In standard automatic cars, checking the transmission fluid is quite easy because the dipstick is the same as the one used to check engine oil. If you do it wrong, though, the dipstick’s hot and cold markings might surprise and perplex you in addition to giving you unpredictable readings. That being said, this is all you need to know.
When the engine is running, transmission fluid is filled into the torque converter, which alters the fluid level in the pan. This is why you should check the transmission fluid while the engine is running. When checking the fluid while the engine is off, all of the fluid that should be in the torque converter is actually stored in the oil pan. This causes the dipstick to read incorrectly because it indicates that the level is too high.
Reasons to Inspect Transmission Fluid While the Engine Is Operating
Here’s how the system operates before we discuss why it’s important to check the transmission fluid while the engine is running. In contrast to a manual transmission, which employs a clutch and two solid shafts to transmit power from the engine to the wheels, an automatic transmission uses a torque converter. Additionally, a torque converter turns the wheels by means of a transmission fluid coupling.
With a fluid coupling, the engine powers a turbine wheel that forces transmission fluid through an impeller attached to the wheels rather than having a mechanical connection between the engine and the wheels. After going through the impeller, the transmission fluid goes back to the turbine and the cycle is repeated.
Transmission fluid is used by the torque converter for this purpose as well as for lubricating the transmission gears. This implies that there must always be sufficient transmission fluid in the pan to completely fill the torque converter and the gears. Remember that the torque converter is only in motion and filled with transmission fluid when the engine is operating. The transmission fluid, on the other hand, drains from the torque converter and settles in the pan when the engine is off, which is where the dipstick measures the fluid level. Furthermore, the dipstick is marked to show high and low levels during operating conditions (when the torque converter is full), as those are not the relevant running conditions. This means that if the engine is off, the dipstick will indicate an unusually high fluid level.
Now, depending on its size, a torque converter can hold anywhere from two to five quarts of transmission fluid while it’s operating, so the dipstick reading will be wildly off. In order for the torque converter to remove any extra fluid from the pan and provide an accurate reading, you should always check the transmission fluid while the engine is running.
Testing Transmission Fluid While the Engine Is Hot
It is equally important to check transmission fluid while the engine is running, regardless of whether it is hot or cold. The transmission expands and the dipstick’s level rises as it warms up. Car manufacturers consider and bear that in mind when calibrating the dipstick markings. When the engine is cold and you check the transmission fluid, the dipstick will read lower than it actually does. When you notice that, you’ll add more fluid—which, in most cases, will be excessive—which runs the risk of damaging the torque converter, shift solenoids, and seals. And for good reason—you should never check transmission fluid in the cold.
A hot and cold mark can also be seen on the transmission fluid dipstick of some vehicles. When the engine is cold and you are checking the fluid, you will notice that the cold markings are lower than the hot ones. The cold marks, however, are still calibrated to a specific temperature that you cannot duplicate unless the ambient temperature is correct.
Because of this, even if your car’s dipstick indicates a cold mark, the engine should be running at operating temperature when you check the transmission fluid level. Before you go back home, drive it for a typical 5–10 mile distance to bring the engine up to operating temperature. Then, check the oil level.
Other than that, ensure that the vehicle is on level terrain to prevent a slope from causing the liquid level to rise or fall. Finally, go through every gear while the engine is running and then check the fluid level. This provides you with a more accurate reading by allowing the transmission fluid to fill up all of the shift solenoids. Here is a step-by-step guide to help simplify the entire process.
Step-by-Step Instructions for Monitoring Automatic Transmission Fluid Level:
Make sure the engine is running by taking the car for a five to ten mile drive.
Go through each gear three to four times while the engine is running.
It doesn’t matter if you check the transmission fluid in park or neutral; if you do so in neutral, apply the hand brake.
Verify the level of the transmission fluid while the engine is running.
Verify the hot fluid level in your car if the dipstick shows a hot and cold mark.
While inspecting the fluid in a manual transmission, should you run the engine?
Because manual transmissions lack a dipstick, checking the fluid in them is far more difficult than it is in automatic cars. So, without using a dipstick, here’s how to check transmission fluid.
Find the filler plug on the side of the transmission by looking underneath the vehicle. After that, take out the plug. If transmission fluid is dripping out, the level is acceptable. If not, begin adding fluid to the transmission until the drain plug begins to overflow. Although this process is much more complex, it can be completed fairly easily if you have some mechanical aptitude.
If you do, the engine should be off because the transmission shafts will force fluid out of the drain plug when the engine is running, making measurement impossible. Moreover, unlike automatic cars, the engine ought to be cold. Finally, ensure that the car is level. It is not required to shift gears or consider the gear the transmission is in before checking the fluid.
FAQs:
Is it possible to examine the transmission fluid while the engine is off?
Yes, technically, you can check transmission fluid while the engine is off, but the reading you get will be wildly off. The dipstick indicates that the transmission has two to five quarts more fluid than it actually does when the engine is off. Thus, while the engine is hot and operating, always check the transmission fluid.
How long after starting my car should I wait to check the transmission fluid?
To make sure the transmission is completely warmed up, you should drive your car for at least five miles before checking the transmission fluid. Additionally, do not warm up the car without first starting it up, as this will only warm the engine and leave the transmission cold.
Why add fluid to the transmission while the engine is running?
In order to obtain an accurate reading, you should first always check the transmission fluid while the engine is running. This allows the torque converter to fill up with fluid and expels any excess. Although adding fluid while the engine is off is not prohibited by law, you should constantly check the fluid level. Therefore, the best course of action is to keep the engine running until you reach the desired level.
When is it appropriate to stop changing transmission fluid?
Since new lubrication is always welcome, there are no manufacturer recommendations specifying when not to change transmission fluid. Nonetheless, some manufacturers claim that transmission fluid never needs to be changed, while others advise flushing it every 100,000 to 150,000 miles.
Does the transmission fluid heat up while it is idle?
Transmission fluid does, in fact, warm up at idle, but it does so very slowly, and you cannot determine when it reaches operating temperature. Because of this, if your primary objective is to warm up the transmission fluid, you should always drive your car for a minimum of five miles.
What is the average lifespan of a good transmission?
With proper upkeep and servicing, a well-maintained transmission with few manufacturing defects or design flaws can last up to 300,000 miles or longer. Nonetheless, if properly maintained, the majority of transmissions can last up to 250,000 miles or 200,000 miles.
Essentially, the rationale behind consistently checking the level of transmission fluid while the engine is running is fairly straightforward: accurate dipstick readings require the fluid to fill the torque converter, which is only possible when the engine is operating. In addition, make sure the transmission is warm because cold-temperature-induced fluid contraction results in readings that are also off. Lastly, to ensure that transmission fluid fills all the solenoids, shift through every gear a few times before taking a measurement.
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