Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

2006 Porsche Cayenne - Fuel Question

Years ago, a caller to the show asked about mixing 87 octane regular and 89 octane mid grade gasoline. You and Tom agreed (surprisingly) that for whatever reason the octane rating would be 92. Is this still the case? I can’t find it anywhere in the Car Talk chats. Thank you for so many great years of laughs and occasional useful info.

No longer true. I do remember something about that, but it may have dealt with mixing ethanol blends with none ethanol gas and achieving an octane greater than the two fuels.
When mixing pump gas you will get a value between the two ratings.

( [ % Fuel A ] x [ Octane of Fuel A ] ) + ( [ % Fuel B ] x [ Octane of Fuel B ] ) = Octane of mixture.

Thank you!

I also remember that, but I thought it was mixing leaded and unleaded gas.

That may be correct, just too long ago for me to remember.

Yeah, forget about getting higher octane by mixing two lower octane gasolines. Not true now, I’d be very surprised if it ever was.

… and then there is the question of why somebody who chose to buy a high-performance luxury vehicle would be trying to cheap-out on gas, rather than buying the octane specified by the vehicle mfr…

Just trying to get a higher octane than basic premium. According to Tom and Ray all those years ago, (it seems like we are all getting old) 87 + 89 gets you to 92 totally defying the laws of nature. If I recall correctly, they were betting their MIT degrees on it…

Why ? It is not as if you will be able to tell the difference in daily driving . If your vehicle requires Premium ( and I think it does ) then that is all you need to use. Don’t make things complicated.

1 Like

I miss Tom and Ray!!!

Sorry, I don’t care what the wager, I can think of no way that could work. Find me something more than your memory…

The only time I heard of this being possibly true was if you mixed unleaded Amoco high test 102 octane (old style measurement) with a leaded high octane like Golden Esso 103 octane. since the Amoco was unleaded and 102 octane it got a real boost from the lead in the Esso, More boost than the Esso lost. Back in the day, I used unleaded Amoco in my Desoto. It let me run 6 degrees more timung and didn’t lead foul the plugs/ Something the early Hemi’s did when you used a colder plug. If you didn’t run a colder plug you could burn them up if you were really pushing it.