Fluids, Fluids, and More Fluids!

Oil, coolant, transmission fluid, brake fluid, gear oil, clutch fluid, shifter turret fluid—there's a lot of liquids needed to keep our cars on the road!

And more than that, there are a lot of options! From the unbranded stuff at the gas station to crazy expensive brands that require a special dealer to access, what is the best thing for your car?

Engine Oil and Filters

Let's talk engine oil first. We have tried and tested dozens of oils over the years and, like everyone else, we have landed on our favorites.

For a street car, generally it's not super critical. The engine won't be seeing temps or durations in the extremes, so almost any off-the-shelf oil will do the job.

We have landed on Mobil 1 Full Synth as our oil of choice. We run this in everything from our Sunday cruisers to our all-out race cars. We selected Mobil because they were able to provide us with test data for their oils so that we can accurately see at what temps it will break down. There are other oil brands that will provide this info but they are more expensive and/or harder to obtain.

For filters, we run Mazda OEM filters exclusively. They are comparable in price to parts store options but have higher quality filters and bypass valves—and the added assurance of running a filter that was designed for this engine.

Differential and Transmission Fluids

For the differential and transmission, we like Red Line Oil products: MT-90 for the transmission and shifter turret, and 75W-90 for the diff. The MT-90 gives the smoothest shifting of the oils we've tested and works for all 90-15 transmissions (5-speed and 6-speed). For the diff, you want a gear oil that's the correct weight and doesn't have any unneeded additives (no limited-slip additives needed for the Miata); Redline 75W-90 is the perfect fit!

Brake, Clutch, and Power Steering Fluids

For brake and clutch fluid, you want something with a temp rating to match your application. For street driving, parts store DOT 3 is totally fine. For aggressive driving on curvy roads, autocross, or especially track days, you need a higher temp fluid. Hawk HP660 is our brake fluid of choice.

Lastly, power steering fluid. I have personally boiled power steering fluid on an autocross track. (If you haven't seen our video on how much HP it takes to run a power steering pump, go check it out—that pump is really working!) Red Line makes a high temp power steering fluid that does a great job of handling the heat!