Why Check Transmission Fluid When Engine Is Running? [Answered]

In cars and vehicles, the transmission fluid is a liquid that is there to offer protection to the transmission gear and clutch packs. It ensures the smoothness and crisp shift when you use them. 

So, keeping a check on transmission fluid in your car is very important. But why check transmission fluid when the engine is running is a valid question. 

After all, why is it important to check when the engine is still in working state? Can you check it after turning off the engine? Let’s find the answer to this right now.

Checking transmission fluid while the engine is still working is important because the fluid expands in the presence of heat. In heat, the expanded fluid of transmission gives a better accuracy level. 

On the other hand, if you check the transmission fluid when the engine is cold, you may end up getting the wrong results about low levels of fluid.

When To Check Transmission Fluid Hot or Cold?

Checking transmission fluid level is always a wise move that tells you how much you care about your vehicle. So if you are checking it on your own, at home, it’s best to warm up your car in order to infer the right information. The warmed up car will give you better insight as the fluid will expand. 

Cold car engine will most certainly give accurate information when you use the dipstick. So it’s better to drive the car for about 10 minutes and park it on the smooth even surface and leave the engine running to check the transmission fluid.

Read Also: How Long To Let Engine Cool before Adding Oil

How do I check the Transmission Fluid level in my car?

It’s not complex to check the transmission fluid level in your car. For that you need to use the transmission fluid dipstick which resembles the oil dipstick as the names suggest the transmission fluid dipstick is used to measure the level of transmission fluid as the oil dipstick does.

Here is how you can check the transmission fluid level;

  • Park the car on the leveled ground and leave the engine on for about 15 good minutes for warm up of the vehicle.
  • Now, lift the hood of the car and find out the dipstick (near the oil dipstick in front-wheel drive vehicles and near the rear of the engine for rear-wheel-drive engines)
  • After finding the dipstick, pull it out, clean it using a cloth or some fabric piece and place it back into the coolant reservoir. Remove the dipstick once more and check the indicator on the stick. Check out if the fluid is at  “full” or “low”. If the coolant is filled up to the full level, close the hood, however if it’s low, top it up!

When should I check the transmission fluid in my car?

Usually, you should check the level of transmission fluid after 30,000 miles. But  you should not wait more than 6 months to overlook the transmission fluid. It’s always important to keep your vehicle well-checked and ideally maintained.

What should I check when checking transmission fluid?

There are three things that you should check while checking the transmission fluid, smell, consistency and its color.

The smell

The smell of the transmission fluid, if it’s cleaned, should be odorless.  If it’s like burnt toast, you need to change the fluid. It could mean that the transmission has some fault.

The color

The color of the transmission fluid should be a bright, transparent red color; if it’s darker in color, such as red and brown in dark color, it means the fluid has aged. But if it’s blackish, it means that the fluid is burnt. So you need to replace it with a fresh one.


Although the transmission becomes thick enough after some time, if the fluid also contains some contaminants or some particles such as metal it’s a dangerous sign. The foamy fluid means that there is too much fluid present or it’s overheating. If that is not the case, you might be using the wrong transmission fluid.

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