Transmission fluid is essential for your car to run smoothly. They help to lubricate the insides of your transmission and keep everything cool. However, there is such a thing as too much transmission fluid and it can lead to damage if left ignored. We’ll tell you the signs that your car has too much transmission fluid, what it can do to your car, and how to rectify the problem.
- How a transmission works
- Consequences of too much fluid
- How to change transmission fluids
How a Transmission and Transmission Fluid Works
The transmission in your car is quite complicated, but we’ll try to keep it simple. In essence, its job is to convert power from your engine and transfer it to your wheels via a driveshaft. By using a transmission, your engine can transfer power more efficiently. They keep your engine RPM low while delivering power to your driven wheels.
Transmissions work by using gears and gear trains to transfer power. These gears will obviously be grinding against each other which creates friction, and friction creates heat. This is where the transmission fluid comes in. It lubricates the components inside of the transmission which reduces friction and ultimately reducing heat. Additionally, some transmission fluids have cleaning properties as well, which helps to clean and protect the metal surface of the gears. As a result, the transmission works smoother, cooler, and can last longer.
Also, if you have an automatic transmission in your car, then the transmission fluid serves another purpose. An automatic transmission works by using a torque converter that connects the engine to the transmission and uses pressurized fluid to transfer power. The torque converter serves as a clutch that lets the car slow down or stop without stalling the engine.
There are many different types of transmissions out there, including manual, conventional automatic, dual-clutch systems, and CVTs. Today most cars use an automatic for their transmission, but they all require lubrication. You can learn more about how an automatic transmission works in the video below:
Consequences of too Much Transmission Fluid
Carmakers have very specific recommendations for the different types and amount of fluid that goes into different parts of their cars. It goes without saying, this includes the transmission fluid. Your transmission will require a certain amount of fluid to maintain the right viscosity. With the right amount, it won’t be so thin that it’s not protecting the components, but it won’t be so thick either that it increases the load for the gears. Needless to say, while transmission fluid is necessary, overfilling can cause several problems:
Increased Transmission Fluid Pressure
As mentioned, in automatic transmissions the fluid is also pressurized to operate the gears. Overfilling your transmission fluid will increase the pressure, and in a transmission, this can lead to air contamination. This occurs when the rotating gears inside of the transmission splashes the fluid around and cause a formation of air bubbles or foam in the fluid. This air contamination then will affect the viscosity of the fluid and reduces its lubricating capability.
When the fluid has bubbles or foam, it will deliver pockets of air instead of fluid to some parts of the gears. These parts won’t get lubricated hence the decreased lubricating capabilities. When the gears aren’t lubricated, the metal surface will grind against each other. This will then lead to premature wear, as well as making the transmission more sluggish and unresponsive.
In addition to the increased wear, excess grinding means more friction. And as mentioned, friction creates heat, and finally, it will overheat your transmission (which is what the “AT oil temp” light in your Subaru wants to tell you). Overheating doesn’t directly affect the gears, but it can break the transmission seals. Since the seals are responsible for keeping the fluid inside the transmission, fluid will leak out once these seals fail.
If the fluid leaks out, then the fluid levels inside the transmission will decrease. Once the fluid goes below the minimum, the gears won’t be lubricated and will create even more friction. If left unserviced, lack of fluid can result in loss of ability to shift the transmission as you drive along.
To summarize, excess transmission fluid can cause overheating in the transmission. Then when the transmission overheats, the seals may break down and fluid will leak out. Finally, when the fluid leaks out the transmission won’t have enough fluids, the transmission will overheat even further and will develop shifting problems.
If this is left unfixed, it will eventually lead to transmission failure. Once the transmission fails, your options are either to rebuild it, buy a secondhand, or a remanufactured transmission. All of which are very expensive options. Because of this, it would be wise to pay attention to your transmission fluid level; making sure it is neither too low nor too much. This segues us perfectly into the signs you should look out for.
