When checking transmission fluid should car be running

There are two main things about tranny fluid:

1. Transmission fluid is checked when it's hot (up to running temperature). As the fluid gets up to temperature it expands. If the fluid is cold, it won't give the proper level reading, thus overfilling will ensue.

2. One of the main fluid compartments of the transmission is the torque converter. When full, the fluid level of the torque converter is much higher than is the level of the pan (almost entirely above the pan in most cases). Due to this, when the engine is stopped, a significant amount of the fluid will drain down into the pan, showing the wrong amount of fluid on the dipstick. With the engine running, not only is the transmission paths filled with fluid, but the torque converter is as well. Then a check of the fluid will give you a proper level.

Checking engine oil is a lot different. It needs to be checked when it's in the oil pan. In order for it to be in the oil pan, it needs to drain after it's been up in the engine. This takes a little bit of time. Engine oil doesn't expand as much as transmission fluid, so can be checked hot or cold. While engine oil is important to how an engine operates, the level isn't as imperative as transmission fluid. Transmissions are very sensitive to line pressure. As you get more transmission fluid into the transmission, the pressures rise. If left unchecked, the fluid will find an escape hatch somewhere and that somewhere is usually a seal. Blowing out the front main seal (or where the torque converter rides) requires a transmission pull to fix. This isn't something you want to do every day.

Engines don't have the pressure effect which transmissions do. The pressure is regulated at the pump and mainly needs to have oil flow in order to operate efficiently. Most engine manufacturers are good down to even 5psi of oil pressure. There is also a lot of space in an engine for oil to hide. As oil gets pumped around, it sticks to walls and is all over the place. It needs to drain back into the sump, thus the 5 minutes of drain time. Not everything will drain down, but the vast majority of it will. This isn't how every manufacturer likes to have it read, but leaves things in a pretty good state as far as the level goes.

I don't read this as a discrepancy in either case. I look at it as how they are designed/engineered to be checked.

I always thought the car should be off before you go under the hood. But the mechanic told me that’s not the case. Do you check transmission fluid while the car is running?

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To check transmission fluid while the car is running, keep the engine running and remove the dipstick.

Your mechanic is correct. The car must be warm to get an accurate reading, as fluid expands when warm. Here are the steps to follow to check the transmission fluid:

• Wear protective gear like eyeglasses and gloves.
• With the engine running and parking brake set, prop open the hood.
• Find the dipstick, usually located near the car battery.
• Remove the dipstick and gently touch your gloved fingertips to the end.

The first check is whether the fluid is clean and grime-free. Then, you’ll wipe the dipstick and re-insert it before pulling it out again to read the level. It should reach the FULL line.

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Published Sat November 3, 2018

If your vehicle has an automatic transmission—and it probably does—then shifting gears should be a relatively simple, seamless matter. If the engine seems to hesitate or stall before shifting from one gear to the next, that could point to a maintenance issue, and potentially to a mechanical problem.

• Before you panic, though—and before you take the vehicle in for servicing—note that the solution could be as simple as replenishing the transmission fluid.
• This may be something you have never done before, but it’s an easy DIY vehicle maintenance task that could save you a few bucks and a trip to the shop.

Locating Your Transmission Fluid Dipstick

The first step is to locate the dipstick; this will look basically like your oil dipstick, although color-coded, to help you tell the two apart. The exact location of the dipstick can vary. In rear-wheel-drive vehicles, it is usually toward the rear of the engine. In vehicles with front-wheel drive, the dipstick will usually be found sticking out of the transaxle, and in most cases is toward the front of the engine.

Checking Your Transmission Fluid Level

Once you have located the dipstick, you can now check your fluid level:

1. Ensuring that your vehicle is in Park or Neutral and that your parking brake is on, start running your engine. Leave the engine running for a moment as you pull out the dipstick, ensuring the engine is warm as you check the fluid level.
2. Next, dip your index finger into the fluid on the dipstick, and rub it between your finger and thumb. Hopefully, what you see is some pink- or red-tinted, mostly clear liquid. Pay attention to the smell of something burning, or to particles present in the fluid. Both of these are signs that you need to change the fluid right away.
3. Use a clean, lint-free rag to wipe the dipstick clean, re-insert it, and check the fluid level again. If you see some of that pinkish liquid but it does not quite reach the “full” level, use a funnel to pour a bit more transmission fluid into the tank—enough to reach that line, but no more! Don’t overfill!
4. Make sure to reinsert the dipstick when you’re finished.

Final Tips for Fixing the Transmission Fluid

Note, if you do add more fluid, there are many different types of transmission fluids out there. For optimal performance, you will want to use the type specified in your owner’s manual. Make sure you double-check this before purchasing the new fluid.

If you identify the signs that your fluid needs changing, and if you’ve never done that before, your best bet may be to bring it in.  Make an appointment at Meineke today, and ensure that your fluid is changed out before you experience any bigger issues or more serious problems with the vehicle!

Is my car supposed to be running when I check my transmission fluid?

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