Gas Type

I have a 2003 Acura MDX. The manual recommends using premium gas. What is the difference between 87,89, 91 or 93 gas? What happens if I use 87%?

If you use less then 91 octane you could damage your engine, if the computer doesn’t detune the motor. Your motor will start to ping and cause detonation in your motor, and could burn a piston or valve.

mopar man

The engine control module will likely detune the engine to prevent premature detonation. Lower octane gasolines may explode due to compression rather than spark. That is the knock you may hear. Many modern ECMs monitor the ignition process and will detune the truck so that it will run on lower octane gasoline. It will cost you power, though, since the truck is not running as it was intended to. Use 91 octane in your MDX. Less than 90 is not premium.

OH, the difference between octane ratings is the percentage of octane in the gasoline. The balance is heptane.

Try a tank of 87 (regular) and then a tank of 92 (premium) See if you can tell any difference in the way your engine runs and responds. Check the mileage too if you like. If you can not detect any difference, if the engine sounds the same, especially under heavy acceleration, then you can use the cheaper regular fuel without any problems.

Google “octane” to learn more…

If the book "recommends" premium it does not "need" it however if it says you must use premium then it does need it. 
  • If it needs high octane, using regular can damage the engine.

  • If it should use high octane then it has a system to sense the low octane and to make adjustments to the car that will protect the engine. However the adjustments will result in lower mileage (reducing or wiping out any economic advantage) and will reduce the power, defeating the reason most people buy cars that require high octane.

  • Using high octane in a car that does not recommend it does cost you more and will not make the engine more powerful, run better or last longer, in fact it could (not likely) actually cause damage.

I checked out the new MDX at the Acura URL. They recommend 91 octane fuel and say in the footnote that using lower octane gas could damage the engine. That sounds like Acura may not honor your engine warranty if you use regular fuel and encounter problems. I’ll bet your older Acura is the same.