Octane needed for older cars

Is 85 octane gas equal to 91 octane gas for use in a 1973 VW Thing? Owners manual calls for 91 octane.

85 octane is 85 octane, not 91! I would use prmium gas in this “Thing”, as called for. If you can find a 91 mid-octane that would be great.

Good luck!

85 octane is 85 octane, not 91

Well, not exactly. There are 3 different octane ratings. First is “research” octane, next is “motor” octane, and third is the average of research and motor. On US fuel pumps the third type is used, by law. But, in Europe they commonly use research octane on their pumps, though they frequently also list the motor octane. Back in 1973 when the Thing in question was built, most European manufacturers specified research octane in their manuals, so it is possible that 91 listed in the manual could be 85 listed on a modern American fuel pump.

Newer cars, I think, all list the average value for cars sold in the US, but that was definitely not the case in 1973.

Oh, FYI, research octane is generally about 10 points higher than motor octane, so assuming (R+M)/2 is (91+81)/2 the correct average is 86. Now, the normal regular gas sold in the US is 87, but the mountain states often have 85 because the thinner air allows cars to use a lower octane than specified (in many cases).

Thanks for the explanation. I was aware of the various octane designations, but assumed OP was referring to the same US rating and wanted to save on gas with his Thing.

Your “Thing” will run fine on todays 87 octane regular. If you live in a high altitude area, it will run fine on 85 octane…