How to Replace the Oil Pan in a Subaru Impreza WRX

I completed this job on my 2002 Subaru Impreza WRX Wagon (stock) in about 8 hours. That included a lunch break and a trip to Autozone for a 24mm deepwell socket. The vast majority of my time was spent on my back in the driveway trying to reach the bolts around the oil pan, several of which are located up under a frame member.

RTV vs Gasket
There seems to be some debate about whether RTV or a premade gasket makes a better seal. Most people I talked to advised using RTV, and since that is what Subaru used originally, that's what I did. I was not able to get as clean a bead as I hoped because of the awkward position under the car and I still had no leaks, so I'll add my voice to the opinion that RTV is a good option.

Finding the Oil Leak
A piece of advice: If you're looking to fix an oil leak, take the time to find out where your oil is leaking for sure and don't just assume its the oil pan. In my case I was pretty sure, because I damaged the oil pan driving over something, which must have bent the pan enough to start a leak around the gasket.

Choosing an Oil Pan
Finally, choose a new oil pan. I just ordered one from RockAuto. You could also choose to upgrade to the STI oil pan, which has baffles to keep from starving the engine of oil while cornering at high speeds. Be aware that you'll need to replace your dipstick as part of the upgrade if you do.

Tools Needed:

• Ramps or jackstands
• Metric socket set
• Deepwell 24mm socket (to loosen the oil cooler)
• Extension & universal joint for the 10mm socket
• Chisel or prybar
• Breaker bar
• Floorjack

Parts/Supplies:

• New Oil Pan
• Gasket Maker (I used RTV Black)
• Oil Filter
• New Oil
• Brake cleaner or some other solvent that won't leave a residue
• Scrubber pad
• Box of disposable gloves
• Some cardboard or foam to lie on

Job Steps:

1. Drive onto the ramps
(or put the car on jack stands if you don't have ramps)

2. Disconnect the battery.
Really just an extra safety precaution.

3. Drain the oil and remove the oil filter.

4. Loosen the 4 bolts holding the radiator and air intake to the frame.
If you skip this step, lifting the engine will twist these brackets.

5. Remove the dipstick and loosen the tube hanger from the engine block.
10mm socket on a 3" extension works well for this.

6. Remove the two nuts from the motor mounts on the lower frame member.
Use a 14mm socket. I did not have a deepwell, but it would have helped as the socket was barely grabbing the nut for the first couple turns. Also, a good breaker bar or impact wrench will be needed to get enough torque to loosen these and reinstall them properly.

7. Use the floor jack and a block of wood to lift the transmission and engine about an inch

Just enough to reach the screws up under the frame (don't raise it too far, you'll break something).

8. Use a 10mm socket to remove the bolts all the way around the oil pan.
This is a royal pain. I used a universal joint and a 9" 3/8" drive extension to reach the ones in the back.

9. Use a chisel or prybar to loosen the oil pan.
They sell a special tool for this, but mine popped off easily after a few taps with a rubber mallet.

10. Use the 24mm socket to remove the center bolt from the oil cooler above the oil filter.

11. Fanigle the oil pan out until it is hanging by the oil pickup tube and the dipstick tube.
This took me a long time; everything is in the way (the frame, exhaust heat shielding, the dipstick, and the oil cooler). 
Check out the video linked at the bottom for more on this.

12. Twist/pull the dipstick tube loose.
Not as easy as it sounds; I finally got it using vice-grips.

13. Loosen the two bolts on the oil pickup/strainer until it shifts enough to pull the oil pan down.
Some people haven't mentioned this step, but it's the only way I was able to get the oil pan off.

14. Clean the gasket surface on the engine and on the new oil pan.
Use brake cleaner, or some other solvent that won't leave a residue.

15. Do a "dry run" to make sure you are able to fit the new oil pan back to the mounting surface.

16. Apply a bead of gasket maker all the way around the oil pan, going inside the mounting holes.
I used RTV Black and tried to get about a 1/4" bead. 
I had to do this with the oil pan dangling from the oil pickup (since I couldn't get the oil pan over the pickup with the pickup tightly attached). It was a pretty ugly bead, but I didn't have any leaks when I finished.

17. Insert the dipstick tube into the new oil pan.
I only got it started from below, and used a mallet and a block of wood to tap it in the rest of the way from the top later.

18. Press the oil pan into place and start all the bolts.
Easier said than done. I spend well over an hour trying to get each hole to align so I could start the screws.

19. Let the gasket maker cure for about an hour, then tighten all the bolts.
Since it took me so long just to get all the bolts started, I just tightened them the whole way when I finally did.

20. Retighten the oil cooler, being careful to seat the gasket correctly.

21. Install new oil filter.

22. Drop the engine, and retighten the motor mounts.
(51 ft-lbs according to the Subaru Manual)

23. Retighten the radiator, oil intake, and dipstick bracket.

24. Add new engine oil.
There are varying opinions on how long to wait before running the car. I started it up after an hour to roll it off the ramps, but then let it sit another day before driving it, since the RTV said 24hrs for a full cure.

References:
This is a very helpful video on how to do this job. Thanks to briansmobile1 for putting it together.

https://www.youtube.com/watch?v=bQcABlBktQw

Always nice to see what the manual says, although a few steps seem unnecessary.
http://ken-gilbert.com/impreza-manuals