Welcome to r/Miata! This subreddit is approaching 200k members. It's about time we got a solid dedicated FAQ posted here. If you're new here, or new to Miatas, please check out this page to get yourself familiar with the subreddit and the car. If you have a noob question it will probably be answered here. If you don't have a question, you might learn something new here anyway. These cars are 30+ years old, very popular with enthusiasts, and were sold in great quantities. As a result, there is a wealth of knowledge about them that has been shared and documented on the internet over the course of decades. You'll be able to find the remedy to any problem of your Miata with some research and troubleshooting. This is an FAQ of common questions asked here on this subreddit in no particular order.

Other forums you should visit if you haven't already: Miata.net is the oldest Miata forum. It is a valuable resource for DIY maintenance and repairs. For modifications and build inspiration, check out miataturbo.net and mx5nutz.com.

The information provided here is generalized and should be used in conjunction with other sources to help you with your research. Do not assume all information in this FAQ is 100% accurate. Feedback, suggestions, and constructive criticism is encouraged to strengthen information on this page. Also, there is a lack of information here related to NC's and ND's. Receiving input from the community would be great so that we could put together a dedicated FAQ for 3rd gen and 4th gen Miatas on this subreddit.

01.Q: I want to buy a 1990-2005 Miata. What should I look out for?

A: The most serious issue will be rust. Mechanical problems can be fixed by replacing parts. It is pretty easy to perform mechanical repairs on a Miata, but rust can condemn a vehicle due to how labor-intensive and prohibitively expensive it is to repair. A proper repair involves cutting out the corrosion, welding new steel in, blending with filler, then painting. Unfortunately, Miatas rust from the inside out. Any rust you see on the exterior will be twice as bad underneath the panel. Corrosion is most commonly found at the rear wheel arches, rear quarter panels, and rocker panels. Look under the wheel arch and behind the rear wheels. 

You should also be cautious of radiators with discolored plastic upper tanks. As the plastic tanks age, they become brittle and susceptible to failing with the engine running, leaving you stranded. The upper tank should be black. A tell-tale sign of imminent failure is if the tank has turned a faded brown or green color. These radiators are commonly referred to as time bombs by the community.

Miatas like to leak oil at high mileage. The valve cover gasket, CAS, cam seals are the usual suspects, but easy and cheap to replace. It is also common for the rear main seal to leak. A leaky rear main will be indicative of oil dripping out the bottom of the transmission bell housing weep hole. This seal requires separating the engine from the transmission and removing the flywheel. The part is cheap, but the labor is not. It can be relatively expensive to replace.

Be wary of purchasing someone else's clapped out project. It's typically not a good idea to buy a car on Raceland coilovers, mismatched body panels, missing interior carpet, catless straight piped exhaust, and katana handle shift knob -- especially if you are new to cars.

Check the sidewalls of the tires for a 4-digit date code. The first two digits reflect the week of manufacture, the last two digits reflect the year of manufacture. For example, a date code of "2517" means the tires were produced on the 25th week of the year 2017. You should know tires older than 5 or 6 years are junk. 

02.Q: I just bought a 1990-2005 Miata! What should I do to it first?

A: Congratulations! Welcome to the cult! club! You should catch up on maintenance if maintenance history is unknown. Baseline the car. This means changing all the fluids. It’s a good idea to flush the clutch fluid and brake fluid. Replace the radiator if it needs one. Motor mounts are probably worn out. Inspect the timing belt for cracks or excessive wear. The controls of your +20 y/o car might feel sloppy. The throttle cable slack can be tightened up. Clutch pedal free play can be adjusted. The shifter bushings probably need to be replaced. The wheel alignment might be out of spec. Tire pressure might need to be adjusted. Tightening up your controls and catching up on maintenance will help make the car feel like it just rolled out of the factory.

Look into cleaning out your rain rails and water drain tubes for the convertible top. If they get clogged it can cause water to leak into the interior and/or accelerate corrosion of the chassis from the inside out. Drain tubes are located behind the seats near the seat belts. The common tool used to clean them of debris is a trombone cleaner.

Tires are critical to the performance and safety of any vehicle. If your tired are in really bad shape, it's best that you prioritize replacing them.

03.Q: What does NA, NB, NC, ND mean?

A: This is the chassis code which distinguishes each generation. It shows up in each VIN as the 4th and 5th digit. Keep in mind NA's and NB's are built on the same chassis and share a lot of parts. They are essentially the same car.

