David, this is a beautiful response.  

The key part is:   "And that 
> number is 87, regular grade fuel.  If you're 
> really flogging the beast the owner's manual says 
> you can use higher octane (mid-grade) if you want, just in case."

My Canadian owner's manual says to use 87 octance, but recommends the mid-grade, 89 octane, for "heavy loads and high speeds under hot conditions".  When up in the Appalachians of New Hampshire or New Brunswick, I buy 89 octane.  (Actually in NB, I often buy the 91 octane, as NB regulates gas prices and 91 octane is only 6 cents a litre/23 cents a US gallon more than 87 octane there, unlike Ontario, where the spread is 14-16 cents a litre or more!)

James
Ottawa, ON 

> Date: Fri, 15 May 2015 15:11:13 -0400
> From: dbeierl@ATTGLOBAL.NET
> Subject: Re: Fwd: Gas - Cheap vs Expensive
> To: vanagon@GERRY.VANAGON.COM
> 
> At 02:23 PM 5/15/2015, PB wrote:
> >About a year and a half ago there was a thread about which gasoline to
> >use.  If I remember right, there was a general consensus that Vanagons were
> >made to use cheap gas,
> 
> Stop right there, please.  If we think in cheap 
> vs expensive it all gets very confusing.  After 
> you figure out what sort of gas you want to use 
> then you can try to find it cheaply.
> 
> The Vanagon requires fuel with a certain octane 
> rating to operate correctly.  Octane rating is a 
> number that rates the gasoline's ability to 
> resist exploding inside your engine.  You don't 
> want it to explode.  You want it to burn rapidly 
> but smoothly, and for the Vanagon at sea level 
> you need to use fuel with octane rating of at 
> least 87, American style.  Butbutbut, you 
> say.  There are two common methods for rating 
> octane, called the Research method and the Motor 
> method.  In Europe they like the Research method, 
> and the Vanagon needs gas with a Research Octane 
> Number of 91, just like it says on your sticker 
> (you can see the RON if you look).  In the US for 
> some reason we like both methods.  We like them 
> so well that we use the average of the two for 
> the octne number we stick on th epump.  And that 
> number is 87, regular grade fuel.  If you're 
> really flogging the beast the owner's manual says 
> you can use higher octane (mid-grade) if you want, just in case.
> 
> If you go up in the mountains you'll get another 
> scare because the pumps will say 85 on them -- 
> that's ok, because of the altitude 85 octane is 
> sufficient.  Note that "high-octane" gas isn't 
> filled with more energy than regular -- it's 
> actually filled with a bit less.  Its virtue is 
> burning smoothly in high-compression engines that 
> tend to make the fuel explode.  Its other virtue 
> is that in order to encourage you to buy  the 
> fancy gasoline, the blender/refiner/brand may put 
> lots of lovely detergent and ssuch in their 
> high-test, but skimp on it in their regular 
> grade.  If that were true, either using Techron 
> from time to time or switching to the expensive 
> gas would keep your engine from getting all crudded up internally.
> 
> And that brings us to Top Tier gasoline.  Some 
> brands have agreed to sell only gasoline with a 
> superior detergent package and other good 
> qualities, and in turn VW and other mfrs suggest 
> that you buy this high-quality gas carried by the 
> Top Tier brands.  It comes in high, mid, and low 
> octane, but they all have the good detergent 
> package.  VW thinks it's a very good idea for you 
> to use gas meeting the Top Tier standard as it 
> will keep your engine clean and happy 
> inside.  But they don't care which brand you use, 
> and they don't forbid you to use gas that is not 
> Top Tier.  They just warn that you may not like 
> the long-term results when your engine 
> potentially gets all clogged up with stuff.
> 
> Yours,
> David
> 
> >  so I immediately switched from 91 octane Costco gas
> ><http://blog.modbargains.com/what-is-top-tier-gas-and-why-it-matters-its-at-costco/>
> >to 87.
> >
> >A few weeks ago, after a tuneup and compression
> >​ adjustment​
> >in all 4 cylinders, my mechanic, Bela, told me I was using "BAD GAS."  He
> >told me that Costco gas was BAD, and would ruin the cylinders, and that I
> >needed to use 91 (89 at the lowest) octane *MOBIL* gas for the best
> >performance.  (Mobil gas is extremely high-priced, and averages $.3
> >​5
> >  - $1.00 per gallon above all other brands.)  OK.  So I switched to Mobil
> >91 octane - for my van ONLY, and I actually have been getting better
> >mileage.  (Had to use Gas Buddy to find the lowest priced Mobil, which is
> >​
> >on my daily route, and pay cash to avoid credit card surcharge
> >​.)​
> >
> >
> >Yesterday, I noticed the dog-eared stickers on my passenger door, and was
> >able to see that 91 octane was recommended when the vehicle was made