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How to Check Transmission Oil – Everything You Need To Know!

How to Check Transmission Oil

Checking the transmission oil in your car, also called transmission fluid, is part of the routine maintenance that you should be doing to keep your car running smoothly and safely all the time. Just like engine oil, transmission oil is one of those things that you should be aware of and observant of on a regular basis. If you know the quality of your transmission oil, and if you know that the levels are good, this can go a long way to staving off any problems that may develop in your transmission in the future.

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If a transmission problem gets bad enough and you require a major transmission repair, or even a new transmission to be installed in your vehicle, you could end up paying as much as $4,000 or more in repairs. Odds are you don't want to be spending that kind of money so it's a good idea to keep an eye on your transmission fluid levels before you develop a problem that requires a massive repair bill down the road. That's just good sense and being a responsible car owner. The more care you take to ensure that all your fluids are working properly and are in the right amounts in your vehicle, the better it's going to run and the longer it's going to last.


So, knowing that you need to maintain your transmission fluid, how exactly do you go about doing that? Let's take a look at everything you need to know about checking your transmission oil, what to do when it's low, and signs that it needs to be checked in the first place.


 Do You Check Transmission Fluid When It's Hot or Cold?


When It comes to checking your transmission fluid this is not done the same way as checking things like motor oil or coolant.  Both motor oil and coolant are best checked when your engine is cold or at most just barely warm. Ideally you wouldn't want to check either one if your car has been running recently at all because of the risk of burning yourself or sustaining some kind of injury. Coolant especially is very dangerous to check when your engine is still warm and could escape as steam that could cause serious damage.


Transmission fluid however is best checked when your vehicle is running. The reason for this is that transmission fluid, like any fluid expands when it's warm and contracts when it's cold. You'll get a better reading of how your transmission fluid levels are in your vehicle if you check it when it's running warm. If you check it when it's cold, the levels may seem low and you could end up over filling the reservoir as a result.


 Do You Check Transmission Fluid with the Car Running?


Not only should your engine be warm when you check your transmission fluid levels, it's best to check when your engine is actually still running. In part this is because of the torque converter in your transmission. This is one of the main compartments in your transmission that holds fluid and when it's full the level of the torque converter is higher than the level of the pan. However, when your engine is stopped fluid drains from the torque converter into the pan and you'll end up with an incorrect reading on the dipstick when you check it. So, when your engine is running, you'll have fluids all through the transmission system including the torque converter which will give you a more accurate reading of the levels that your car is using when you're driving it, this is of course more important than what the transmission fluid is doing when your car is just sitting still not being used. 


This is essentially the opposite of how oil is checked in your car because the level of oil in the pan is actually important when it comes to motor oil.  Motor oil doesn't expand nearly as much as transmission fluid does when it's warm, so they need to be measured differently. Likewise, transmission fluid is very much dependent on pressure in the lines where motor oil is much less so.


How to Check Your Transmission Fluid the Right Way


Now that you know when you're supposed to be checking your transmission fluid you just have to know how to check your transmission fluid.  Much like the oil in your car, the transmission fluid will have a dipstick that you can check to determine your levels. This will not be true of every make and model of car however so you're going to need to find out whether or not your car has a transmission fluid dipstick. Make sure you're not mistaking this for the engine oil dipstick as they are very different things. Your transmission fluid dipstick will be a different color and it will probably be located near the back of the engine if you have a rear wheel drive vehicle or the front if you have a front-wheel drive vehicle.


Step 1:  Once you have located the transmission fluid dipstick you can pull it out of the reservoir and look at where the level is marked on the stick. Just like your engine oil dipstick there will be lines that show the maximum and minimum fill level. If your transmission fluid is showing below the minimum line, then you know you need to add more fluid to the reservoir. Aside from checking the levels, this is a good time to check the quality of the fluid as well.


Step 2:  Using a clean rag or a paper towel you can wipe the dipstick free and take a look at the fluid colour. Transmission fluid should be red, if the fluid that you've wiped off the dipstick is brown to black in colour then your transmission fluid is contaminated and is going to need to be flushed from the system. You may also take this opportunity to give it a feel with your fingertips. Just rub some between your thumb and forefinger and see if there's any grit or debris that you can feel. If you can, then there's also a problem with the quality of your fluid. There should be no grit or texture at all in your transmission fluid. What you're looking for is clear liquid that is pink to red in colour. It should have a bit of an oily consistency but nothing too thick and muddy and certainly never gritty or chunky.