Signs You Have too Much Transmission Fluid
1. Shifting Problems
As mentioned, shifting problems may develop if you have too much transmission fluid. However, keep in mind that shifting problems may be caused by something else. If you have an automatic transmission, it may be caused by a faulty solenoid. The solenoid is a valve that controls fluid flow in the transmission. If the solenoid has gone bad, then you may experience shifting problems, especially when downshifting.
A transmission solenoid typically lasts for about three years, but you can easily extend its lifetime with proper maintenance. If it has gone bad, then expect to pay between $250 – $400 for a replacement job.
In any case, your transmission should shift smoothly under normal driving conditions. If you notice shifting problems when you drive along, it would be wise to take the car to a repair shop and have it examined. Hopefully, you’ll catch the problem early and won’t need expensive repairs.
2. Transmission Fluid Leak
As mentioned, overfilling your transmission can cause overheating which will lead to damage to the transmission seals. When the seals are damaged, fluid will leak out of them. If you notice a puddle under your car, take a look at that puddle. If the fluid is red, then that’s the transmission fluid and you will need to have the seals replaced to stop the leak. While we’re at it, transmission fluid should be bright red. If the fluid is dark red, then the fluid is burnt and you will need to change them.
You might be wondering, how much will it cost to fix your car if you have a fluid leak? Well, this depends on where the leak is coming from. Most transmission fluid leaks are around $250 – $500 to repair, depending on the car’s make and model of course. However, things get more costly if the front seals are cracked and that’s where the leak is coming from.
If your front seals are cracked, replacing them can cost anywhere between $400 – $1,000. This is because your mechanic will need to remove the transmission to gain access to the front seal, and it’s a long and laborious process, hence the high labor cost. If your car has done over 100,000 miles, we recommend taking better care of your transmission since the seals often fail at around this mileage.
3. Whining or Grinding Noise
When the transmission has a problem, it will often make a noise. If you hear a low-frequency hum from the transmission, this is usually a sign of excess transmission fluid. Meanwhile, a whining noise from the transmission usually means there’s a problem with the fluid pump. And if you hear a grinding noise, then this means that the gears are rubbing against each other, which is really bad.
In any case, these unusual noises are an indication that there’s a problem with your car. Whether it’s coming from the engine, the transmission, or parts of the suspension assembly such as the CV joints, you’ll want to check your car. Catching the problems early can help you to avoid costly repair costs.
4. “Overfilled” Transmission Dipstick
Thankfully, you can quite easily check your transmission fluid level since most cars have a transmission dipstick. While some would say it isn’t entirely accurate, checking your transmission dipstick will give you a good idea of how much fluid you have in your transmission. To do this, you will first need to locate the transmission dipstick in your engine bay, it usually sits further back in the engine bay. It’s usually marked, so you can tell which one’s your engine dipstick and which one’s the transmission’s dipstick.
After you locate the dipstick, make sure your car is on a level surface and is running at operating temperature. Then pull the dipstick out and wipe it clean. Afterward, put it back all the way in, and pull it out again. The dipstick has indicators on how much fluid is in the transmission. If it’s below the minimum level, then you will need to add more. If it’s above the maximum level, then you need to drain some of it out.
While we’re at it, this is also a good opportunity to check the condition of your transmission fluid. Wipe the dipstick on a white tissue or towel so you can see the color. As mentioned, a good fluid should be bright red. If it’s dark red or even black, then you will need to change the fluid.
Keep in mind some cars have different requirements when checking the transmission fluid level. For some cars, it would be best to have the engine running, while others would be better when the engine is off. We recommend consulting with your owner’s manual on how to check the transmission fluid level in your car (to learn more, check out our explainer on when to check transmission fluid). If you need a visual guide on how to check your fluid level, watch this video from Eric The Car Guy:
If You Have a Sealed Transmission
Some cars, such as the Ford Fiesta, have a “sealed” automatic transmission. This type of transmission does not have a transmission dipstick, so checking them will be more difficult. First, you will need to locate the transmission’s inspection plug. Afterward, the transmission has to run at a certain temperature to give you an accurate reading. This will vary from one car to another, so you will need to check your manual. To make sure the transmission is at the correct temperature, you can use an OBD scanner to monitor the temperature.
