WHEN TO CHANGE YOUR TRANSMISSION FLUID – AND WHAT HAPPENS IF YOU DON’T!

Your car will have great difficulty moving, in either a forward or reverse direction, unless your transmission is in proper working order. Your transmission is your car’s “middleman,” responsible for transmitting the power from your engine to the wheels that drive it. Whether your transmission is an automatic or a manual, it is used to apply the right amount of power to the road.

Inside your transmission is a complex set of gears, which are constantly engaging and disengaging. The transmission does this in response to your car’s speed, the road you are driving on, the weather conditions, and how much power you are demanding at any given moment. All these transmission gears are immersed in a liquid that is generally known as transmission fluid.

The transmission fluid is subjected to a lot of stress. Knowing more about your transmission fluid can help your car to run better and last longer. Join us for an insider’s view of what transmission fluid is, what it does, why you have to change your transmission fluid, what happens if you don’t change it, when you should change your transmission fluid, how to check it, signs that you need to change it, what a transmission fluid change costs, and finally, how to change your transmission fluid.

What is the transmission fluid?

Transmission fluid has a variety of important jobs, depending on what type of transmission your car has. While the vast majority of cars today have automatic transmissions, there are many cars on the road that have manual transmissions. Here are the differences:

What is the transmission fluid and how does it work?Automatic transmission fluid

Because automatic transmissions shift themselves, they are much more complicated mechanisms than manual transmissions. In line with its mission, the fluid in an automatic transmission is required to do a great many things to help the automatic transmission do its work. While automatic transmission fluid is oil-based, it is designed to have lubricating, cooling, and hydraulic qualities. Automatic transmission fluid is made with a special additive package that allows it to do all this:

  • Pour easily at all temperatures
  • Maintain thickness at high temperatures
  • Flow better at low temperatures
  • Clean and protect metal surfaces
  • Lubricate better
  • Prevent seals from leaking
  • Reduce wear
  • Inhibit rust and corrosion
  • Improve viscosity
  • Reduce oxidation

There was a time, nearly a century ago, when all cars with automatic transmissions used the same automatic transmission fluid. That is no longer the case. Today, there are many different types of automatic transmission fluid on the market, and it is important to use the specific type that is recommended by your vehicle’s manufacturer.

Another key point is that automatic transmission fluid is usually a different color from the other fluids found in your car. It is most commonly a cherry red color, but it can be a different color. This makes it easy to identify an automatic transmission leak – if the fluid is red, that’s where the leak is coming from!

How does automatic transmission fluid work?

The automatic transmission in your car is filled with automatic transmission fluid. As the power of the engine flows through the transmission, the automatic transmission fluid circulates through the transmission, doing these very important jobs:

  • It lubricates the moving parts in the transmission
  • It reduces friction inside the transmission
  • It absorbs and dissipates the heat created inside the transmission
  • It operates the hydraulic gear-shifting mechanisms in the transmission

Your automatic transmission fluid is sealed inside the automatic transmission. As a result, it is not exposed to the damaging byproducts of combustion, like your engine oil is. Because of this, your automatic transmission fluid will need changing much less often than your engine oil. The owner’s manual or service booklet that came with your car will tell you what the recommended service interval is.

How does manual transmission fluid work?

A manual transmission is a much simpler device than an automatic. Because the driver does all the shifting, the fluid in a manual transmission has a much easier job. Lubrication, heat dissipation, and wear reduction are the primary missions of manual transmission fluid.

While some manual transmissions use automatic transmission fluid, most use oil. This can range from something similar to the viscosity of motor oil, to a very thick version of it that is known as “gear oil.” Special additives are blended in, to reduce friction and make shifting smoother.

Once again, it is important to use only the manual transmission fluid that is recommended by the manufacturer of your vehicle. This is the fluid that the designers of your manual transmission intended it to have inside.

Why do you have to change the transmission fluid?

It is important to remember that even though it is sealed inside the transmission case, your transmission fluid will eventually degrade. The transmission fluid in your vehicle can become contaminated with metal particles, use up its additives, get dirty, and suffer a loss of its lubricating and friction-reducing qualities. When this occurs, your transmission will not run or shift properly. This could lead to damage and overheating if the correct servicing schedule is not followed.

Changing your transmission fluid at the proper intervals will prolong the life of your transmission, avoid expensive repairs, and will help your car to be more reliable and run much better.

Here are some additional good reasons to change your transmission fluid, depending on whether your car has an automatic or a manual transmission:

Reasons to change your automatic transmission fluid

  • Automatic transmissions operate at high temperatures
  • Worn friction materials and debris accumulate in the transmission fluid
  • Extreme uses like trailer towing and hauling heavy loads wear the fluid out faster

Reasons to change your manual transmission fluid

  • Metal particles from gear wear build up in the fluid
  • Lubricating qualities of the fluid wear out

What happens if you don't change the transmission fluid?

