Mazda MX-5: Transmission Fluid Flush at 55,000 miles with Pennzoil Platinum High Mileage ATF

Update: (Feb 2017) I see a lot of traffic to this page so in the interest of fairness and sharing accurate information I should do a follow-up about this trans-flush. So my car is nearing 60k miles now, almost 5k since the trans flush. After the first 300 miles Chris and I went ahead and raised the car up, released the check cap and some fluid came out… like a bunch of it, 500mL or so. After that the tranny felt absolutely perfect. Precisely like it did on the original Mazda fluid except obviously on brand new Pennzoil Platinum. Since then I’ve driven the car on long road trip, going down to Daytona Beach, Florida and the car performed flawlessly. I thought that maybe synthetic fluid would make the tranny run cooler. I don’t know if it does. The tunnel between the seats still gets warm, especially on longer more spirited drives. But there’s no funny business happening with the shifting. It works perfectly. So I’m going to say that Pennzoil Platinum High Milage ATF JWS3309 works!

My 2007 NC1 GT PRHT has an Automatic Transmission that Mazda considers a sealed unit that does not require servicing. I wish I would have listened to that advice!

Obviously, I could not leave well enough alone. So I researched all the necessary instructions on how to go about the tranny fluid flush DIY and not spend several hundred dollars at the dealership or a Quickie Lube place (which I would never go to in the first place). Turns out the Automatic Transmission in our cars uses an Aisin-Werner unit that requires a special type of fluid called JWS-3309 which is different from other more readily available fluids out there. Plenty of cars use JWS-3309 fluid and yet it was surprisingly hard to find. Mobil 3309 was the likely contender and the cheapest I found was via eBay at $63 for a box of 12 QT shipped from somewhere in California. But that fluid isn’t synthetic ATF. Neither is Mazda JWS-3309 or Aisin branded JWS-3309 which is apparently made by ExxonMobil in the US. I kept searching and came across Pennzoil Platinum fully synthetic High Mileage ATF which has right on the face of the bottle JWS-3309 as a fluid type… great! I even found it available locally at Pep Boys… so I purchased a discounted gift card, went to Pep Boys and asked them to order a case of 12 for me since there were only a few on the shelf… they did, and I was ready to work on the trans paying $60 out the door with tax and all. I also picked up a bottle of Mobil 1 ATF for the power steering flush, but I’ll write about that separately.

The procedure for changing the trans fluid was also slightly complicated. In order to flush the old dirty fluid out we would need to drain as much as would come out of the pan, refill with new stuff, let it circulate through the system and drain again… Repeat the process two times and the fluid would be clean(er).

The reality though wasn’t so straightforward.

Draining the fluid was very easy. There’s a drain plug which comes undone quite easily, but from a 7.8QT capacity system only about 2.5QT drains. We put the plug back on, started the car, put it thru gears for under a minute spending about 2 seconds per shift, and another 0.5 to 1 QT came out… well short of the 4 QT that people were saying online while giving instructions.

What’s worse, we were afraid to overfill the transmission with new fluid. The instructions called for filling it with 4 QT of fresh fluid, running the car through the gears and draining, but we thought overfilling would be damaging so the idea was to put the exact amount that came out. This was not so easy. As soon as we started pumping fresh fluid in for the first time only about 1.6 QT went in before the fluid started gushing out of the “Check” plug. Not good! So our already long job working on the transmission was extended by us Googling to do research on what the proper procedure was to fill the damn fluid and get as close to the 4 QT that so many people recommended online. The only way it was possible it seems was to fill the cold level 1.5 QT until it started dripping out from Check plug, then turning the car on made the dripping stop, so we pumped more in until it started dripping again. And then Sakshik started going thru the gears while the dripping stopped and we pumped more in. In total I think we pumped no more than 3 to 3.5 QT’s in before the fluid started gushing out of the Check hole. We sealed it all, shut the engine off and went for the test drive while shifting the car automatically through every gear from 1 to 6 and then manually using the lever and then using the steering wheel paddles. We did this for acceleration and deceleration and everything seemed to work perfectly.

So we returned to the garage and gave it one more final flush. Drained the fluid. Ran the car, drained it again. Then refilled cold, refilled while the car was running, and then finally refilled while the car was being put thru gears.

In all we used 10 QT total, not the 12 QT that I bought based on recommendations. 1 QT I never opened, 1 QT we put back together by draining all the 11 other QT’s that had a few mL’s of fluid left in there that the siphon pump missed as we were pumping the fluid in.

This was not a fun project at all.

The whole garage smelled like ATF.

And on the drive home I noticed that it didn’t sound as good as the car sounded before the ATF flush. Which makes me wonder:

Did we fuck something up?

Car goes thru all the gears just fine. But there’s this faint dronning that wasn’t there before. I don’t know if the new synthetic trans fluid must break in over a period of time (someone mentioned 500 miles) and then it would normalize, or if I am damaging the tranny every time I drive it now.

I just don’t know.

I wish i didn’t touch it.

If the whole thing normalizes over the next few weeks though I’ll be happy that the car has clean fluid slushing around in the transmission. At 55,000 miles it wasn’t filthy but it was pretty dark.

We will see…

Some pix:


The Pennzoil Platinum High Mileage ATF full synthetic JWS3309


The tool needed to siphon the new fluid into the transmission through the fill plug on the top of the transmission fluid pan.



That’s a lot of fluid at $5.79+ tax a pop just to be put to waste to wash out the dirty fluid from the system. But still cheaper than doing the flush at the dealership.




Big props to Chris for taking on this job. And even bigger props for keeping the garage floor so clean. We had a few opportunities to splash the stinky ATF fluid all over the place but he was well prepared with a big tarp under the car and lots and lots and lots of paper towels. I owe him big time!


As the sticker on Eric’s RX-8 says… Never Give Up! (signed Mazda)

Read more about our Oil Change from the same evening here, or the Power Steering fluid flush here.