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Why Check Transmission Fluid When the Engine is Running?

Why Check Transmission Fluid When the Engine is Running?

When it comes to automotive maintenance, checking the transmission fluid is an essential task. However, one common question arises: should you check the transmission fluid when the engine is running?

In this article, we will delve into the reasons why it is important to check your transmission fluid while the engine is running, ensuring optimal performance and extending the lifespan of your vehicle.

Why Check Transmission Fluid When the Engine is Running?

1. Accurate Fluid Level Measurement

Checking the transmission fluid while the engine is running provides a more accurate measurement of the fluid level. The transmission fluid circulates throughout the transmission system, lubricating the gears and cooling the components. Running the engine activates the transmission pump, which helps to distribute the fluid evenly. By checking the fluid level in this state, you can ensure that it is at the proper level for optimal performance. Insufficient fluid can lead to overheating and excessive wear, while overfilled fluid can cause foaming, leading to poor lubrication.

2. Correct Fluid Color and Consistency

Transmission fluid plays a vital role in lubricating and protecting the transmission’s moving parts. Checking the fluid while the engine is running allows you to observe its color and consistency accurately. Fresh transmission fluid typically has a bright red or pink color, while older fluid may appear darker due to oxidation. If the fluid appears cloudy, foamy, or has a burnt odor, it may indicate a problem such as contamination or overheating. Addressing these issues promptly can prevent further damage to the transmission.

3. Identification of Leaks

Checking the transmission fluid with the engine running enables you to identify any leaks in the system. Leaks can occur in various areas, such as the seals, gaskets, or cooler lines. Running the engine creates pressure within the transmission, making it easier to spot leaks as fluid seeps out. Identifying and fixing leaks promptly can prevent fluid loss, which can lead to serious transmission damage and costly repairs.

4. Ensuring Proper Shifts and Performance

The transmission is responsible for transferring power from the engine to the wheels, allowing your vehicle to shift gears smoothly. Insufficient fluid or contaminated fluid can hinder the transmission’s performance, leading to erratic shifts, slipping gears, or delayed engagement. By checking the fluid while the engine is running, you can ensure that the transmission has adequate lubrication and cooling, promoting smooth shifts and optimal performance.

5. Prevention of Costly Repairs

Regularly checking the transmission fluid while the engine is running can help prevent costly repairs in the long run. Catching potential issues early on, such as low fluid levels, leaks, or contaminated fluid, allows you to address them before they escalate into more severe problems. Neglecting transmission maintenance can result in significant damage, requiring a transmission overhaul or replacement, which can be a substantial financial burden.

Why Check Transmission Fluid When the Engine is Running?

How to Check the Level of Transmission Fluid

Similar to the oil dipstick, the transmission fluid dipstick measures the amount of transmission fluid in your car as opposed to the oil dipstick, which measures the amount of engine oil. Remember that a lot of transmission issues are brought on by low fluid levels. If the fluid level is low, there probably is a leak, which needs to be located and fixed straight once by a professional. 

Precautions should be taken to avoid overfilling the reservoir if you need to add more fluid. It is possible for transmission fluid to foam if it is overfilled, which will increase pressure inside the transmission and force fluid out of a vent or a seal. This can cause instability and slippage.

  1. Lift the hood once you’ve parked your automobile on a level surface.
  2. As soon as you start your automobile, leave it in the park, and allow the engine to warm up for a few minutes. Heat causes transmission fluid to expand; thus, it must be running normally to get the correct results. When the engine is cold, and the fluid is examined, you risk getting inaccurate reports that the fluid level is low. As you check the level, let the engine continue to run. Notably, Honda is the only manufacturer to advise stopping the engine before checking the level.
  3. Zip up the hood. Take your car as soon as possible to an auto center for a fill-up if the fluid level is low.
  4. Find the dipstick. It is conveniently labeled for access and can have a red, pink, or yellow-colored handle. It is frequently located close to the oil dipstick in front-wheel drive automobiles and close to the rear of the engine for rear-wheel drive engines.
  5. Remove the dipstick, clean it with a fresh rag, and then reinsert it into the reservoir. Once more, remove the dipstick, and look for the signs to determine if the fluid is “full” or “low.” Close the hood and replace the dipstick if the fluid is full. Take your car as soon as possible to an auto center for a fill-up if the fluid level is low.

How to Check Your Transmission: What to Look for 

Why Check Transmission Fluid When the Engine is Running?

Fluid Color: The majority of brand-new transmission fluids ought to be vivid, transparent crimson. It’s typical for the color to become darker or lighter as it ages. If the fluid is a darker shade of brown, it has to be changed. However, black is a terrible omen. This indicates a burnout of the fluid due to some transmission issues. 

Viscosity: Fluids may, over time, appear thicker than usual due to consistency issues. Although this is typical, good transmission fluid ought to seem brand-new. Fluids must be free of pollutants and particulates, including metal shavings. 


Checking the transmission fluid while the engine is running is crucial for maintaining a healthy transmission system. By ensuring an accurate fluid level measurement, identifying leaks, assessing fluid color and consistency, and promoting proper shifts and performance, you can extend the lifespan of your vehicle’s transmission and prevent costly repairs.

Remember, regular maintenance and attention to your transmission’s health will keep you on the road with confidence and save you from potential headaches down the line.

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