Your transmission fluid is important for the smooth running of your automatic transmission. Your transmission creates a lot of heat from friction, and the transmission fluid is designed to keep this heat from damaging your car.
Most people rarely change the fluid, and those who do usually leave the replacement to their service garage. You can replace the fluid yourself with a few tools, but the level of fluid is critical to the smooth running of the transmission.
TIP: Make sure you use the recommended fluid for your vehicle as the wrong one can damage some vehicles. Check your owners manual to see if your car needs a particular type of fluid. The most problematic vehicles for this situation are newer ones with electronically controlled transmissions.
How Much Fluid Should You Put In?
You should only add fluid about half a quart at a time. The dipstick might show full, but it really isn’t. Start the engine and idle it, apply brake and shift through all gear positions returning to Park, then recheck the level when the engine is hot. Add as much as you need till the dipstick reads full.
In a cool engine, the fluid level should be at the top end of the cold mark, while it should be at the top end of the hot mark when the engine is hot. In a warm engine, make sure the level is in the safe zone between the two marks.
Most transmissions will take about 9-13 quarts to fill completely. How much you add will vary depending on whether you're draining and replacing all of your fluid or just topping it off. Again, add a little at a time to avoid overfilling.
How Does Overfilling Cause Problems?
If you overfill the transmission, you will find that the fluid may foam, and that can lead to erratic gear shifting. Other problems can include transmission damage and oil starvation.
Some transmissions can’t be overfilled because of the way they are designed. They might have a hole in the side, and any extra will just flow out.
When to Change the Transmission Fluid
Wipe the dipstick on a white cloth or wipe, and check the color left. It should be clear; if the color is brownish or there are some spots of black deposit, you must have the fluid changed soon.
If your vehicle is often used in stressful situations where the transmission is getting hotter than usual, you should frequently check the fluid for burning and wearing out.
Some people may tell you that changing the transmission fluid is not necessary, but it does a lot of work and does wear out eventually. The heat produced by driving can often get so hot that the fluid starts to lose its lubricating qualities, and the seals will start to harden, leading to pressure losses and leaks. The transmission will eventually die in this condition. Keeping an eye on the level and the health of the fluid can save you a huge repair bill later on. You should change the fluid and filter every 30,000 miles.
Removing Excess Fluid
You can use a hand pump to remove excess fluid if you have overfilled the transmission, or use a thin tube to siphon it out.