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Discussion Starter #1
Quick guide on changing manual transmission gear oil.

This is specific to 2012 2.0L Skyactiv 6-speed manual transmission. Location of drain/fill plug, gear oil specs, and amounts will be different for other manuals on the Gen 2 Mazda 3 so verify with your owner's manual and factory service manual.

What you'll need.

1. 2 quarts Redline MTL 75W80 GL-4 Gear Oil.
2. Jack/Jack stand/ or ramps
3. 23mm socket (both fill/drain bolts are 23mm)
4. Fluid pump kit or .5 inch vinyl tubing with funnel (mine had a nice retaining clip on one end)
5. 10mm socket (removing underpanel tray)
6. Phillips head screwdriver
7. Work light.
8. Drain pan
9. Heavy duty shop towels

Time required:

45 minutes - 1.5 hours


1. Use ramps on the front of the car or jack up one side. I jacked up the front right side just so I had decent clearance for removing the under panel. You could probably remove it without jacking up the car, but I had trouble reaching the bolts in the very back of the panel.
2. You’ll need 10mm socket and x-head screwdriver. There are 2 plastic retainer clips on the front part of the panel. These are a pain to remove. I used a Lisle Plastic fastener removal tool: Amazon.com: Lisle 35260 Plastic Fastener Remover: Automotive. I basically destroyed these fasteners removing them, and see no reason to replace them as the panel is completely secure without them.
3. Removing underpanel DIY:
4. Locate the fill and drain bolts. See attached photos.
5. Remove the fill bolt first - do not attempt to remove drain bolt until after the fill bolt is removed just in case you have trouble getting it off. Mine was very easy to remove and probably not torqued to spec.
6. Place the drain pan under the drain bolt. Remove the drain bolt and allow fluid to drain. Remove the fill bolt as well.
7. Lower the car to a completely flat position to allow as much fluid to drain as possible. (this only takes around 5 minutes). I changed mine at 40K. Old fluid was completely black, so can’t imagine why Mazda doesn’t recommend a change interval. I will likely change it again at 80K.
8. Insert the drain bolt and hand tighten. Torque drain bolt to around 29 ft/lbs.
9. If you have a fluid pump - do this:
Use the fluid pump to fill 2 full quarts of Redline MTL into the transmission
Owner’s manual says 1.74 quarts, but I filled it until fluid dripped out at just under 2 quarts.
10. If using clear tubing and gravity - do this;
Open the hood and route the vinyl tubing down near the fill bolt. I have a corksport intake so passage down to fill bolt is clear. If you have a stock intake you may need to loosen or remove some components in order to get a clear path. Place the end of the tubing in the fill hole and secure with retaining clip. Place the other end of the tubing on the end of a small funnel.
Slowly pour 2 full quarts of Redline MTL into transmission.
Owner’s manual says 1.74 quarts, but I filled it until fluid dripped out at just under 2 quarts.
11. Remove fluid pump/tubing.
12. Insert the fill bolt and hand tighten. Torque fill bolt to around 29 ft/lbs.
Start the car and allow engine to warm. Check both bolts for leaks.
13. Replace the underpanel. I jacked the car up again to do this. This step probably took the most time as it was kind of a pain to line everything up and reattach all the bolts.
14. Enjoy nice smooth shifting.


5 Posts
This is conveniently well written and posted the day before I do it myself. Thank you.

Edit: I guess i have the bigger transmission as mine took just over 2 quarts. The old fluid was dirty black with only trace amounts of metal in the bottom. I expected worse at 42Kms.

124 Posts
Very nice write up. Thank you. I'll be doing it this month to mine. Have about 47K miles and stating to notice some notchiness in shifting.
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