Here's a general overview of the steps involved. This is NOT a substitute for a proper repair manual:
1. Preparation:
* Safety First: Work in a well-ventilated area. Use jack stands (NEVER work under a vehicle supported only by a jack), wear safety glasses, and gloves. Disconnect the negative battery terminal.
* Gather Tools: You'll need jack stands, a jack, socket wrench set (metric), various sizes of wrenches, a drain pan, oil filter wrench, new oil pan gasket, new oil pan (if necessary), possibly a sealant, a torque wrench, and possibly a pry bar or plastic scraper.
* Drain the Oil: Warm the engine slightly to thin the oil, then drain the oil using the oil drain plug.
2. Accessing the Oil Pan:
* Raise and Support the Vehicle: Securely lift the Grand Prix and place it on jack stands.
* Remove Underbody Components: You will likely need to remove some underbody components to access the oil pan. This could include splash shields, exhaust components (possibly lowering or removing parts of the exhaust system), and potentially other parts depending on your specific engine and subframe design. The repair manual is essential here.
* Disconnect Components: There may be sensors, wiring harnesses, or other components attached to the oil pan or near it that need to be carefully disconnected.
3. Removing the Old Oil Pan:
* Remove the Oil Pan Bolts: Carefully remove all the bolts securing the oil pan to the engine block. They are likely to be in tight spots, requiring various extension bars and wobbly sockets.
* Lower the Oil Pan: Gently lower the oil pan. Some residual oil will likely remain, so have a drain pan ready. The old gasket will likely stick to either the engine or the pan.
4. Cleaning and Preparing for the New Oil Pan:
* Clean the Surfaces: Thoroughly clean the mating surfaces of both the engine block and the new oil pan to remove any old gasket material, sealant, or debris. Use a plastic scraper or a suitable cleaner. Any imperfections can cause leaks.
* Install the New Gasket: Carefully install the new oil pan gasket according to the instructions provided with the gasket or in your repair manual. Some gaskets are designed to be installed with sealant.
5. Installing the New Oil Pan:
* Position the New Oil Pan: Carefully position the new oil pan onto the engine block, ensuring the gasket is properly seated.
* Install the Bolts: Install the oil pan bolts, tightening them in a crisscross pattern to ensure even pressure. Use a torque wrench and tighten to the manufacturer's specified torque values (found in your repair manual). Overtightening can strip the threads or crack the pan.
6. Reassembly:
* Reconnect Components: Reinstall any components previously removed, such as sensors, wiring harnesses, and underbody parts.
* Lower the Vehicle: Carefully lower the vehicle from the jack stands.
* Check for Leaks: Inspect for leaks around the oil pan. Start the engine and run it briefly, carefully checking for leaks. Let it run for a few minutes, then check again.
* Add New Oil: Add new oil to the correct level. Replace the oil filter.
7. Disposal: Properly dispose of used oil and other waste materials.
This is a general outline. The precise steps and tools required will depend on your specific 1999 Grand Prix model and engine. Refer to a repair manual for your vehicle before attempting this repair. If you are not comfortable performing this repair yourself, take your vehicle to a qualified mechanic. It's much safer and likely cheaper than fixing mistakes.
