If you are used to tackling the odd mechanical job at home, you may be used to changing the engine oil and filter on your car when needed. Now, your attention has turned to the transmission, and as it has been some time since you paid any attention here, you may be getting ready to do the same with this component. However, you should think twice before attempting this type of service job at home, especially as it has been quite a while since you did. Why do you need to exercise caution here?
Engineers design an automatic transmission system so that it will last for a long time under average load. The fluid is very sophisticated and designed to put up with tremendous heat and pressure while maintaining its ability to protect all of the components. Yet it will degrade, and you should replace it periodically if you want to protect its efficiency. So additional work may be needed if you've let it go for too long.
Flush Versus Drain
You may well be able to find the drain plug at the bottom of the transmission case, but be aware that you will not be able to remove all of the transmission fluid without an additional tool. Certainly, the fluid within the sump and surrounding components will drain out, but the liquid that is within the torque converter will not. Therefore, if you want to remove this as well, you will have to perform a transmission flush, and this is a job for a fully qualified mechanic.
If the fluid itself has a dark brown appearance and may even have tiny flakes of metal in suspension, then the mechanic may need to take additional action. They will need to see if any of those foreign particles have become lodged in sensitive parts of the valve structure and will need to clear all of this up before refilling the fluid. If not, the transmission could slip when you take it back out onto the road and may overheat. You may also risk additional damage which could be very expensive and could take much longer to fix.
Always take the vehicle to a mechanic to perform any automatic transmission service. You will then ensure that all of the fluid is removed and replaced by a professional, and this will help you to avoid any major damage.