Afterward, open the transmission’s inspection plug and see if any fluids flow out. If it does, then you have an overfilled transmission. In which case, you will need to drain some of them. Watch this video below on how to check the transmission fluid without a dipstick:
Changing Transmission Fluid
Since the transmission fluid is crucial for the smooth operation of your car, you will need to change them regularly. They usually need to be changed around 30,000 to 60,000 miles. While there have been arguments on whether or not you should change the fluid, especially in high-mileage cars, the consensus is that you should do it. This is because the fluid can deteriorate over time, and you don’t want to run on burnt transmission fluid. Check your owner’s manual to see just how often you need to change them.
Also, the manual usually will tell you whether you need to change or flush the fluid. If the manual recommends you do a flush, then you will need to go to a repair shop that has the flushing machine. It typically costs around $150 to do a transmission flush.
We’ll give you a guide on how to change the transmission fluid, as well as what you should do if you’ve overfilled your transmission.
How to Change Transmission Fluid
- Use a jack to raise your car and then put it on a jack stand. Ideally, you should be working on a level surface, and you should use wheel chocks to prevent the car from rolling.
- Place a container under the transmission fluid pan to catch the old fluid as you drain it.
- Loosen the pan bolts to drain the fluid. The fluid will immediately gush out once the bolts are loose, so be sure to be safe and not be in the way of the fluid.
- Once completely drained, you will need to replace the pan gasket and filter (if your car still has a transmission filter). A new pan gasket will cost you between $40 – $150, while the filter is usually around $160 depending on the make and model. Don’t forget to tighten the transmission pan bolts once you’ve fit in the new parts.
- To fill the fluid, open the hood and pull out the transmission dipstick. Insert a funnel and pour the new fluid through the funnel. Make sure you have the right type of transmission fluid and fill it with the correct amount.
- Once done, pull out the funnel and reinsert the dipstick.
- Afterward, start the car and get it to operating temperature. Then check the dipstick to see if you’ve overfilled the fluid. If you haven’t, give yourself a pat on the back and marvel at your work.
If you need a visual guide, we recommend watching this how-to video from ChrisFix:
Changing the transmission fluid is an easy to moderate job to do. But if you don’t feel like doing this on your own, you can have your repair shop do it for you. They will typically charge you around $250 for the job.
If You’ve Overfilled Your Transmission Fluid
After you fill the transmission fluid (to find out more, check out our discussion on will a torque converter fill itself), if you’ve overfilled it then you will obviously need to drain some of them out. Repeat steps 1 to 3 on our transmission fluid change guide, and let out some of the fluid. Then reinstall the transmission pan to seal it. Obviously, a bit of guesswork is going to be involved, but simply drain out some of the fluid, measure how much you’ve drained out, and check the dipstick again.
If the fluid is now at the appropriate level, then job done. But if it’s now below the recommended level, then you need to make an educated guess on how much you should add based on the amount of fluid that you’ve just let out.
Maintaining Your Transmission
On top of changing the transmission fluid, there are other things you can do to prolong the life of your transmission. While most transmissions usually fail at around 150,000 miles, you can easily prolong its lifetime with proper care and maintenance. If you take proper care, they can last for up to 300,000 miles.
1. Check Transmission Fluid Periodically
We’ve mentioned it before but we’re mentioning it again: check your transmission fluid. You should check every 60,000 miles or so. If your car has a transmission dipstick, then simply pull it out and wipe it on a bright rug or a paper towel. If it’s bright red, your transmission fluid is in good condition. And if it’s dark red or black, then it’s burnt and you will need to change it.
2. Use the Correct Transmission Fluid
Again, carmakers make specific recommendations on what type of fluid should go in each part of the car, including the transmission. Using the wrong type of fluid can cause damage to your transmission and eventually lead to costly repairs.
Your owner’s manual should have this information. If you’re not sure, check with owners forums online or ask a professional mechanic what type of fluid you should use for your car.
