Just like engine oil, you must also ensure that your vehicle’s transmission fluid is always in good condition. Most car mechanics recommend that you need to check the level of the transmission fluid while your engine is running. Why check transmission fluid when the engine is running?
Like any other liquid, the transmission fluid expands when subjected to heat. So, to ensure that checking the transmission fluid level is accurate, you should measure it while your engine is working under normal operating conditions. Run the engine for a few minutes before checking the TF level.
Checking the transmission fluid level while the engine is cold will not give you an accurate reading. In cold conditions, the transmission fluid level in its reservoir drops. If you top up the transmission fluid, you may overfill the reservoir.
Read on to learn more about why you need to check your vehicle’s transmission fluid while the engine is running and how you can do it properly.
Why Should You Check the Transmission Fluid When the Engine Is Running?
Transmission Fluid Swells Under Normal Operating Conditions
Automotive oils and fluids expand under heat. Transmission fluid swells under normal operating conditions like motor or engine oils. So, to get an accurate reading, you should check the transmission fluid level while your car engine is running.
If you check the transmission fluid when the engine is not running, your reading will be inaccurate because the liquid is cold. The fluid level will appear low and lacking. If you top it up at that time, you will overfill the reservoir.
Overfilling May Lead to Transmission Issues
That is not good for transmission because it may lead to transmission issues. You should run the engine first so that the fluid will get warm. Then, check its level only when the engine has been running for a few minutes.
You should understand that your car uses a torque converter, an ATF cooler, and other tubes in the transmission system that only hold fluid while there is circulation. The torque converter is one of the compartments of the transmission fluid. It is located inside the transmission.
Filled Transmission and Torque Converter
When you have a full transmission fluid reservoir, the level at the torque converter is much higher than the fluid level at the TF reservoir. For this reason, if the engine is not running, a considerable amount of fluid will go down to the reservoir.
As a result, you will get the wrong reading of TF on the transmission dipstick. However, if you check the TF level while the engine runs, fluid will fill the transmission and the torque converter. Your reading will be accurate when you check the TF level in this condition.
Working Transmission Fluid Pump
If the engine is not running, the transmission fluid pump is not working, and the fluid goes back down to the reservoir because of gravity.
That’s why your fluid level reading will be incorrect since all of them are holed up in the fluid pan or reservoir. However, when it heats up during normal operation, its molecules expand and spread out. So, the recommendation is to check the transmission fluid level while the engine is running.
What Is Transmission Fluid?
Transmission fluids perform a critical function in the operation of a vehicle, particularly its gearbox. It ensures that the transmission system of the motorized vehicle will continuously operate efficiently.
Automobiles use two kinds of transmission fluids. The type used in a particular vehicle depends on the transmission type. There are two types of transmissions in vehicles – manual and automatic.
A vehicle with manual transmission uses regular motor oil and sometimes automatic transmission fluid (ATF). ATF is the fluid that should be used on vehicles with automatic transmissions. Your car operator’s manual specifies the type of transmission fluid you should use in your car.
Do You Check Transmission Fluid with the Engine On or Off?
You need to remember one thing when it comes to transmission fluid. The process of checking this fluid is very different from checking other fluids, such as coolant and engine oil, in a vehicle.
Checking the transmission fluid level while the engine is running is essential in verifying its correct amount.
If there’s enough transmission fluid in the system, the fluid level in the torque converter (housed inside the transmission) is higher than what is inside the reservoir because it is the primary area where the fluid is kept.
So, when the engine is parked for some time, the transmission fluid will flow from the torque converter back to the reservoir. Your measurement of the fluid level will be incorrect if you check it at this time.
The right time to check the transmission fluid level is when the engine runs because the fluid is channeled around the system, including the torque converter. So, you can’t measure its level, just like how you measure the engine oil or coolant liquid.
For one thing, transmission fluid is much more sensitive to pressure than engine or motor oil. In addition, its expansion rate in hot conditions is very different from that of motor oil. That’s why the process of checking their levels is also very different.
Again, why check transmission fluid when the engine is running? Transmission fluid expands when heated. To get an accurate transmission fluid reading, you should measure the fluid level when the engine works.
What Should You Look for When Checking Transmission Fluid?
Aside from checking its level, there are other things that you also need to take notice of when checking the transmission fluid:
1. Bad Smell
If the transmission fluid is entirely fresh, it does not emit any odor. However, a much-used TF smells like burnt toast. If the fluid in your transmission smells like this, it has already developed some issues. It needs to be changed as soon as possible.
2. Fluid’s Consistency
Transmission fluid that is already overused will look thicker compared to fresh liquid. If the fluid is still good, it will look clear and new.
However, if the fluid looks unclear, it is filled with contaminants. It can contain tiny particles from metal parts of the transmission system, such as the gears.
If this is the condition of your transmission fluid, you should ask a qualified mechanic to inspect it immediately. Additionally, if foam has already developed in the fluid, or if it overheats, there is too much fluid in the system, or you have added the wrong kind of transmission fluid.
New and fresh transmission fluid looks bright, transparent, and clear. If its color is getting darker and unclear, it has already aged. That means you need to change it as soon as possible.
This darker color indicates that the fluid is already burnt out and can no longer provide the lubrication that the transmission system requires.
How Do You Check Transmission Fluid Properly?
Before checking the transmission fluid level of your vehicle, you should park it where the pavement is flat. Remember: you need to run the engine before checking the TF level. The step-by-step process for checking the TF level of a vehicle is as follows:
1. Pull the TF Dipstick Out
The color of the handle of the TF dipstick is usually red, yellow, or pink. Its usual location is in the engine compartment, particularly under the hood. On front-wheel drives, it is on the driver’s side, near the transmission. On rear-wheel drives, it is on the passenger side, close to the engine.
You should also understand that the transmission fluid’s dipstick differs from the engine oil’s dipstick. After locating the TF dipstick, please remove it from the TF pan or reservoir. Do this while the engine is running.
2. Check the TF Level
Check the level of the transmission fluid on the dipstick. Use your index finger to touch the fluid. This will give you an idea of the condition of the TF. Now, rub it between your finger and your thumb.
The color of the fluid should be clear and pinkish. If the fluid is still pinkish, but its level is already low, top it up with the same type of fluid. Ensure the level reaches the marked line close to the reservoir’s edge.
3. Change the TF and Recheck Its Level After
If the fluid has little particles in it or emits a burnt smell, you need to change it immediately. Here’s how you can change the TF properly:
- Remove the old TF and change it with the same type and amount of fluid.
- Clean the TF dipstick before inserting it back into its receptacle in the TF reservoir.
- Recheck the level of the TF and ensure it is of the right amount.
- Put the TF dipstick back on its receptacle.
- Close the hood of the engine.
How Often Should You Check the Transmission Fluid?
How often you need to check the transmission fluid depends on how you use your vehicle and the type of climate in the locality where you frequently drive your vehicle. If you usually drive it in severe hot or cold climates, you must check it (and probably change it) more regularly.
Usually, you should check your vehicle’s transmission fluid once every six months. As I’ve mentioned, you should conduct these regular TF checks more often if you usually drive your car in severe weather conditions.
It is essential to follow these general guidelines if you want to extend the use of your transmission fluid and, of course, the transmission system itself.
Just like other motor oils, transmission fluid expands when subjected to a hot temperature. So, to ensure that the measurement of the transmission fluid level is accurate, you should run your engine for a few minutes before checking the TF level.
You may get a low reading if you check the fluid level while the engine is not running. Topping up the level at this condition may cause you to overfill the transmission fluid reservoir. This will lead to overfilling the reservoir, which is not good for transmission.