Step 3: Reinsert the clean dipstick into the reservoir and then pull it out one more time. This is just double checking the levels to make sure you can see exactly where it's at. If you do have low transmission fluid, you can use a funnel and put it into the dipstick tube right now to add new transmission fluid in. Again, you only want to do this if the fluid that's already in the reservoir is clean and uncontaminated. Just top up the reservoir until you're able to measure between the minimum and maximum fill lines on the dipstick itself.


Step 4:  If the transmission fluid in the reservoir is showing that it's not clean, either because there's contamination in it or it seems to be burnt, that you don't want to add new fluid to the reservoir at this time. What you're going to need to do is conduct a full flush of your transmission before you add anything to it. A transmission flush at a mechanic will probably cost you in the neighbourhood of $100 to $200. Depending on the kind of car you drive this may end up being even more expensive, sometimes as much as $400, but that's usually reserved for some more higher-end vehicles.


 A transmission flush is absolutely necessary if you have contaminated fluid. Contaminated fluid will cause your transmission to wear down quickly and overheat or seize up on you. As we said, the potential damage associated with transmission problems like this can be very costly. The sooner you can get it fixed the better. And for the cost of a transmission flush, rather than transmission replacement, it's definitely worth it.


 How to Check Your Transmission Fluid Without a Dipstick


If your car is a kind that does not actually have a transmission fluid reservoir you can check with a dipstick, you still can get this job done. It's going to take a little more work however and a little more technical skill to get done. In order to do this job, you're going to need to get under your car, so that means getting it up on jack stands. If you're not comfortable with this level of car maintenance, then you're going to have to take it into a mechanic to get done. However, if you are up to the challenge, then make sure your car is secured on jacks on level ground so that you can get underneath it and access the transmission.


Step 1: As with the previous method, your vehicle needs to be running for this to work. It's a good idea to put your foot on the brake and cycle through the gears to make  sure the transmission fluid is in all parts of your transmission before you go any further. Then you can let your engine idle for a moment.


Step 2:  You need to access your transmission from below the vehicle. Your transmission should have a fill plug on the side and a drain plug at the bottom of the sump. Make sure you identify which is which. You're going to want to remove the fill plug and not the drain plug to check levels. Removing the fill plug will allow a little bit of transmission fluid to leak out. If it doesn't come out when you remove the fill plug, then you know you have low fluid levels.


Step 3: If you need to add some more fluid then you're going to need to get a fluid transfer hand pump. You can get these for about $30 and they're necessary for this job because a funnel will not work in this situation. With your engine still running, you need to use the pump to add fluid until it begins to overflow a little bit and run out of the fill hole. Once that happens, you can put the fill plug back in place and then wipe up the spill.


Step 4:  As with the dipstick method, if you notice that the quality of your fluid is not good when you check it from below your vehicle like this, then adding fluid is not really something you want to do at this time. You're going to need to do a fluid flush to remove the contaminated fluid from the system before adding new, clean fluid. Again, this is best done by a mechanic.


If you're interested in doing a transmission fluid flush on your own at home it's not impossible, but it will take a bit of work. You can find some videos that will show you the process of how to do it, but keep in mind this is a bit of a complicated job to do on your own and even the professionals who make videos will point out that it's not always easy to do a full, thorough flush of your transmission at home.


The Bottom Line


If you're experiencing things like your transmission slipping, which is to say that when you change gears while driving it slips back into the gear you used to be in, or if you're having problems with slow shifting then it's likely you have an issue with low transmission fluid. Likewise, if your transmission is overheating, or you can't shift gears, or you find your transmission is grinding or making other noises, then you definitely have an issue.


Before you take it to a mechanic to get it fixed it's a good idea just to check the fluid levels on your own. If the fluid is still clean, it's just a little bit low, that could be the only thing you need to do to get the problem taken care of. For about $40 or $50 you can probably buy a few quarts of transmission fluid and get your system topped up if that's all that's required.


Remember, if the quality of your fluid is looking bad or you have some obvious leaks causing the fluid to go low in the first place, your best bet is to take it in to a mechanic to get the job done professionally so this won't be a recurring issue for you and you can prevent bigger damages down the road. 


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