How to check transmission oil level
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The transmission is a mechanical system that transmits power from the engine to the wheels of an automobile.
Transmissions use transmission oil for both lubrication and cooling. Filling the transmission oil to the correct level (not overguaged or underguaged) is very crucial to the operation and lifespan of the transmission.
Knowing how to properly check the fill level of automatic transmission is key to proper preventive maintenance of the transmission.
THERE ARE TWO CATEGORIES OF AUTOMATIC TRANSMISSIONS WHICH WE SHALL BASE OUR DISCUSSION ON.
1. Automatic transmission with dipstick
2. Sealed automatic transmission without dipstick
The methods used in checking the fluid levels of these two types of transmission are different.
We shall look into the procedures for both types of transmission differently.
AUTOMATIC TRANSMISSION WITH DIPSTICK
This types of transmission has dipstick similar to engine oil dipstick but it differs in the sense that the engine oil dipstick has minimum and maximum level marks while the transmission oil dipstick has cold and hot marks.
Front wheel drive automatic transmissions have their dipsticks at the front driver side of the engine while the rear wheel drive cars have their dipsticks at the rear passenger side of the engine.
Let's go straight to checking the correct transmission oil level now.
° When the car has not been started for the day (preferably in the morning), start the car while the emergency brake is engaged, cycle through all the gears (P R N D) pausing on each gear for about 5 seconds.
° GENTLY pull out the transmission oil dipstick and wipe the oil off with a clean towel. Pulling the dipstick out gently is very crucial to getting an accurate reading when you dip the second time or subsequent times.
° Dip the stick again, pull stick out gently ensuring that you keep it in vertical position to keep the oil mark clear.
If the oil mark is below the cold mark of the dipstick, the transmission is likely under filled. The check should not stop here. Go ahead to check the level when the transmission has attained normal operating temperature as described in the next points.
° Drive around for few miles to bring the transmission up to operating temperature.
° Park the car while it still idles, engage the emergency brake.
° Gently remove the dipstick and check the oil level.
This time, the oil mark should be around the hot mark of the dipstick.
If it is way below the hot mark, it signifies an under filled transmission which can cause the transmission to over heat and burn and also cause transmission performance issues.
If the transmission oil level is above the hot mark of the dipstick, it means that the transmission has been overfilled. This can lead to splashing of the transmission fluid which will cause foaming and then consequently lead to less lubrication and transmission overheat.
As temperature rises, the volume of the automatic transmission fluid also rises. That is why there is both cold and hot marks on the transmission dip stick.
Note: Honda has a slightly different procedure for checking the fluid level. They recommend turning the engine off and then immediately checking the fluid level on the dipstick.
SEALED AUTOMATIC TRANSMISSION (WITHOUT DIPSTICK)
Checking the fluid level on this type of transmission requires a greater level of expertise as compared to checking fluid level on transmission with dipstick. The job is better handled by an expert but it is not difficult nor impossible for any DIY inclined car user to do.
This type of transmission does not use a dipstick for checking the transmission oil level. The fluid level is rather checked mostly through the transmission refill hole.
It is important to strictly follow the procedure spelt out in the owners manual as it can slightly vary for different cars.
Checking the fluid level is best done in the morning.
Let us go straight to the procedure for checking the fluid level. Remember that it can vary for different cars. Your owner manual or repair manual is your best reference for this task.
Before you begin checking the fluid level, get an OBD2 reader that can read transmission fluid temperature handy. You can also use an infrared handheld thermometer to measure the temperature by pointing at the transmission pan. Take a look at a detailed article on checking transmission fluid temperature.
Let the car be on a leveled surface, preferably above a workshop pit for easy access to under the car. In the absence of a pit, four strong jack stands can be used. It is important to ensure the car is stable on the jack stands for safety.° Before you start the car, slightly losen the fill plug to check whether it will not be hard to loosen it when you need to without allowing fluid to come out. Lock it back.
° Start the car, engage the emergency brake and cycle through each gear, holding it on each gear for about 5 seconds.
° Connect the OBD2 scanner and begin to monitor the transmission fluid temperature. There is a temperature sensor inside the transmission that sends a temperature signal to the transmission control unit which could be a dedicated control unit or integrated into the engine control unit.