In much the same way that engine oil is used to lubricate and cool your engine, transmission fluid is used to lubricate and cool your automatic transmission. Depending on the type of transmission you have, whether it's dual-clutch automatic, continuously variable transmission, or just conventional, you may be required to use a different kind of transmission fluid but they all need something. The best thing to do is to check your owner's manual to find out for sure what you should be using in the event that you need to replace yours. Of course, before you do that you need to check the levels of transmission fluid in your vehicle to make sure it's still at the right level and in good enough condition to keep doing its job.
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Do You Check Transmission Fluid with the Car Running?
It's worth noting before you take the time to check your transmission fluid your vehicle should be running when you do this. It's always best to check transmission fluid when it's warm and the car is running rather than from cold. You should have your vehicle in neutral or park with your parking brake on. You don't want to do this with an engine that's been running for hours and is very hot, but if it's been allowed to warm up for a moment that's a good time to do it.
How to Check Your Transmission Fluid
With your engine running, you need to locate your transmission fluid dipstick. Not every car has one of these, but if yours does, you need to make sure you're looking at the right thing. You don't want to mistake this for the oil dipstick, which is also going to be present under the hood. It should be a different colour than your oil dipstick so you can tell that it's something else and it will likely be located near the rear of the engine if you have a rear wheel drive vehicle but towards the front of the engine sticking out of the transaxle if you have a front-wheel drive vehicle.
Step 1: Pop the dipstick out of the reservoir and take a look at the level. There should be a line that lets you know the maximum fill level so you can see if the fluid mark is at all in the ballpark. If it's very low, you know you're going to need to add some more fluid to the reservoir.
Step 2: You may want to use your finger to test the quality of the fluid at this point. Just touch your index finger to the fluid on the dipstick and rub it between your finger and thumb. What you should be seeing is a pink to red coloured liquid that is clear and not gritty or thickened in any way. If it smells burnt at all, if it's muddy in color or texture, or there is grit in it, then you have a problem with your fluid, and it is going to need to be changed.
Step 3: You can use a clean, lint-free rag to wipe off a dipstick before you reinsert it. Take another look at the fluid on the rag to make sure the colour is right and there isn't any debris or particulate on the rag.
Step 4: Pull up the dipstick again to double check the levels. If it's not full, you can insert a funnel into the dipstick tube and add more transmission fluid until it reaches the full line. You want to make sure you have the exact same kind of transmission fluid that you're already using in your vehicle before you top it up with any. Also, if the fluid in your reservoir is burnt, dark brown to black, or full of grit then you're going to want to actually do a full transmission fluid flush rather than simply adding new fluid into the tank. If it is badly contaminated; you won't be doing yourself any favours by just adding a little bit more clean fluid to the tank.
How to Check Transmission Fluid Without a Dipstick?
Not every car has a dipstick for checking transmission fluid levels. That obviously makes it harder to find out how much transmission fluid you have. It also makes it difficult to top up the fluid because most methods of doing this require you to pop a funnel in the dipstick tube and add more fluid. So, what can you do if that's not an option?
There are a number of manufacturers that produce vehicles with no dipstick automatic transmissions. Generally, these are European vehicles with automatic transmission but that's not a hard-and-fast rule.
If your transmission doesn't have a dipstick then the fluid has to be checked at the transmission itself. That means you need to get the car up on jack stands and keep it level. Your transmission will have a fill plug on the side of the case which is not the same as a drain plug which is at the bottom of the sump.
You need to have the transmission fluid warm for this to work, and your foot on the brake so that you can cycle through the gears to make sure the fluid is in all parts of the transmission. Then, allow your engine to idle and remove the fill plug. That should allow a small amount of fluid to stream out. If it doesn't happen, then you have low transmission fluid. It's a complicated method of getting the job done, but that's the only option you have if you want to check the levels.
When it comes to adding new fluid to a system like this you need something like a fluid transfer hand pump. These aren't very expensive, you could probably get one for under $30, and you need it because you can't get a funnel into the plug to add more fluid. With the engine still running you can use the pump to add fluid until it begins to overflow a little bit. When some starts running out, then you know you've got it filled. So, you can tighten the plug as necessary and you're good to go.
