Automatic transmissions can run reliably for tens of thousands of miles without needing any significant service. The transmission itself is full of fluid that keeps everything running smoothly. The transmission transfers all of the power coming from the engine to the wheels, so if the parts inside experience too much friction then something will eventually fail. To avoid this, you can use the transmission fluid dipstick to monitor the level of fluid inside of the automatic transmission and, if necessary, add fluid to the transmission.
Some newer vehicles do not have an accessible dipstick or may have a fluid level sensor and should be checked by a professional if the level is suspected to be low.
- Note: Some manufacturers do not recommend that the transmission fluid be changed for the life of the transmission and do not have a normal fill or level checkpoint in the engine compartment.
Part 1 of 2: Checking automatic transmission fluid
- Paper towels or rags
Step 1: Park on a level surface. The car needs to be parked in order to check the fluid level, so find a level surface on which to park.
If the transmission has a manual gear selector (usually 1, 2, and 3 beneath “Drive” on the shifter) then it is a good idea to shift through each gear before shifting into “Park” and letting the engine idle.
- Note: The engine needs to be running in order to be able to read the fluid level. Note that some vehicles specify having the transmission in Park and the engine running and others may specify the transmission be in Neutral with the engine running to check the level of the fluid.
Step 2: Open the hood. To pop the hood, there is usually a switch inside the car that pops the hood up a small amount and there is a lever on the front of the hood, usually accessible through the grille, that needs to be pulled in order to raise the hood.
- Tip: If the hood does not stay up on its own, look for a metal bar that hooks into the underside of the hood to hold it up.
Step 3: Find the transmission fluid pipe. Under the hood, there is an automatic transmission fluid pipe. This is usually fairly out of the way, so expect to search for a moment before locating it.
The vehicle’s manual will show exactly where it is, but if that is not available, here are some tips for finding the automatic transmission fluid dipstick:
The dipstick will have some sort of handle to pull on in order to remove it from the pipe, so look for that first. It may or may not be labeled.
If the vehicle is a front-wheel drive, the dipstick will be up in front of the engine. If the vehicle is rear-wheel drive, the dipstick will probably be towards the rear of the engine.
It may be difficult to pull up at first, but don’t force it.
Step 4: Pull out the dipstick. Get a rag or paper towel ready before pulling the dipstick out all the way.
When pulling it out, use your free hand to grip the dipstick with the rag and clean the fluid off of it. To check the level accurately, re-insert the dipstick all the way and pull it out.
There are two lines or marks on the dipstick labeled either; “Hot” and “Cold” or “Full” and “Add.”
The fluid needs to at least be between these two lines. If it is below the bottom line, then more fluid needs to be added. Between the add and full line on most small to mid size vehicle transmission dip sticks will equal about a pint of fluid.
Before adding any fluid, take a moment to inspect what the actual fluid looks like. It it usually a clear amber color, but some types are more brown and some are more red. Watch out for fluid that looks dark or any fluid that is not very clear. If it is too dark it may be burnt, and if the fluid is milky then it is contaminated. Also watch out for air bubbles.
Step 5: Address issues. Now is time to address any issues uncovered in the process of checking the fluid.
If the fluid is burnt, then the radiator fluid needs to be flushed out as it is not going to adequately protect the parts inside of the transmission. If the fluid is burnt the transmission may need repairs and you should seek the services of a professional mechanic.
Milky automatic transmission fluid is contaminated and is possibly a sign of other problems. Shut off the vehicle and call a mechanic to avoid serious damages. If the fluid is milky the transmission may need repairs and you should seek the services of a professional mechanic.
Air bubbles indicate that the fluid may not be the right type for the transmission, but are also caused by there being too much fluid in the transmission.
- Warning: If the wrong fluid is put into the transmission it could cause internal damage to the system.
Part 2 of 2: Adding transmission fluid
- Automatic transmission fluid
Step 1: Get the right type of fluid. Once you have established that the transmission needs more fluid to be added to it, then you need to obtain both the proper type of transmission fluid for your vehicle (the vehicle’s manual will specify) and a long, thin funnel to aid in adding it to the existing fluid.
- Warning: Do not add fluid if it is not the correct type. Some dipsticks will say the correct fluid if you do not have an owners manual.
Step 2: Add fluid through a funnel. You can add more by inserting a funnel into the tube the dipstick was withdrawn from and pouring a small amount of automatic transmission fluid into the pipe.
Check the level each time you add a little until the level is right between the two lines.
- Note: Add fluid while the engine is running in the proper gear for checking the fluid levels.
If the transmission has been drained, you will need 4-12 quarts of fluid to fill it back up. Follow the vehicle service manual for the recommended type and amount of fluid to use.
If the fluid is very low when it is checked, then add more fluid and look closely for any leaks. Low fluid may be a sign that fluid is leaking out. Expect to add about a pint before checking the level again.
Step 3: Go through all the transmission settings. If there are no leaks and the fluid is at an adequate level, get back behind the wheel (but keep the hood open) and, with a foot on the brake, take the transmission through all of the settings on the transmission. This will stir around the fresh fluid and allow it to coat all of the parts in the transmission.
Step 4: Check the dipstick. Make sure the fluid level is correct even after shifting the transmission through all of the settings. Add more if the level has dropped too far.
Proper transmission maintenance will keep your car running smooth, and it will stay that way for many more miles than one with a neglected transmission would. The only thing keeping all of the very precise parts inside of the transmission lubricated is the automatic transmission fluid, and routinely checking on the level and adding fluid if it is needed is a good practice.
If you would rather have a professional mechanic, such as one from YourMechanic, add your transmission fluid for you at your home or office.
This article originally appeared on YourMechanic.com as How to Check and Add Fluid to an Automatic Transmission Car and was authored by Ian Swan.