Your Jaguar XJ8 requires you to add transmission fluid while the engine is warm. This procedure varies by car make--some require fluid to be added with a cool engine or else it will overflow. Fluid levels are measured with the dipstick that came with your vehicle. When you pull the dipstick, transmission fluid should lie in between of the top and bottom lines at the very end of the stick. If the fluid level is too low, you must add more transmission oil.
Start the car. Let it sit for about 2 minutes.
Pop the bonnet of the car. Pull the dipstick from the transmission. The dipstick is located at the front of the engine underneath a few hoses and cables; use a flashlight to find it if necessary. Wipe it clean with an old rag or a set of paper towels, and then reinsert the dipstick. Pull it once more so that you can measure the transmission fluid levels.
Check the transmission fluid level using the lines at the end of the dipstick. To add more, place the funnel into the transmission fluid cylinder, which is the same hole you pulled the dipstick from, and pour in the fluid.
Re-measure your fluid levels. Repeat this process until an adequate level is reached.