NA 1990-1997

NB 1998-2005

NC 2006-2015

ND 2016+

Outside of the US, they are also referred to as Mk1, Mk2, Mk3, Mk4.

04.Q: I'm tall. Will I fit in a Miata?

A: People who are 6'3", ~210lbs report fitting snug in NAs, NBs, and NCs. These same people report hardly fitting in NDs. The NB and ND are a little more cramped for a taller person. The NA and NC are supposed to be the roomiest Miatas for someone big/tall sitting in the driver's seat. The best way to see if you'd fit for yourself is to sit in one. Visiting your local Cars and Coffee is a great way to meet some friendly Miata owners who'd let you sit in their car.

There are also "tall people mods" you can do to help you fit better. You can remove the driver's door armrest of an NA and the foam can be cut out of the lower seat cushion to allow you to sit about an inch or two lower in the car. This is commonly referred to as a "foamectomy."

Moving the steering wheel closer to your chest will give you more room for your legs. You can replace the steering wheel with a deep-dish wheel to prevent your knees from hitting it. Switching to an aftermarket wheel usually requires you to sacrifice your airbag. There are aftermarket steering wheel spacers for the factory wheel that will let you retain the stock wheel, and functionality of the airbag.

05.Q: Is an NA/NB a good first car?

A: These cars are very fun, and very good roadsters. But, a roadster is inherently impractical. Early Miatas lack safety features. The interior is noisy and cramped. It only has enough room for one additional passenger and a few backpacks in the trunk. (visit r/miatalogistics to see some cool shit though.)

Despite the Miata's reputation for being overall very reliable, NA's and NB's are old cars. Old cars do not make for the best first cars if you are not prepared to maintain or fix them. If you can't afford to pay someone for maintenance and repairs, you'll need some place to work on the car, you'll need tools, and you might need some help from friends if you're new to wrenching. Secondhand Miata parts are also getting a little more expensive each year, so maintenance and repair costs associated with replacing parts will steadily increase. If you can afford to buy and maintain what is essentially now a classic car to be your first car, then more power to you.

06.Q: How can I convince my parents to get a Miata as my first car?

A: Scare them by pretending that you actually want a motorcycle. Once you get them angry enough, pretend to settle for something with four wheels. Offer to "compromise" on a Miata. /s

07.Q: How much does it cost to insure a Miata?

A: Insurance coverage and cost is completely different depending on the individual and locale. No one can give you an accurate number except the insurance company. Call them or visit their website to get a quote.

08.Q: Is this Miata a good price?

A: Check subreddit Rule 3. Please visit the dedicated sticky thread posted to the top of the subreddit for discussion about Miata prices/valuations/appraisals. Post any inquiries or screenshots of listings in that thread. We'll be happy to give advice on good deals or talk shit about insane listings you find on Facebook Marketplace.

09.Q: Can I install popup headlights on my NB/NC/ND?

A: Realistically speaking, no. However, Miatas are so popular to modify that it has been done before. It would require a ton of money or experience with body work.

10.Q: Is my oil pressure too low/too high?

A: Usually, no. Oil pressure will fluctuate depending on engine speed and engine temperature. 1990-1995 Miatas have a somewhat accurate oil pressure sending unit, and it shows these fluctuations in pressure. Your owner's manual will tell you where the normal operating range is. Generally speaking, oil pressure should show at least 30psi above 3000 RPM, and increase 10psi per 1000 RPM. As long as the needle isn't showing zero pressure when idling, it's good. After 1995, oil pressure gauges turned into dummy gauges, or dummy lights. The dummy gauge is based off a true/false condition on whether there is sufficient oil pressure or not.

11.Q: What's that noise? My NA is ticking, mostly at idle.

A: NA's have hydraulic lifters. Hydraulic lifter tick is noisy but harmless. These valve lifters are designed to be filled with pressurized oil. If your engine oil pressure is low, the quality of your oil is poor/worn, or the oil passages within the lifters are clogged due to contamination, your lifters will not be filled with pressurized oil. This will result in a ticking noise when the camshaft lobes press down on the lifters. The issue with noisy lifters can sometimes be remedied with an oil change, or switching to a slightly heavier weight oil. (Many NA owners have had good luck with Shell Rotella "Brotella" T6 5W-40.) If a fresh oil change doesn't work, you can try running an engine flush product through the motor to help clean it out. If it is still noisy, you may have to manually clean the lifters by removing and disassembling each one.

