Just bought a Miata with unknown history? Do these before you trust it: timing belt, all fluids, cooling system, brakes, and a quick electrical and rust check. Assume nothing was done and reset the clock. A few weekends here buys you years of reliable top-down driving.
Do first, in order.
- Timing belt (1.6/1.8) unless you have paperwork proving it. These are non-interference engines, so a snap will not bend valves, but it will strand you, and an unknown-age rubber belt is a gamble; replace it with the water pump, tensioner, and idlers. This is the single most important item.
- All fluids. Fresh engine oil and filter, flush the brake and clutch fluid, change the trans and diff oil, and flush the coolant. Now you know what is in the car.
- Cooling system. A new thermostat and radiator cap are cheap; confirm the electric fan runs and the system is fully bled. These heads punish neglect.
- Brakes. Inspect pads, rotors, and flex lines; bleed until the fluid runs clear.
- Tune-up basics. Fresh spark plugs cure many rough-running gripes. Inspect coil packs/wires and the intake boot for cracks.
- Electrical once-over. Cycle the pop-up headlights, all windows, mirrors, and every fan speed; clean grounds where anything is sluggish.
- Rust check. Look at the rear frame rails behind the front wheels, the rockers, and the floors. Rust here matters more than cosmetics on any Miata purchase.
Fix the timing belt and cooling first; they are the failures that strand you or destroy the engine. Everything else you can stage over a month.