The point of a transmission drain plug is to be able to drain the fluid in the transmission without having to drop the transmission pan. Any mechanic will tell you dealing with rusted on parts is one of their most common problems. Transmission fluid is to be changed approximately every 15,000 to 30,000 miles, lots of time for rust and corrosion to build up. Removing a transmission plug that has rusted on can be tricky. Follow these steps before you give up and are forced to remove the transmission pan. Most importantly, take your time.
Step 1 - Position the Car
Use the jack and jack stands to lift the car onto the jack stands while you work under the car.
Step 2 - Fill Plugs
Remove the fill plugs first to insure they have not rusted. You will need to be able to refill the fluid you remove.
Step 3 - Apply Oil
Use the penetrating oil, corrosion block used for boats or a heat valve lubricant. These are all effective. These oils come either in a spray or spout container. Lubricate the drain plug and leave it on as directed by the manufacturer, generally at least an hour. Try and free the plug with a wrench gently. Depending on the results you see, you may only need to give it a few applications and it will come free.
Step 4 - Apply Heat
You will have removed some portion of the rust with the oil. If the drain plug still can't be removed, your next step is to use heat. First turn on the engine and get the transmission hot. Once the transmission is hot turn off the engine. Try to remove the plug with the hex wrench or drain plug remover tool, but be very cautious. If this works, the fluid will be very hot when it is released. If this does not work, allow the transmission to cool completely. Once the transmission is cool, use a torch to heat the pan around the transmission drain plug. The rusted drain plug should come loose.
Step 5 - Power Saw
If the drain plug still cannot be removed, use a rotary hand tool such as a Dremel. Make sure the transmission is cool. On each side of the drain plug, cut a straight edge to but not through the metal washer. For most transmission drain plugs the piece should fall off once the cut is made on the bolt top of the plug. You can now use vice grips to loosen and remove the plug.
Step 6 - Remove the Transmission Pan
As a last resort, you will have to remove the entire transmission pan. Once you have removed and drained the transmission pan you can use a drill to make a notch in the center of the drain plug. Use a small chisel and vice grips to work the drain plug out of its thread. You will need to clean the transmission pan thoroughly after this to remove any metal shavings from the pan.