If you do not change your transmission fluid, all the bad things that happen to your transmission fluid as it gets old will eventually result in serious transmission damage. The contamination, particles of dirt and metal, lack of additives and lubrication, fluid leaks, and heat-related deterioration will take its toll on the precisely assembled internal parts of your transmission. It will slip instead of shifting, it will not dissipate the intense heat well enough, and the transmission components will wear at an accelerated rate.

Bottom line? Changing your transmission fluid is cheap insurance, and costs much less than repairing or replacing your transmission!

Recommended Transmission Fluid Change Intervals

Automatic Transmission Fluid

When is it recommended to change the automatic transmission fluid?

The manufacturers’ recommendations on when to change the automatic transmission fluid in their vehicles vary widely. The automatic transmission fluid change interval will also be more frequent if your vehicle is used in “severe service,” which typically means that you routinely tow, plow snow, carry heavy loads, live where high temperatures are common, or spend a lot of time in stop-and-go traffic. The best source for this information is your owner’s manual, which should list both the normal and the severe service automatic transmission fluid change intervals for your vehicle.

As a rule of thumb, you are usually safe to change your automatic transmission fluid every 30,000 to 60,000 miles, although some manufacturers have much longer intervals. Some have eliminated automatic transmission fluid changes entirely, unless you are driving in severe service mode.

There is a good way to know whether your car’s automatic transmission fluid needs changing, regardless of how old it is, or how you drive your vehicle. That is to check your automatic transmission fluid regularly. A simple visual and smell check will tell you if your automatic transmission fluid is in good condition, or whether it needs to be changed. We will get into the details of checking your automatic transmission fluid in a special section below.

Manual Transmission Fluid
"Lifetime" Transmission Fluid

Checking Your Transmission Fluid

How do you check the transmission fluid?How to check your automatic transmission fluid

When checking your automatic transmission fluid, you are really checking two things:

  1. The level of the automatic transmission fluid
  2. The condition of the automatic transmission fluid

Have a clean, white cloth or towel handy as we go through the process.

Checking the level of the automatic transmission fluid

If you have an automatic transmission that comes with a dipstick for checking the transmission fluid, you can easily check its level. Here are some general guidelines, but we highly recommend that you use the exact procedure that is outlined in your owner’s manual. Some manufacturers and some vehicles require you to do things differently than most others, so keep that in mind as we go through the most commonly used process for checking your automatic transmission fluid:

  1. Park your car on level ground. Start your engine and let it run until it has warmed up. Keep it running throughout the entire procedure.
  2. Locate the automatic transmission’s dipstick. The dipstick should be emanating from the transmission itself. On most rear-drive vehicles, it’s located near the back, closer to the windshield, behind the oil dipstick. In front-drive vehicles, it’s typically positioned near the front of the car.
  3. Pull the dipstick all the way out, wipe it off completely with your white towel, and reinsert it fully into its opening. After several seconds, pull it out again. On a side note, you should always check your transmission when the vehicle is on and the engine is warm.
  4. Look carefully at the markings on the dipstick. There will normally be “Full Warm” and a “Full Cold” markings. Sometimes there will be “Full” and “Add” marks. Check the level relative to the “Full Warm” or “Full” mark. If the level is below the mark, your automatic transmission fluid is low and requires that some be added (use a long-necked funnel that fits into the dipstick tube and the correct fluid for your car). Be careful not to overfill. If the level is at or very close to the mark, your fluid level is fine.

Now let’s move on to checking its condition:

Checking the condition of the automatic transmission fluid

Wipe the dipstick on your towel again. Put it back by reinserting it firmly into its opening. Now look at the fluid on the towel closely:

  • Is it bright red, dark red, or light brown in color? If so, your fluid is fine. No problem so far.
  • Is it dark brown or black? That is bad, and it means that your transmission needs immediate attention.
  • Does it smell burnt? That is also bad, and servicing is required right away.
  • Are there particles of debris or metal shavings floating in it? This indicates a damaged transmission.
  • Is the consistency of the fluid very thick, or does it look foamy? Have your transmission checked without delay!

If you have a “sealed” automatic transmission

There are many cars that have automatic transmissions that are sealed at the factory, after being filled with fluid. They have no dipsticks, and therefore no way for you, the owner, to check the level or condition of the automatic transmission fluid. Checking the fluid in these transmissions involves using electronic scanners, or other tools unavailable to the average driver. If your car has a sealed transmission, it will normally be checked by a mechanic during specified maintenance intervals.

