Time for another installment of Mazda3 maintenance! This time it’s the manual transmission fluid and the differential fluid. They are one in the same. Mazda calls this a “lifetime fluid” and never calls for it to be changed out. In my humble opinion, that’s not good. Nor is it right. So here’s how you change it.
Without getting into an oil debate, this is my preferred lube. Redline MT-90. It is a 75w90 GL-4 gear oil. That satisfies Mazda’s requirements perfectly. I’ve used it in my Miatas for 10 years and have always been happy with it. When I saw the oil spec was the same on the 3 as on the Miata, I didn’t even question which fluid to buy.
You need something like 3.1 quarts. Four of these bottles will cover you. I happened to have a space 1/2 quart in my garage, so I got by with buying three. You will also need a drain pan, some paper towels, and a 23mm wrench/socket. And, perhaps most important, a fluid pump.
You’ll need to get the car up into the air where you can get to the transmission fill and drain plugs. You’ll also need the car to be level. I’d suggest 4 of the strongest jack stands you can find. I love my ESCO stands. You can read about them in my Mega Jack Stand Review.
I place the stands on the factory jack points at the back of the pinch welds and under the front control arms. The car is extremely stable when held up by these four points. Don’t forget to give the car a good shake after you get it up on the stands. Better to find a wobbly stand when you’re beside the car rather than when you’re under it.
The transmission is to the driver’s side of the engine bay. It’s the big, shiny metal housing. My wrench is on the fill plug facing toward the front of the car. Always remove the fill plug before removing the drain plug. Life gets exciting when you have a completely drained transmission but no way to fill it…
Sorry about the cropping on this shot. This was the best one of the batch.
The drain plug is the same size as the fill plug, just on the bottom of the transmission. It is the only plug on the bottom of the engine that looks like this and is 23mm.
Make sure to leave the fill plug off. The fluid drains much faster this way. Feel free to be as thorough as you like. I let mine drain for a good 20 minutes.
I chose to reuse my crush washers. Neither were very tight from the factory and my car is still fairly new. I will change the washers out when I do the fluid again in 30,000 miles.
Torque the drain plug to 29-43 ft/lbs once you’re done draining the old stuff out.
It would probably be possible to fill the transmission with a long run of hose and a funnel from the top side, but I like my little fluid pump. It fits a Redline bottle perfectly and goes through a bottle pretty quick. But to each their own. As I said above, you’ll need a little more than 3 quarts. I just pump until fluid starts to come out of the fill hole.
When you’re done, torque the fill plug to 29-43 ft/lbs. And in case you missed it above, the transmission fluid is also your differential fluid. You just changed both. Congratulations!