This is a very basic breakdown of how this job is done, however. Some manufacturers have additional requirements for how transmission fluid needs to be added to a vehicle like this. For instance, Audi and BMW have temperature requirements for the transmission fluid. According to their recommendations your fluid should be between 86 degrees Fahrenheit and 122 degrees Fahrenheit before you check or add any new fluids. Audi, in addition to this, recommends you cool new fluid to ambient temperature before refilling it. That just makes it a longer process.
For vehicles like Toyotas and Volkswagens, they recommend that a scan using a certain tool be done that opens specific passageways in your transmission before checking fluid levels, something that your average driver is unable to do at home because these are proprietary tools.
What are the Signs of Low Transmission Fluid?
There are generally a few signs and symptoms you can be on the lookout for to let you know that your transmission fluid may be low and that you should give it a look in the first place. Obviously this isn't the kind of thing you're going to do every time you go out for a drive, so something has to happen to make you want to check the transmission fluid levels.
Low transmission fluid levels can cause some serious problems with your transmission seizing up and failing on you, the cost of replacing damaged transmission can be incredibly expensive. The complete replacement of your transmission may cost you around $4,000 or more, so you definitely don't want to slack on making sure your fluid levels are where they need to be. If you're experiencing any of these symptoms, make sure you take a look at your fluid levels to find out what's going on.
Transmission Slipping
You'll notice this happening as you change gears when you're driving, and your transmission simply drops back to the gear you were in previously for no reason. It may also shift into a higher gear unprovoked as well. This can cause some erratic RPMs, unusual sounds and problems with your speed. The most serious concern here is that if you are driving in traffic at a high rate of speed and your transmission slips to a low gear causing you to drop speed, you could be at risk of a serious accident.
Slow Shifting
If your transmission fluid is low enough when you try to shift gears you may notice that the transmission will not engage right away. There could be a pause of several seconds before the new gear engages. Again, this can lead to serious accidents if it happens in a tense situation when your reaction time is of critical importance. This is especially true if it happens when you're shifting into drive or reverse. The reason it happens is because the hydraulic pressure is so low that the gear change can't fully engage.
Overheating
This makes sense as transmission fluid is required to maintain the temperature of your transmission. If you're finding that your vehicle is losing power and there's smoke coming from under the hood, a burning smell and your shifting isn't working the way it's supposed to then your transmission is likely overheating which is caused by problems with your fluid levels. If this is happening, you need to get it fixed right away because the likelihood of expensive or irreversible damage to your transmission is very high.
Inability to Shift Gears
When your transmission fluid levels are too low or the fluid itself is too contaminated then your ability to shift from one gear to another will be greatly diminished or may fail entirely. If this happens when you're driving, it could lead to some serious accidents. Being unable to shift means not only can you not shift to a lower or higher gear, but you may not be able to shift into park even.
Noises
One of the clear signs that you have a problem with your transmission are the sounds that will come from it when it's not working properly. A smooth running transmission should be silent as you shift through gears. When your transmission fluid is low then the transmission will start producing very noticeable grinding or clunking sounds. They will also continue to get worse as your fluid levels get worse. It's possible these noises are indicative of a different issue, but in particular with grinding noises, the first place you want to look is your transmission, especially if it occurs while you're actively changing from one gear to another.
Fluid Leaks
Another sure fire sign that you have a problem with your transmission fluid is if you can actually see the fluid leak itself. Transmission fluid is usually bright red in colour so if you notice any drops of red fluid that have pooled under your vehicle when you park, or if you can do a quick visual inspection of your engine and see red fluid pooling somewhere, then you know you have a transmission fluid leak that needs to be addressed.
Check Engine Light
Problems with your transmission are just one of many hundreds of potential causes for a check engine light to come on. In and of itself a check engine light is not very helpful in diagnosing any particular problems you're experiencing. If this is related to your transmission you will likely have to rely on both the check engine light and some of these other symptoms to help you determine what the problem is.
If you're not 100% sure you can help get to the root of the problem by using your own OBD2 scanner to find out why the check engine light came on your dashboard. An on-board diagnostic tool as they are also known is the tool that a mechanic will use to determine why a check engine light came on and what it's alerting you to. You can buy your own on Amazon.com for as little as $30. When you plug it into your car it will give you a code that can identify the nature of the problem that caused it to go off in the first place.
The Bottom Line
Keeping your transmission working properly is integral to ensuring that your car is able to do what you want it to do. The transmission is one of the most important systems in your vehicle and if it fails on you then your car simply will not work. For the cost of a new bottle of transmission fluid, you may be saving yourself thousands of dollars worth of repairs down the road.