Under hood Maintenance: Transmission Oil/Fluid

Check Manual Transmission Lubricant Level

The manual transmission is lubricated by a lubricant that is splashed throughout the transmission by the moving gears. The lubricant must be at the correct level or the transmission parts could wear out in a very short time. The interval for lubrication level check is specified in the maintenance schedule in the owner's manual. Most technicians make this check whenever the car is up on a hoist for an undercar inspection.

Some imported cars have a dipstick to check manual transmission fluid level. This dipstick is found under the hood. The engine must be off to check the fluid with a dipstick. Remove and wipe the dipstick with a clean rag. Then insert the dipstick back into position. Remove it again and note the reading. Lubricant must be between the "full" and "add" marks on the dipstick. When you are done, replace the dipstick.

CAUTION: Make manual transmission checks with the engine off. Never put your finger into a transmission fill plug hole. If the drive wheels are turned, your finger could be caught in the gearing.

WARNING: A car that is not level on a hoist or jack will not show a true lubricant level in the transmission. If the engine has been running, allow two or three minutes before checking for a more accurate reading.

You will have to check most cars up on the hoist or jack. Raise the car and be sure it is level. Locate the transmission fill plug on the side of the transmission. You may have difficulty locating it. If you do, look for an identification diagram like the one shown below. Do not confuse the fill plug with the drain plug, which is located at the bottom of the transmission.

Clean the area around the fill plug to avoid getting dirt into the transmission. Remove the fill plug with the correct size wrench. If the transmission is full, you may see lubricant begin to leak out of the fill plug hole. If this happens, replace the plug.

You will probably find that the lubricant level is below the level of the fill plug hole. Bend a short length of metal wire and insert it into the fill hole. Pull the wire out and note the lubricant on the end of the wire. The lubricant level should be very close to the level of the fill plug.

If the lubricant level is satisfactory, replace the fill plug. If the level is low, add lubricant as explained in the next section.

Drain and Refill Manual Transmission Lubricant

The car manufacturer specifies regular time and or mileage intervals for the changing of manual transmission lubricant. You can find this information in the owner's or shop service manual. You will also need to look up the type and quantity of lubricant required. A lubricant chart can usually be found in a shop manual.

WARNING: Manual transmissions for different cars use many different types of lubricants. These include engine oil, automatic transmission fluid, and gear lubricant. Always determine and use the correct lubricant type. The incorrect lubricant can cause major damage to the transmission.

Drive the car long enough to heat up the lubricant. Lift the car on a hoist or jack and jack stands. The car must be level for accurate refilling of the transmission. Locate the drain and fill plug on the transmission as described in the previous section.

CAUTION: Be careful when draining a transmission because the oil could be hot enough to cause burns.

Position a clean drain pan under the drain plug. Clean around the area of the fill and drain plug. Remove the drain and fill plugs and allow the transmission to drain.

Inspect the fluid that collects in the drain pan. Look for metal in the oil. Metal shows up as shiny, metal particles or flakes. An excessive amount of metal could mean internal damage to transmission components.

When the lubricant is completely drained, clean the drain plug. Replace any sealing washer or use the recommended type of sealant on the drain plug threads. Install the drain plug and tighten it to the recommended torque.

The new lubricant will need to be pumped into the transmission through the fill plug hole. There are two types of lubricant pumps. Small hand pumps that attach to the container of lubricant are available at auto parts stores. Larger containers hold several gallons of lubricant. These have a hand pump that forces the lubricant through a hose and out a nozzle.

Place the delivery nozzle from the pump into the fill plug hole. Slowly pump the lubricant into the transmission. Stop pumping a few seconds after each pump to give the lubricant time to flow to the bottom of the transmission. Stop filling when the lubricant reaches the bottom of the fill plug hole. Wait several minutes, then check the level again. Sometimes the level will drop as the lubricant settles to the bottom of the transmission. Install the fill plug and wipe away any spilled fluid.

Check Automatic Transmission/Transaxle Fluid Level and Condition

Automatic transmission or automatic transaxle fluid should be checked at regular mileage and time intervals as specified in the owner's manual. Anytime you are doing lubrication work on a car you should check the fluid level.

Make sure the engine and transmission are up to operating temperature. Locate the fluid level checking procedure in the owner's or shop service manual. Drive the car onto a level surface. Most cars must have the engine running to make a fluid level check. Some cars must have the transmission in NEUTRAL and others require that it be in PARK for testing. Set the selector in the correct mode. If the transmission is checked in NEUTRAL, block the wheels and set the parking brake.

WARNING: Failure to have the transmission in the correct gear when checking fluid level can cause a large error in the reading.

Raise the hood and locate the automatic transmission/transaxle dipstick. Typically you will find the dipstick near the transmission end of the engine at the opposite end of the drive belts.

WARNING: Never wipe a dipstick with a rag with lint. Lint from a rag could get into transmission control valves and cause them to stick. It could also plug up fluid passages. Use only lint-free rags or shop towels.

Remove the dipstick and wipe it with a clean, lint-free rag. Observe the markings on the dipstick. There is no standard marking system, so you may need to look up an explanation of the marks in the owner's manual. A typical marking system is shown below. This dipstick has a full hot level mark and an add 1 pt (pint) or 0.5 L. (liter) mark. The word hot means the fluid must be hot when checked. There can be a large difference in fluid level between hot and cold fluid levels. Some dipsticks have a cold reading on the dipstick, which should be used if the transmission is cold.

Insert the dipstick back into its housing and push it down until it seats. Pull it back out and observe the fluid level in relation to the dipstick markings. If fluid must be added, refer to the section on adding fluid.