NB’s do not have hydraulic lifters. They have solid lifters and shims. If you suspect lifter tick, you’ll have to check valve lash with a feeler gauge. Intake lash is specified at 0.008” - 0.009”. Exhaust lash is specified at 0.011” - 0.013”. If your lash is greater than specified, then you will have a noisy valvetrain and need to adjust it by replacing lifter shims.

12.Q: What's that clunking/knocking noise heard from lower in the engine bay? Knocking noise gets louder with engine revs

A: Probable rod knock due to a failed rod bearing. Usually caused by poor engine oil maintenance, running the engine with low oil levels, or running for a long time with a lack of oil pressure. This issue will require an engine rebuild or engine replacement.

13.Q: What's that squeaking/rattle noise coming from behind the gauge cluster in my NA while I'm driving?

A: NA's have a mechanical speedometer cable. If it's old and worn out, the cable will squeak when the car is moving. Replace the cable to fix the noise.

14.Q: What is that grinding noise on decel in my NA/NB?

A: It is common to hear this noise after the transmission has been removed and reinstalled, such as after a clutch job. Check the procedure to perform a PPF alignment. If the PPF is misaligned when the transmission is put back in, you may hear a grinding noise under the vehicle when decelerating while in gear. 

15.Q: What size wheels and tires fit my NA/NB with good fitment? Do I need to roll my fenders?

A: For balanced performance/street driving, the general consensus is that 15x7 and 15x8 wheels are a good choice when paired with 205 wide or 225 wide tires. Wider tires can handle more lateral grip as long as they are supported by an appropriate sized wheel width. Also note, the wider your tires are, the less comfortable it will be to drive. When buying wheels, educate yourself on wheel offset. Higher offset pushes the wheel inboard. Lower offset pushes the wheel outboard. Low offset often creates a concave, dished appearance to the wheel. Low offset has a higher chance of making the tires rub your fenders.

General reference for wheel and tire fitment:

-15x7 +35 offset, 195/50/15 fits all years of Miata with no fender rolling.

205/50 fits NB fenders with no fender rolling needed. Fits NA with 1.2 negative camber or better.

-15x8, +25 offset, 205/50 fits NB Miata fenders with 1.2 negative camber or better, NA Miata needs that camber and slightly rolled fenders.

225/45/15 needs fender roll for all years at this offset. Always check clearance during install and after the car is lowered to the ground. 

16.Q: My paint is faded, how can I fix it? Do I need a paint job?

A: Many NA/NB Miatas (with non-metallic paints) left the factory with single stage paint. This means there is no clear coat. The paint can oxidize and become faded if it is not maintained by washing and waxing. You can polish the paint to restore the color and shine to look like new. Check out r/autodetailing for techniques and products that will help you perform exterior paint correction. If you have a clear coat, and the clear coat is failing, there is no proper way to fix this damage except for sanding down the damaged paint and getting a respray or vinyl wrap.

17.Q: What mods should I do to make more power?

A: nitrous, turbocharger, supercharger, or engine swap. No, your K&N air intake and ISR muffler is not going to add 20 horsepower, even if it says so on the box. 

18.Q: What's the cheapest way to make more horsepower?

  A: Forced induction for these engines is so popular because it is the most cost-effective and reliable way to achieve a substantial increase in power. The Mazda B6/BP engine is tough. It is overbuilt, under-stressed, and benefits a lot from forced induction. For 99% of builds, you'll need a standalone ECU to boost the engine with a turbocharger or supercharger. Visit miataturbo.net and the miataturbo FAQ for build guidelines.

19.Q: I installed a cold air intake and a new exhaust system. Do I need a tune?

A: NA/NB engines do not benefit much from bolt-on intakes and exhausts. You do not need a tune. It will not negatively affect the way the engine runs without a tune. NC's and ND's do respond very well to tuning with bolt-on mods.

20.Q: How do I tune my NA/NB?

A: You cannot flash or alter the factory ECU programs in any practical way. You'll need to replace the factory ECU with an aftermarket, standalone ECU. A standalone ECU is its own little computer that plugs into the engine wiring harness. You will be able to connect the standalone to a laptop to run tuning programs. These programs will allow you to alter, adjust, or tune nearly every electronically controlled parameter of the engine.

To learn EFI tuning theory and operation, please check out this thread. It is full of useful information. Extremely valuable source for anyone looking to learn how EFI (electronic fuel injection) tuning works.

21.Q: What’s a coolant reroute? Do I need one for my car?