How to check your manual transmission fluid

Checking the fluid or oil in a manual transmission is a bit more complicated, compared to an automatic. Because the fluid in a manual transmission usually leads a much easier life, and experiences lower operating temperatures, it does not need to be checked very frequently. In fact, most manual transmissions do not even have a dipstick!

The easiest way to check your manual transmission’s fluid is to have your mechanic do it during your next oil change or recommended service interval. If you feel comfortable doing it yourself, you will need to raise your car off the ground, which will provide access to the transmission from the underside of the vehicle.

Be sure that your vehicle is securely supported, either on sturdy jack stands or with a lift. Once that you have room to work underneath the car in a safe manner, here’s what to do:

Step-by-Step:
  1. Locate the transmission’s filler plug. It will be a bolt on the side of the transmission, located between the top and the bottom of the transmission case.
  2. Remove the filler plug.
  3. Check the fluid level. If the filler hole is large enough, insert your finger into the transmission case to feel the fluid level. It should be up to the filler hole, so you should be able to feel the fluid on your fingertip. If the hole is too small for your finger, insert a clean screwdriver into the hole to check.
  4. Check the fluid condition. Put the oil from your fingertip or screwdriver onto a clean, white cloth. Take a close look. If the fluid is dark, or has metal particles or other debris in it, consult your mechanic.
  5. Add transmission fluid or oil if needed. This will require a hand pump to get the fluid into the filler hole. Use a fresh container of the correct fluid, and pump until the fluid comes out the filler hole. Wipe off any excess.
  6. Reinsert and tighten the filler plug.
  7. Safely lower the vehicle to the ground. You’re done!

Signs You Need to Change Your Transmission Fluid

You can get a general idea about how often you should change the transmission fluid by consulting your vehicle’s operator manual. However, some tell-tale signs to watch out for that may indicate poor-quality transmission fluid include hesitation when the vehicle is changing gears, issues staying in gear, and signs of gear slippage. (For more details, read on.)

Generally, transmission fluid should be serviced about every 30,000 to 50,000 miles, though there may be some exceptions to this rule. For instance, those who drive in stop-and-go city environments and regularly haul heavy loads put more wear and tear on the transmission and thereby require more frequent fluid changes.

Automatic Transmission Fluid

As you are driving, you may notice symptoms that indicate the need to change the automatic transmission fluid in your car. These symptoms include:

Shifting problems: These can appear as difficulties shifting into Drive or Reverse, shifts between gears that are harsh instead of smooth, and shifting that is earlier or later than normal.

Odd noises when transmission shifts: These can sound like squealing, grinding, or whining noises. They will be noticeable when your automatic transmission shifts between gears.

Delayed acceleration after gears shift: This will appear as a noticeable pause between the time that the transmission shifts and the time that it sends power to the wheels.

Your car “surges” when the transmission shifts gears: This will feel like an inconsistent flow of power through the transmission, with moments of too much acceleration quickly alternating with a loss of power.

Your transmission slips out of gear: This happens when your automatic transmission shifts, and it suddenly feels like you are in Neutral, with no power to move you forward (or reverse, if you are backing up).

A burning smell: If you smell burnt transmission fluid, you definitely need to change it.

Manual Transmission Fluid

Costs of a transmission fluid change

Changing your transmission fluid is an important part of your vehicle’s overall maintenance requirements. A transmission is a very expensive component to repair, so the cost of changing your transmission fluid can be considered as insurance against a high repair bill, at some point in the future.

Beyond that, the cost of changing your transmission fluid has quite a wide range. It depends on many factors, such as:

  • Who is changing it? (dealer, repair shop, or you)
  • Is your car a mass-market or a luxury brand?
  • What are labor rates like in your area?
  • What type of fluid does your transmission require?
  • How much fluid does it take to fill your transmission?

At the lower end of the scale, we have you, changing the transmission fluid yourself, on your Toyota or Hyundai. At the other extreme is the Lamborghini owner, having his fluid change done by the dealer. Everyone else falls somewhere in the middle. Here are some ballpark estimates for what a transmission fluid change might cost:

  • Doing it yourself: Under $100
  • Mechanic/repair shop: $100 to $200
  • Dealer: $200 to $300 for mass-market brands, much higher for luxury brands

How do you the change the automatic transmission fluid?

When it comes to changing your automatic transmission fluid, you have a few different options. If you are having a professional do the job, you can choose from a dealer, an independent repair shop, or a dedicated transmission shop. As we stated in the “Costs of a transmission fluid change” section above, prices will vary greatly. Contact several dealers and shops in your area, to find one near you that fits within your budget.