While you have the fluid on the dipstick you should observe its color and condition. This information can help you decide if the fluid requires changing. Clean, uncontaminated fluid has a pinkish or reddish color. Fluid that has been overheated turns a darkish brown or black. A white milky appearance can mean that the engine coolant is leaking into the transmission.

Another fluid check to make is to wipe the fluid off the dipstick with a white absorbent paper. Look for foreign particles in the fluid. Silvery particles can mean there is wear on metallic parts. Dark particles can be friction material that has come off transmission parts. Also look for a dark gummy material on the dipstick. This is usually a varnish buildup in the fluid. Fluid that shows any of these problems should be changed, as explained in the following section. Replace the dipstick and make sure it is seated properly.

Drain Fluid, Change Filter, and Refill Automatic Transmission/Transaxle Fluid

The fluid in an automatic transmission or automatic transaxle has many important jobs to perform. All of these depend on the fluid being clean and in good condition. Fluid should be changed if your dipstick test shows any of the problems described previously. Fluid should also be changed at the regular time and mileage interval specified in the owner's manual.

The first step in fluid changing is to get the transmission/transaxle up to normal operating temperature. The contaminants in the fluid will flow out better when the fluid is warm.

Raise the car on a hoist or support it on a jack and safety stands. Place a large drain pan under the transmission area. Some transmissions have a drain plug. If the car you are working on has one, use the correct size wrench to remove it as shown below.

CAUTION: Wear eye protection when draining a transmission/transaxle to protect your eyes against hot fluid splash. Be careful not to spill hot fluid on yourself.

Many transmissions do not have a drain plug. In these cases the manufacturer wants the technician to remove the pan and to change the fluid filter. To remove the oil pan, first remove any parts that interfere with the oil pan being removed. Use the correct size wrench to loosen but do not remove all the pan bolts. Remove all the bolts except the ones on one end. These bolts will keep the pan from falling off while the fluid drains. Make sure your drain pan is in position. Gently tap the pan with a rubber mallet to get it to break free of the transmission.

WARNING: Never use any tool to pry between the pan and the transmission/transaxle sealing surface. If you damage this surface, the transmission pan may not seal properly and will leak.

Allow the transmission to drain. Then remove the remaining bolts and the pan. Carefully check the bottom of the pan for foreign material. The material that collects in the pan is a good indicator of the transmission condition. A small amount of deposits from friction and metal parts is normal. A buildup of particles of metal or friction material is a sign of transmission wear.

Carefully remove the old gasket from the pan. Do not use any sharp tool to scrape the gasket or the sealing surface could be damaged. Use a lint-free rag to clean the pan.

Now you are ready to change or clean the fluid filter or screen. The filter or screen is mounted on the bottom of the valve body assembly as shown below. The filter or screen works like the oil filter in the engine. It cleans the fluid being pumped into the transmission parts from the pan. The filter or screen must be changed or cleaned each time you change the fluid.

WARNING: Before removing any filter or screen, check the procedure in a shop service manual. Some transmissions use the screen or filter to hold some small check valves and springs in position. These valves can fall out if the filter or screen is not carefully removed.

Filters and screens are often held in place with several screws. These screws may be regular Phillips or hex head or special torx head type. Use a torx head screwdriver to remove these screws. Some screws may be longer than others. Be careful to note size differences so you can reinstall them in the correct position.

There are two basic types of filters. One type is made from paper or cotton. This type is made to be replaced. The screen type has a metal screen with a washable filter element inside. This type is made to be cleaned and reused. Wash the replaceable screen with recommended solvent or spray cleaner and air dry.

When you are ready to reassemble, place the new pan gasket and filter next to the old ones. They will match up if they are the correct parts. Install the new filter or cleaned screen on the valve body and tighten all the fasteners to the correct tightening specifications.

Place the new gasket on the sealing surface of the fluid pan. Check the shop service manual for recommendations regarding any sealant to be used on the gasket. Also look up the pan bolt tightening sequence and the required torque. Place the pan and gasket in position and start all the screws. Use the correct type torque wrench to tighten the bolts in the correct sequence and correct torque.

WARNING: Some pan tightening specifications call for the use of an inch-pound torque wrench. Do not confuse these specifications and use a foot-pound torque wrench. Mixing up these specifications could cause the part to be over-tightened and damaged.

Most late model cars do not require that the torque converter be drained. Although there are no drain plugs on most late-model torque converters, some older cars do have them. Torque converter drain plugs are often found by removing an access cover on the bottom of the torque converter housing. The engine then has to be cranked until the drain plug on the torque converter appears in the access hole as shown below. Then follow the procedure for draining the fluid.

When you have finished your work underneath the car, lower it to the floor. You will need the specifications from the owner's or shop service manual on the type and amount of fluid to add to the transmission/transaxle. Some specifications list the amount of fluid required for a pan draining and a larger amount if the torque converter is drained. Be sure not to confuse these amounts.

WARNING: Use only the recommended type of fluid. Using an incorrect fluid type can damage some transmission friction parts.

Open the hood and remove the transmission/transaxle dipstick. Install a clean funnel in the dipstick and filler tube. Open and pour the recommended amount of fluid into the transmission/transaxle through the funnel. Remove the funnel and replace the dipstick.

Start the engine and allow the engine and transmission to warm up to operating temperature. With your foot on the brakes and the parking brake set, move the gear selector through each of the gear selections. Doing this allows the fluid to circulate through the entire transmission. Place the transmission in the correct gear for fluid checking and recheck the fluid level with the dipstick. Correct the fluid level if necessary. Test drive the car and check for proper transmission/transaxle operation.

WARNING: The fluid level is critical to proper transmission/transaxle operation. Too high a fluid level can cause rotating parts in the transmission to whip the fluid up and cause air bubbles. Air in the fluid can cause transmission slippage. Low fluid level can also cause air in the fluid and erratic transmission operation.