the dealer said to only put 87 since the high compression ratio. what is the ramification if one to put 92/93 by mistake? you know, such as when you lend your car to your friend and they come back with a full tank...

we need to have stickers/warning on the car if you can't put anything but 87 in them...

 

No problem. Going higher is fine. It's going the other way where it is an issue. If your car rquires 91 and you put in 87, then it's an issue.

 

If you put 92 into a car that needs 87 it will actually burn worse but there should be no damage to the car, 92 octane fuel is just harder to ignite so in a car made for 87 it will not burn all the fuel as efficiently. Now if you put 87 into a car needing 92, and if that car cannot adjust for it enough then you can have severe engine damage due to pre-ignition, 87 octane will self-ignite in an engine rated for 92, it has a lower ignition threshold so it explodes before the piston is all the way up, it then tries to force the piston DOWN when the piston is still going UP. Also if your dealer said use 87 due to the "high compression ratio" they have no idea what they are talking about, you use HIGHER octane i.e. 92 with high compression engines not 87. Read your manual OR check your fuel filler flap/cap for the correct octane, most manufacturers put the rating there that is required.

 

I see you got your practice typing in! I was busy yesterday, not in mood for typing!

 

I didn't mean to steamroll your answer, was just expanding on it a tiny bit

 

Don't worry about it, harmless.

 

Your answer was great, you should have told me about my spelling mistake. I just fixed it. "Hire" to "Higher".

 

It is indeed 87 with the high compression ratio on the new skyactiv motor and they do know what they are talking about since they develloped that motor to be use with low octane so that you dont have to put more expensive high octane in it.
That's the way it was done.

Edit: Actually if you meant that they didn't know what they were saying when they say "to only put 87 since the high compression ratio" you are right it doesn't make any sense. But that's what you need to put in because it was design to run like that.

 

With a compression ratio of 13:1 they must be using direct injection instead of port injection much like a diesel, this would explain why it can run on 87 since pre-ignition will not be a problem since the fuel is injected at the precise time.

 

I was also surprised a bit even with My 2006 Mazda 6 V6 3.0 a bit. Mine is 10:1 compression. I thought max compression for 87 Octane was 9 or 9.5:1 ! It is amazing as technology changes.