Piston Slap: The Too Cool Miata?

Sajeev Mehta
by Sajeev Mehta
piston slap the too cool miata

John writes:

Dear Sajeev,

Thank you for much good reading and practical knowledge for a very amateur do-it-yourselfer. My auto repair and maintenance skills are very limited, but I enjoy doing what I can myself. Even just the oil changes and having control of the materials used to perform it.

So you are looking for subjects, and here goes-this may resonate with any number of Miata owners. For about a year the CEL has been popping up a code (0126) that I read with a simple device purchased online that evidently means the engine is running too cold, which I have never even heard of, but why not? Insufficient combustion temp?

Anyway, I see that it must be the thermostat which is seriously buried in this car and beyond my meager skills to get to, much less reassemble.

Do you think there is any urgency to getting this repaired? Car runs just fine.


Sajeev answers:

P0126 always takes me back to my time as a wannabe car designer at CCS in Detroit: if I wasn’t spilling venom on the vellum I’d dabble in auto repair consultation. To wit, a good friend spoke of his Merkur XR4Ti that he left in Florida, missing it but hating how it always ate “engine sensors”. Now, as a self-proclaimed expert on all things powered by Ford’s EEC-IV fuel injection system, I found that rather odd. Further questioning lead to this comment: “Oh, I never drove it with a thermostat. It’s Florida, you don’t need a thermostat!”


If only I knew better back then, I coulda put him in check: EFI systems run at a certain minimum temperature to ensure the motor’s ideal health and efficiency. If not, you run the system in open loop, instead of listening to inputs like the Oxygen Sensors, MAF meter, etc to keep emissions down, power up, liquid smooth idle, etc. Take the thermostat out of the system and the sensors are never consulted.

Is that happening in your Miata? It could be running in open loop. Or not: modern EFI systems are somewhat more intelligent than Ford’s antiquated EEC-IV, but this needs attention. My advice is simple, this code is normally produced by a faulty engine temperature sensor or a…like my friend’s Merkur…a problem with the thermostat.

Instructions on removing the T-stat are here, and this suggests that 2006 models are plagued with T-stat problems. So perhaps it’s time for a new Thermostat, or perhaps you should re-install your thermostat and NOT RUIN YOUR MERKUR, SON!

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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2 of 57 comments
  • Art  Vandelay Art Vandelay on Nov 19, 2013

    Drove a 90 Miata year round at Fort Drum. Only issue I had was at 30 below one morning the rear plastic window shattered when I hit a bump. I had non-winter tires and would break the rear loose with the handbrake on occasion to get it to turn. The car also tended to high center on the rear diff when I backed out of the driveway into the street if I didn't wait for the snowplow before I left for work. Good Times. As to your issue, the 1.6 cars had the thermostat right on the top front of the motor. I assume by your use of OBD codes however that this is a 1.8 car or an NC. **EDIT - just saw it was an 06 so NC. Take heart though, my wife's old Saturn VUE had this issue and changing the thermostat required removal of the intake. This started a long string of repairs that ended with the "trade it in on a new Hyundai fix". Good luck man, Ineedless complication is frustrating.

  • Ekaftan Ekaftan on Nov 20, 2013

    Down here it seems like every non-dealer mechanic removes the thermostat from every car they touch. Every one of the cars I have bought used in the last 10 years, except a truck I bought just off lease that was never serviced out of warranty, was missing a thermostat. 100% of those cars had failed emissions. Half of those only required a new thermostat and a week of spirited driving and were passing the test with flying colors.

  • Dukeisduke I know it really isn't, but the central display looks like it's being held by one of those cheap spring-loaded mobile phone mounts. Poor interior design.
  • Fred Remember when radios were an option? Do you know you can use your phone to listen to any radio station in the world? This is just a whole waste of time.
  • Pig_Iron ASTC 3.0 AM radio was successfully demonstrated at CES. It is a common standard shared with terrestrial television, so the audio equipment is commonized for broadcasters. And no royalty fees to pay, unlike HDRadio which has been a less than stellar success. 📻
  • Art Vandelay Crimes that are punished with fines encourage abuse by those enforcing them. If it is truly dangerous to the public, maybe jail or give the offenders community service. People’s time tends to be very valuable to them and a weeks lost work would certainly make a high earner think twice. If it isn’t a big danger why are police enforcing it (outside of raising money of course). Combine it with a points system. When your points are gone you do a week imitating Cool Hand Luke.
  • Cha65697928 High earners should pay less for tickets because they provide the tax revenue that funds the police. 2-3 free speeding tix per year should be fair.