Secondary Oil Pan?

Feeling a little dumb right now and need some pointers.

I changed the oil on my wife's 2013 Mazda2. Not a whole lot came out, which seemed odd. It shouldn't have been particularly low. It was still black fluid, like you expect from old oil. Replaced the filter, lowered it down, and put in about 2.5 quarts.

Dipstick showed it was overfilled, and still had a lot of black oil on it.

Put it back on the stands, and I saw my mistake. When you crawl under the front of the car, there's a pan with a drain plug on the left, and then another pan closer to the oil filter on the right. I had pulled the left plug. The right plug is the correct one.

So I drained that one. Question is, what the hell is that second plug? It appears to be under the automatic transmission, but it doesn't seem to be AT fluid. The owner's manual says there's over 7 quarts of ATF in there; not nearly that much came out.

From this diagram:

https://www.jimellismazdaparts.com/...odel=14355&modelYear=2013&ukey_category=20236

What I pulled from appears to be part 19836, which is listed as "PAN, OIL", so was this just a secondary oil pan? Meaning that filling the oil back up is going to refill that pan, too? If so, should that pan also be drained with every oil change?

Don't want to drive it until I figure out what the hell is supposed to be in that pan. Feeling rather dumb about cars this week--screwed up my Miata's oil change, too (nothing catastrophic, just dumb).

Nope, you drained the transmission fluid. While the system holds about 7 quarts, only 2-3 quarts are actually in the pan -- the rest is elsewhere in the system (torque converter, hoses, the little fluid cooler puck thing, etc). Depending on how many miles are on the car, it's very possible that the fluid could be dark/black, as Mazda's transmissions from that era tended to be "hard" on fluid (unlike its newer SkyActiv transmissions).

The engine oil pan is towards the driver's side and uses a 19mm (IIRC) socket to remove. You'll get about 4 quarts out of it.

What you should do now:

--Drain the engine oil and refill to the proper level. It'll take just a little over 4 quarts.
--Go to the dealer (in another car!) and pick up a few quarts of Mazda branded automatic transmission fluid. Do not use generic fluid. You need fluid that's compatible with "Mazda ATF M-V", which is *not* the same thing as Mercon V (or Mercon 5), which confuses a lot of people.
--Pull the transmission fluid dipstick (the one with the orange knob, on the driver's side) and stick a funnel in the tube. Add the new fluid until the dipstick comes back up to the proper level. (There is no fill plug on the transmission, so you need to fill it through the dipstick tube.)
--Start the car, let it idle for a while, make sure there are no leaks etc. Drive it gingerly at first, pay attention to the shifting. If it feels normal, drive it for a while to let all the fluid circulate.
--At this point, the next step is up to you. Check the dipstick for the color of the transmission fluid; if it's bright red you could probably ride things out for a while. If it's light brown or dark (which it probably would be), strongly consider taking the car into the dealer for a transmission fluid flush. They have a machine that can replace all of the fluid in the transmission (all 7 quarts), instead of just the 2-3 quarts you'd get from draining the pan. You'd do well to keep to transmission fluid flushes every 30,000-40,000 miles, at least if you plan to keep the car for a while.

OK, thanks for the quick reply. That helps a lot.