Knowing when to change transmission fluid can keep your car shifting smoothly

When to Change transmission fluidA smoothly operating transmission can be the difference between an enjoyable driving experience and a frustrating one. Grinding gears or slipping transmissions make driving your vehicle a lot of work. A major factor in keeping your transmission in top condition is knowing how often you should change transmission fluid.  Many people are aware of how often to change your engine oil but are oblivious when it comes to knowing when to change transmission fluid.  So how often should you change your transmission fluid?  Let’s take a closer look at some variables.

Automatic or Manual?

Automatic transmission fluid or ATF is different than manual transmission fluid. ATF has a number of things added to it such as friction modifiers and anti foaming additives. This is because an automatic transmission has clutches inside that are in contact with the oil. If the clutches are slipping because of bad or improper ATF it will cause shifting issues. A manual transmission has it’s clutch system separate from the transmission fluid so it doesn’t need the additives to work correctly. In fact some transmissions such as those found in a 1st generation Jeep Wrangler use 10W30 motor oil.

How often should I change my transmission fluid for an Automatic?

You’ve checked your automatic transmission fluid and now you think to yourself “hmm, should I change my transmission fluid?”. Before you can answer that question you need to know about some variables. These variables all come down to one thing however, and that’s how quickly your automatic transmission fluid is degrading. The number one factor is heat. Normal driving conditions will raise the fluid temperature in your transmission to about 175 degrees F which is what most automatic transmission fluid is designed to operate at. Let’s say your fluid is designed to last 100,000 miles at the normal operating temperature. As the temperature in your transmission rises, the ATF degrades more quickly. A 20% increase in heat can reduce the life of the ATF by half. So if the temperature is 195 degrees F you’re fluids life is decreased to 50,000 miles. At 220 degrees F, which is a very common operating temperature, the life of the ATF is only 25,000 miles. Temperature increases can be caused by towing, hard accelerations, higher than average ambient air temperature, and other things.

I said all of that to arrive at an average number of miles for which you should be changing your automatic transmission fluid. 30,000 miles is a good benchmark, although many manufacturers claim 50,000 is plenty. You can get some clues as to whether or not you’re getting close to needing a change. When you check the fluid it should be red, as the fluid heats up it will oxidize and turn brown over time. If you check the fluid and it looks more brown then red, you’ll want to consider changing it or having it changed in the near future. When the fluid is changed on an automatic transmission, the filter should also be changed. You’re going to be in there anyway, and the cost is negligible. Keeping a good clean filter and clean fluid in your transmission will help ensure a long functional life for it. If you are doing the service yourself, be sure to consult your repair manual or local parts store for the correct ATF as there are a number to choose from.

When should I change my transmission fluid for a Manual?

Manual transmissions are often overlooked when it comes to changing fluid. Many owner’s manuals only list the mileage at which you should change automatic transmission fluid. However, it is just as important to keep good fluid in your manual transmission. Why? Because it will reduce wear on the gears and bearings and keep your transmission shifting smooth. Over time small metal shavings build up in the transmission and float around in the oil. The effect is almost exponential because the more shavings are in there, the more wear it causes putting even more shavings into the oil. Much like automatic transmissions, towing and hard use will put extra wear on the components and the fluid itself prompting an oil change at a lower mileage.

We’re back to answering the question of how often should you change transmission fluid in your manual transmission. The answer in my mind is at the same intervals you would change an automatic transmission’s fluid.  Manual transmission fluid is just as susceptible to breaking down and losing its effectiveness. I would plan to change it every 30,000-50,000 miles depending on how hard it has been working. If the vehicle tows a lot, I’d change it closer to 30,000 miles.  It’s hard to inspect the fluid as there is no dipstick you can pull out.  You can try dipping your finger in and getting some fluid on it so you can inspect it, but it’s probably just as well to plan on changing it at about 30,000 miles.  There is no filter to worry about on a manual transmission so it’s just a matter of draining the old fluid and adding the new fluid.

Whether you prefer to drive an automatic or manual transmission vehicle is neither here nor there, but what is important is that you take care of that transmission. At the simplest level, that means checking and changing the transmission fluid.  Now that you know when to change the transmission fluid in your car, stick to it and keep your car happy and healthy.  Be sure to use a quality fluid that is designed for your transmission. Your manual or the local parts store can help you figure out what’s right for your transmission. In general you get what you pay for in terms of quality when it comes to oils and fluids for your vehicle.

Jason

Jason has been working on cars since he was 11 years old helping his dad fix up an old Jeep. Since then he's done partial rebuilds on car engines and two complete rebuilds on motorcycle engines. As an avid backyard mechanic Jason maintains and rebuilds his Jeep. Connect with Jason on Google+

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