If you plan to change your automatic transmission fluid yourself, you have a choice in how you approach this process, based on the condition and age of your car:

If your car is not too old, does not have lots of miles on it, and you plan to keep it for a while

We recommend the traditional way of changing your automatic transmission fluid, which is messy but thorough. It includes replacement of the transmission filter, a new transmission pan gasket, and cleaning of the pan before reassembly. This will give your car’s automatic transmission the best chance of living a long, trouble-free life.

If your car is old, has very high mileage, and you are not sure how long it will last

In this situation, there is an easy way to change your automatic transmission fluid. It will give you some, but not all the benefits of the traditional method. It is not messy at all, and it does not require you to get underneath your car. The filter and gasket are not removed and replaced, and the pan does not get cleaned. For a car with an uncertain future, this is much less expensive, puts fresh fluid into your transmission, and is way better than doing nothing.

The traditional method of changing your automatic transmission fluid

This is the same technique that most professional shops use to change your automatic transmission fluid. Your car must be raised off the ground, to provide access to the pan located on the bottom of the transmission case. Remember to wear suitable gloves and eye protection. If you haven’t done this before, search online for video tutorials.

Here are the parts and tools that you will need:

  • Transmission service kit for your car – includes new filter and gasket
  • Correct type and amount of fresh automatic transmission fluid (check owner’s manual)
  • Jack stands, ramps or a lift to raise car up
  • Wheel chocks if needed
  • Drain pan big enough to catch fluid from transmission pan opening (at least 2-gallon capacity)
  • Tarp to catch excess drained fluid
  • Socket wrenches
  • Torque wrench (if available)
  • Screwdrivers
  • A mallet
  • Long-necked funnel that fits into transmission dipstick tube
  • Several clean, small microfiber towels or shop rags
  • 2 Empty gallon water jugs to measure drained transmission fluid
  • Cleaning solvent

The Process: Let’s get started!

  1. Let your engine idle for a few minutes, which will warm up the transmission fluid so that it flows and drains faster when the time comes. Once this is done, shut off your car.
  2. Raise your car safely off the ground.
  3. Put the tarp down, under the transmission pan. Place the drain pan on top of the tarp.
  4. Remove the pan bolts on one side of the transmission. Watch out for hot leaking fluid, as well as hot parts of the engine.
  5. Slowly loosen the rest of the transmission pan bolts. This should let the old fluid flow out of the transmission and into the drain pan. If the gasket remains sealed, gently pry it loose with a screwdriver (and the mallet if necessary). Once that the flow of fluid slows down to a trickle, completely remove the pan and pour its contents into the drain pan.
  6. Visually inspect and clean the gasket mating surfaces on the pan and the transmission with the solvent. Be sure that these surfaces are smooth and clean, with no old gasket residue remaining.
  7. Look closely at the pan for any evidence of metal shavings or other residue that may have been deposited there. Then clean the pan with the solvent.
  8. Remove the old transmission filter (which contains fluid, so drain it into the drain pan). Check the mounting hardware and remove any residue, then install the new filter.
  9. Attach the new gasket to the pan, using only oil-soluble grease. Do not use any other type of gasket sealer.
  10. Reattach the pan to the transmission with the original bolts, hand-tightening them. Tighten the bolts, or torque them to the recommended setting, using a spiral or “X” pattern, so that even pressure is applied to the gasket, all the way around the pan. If your car’s manufacturer has any specific requirements for this process (check online or in the car’s shop manual), follow them to the letter.
  11. Lower the car to the ground. Pour the drained fluid into your empty water jugs, to measure how much was drained out. Add that amount of fresh fluid, using the funnel inserted into the transmission dipstick tube. Start the engine and let the car run until warm. Check the fluid level and add fluid if necessary, until it is full. Shut the car off and check for leaks around the pan before driving the car.
  12. Dispose of the old transmission fluid properly, according to your local requirements. Many auto parts stores will recycle the used fluids for you – call around or search online.

The non-traditional way to change your automatic transmission fluid

If you really don’t want to make the investment of time and/or money into the traditional method, but you do understand that your older car would benefit from some fresh transmission fluid, here is a simple procedure to try. Your car stays on the ground, the transmission stays closed, you don’t need any special tools, no electricity is required, and it will be over quickly. Wear protective gloves and safety glasses.

