Why it's difficult:
* Accessibility: The rear main seal is located at the very back of the engine, where access is extremely limited. You'll likely need to partially or fully remove the transmission to get to it.
* Transmission Removal: This is a major undertaking involving disconnecting numerous components, draining fluids, and potentially needing special tools.
* Engine Support: Proper engine support is critical to prevent damage during this process. A transmission jack is usually necessary.
* Potential for Further Damage: Improper removal or installation can lead to further damage to the engine or transmission.
How to determine if it's the rear main seal:
Since you've already ruled out other external leaks, a few things can help confirm the rear main seal:
* Dye Test: A mechanic can add dye to the engine oil. If the dye appears on the back of the engine, near the bell housing (where the transmission connects), it strongly suggests a rear main seal leak.
* Detailed Inspection: Even though it's difficult to see, carefully inspect the area around the rear of the engine block where it meets the transmission bellhousing for oil residue. Look closely. Small amounts of oil can indicate a leak even if not immediately obvious.
Replacing the Rear Main Seal (General Steps - *This is NOT a complete guide and should only be attempted by someone with mechanical experience*):
1. Safety First: Disconnect the battery negative terminal. Wear safety glasses and gloves.
2. Preparation: Drain the engine oil and transmission fluid. Gather all necessary tools, including sockets, wrenches, screwdrivers, a transmission jack, and a new rear main seal (the correct one for your Aerostar's engine – 3.0L V6 or 4.0L V6). Consult a repair manual for your specific engine for torque specs and procedures.
3. Transmission Removal (most likely necessary): Disconnect the driveshaft, shift linkage, and any other components connected to the transmission. Carefully support the transmission and remove it. This requires patience and methodical work.
4. Remove the Flywheel (often): In many cases, the flywheel must be removed to access the rear main seal.
5. Rear Main Seal Replacement: Carefully remove the old seal, usually by using a seal puller (avoid damaging the crankshaft). Clean the area thoroughly. Install the new seal using a seal installer tool (improper installation is a common cause of seal failure). Avoid damaging the seal during installation.
6. Reassembly: Reinstall the flywheel (if removed), transmission, and all previously disconnected components in the reverse order of removal. Ensure proper torque specs are followed.
7. Refill Fluids: Add new engine oil and transmission fluid to the correct levels.
8. Test: Start the engine and check for leaks.
Strongly Recommended:
* Repair Manual: Obtain a repair manual specific to your 1994 Ford Aerostar. This is absolutely essential for detailed instructions, torque specifications, and diagrams. Haynes and Chilton manuals are popular choices.
* Professional Help: Unless you have significant experience with engine repair, this is a job best left to a qualified mechanic. The cost of a professional repair may be significantly less than the cost of damaging the engine or transmission during a DIY attempt.
Replacing a rear main seal is complex and risky. Weigh the cost of professional repair against the potential for further damage if you try it yourself without the proper skills and tools. If you're unsure, a professional mechanic is your safest bet.
