Mazda MX-5: First Diff Fluid Change with Mobil 1 75W-90 Synthetic

Another maintenance project that I completed on my own, this time it was changing the rear differential fluid in the Miata. I actually practiced the fluid change on my Ford Explorer which badly needed this fluid changed, but this post is really about the MX-5. Now I won’t have to worry about this piece of maintenance for another 30,000 miles which should take me a couple of years to accumulate.

This project, like many others, started when I was reading Miata.net forums and saw what people were doing to their cars. Someone posted about doing the rear diff fluid change and how easy and quick it was and I decided to do it myself. At practically the same moment I was thinking that, a $5 off $10 purchase coupon arrived in my e-mail from Advance Auto Parts, so I went on their web site and ordered Mobil 1 75W-90 (listed for $10.99) which the Miata guys on the forums recommended. (Ironic because I’m not the biggest fan of the Mobil 1 0W-20 engine oil having used it for the past two oil changes, but whatever). The coupon from Advance came because I just spend over $60 buying Pennzoil Platinum oil & K&N filters. Had I known I’d get $5 off for every $30 spent, I would have split my Pennzoil order in half. Anyway, after I ordered the Mobil 1 for the Miata, I realized I might as well practice on the Ford Explorer but instead of buying the good stuff, I decided to buy cheaper Valvoline gear oil for the truck. Buying it from Advance didn’t make much sense because their version is marked up to $15+ while Pep Boys down the street had it listed for $12+ and offered a 20% coupon. Fast forward to today, when I went to pick up the oils from two of the stores, the job took no time in the Explorer. Miata was next.

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The most difficult part of doing anything with the Miata, especially when it comes to the bottom of the car, is getting it elevated high enough so I could squeeze in under there. I recently purchased two more jack stands from Sears for a nice $21 bux out the door after a bunch of discounts, so this was a great excuse to use them.

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Once the car was reasonably high in the air it was just matter of minutes of undoing two bolts and letting the oil drain. I left it sitting for a good 20 minutes so all the fluid dripped out, and then siphoned new fluid in via a small hose. Was pretty surprised that it took almost the entire Quart bottle, but eventually oil started seeping from the fill hole. And I was done!

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The bottom of the car still looks pretty good. No rust from the last winter which saw a lot of salt on the roads. And now my car is ready for another 30k interval. Easy peasy! Even dad came over to have a look at the progress…

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So hopefully this Mobil 1 product looks better with age then their engine oil does (I wasn’t too happy with how dark it got at only 5,000 miles especially since they advertise it could go 15,000).