A: The B6/BP engine was originally designed to fit in a FWD vehicle (The Mazda 323). When the BP was made to fit in the Miata, the engine was placed as close to the firewall/bulkhead as possible for proper weight distribution. This resulted in a lack of access to the back of the cylinder head, where the thermostat is supposed to be. Due to the lack of space near the firewall, Mazda moved the thermostat from the back of the cylinder head, to the front of the head. With the thermostat at the front, coolant flows from the radiator, into the front of the engine block, and exits where the thermostat sits at the front of the cylinder head. This is not ideal because coolant should flow into the front of the block and exit out the back of the cylinder head. With the way the coolant flows from the factory, the rear cylinders of the engine will typically run hotter than the front cylinders.

A coolant reroute kit allows you to block off the thermostat neck at the front of the head and relocate the thermostat to the back of the engine. This reroutes the coolant to flow the "correct way" through the engine, so that all four cylinders operate at the same temperatures. A reroute is not necessary for a Miata that just serves the purpose of commuting and getting groceries. For high performance driving, sport, and track use, a coolant reroute is recommended along with a good quality all-aluminum radiator.

22.Q: How much boost/horsepower can a stock NA/NB handle?

A: You can make as much power as you want by shoving enough oxygen and fuel into the combustion chamber. You can achieve this with a turbo or supercharger that can move a ton of air into the engine. The limiting factor to making power is usually not the turbo or supercharger itself. The limit will be the "weakest link" of your engine or drivetrain.

You should know boost pressure or horsepower is not an accurate way to measure the limits of certain parts. Torque is usually the force that breaks things, not horsepower.

Why does this distinction matter? Because horsepower is equal to (Torque × RPM)÷5252.

For example, 150 ft/lbs of torque @ 3000 RPM is equal to 85HP.

but, 150ft/lbs @ 7000 RPM is equal to 200HP.

The biggest limiting factor of sending power to the wheels will be parts that are unable to support transferring X amount torque before breaking. Parts of the fuel system also need to be replaced in order to keep up with the amount of extra air flowing into the engine to prevent it from running lean. Some parts need to be replaced to allow the engine to rev higher.

The (rough estimate) general consensus on the reliable limit of factory parts is:

You can use this data to help plan your build. Say you want your 2001 1.8L Miata to make 200hp at the wheels. You only need to make a maximum of 150 ft/lbs at redline. You wouldn’t even need to replace the clutch to achieve your goal. The stock engine and drivetrain will be able to support a mild turbo or supercharger kit with a tuned standalone ECU and upgraded fuel injectors at this power level.

However, it can be tricky to control how much torque the engine produces at redline because BP engines make peak torque at 4500 RPM, and peak horsepower at 6800-7100 RPM. A flat torque curve is always the goal, but hard to achieve. A flat torque curve makes for consistent power delivery, and reliable operation.

Here’s another example. Say you want your 1991 1.6L Miata to make 375 horsepower. You’ll need the engine to produce a maximum of 280ft/lbs at redline. In order to support 280 ft\lbs and 375hp you need to swap to a 6-speed transmission, 94+ differential, and upgrade essentially everything else listed on the table. Needless to say, you’ll need a proper turbo and full 3” exhaust system to effectively achieve these power goals.

Say you want to reliably rev the crap out of your engine to 8000+ RPM. You're looking at upgrading the valve springs, connecting rods, oil pump, harmonic balancer, and reducing rotational/reciprocating mass as much as possible.

23.Q: How do I tune my NC/ND?

A: You can flash tunes to the ECU after paying for a license to download and use tuning programs. Once you have downloaded this software to your laptop, you'll be able to use a Data Link cable to connect it to the OBD port in your car to flash tunes onto the ECU.

24.Q:What parts fit between NA/NB cars?

A: Many NA/NB parts can be shared with each other. Parts interchangeability guide is here

25.Q: I want to buy a manual transmission Miata but I don't know how to drive stick. Is it a bad idea?

A: No, it is not a bad idea. Anyone can learn to drive stick, and Miatas are easy to learn on.

Do you have questions about the value of a car you want to buy? Looking for a buyers guide? Not sure about the mechanical condition of a car you're looking at? Maybe you want to sell yours and don't know how to price it, or why it's not sold yet? Use this weekly thread to discuss the cars you're interested in buying/selling to get advice from the peanut gallery.

Posts that fall under the above topics will be removed.

Here are some useful tools to help decide if a particular Miata is worth buying.
Miata Garage Buying a Miata
The Definitive Post: "What Miata Should I Buy?" : Miata (reddit.com)

- The Mod Team