises. The outcome depends on fluid type, the method used, and the transmission’s overall health.

• Check the level according to the manual after the service and adjust if needed


• Test drive to verify smooth, consistent shifts across gears and speeds


• Look for signs of leaks around the pan, drain plug, and cooler lines

A proper recheck ensures the service didn’t cause unintended issues and helps you confirm the fluid is circulating correctly.

Special considerations for CVTs vs conventional automatics

CVTs (continuously variable transmissions) use different fluid specifications and service intervals than traditional automatics. Replacing CVT fluid requires the exact CVT grade specified by the manufacturer, and some models may not tolerate certain fluids or flush methods. For traditional automatics, fluids are typically Dexron- or Mercon-type blends, but always use the exact specification listed in your manual to avoid shifting problems or damage.

CVT fluid specifics

When dealing with a CVT, never substitute a conventional ATF with a CVT fluid unless the manufacturer explicitly approves it. Using the wrong fluid can cause slipping, reduced performance, or premature wear. If you’re uncertain, rely on dealership or specialist service and stick to the recommended viscosity and specification (for example, NS-2/NS-3 or JWS3309 variants depending on the model).

In all cases, using the correct fluid specification and considering the age of seals and the transmission’s design are critical to avoid unintended problems.

Summary

For a vehicle with 100,000 miles, changing the transmission fluid is commonly beneficial but should be approached with care. Always follow the manufacturer’s specification, consider a drain-and-fill rather than a flush for older or high-mileage units, and have a professional evaluate if you notice shifting issues or leaks. A properly executed service can restore smoother shifts and help prolong transmission life, though it won’t fix existing mechanical damage.

What fluids should you change at 100k miles?

At 100,000 miles, you should replace engine oil and filter, transmission fluid, coolant, and brake fluid, as these fluids break down over time and can cause damage to critical components. You should also consider replacing spark plugs and the timing belt, which can fail and cause serious engine damage. 
This video explains why it's important to change transmission fluid after 100,000 miles: 39sCar Care ProYouTube · Sep 6, 2025
Essential fluids

• Engine oil and filter: Oil breaks down and becomes contaminated with metal shavings and carbon deposits, which can accelerate wear on engine parts. A new filter ensures clean oil circulates properly. 
• Transmission fluid: This fluid lubricates the transmission gears. Over time, it breaks down and can become contaminated, so it needs to be flushed and replaced to prevent premature wear. 
• Coolant: Coolant can lose its ability to prevent corrosion over time, even if its heat transfer capability remains. Replacing it at this mileage is crucial for protecting the system. 
• Brake fluid: Brake fluid absorbs moisture, which can lead to corrosion in brake components like the ABS module and calipers. Flushing and replacing it is essential for safety and to prevent costly repairs. 

This video explains why it's important to change brake fluid after 100,000 miles: 1mRQs GarageYouTube · Jul 26, 2022
Other important maintenance

• Timing belt: A timing belt replacement is often recommended around 100,000 miles. A broken timing belt can cause severe internal engine damage. 
• Spark plugs: At this mileage, spark plugs may be worn and should be checked and replaced if necessary. 
• Power steering fluid: If your vehicle has hydraulic power steering, the fluid should be inspected and replaced as recommended by the manufacturer, as it may need service around this time. 
• Differential and transfer case fluids: For vehicles with a 4WD or AWD system, these fluids should also be checked and replaced according to the manufacturer's schedule. 

This video explains why it's important to change fluids after 100,000 miles: 57sTire ReviewYouTube · Aug 28, 2024
Important note

• Always consult your vehicle's owner's manual or a professional mechanic to determine the exact service intervals and fluid types for your specific car. 

What needs to be changed after 100k miles?

After 100,000 miles, you should focus on replacing vital components like the timing belt, spark plugs, and transmission fluid. It's also crucial to check the brakes, tires, and suspension for wear, along with ensuring that all fluids (oil, coolant, brake, power steering) are topped up and free of contaminants.

Can you change transmission fluid at 130,000 miles?

If you pour in new clean fluid, it washes that matter away, and the internal clutches begin to slip. This is especially true with vehicles with more than 100,000 miles and no record of regular transmission fluid service. Don't delay changing the transmission fluid according to the vehicle's maintenance schedule.

Why do people say never change transmission fluid?

The saying "never change transmission fluid" is a myth, but there's a kernel of truth to it when the fluid is neglected for a very long time. If a transmission has never had its fluid changed and the fluid is dark and burnt, new fluid can dissolve the "varnish" and debris that have been acting as a temporary sealant for worn parts, potentially causing the transmission to slip or fail. 
This video explains why changing transmission fluid can be beneficial: 57sScotty KilmerYouTube · May 11, 2023
Why the misconception exists

• Worn-out fluid: Over time, transmission fluid breaks down and can accumulate debris and "varnish" from worn internal components. 
• Temporary "fix": In a high-mileage, neglected transmission, this old, grimy fluid may have been holding worn parts together, acting as a makeshift sealant. 
• The risk of a flush: A full transmission flush, which uses high pressure to force new fluid through the system, can dislodge this built-up material and potentially cause seals to fail or clutch packs to slip, leading to a more expensive repair. 

What to do instead

• Regularly change fluid: The best practice is to follow your vehicle manufacturer's recommended service intervals for changing the fluid. 
• Drain and fill: If your car has high mileage with unknown fluid history, a "drain and fill" or "pan drop" is safer than a full flush. 
• Focus on the pan drop: This method removes only a portion of the old fluid and allows for the filter to be changed and the magnet to be cleaned. 
• Use new fluid carefully: Adding new fluid can still be beneficial, even in older transmissions, but be aware of the risks if the fluid is extremely degraded. 
• Don't ignore signs of failure: If the fluid has a burnt smell or contains metal flecks, it indicates a problem, and a fluid change may not be enough. 

This video explains how to safely change transmission fluid: 53sScotty KilmerYouTube · Jun 8, 2021