3. Warm Up Your Car Before You Drive
We’re all guilty of doing this at some point in our driving life. But you should let your car warm up before you drive, especially with older cars. Letting your car warm up will let the engine oil and transmission fluid get to their working temperature which will protect the components better. With most new cars, waiting for about one minute is enough. But with older cars, you should wait a bit longer before you drive away.
4. Don’t Change Gears While Your Car is Moving
Do not change gears from ‘drive’ to ‘reverse’ while the car is moving or vice-versa. Doing so will put a strain on your transmission and can grind the gears. This will lead to damage and eventually some very costly repairs.
5. Change the Transmission Filter
A lot of modern cars no longer have a transmission filter, but if your car has one then you should change it regularly. It’s recommended that you change it every 30,000 miles or two years (whichever comes first). Check with your owner’s manual to see the manufacturer’s recommendation. While you’re at it, don’t forget to change the transmission fluid as well!
6. Don’t Drive on Spare Tires
If you have a flat tire and you need to use the spare tire, then by all means go ahead. But if your spare tire is a smaller space saver, then don’t drive on it for an extended period of time. Doing this will put a strain on your transmission, as well as other components, and ruin your car’s wheel alignment.
Also, don’t mix and match your tire size. Mismatched tires will have the same effect and can damage your transmission over time. Additionally, mismatched tires will cause uneven tire wear and shorten the life of your tires.
7. Avoid Using Your Car for Towing
Unless you absolutely have to, you shouldn’t use your car for towing. Towing will increase the load your car (including the transmission) has to carry, which makes the transmission work harder and can cause damage in the long run. If you absolutely have to use your car to tow, every car has recommendations on the maximum weight it can tow. Be sure you don’t exceed this weight limit.
8. Don’t Tow Your Car with the Driven Wheels on the Ground
This doesn’t get talked about enough. If your car has broken down and it refuses to start, then your only option is to have it towed. Whatever happens, do not let your driven wheels be on the ground and rolling. If your driven wheels are rolling while the car is off, it can damage the transmission.
For example, if you have a front-wheel drive car, then the front wheels should be lifted with the rear wheels on the ground. If you have a rear-wheel drive car, then the car should be towed from the back so that the rear wheels are lifted, and the front wheels are on the ground.
If you have an all-wheel drive vehicle, then ideally you should use a tow service where they put your car on top of the truck. This way, none of the wheels are on the ground.
Transmission Fluid: Need-to-Know Facts
- Proper transmission fluid levels are crucial for a car’s performance, as the fluid acts as a lubricant and reduces friction, controls temperature, and protects metal surfaces.
- Having too much transmission fluid can have negative effects on a car, reducing lubrication within the crankshaft, causing transmission fluid leaks, and making it difficult to shift gears.
- Symptoms of an overfilled transmission include an overheating engine, transmission fluid leaks, difficulty shifting gears, and foamy transmission fluid.
- Foamy transmission fluid is caused by excess fluid mixing with air, leading to poor shifting, high internal temperatures, seal failure, and part pitting.
- If the engine and transmission seals fail, a transmission rebuild may be required.
- It’s important to pay close attention to transmission fluid levels and not add too much fluid to avoid damaging a car’s transmission.
- To check transmission fluid levels, consult the owner’s manual or have a mechanic do it.
- Adding transmission fluid is a delicate process that requires precision and attention to detail.
- Regular transmission fluid checks and changes can help prolong the life of a car’s transmission.
- When in doubt about transmission fluid levels or other issues with a car’s transmission, it’s best to consult with an expert to avoid further damage.
The transmission fluid is essential for your car’s smooth operation. You need to have the correct amount of fluids so it can lubricate the transmission properly. Add too much and it can damage your transmission and cause serious problems in the long run. And since a transmission is essential to a car, repair costs are not cheap. If you need a rebuild or a new transmission, then you’re looking at thousands of dollars for repairs. Some cars can cost up to $4,500 for a transmission rebuild.
Be sure to follow our tips on how to maintain your transmission. And if you’ve overfilled your transmission fluid, hopefully, our guide will help you on how to rectify the problem.