How to Troubleshoot a BMW 325 Series

1. Use the right type of fuel. Using the wrong type of gas can damage the vehicle's catalytic converters or cause a 'knocking' sound in the engine. The 2006 BMW 325i owner's manual reminds drivers to use unleaded fuel in their vehicles and recommends an octane of at least 91. Fuel with an octane of 93 is also permissible. Do not overfill the gas tank, which has a maximum capacity of 16.1 gallons.
2. Maximize your 325's fuel efficiency by keeping the tires properly inflated and aligned. If you've noticed a drop in your miles per tank, use a tire gauge to measure the pressure in all four tires. The recommended reading in pounds per square inch, or psi, will vary based on the type of tires installed on your 325i; page 110 of the owner's manual lists the exact tire pressure recommendations for a wide range of BMW tires.
3. Pop the hood of your 325 series to familiarize yourself with the different parts of your engine. Focus on these three locations: the expansion tank for coolant, located behind the front passenger-side headlight; the jump starter connection, located just below the windshield on the passenger side of the vehicle; and the filler neck for engine oil, located about halfway between your front bumper and the windshield on the passenger side of the vehicle.
4. Check your 325's engine oil level regularly. While the 325 series is equipped with an electronic sensor and alert system, which will display a message on your dashboard when the level is too low or too high, sometimes this sensor can malfunction. If the dashboard indicator says the level is too low, remove the cap on the filler neck and add a small amount of engine oil until the light turns off on its own (BMW recommends using high-performance synthetic oil). If the indicator says the level is too high or that the system is inactive, take the vehicle to a certified BMW repair shop to work on the system.
5. Add extra coolant to your vehicle when necessary. Coolant helps your vehicle operate at an acceptable temperature; if you notice the engine temperature gauge on your dashboard operating at 'high' at all times, you may be running low on coolant. Slowly loosen the coolant cap but don't remove it; this will give the tank time to release pressure gradually. Check to see that the coolant level is below the minimum and maximum level on the dip stick; if it is too low, add enough coolant so that it is properly filled. Even though coolant is made up partly of water, which can evaporate, you may still want to have your system checked for any leaks.
6. Recharge a dead battery by jump-starting it with the help of a second vehicle. Turn off both vehicles completely, then connect one positive (red) clamp on your jumper cables to the positive terminal on the assisting vehicle. Connect the second positive clamp to the 'positive' port located near your 325's passenger-side windshield. Next, connect one negative (black) clamp to the negative terminal on the assisting vehicle and the second negative clamp to the 'negative' port located on the far passenger-side under your 325's hood. Start the engine of the assisting car, giving it a few minutes to warm up before turning on the engine of your BMW. Take your 325 to a repair shop as soon as possible for a new battery.