Things you will need:

  • Transmission fluid vacuum pump (find one here)
  • Correct type and amount of fresh automatic transmission fluid (check owner’s manual)
  • Long-necked funnel that fits into transmission dipstick tube
  • Clean, small microfiber towels or shop rags, for cleanup

Here’s how it works:

  1. Remove your car’s transmission dipstick
  2. Insert the vacuum tube from the transmission fluid vacuum pump all the way down the dipstick tube, until you first feel it contact the pan. Don’t go any further.
  3. Close the valve where the vacuum tube connects to the pump’s tank. Manually pump, according to the directions, until there is a sufficient vacuum inside the pump’s tank.
  4. Release the valve on the vacuum hose, and you should see the old transmission fluid getting sucked into the pump’s tank. Remove the hose from the dipstick tube when the fluid stops flowing.
  5. Check the level lines on the pump’s tank to know how much fluid was removed. Add that amount of fresh fluid using the funnel, inserting it into the transmission dipstick tube. Start the engine and let the car run until it is warm. Check the fluid level and add fluid if necessary, until it is full.
  6. Dispose of the old transmission fluid properly, according to your local requirements. Many auto parts stores will recycle the used fluids for you – call around or search online.

How do you the change the manual transmission fluid?

Changing your manual transmission fluid (or oil) is a much simpler task, compared to an automatic transmission. There is no filter, no gasket, and no pan to remove. Because most manual transmissions do not have dipsticks, it is usually necessary to raise the car to get access from underneath.

Here is what you will need:

  • Correct type and amount of fresh manual transmission fluid or oil (check owner’s manual)
  • Jack stands, ramps, or a lift to raise car up
  • Wheel chocks if needed
  • Drain pan to catch drained fluid from transmission (at least 1-gallon capacity)
  • Socket wrenches
  • Torque wrench (if available)
  • Hand pump for refilling transmission
  • Clean, small microfiber towels or shop rags, for cleanup

Here’s how to do it:

  1. Raise your vehicle safely off the ground.
  2. Put the drain pan under the transmission.
  3. Remove the fill plug from the side of the transmission.
  4. Remove the drain plug from the bottom of the transmission. This will let the fluid drain out into the drain pan.
  5. When the fluid has completely drained out, replace the drain plug. Replace the washer if appropriate, and then tighten it to the proper specs.
  6. Use the hand pump to refill the transmission with the recommended amount of fresh fluid, placing the pump’s exit hose into the fill hole. When you see fluid coming out of the fill hole, it should be full.
  7. Replace the fill plug. Replace the washer if appropriate, and then tighten it to the proper specs.
  8. Clean up any excess fluid and lower the car.
  9. Dispose of the old transmission fluid properly, according to your local requirements. Many auto parts stores will recycle the used fluids for you – call around or search online.

Bonus Content: Transmission Flush

Do you need to have your automatic transmission flushed?

In the course of finding the right place to have your automatic transmission fluid changed (if you’re not going the DIY route), you may be told that instead of having your automatic transmission fluid changed, you need to have it “flushed.” What does that mean?

Transmission flushing is a recent invention

Before the 1990s, there was no such thing as automatic transmission flushing. The only servicing procedure was the traditional way, as we have described it above. Drop the pan, drain the old fluid out, inspect the contents of the pan, replace the filter and gasket, clean and reattach the pan, and refill with new fluid. This worked just fine – until the flushing machine was invented.

Flushing means profits – at your expense

These expensive machines were sold to repair shops of all types, with promises of big profits for the shop owners. Instead of doing things the tried-and-true traditional way, shops could now hook up the machine, use high pressure (and sometimes a cleaning solution) to clean out the old fluid and any other debris, and refill your transmission with fresh fluid. Using the flushing machine requires much less of a mechanic’s expensive time, and the shop can charge the customer a premium for the service. What’s wrong with that? Here’s what:

  • The shop’s need to recoup the cost of the machine makes flushing much more expensive than a fluid change.
  • The pan is not removed, checked for debris, or cleaned.
  • The filter is not changed.

Flushing is just not worth what it costs

All of this makes flushing your transmission a poor value, with no opportunity to see inside your transmission, diagnose any problems in progress, and install a new filter. It sounds rather similar to our quick and easy vacuum pump fluid change explained above, doesn’t it?

Add to this the fact that most vehicle manufacturers do not recommend or require include an automatic transmission flush as part of their vehicles’ recommended maintenance schedule. So why waste the money? Go for the standard automatic transmission fluid change that is specified in the owner’s manual.

The transmission is the second-most important component in your vehicle, so you want to ensure that it gets the proper care and maintenance. Failure to address issues with the transmission fluid could result in premature transmission failure, and new transmissions can cost several thousand dollars. The good news is that it’s very easy to check the quality of your vehicle’s transmission fluid and fluid levels, and then take the necessary next steps from there. You just need to know where to look under the hood.