Which octane fuel

[Spike1306]

Hi
Well we are finally here on our holes in the rented RV
When we picked it up they kept on saying 89 octane fuel or higher, now that did not seem right to me so I googled it and for this RV it just kept saying regular fuel.
It is a winibago Minnie Winnie with the ford engine
Why would they say 89 or higher IF it only needs regular?
Plus there is a bit of a difference in price too nearly 30cents a gallon. And on a 2000 mile road trip that will soon add up.
So I am guessing I will be ok with just regular fuel.

Thanks

 

[HappyWanderer]

I've never burned anything other than 87 octane in my Ford V-10.

 

[Spike1306]

That?s what I thought too.
Just seemed a little strange they kept saying 89 or higher and yet the manufacturer says regular .
Thanks

 

[Gizmo100]

If the engine starts knocking after using the 87 then switch back to the 89. I would be surprised if anyone uses the 89 when it's on a long trip rental.

 

[Utclmjmpr]

A lot of that decision depends on heat load and altitude.>>>Dan

 

[KandT]

87 octane when I had that Ford V10 - No problems.

 

[Larry N.]

When we had our Bounder with the V-10 we used 85 octane (that's regular at 5,000 ft.) and, at lower altitudes it was 87 octane. I never noticed any indication of knocking -- it ran great.

 

[Roy M]

Modern engines have knock sensors that adjust timing. I wouldn't worry about it unless you are traveling south of the border where gas can be sketchy.

 

[Gary RV_Wizard]

Who was this "they" who said use 89 octane?  The guys at the rental agency are rarely experts in much of anything, so maybe it was just one guy's opinion. 

There might conceivably be some reason to go above 87 octane in the mountains (over 5000 ft), but even there a modern engine self-adjust for the thinner air at high altitudes.  I took a 2002 gas V8 motorhome as high as 9000 ft while running 87 octane regular. Never a hiccup or even a noticeable loss of performance.

 

[Isaac-1]

Gary I think more of the problem is 85 and 86 octane being sold as the base level in some of the mountain states.  My 8.1L V8 was not happy with it (knocking and hesitation) in Wyoming a couple of years ago, so I quickly switched (topping off with 91 at the next town to bring the average octane up) then to 87-88 octane for the rest of the trip and it became happy again.

 

[Gary RV_Wizard]

Maybe, Isaac, but my experience in the western states is that anywhere above 5000 ft the "regular" fuel is at least 87 octane.  Heck, 87 is the ubiquitous "regular" even here in Florida, where 50 ft is considered high ground. A few stations advertise 85 grade at el cheapo prices, though.

 

[Larry N.]

Maybe, Isaac, but my experience in the western states is that anywhere above 5000 ft the "regular" fuel is at least 87 octane.  Heck, 87 is the ubiquitous "regular" even here in Florida, where 50 ft is considered high ground. A few stations advertise 85 grade at el cheapo prices, though.

Throughout Colorado and New Mexico (and many others), "regular" unleaded is usually 85 octane, the mid grade is 87, and premium is 91. Most places it's also 10% ethanol. And the F-53 with the V-10 works just fine off of that. Apparently the oil companies figure that the reduced power available at altitude doesn't need the extra 2 octane numbers so they can get by with reduced expense. Of course a turbocharged engine might want the extra, so would use the mid grade.

 

[Gary RV_Wizard]

Thanks, Larry. That's helpful info.

 

[John From Detroit]

Gary I think more of the problem is 85 and 86 octane being sold as the base level in some of the mountain states.  My 8.1L V8 was not happy with it (knocking and hesitation) in Wyoming a couple of years ago, so I quickly switched (topping off with 91 at the next town to bring the average octane up) then to 87-88 octane for the rest of the trip and it became happy again.

I too noticed that when I fueled up on the mountain I got lower than I'm used to seeing octane and the 8.1 did not like it at all.. Next fill I used mid grade and it was happy as the proverbial clam.. (Why is a clam happy when he is in sauce and about to be Someone's dinner? :} )

Now when I find a pump like that I juist go mid-grade and the rig is happy. 

 

[Lou Schneider]

Octane is the ability of the fuel to resist pre-ignition (knock) under pressure. Higher octane numbers = more resistance to pre-ignition.

You don't need as much octane at high elevations because the air is thinner up there so there's less initial charge in the cylinder, thus less pressure.

This also holds true for turbocharged engines, because the turbocharger only increases the pressure a set amount against the ambient pressure.  Again here, higher elevations mean less air going into the cylinders.

John, you spend most of your time on the east coast.  How high was the mountain where you found the lower octane fuel?