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Old 02-19-2020, 05:34 PM   #1
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F53 V10 Fuel (85 v 87 octane)

The manual says use 87 Octane and expresses a preference for premium. They note that in high altitude areas regular is often 85 octane.

I am looking for technical information as to why this makes sense. I have lived at high altitude and used 85 Octane for 50 years with no issues. I also used it in my previous E450 V10 over 30,000 miles with no issues.

I see no difference in mpg or power w 85 octane.

87 is much more expensive where 85 is offered, and 91 octane even more.

I hear no pinging w 85 octane.

Can anyone provide a technical reason why Ford takes this position?
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Old 02-19-2020, 07:37 PM   #2
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Octane rating is the fuel’s resistance to ignition under compression (ping).

At higher elevation the thinner air decreases the amount of compression in the cylinder so the higher octane is not needed on a normally aspirated engine, which the V10 is.
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Old 02-19-2020, 10:11 PM   #3
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Originally Posted by DougW View Post
Octane rating is the fuelís resistance to ignition under compression (ping).

At higher elevation the thinner air decreases the amount of compression in the cylinder so the higher octane is not needed on a normally aspirated engine, which the V10 is.
Thanks. Aware of that.

So why does the F53 manual say not to use it?

And they suggest 91 octane would be a better choice for the F53 (three valve) V 10.
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Old 02-19-2020, 11:20 PM   #4
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Thanks. Aware of that.

So why does the F53 manual say not to use it?

And they suggest 91 octane would be a better choice for the F53 (three valve) V 10.
I have read that the v10 does not have knock sensors in it so it will not adjust fuel flow or timing to correct a ping. The use of a higher octane is insurance against ping.

I canít imagine why Ford would make an engine without knock sensors in this day and age, but that is what I read within the last several months.
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Old 02-20-2020, 09:49 AM   #5
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I’ve learned a few things by researching this. First, it isn’t a new requirement. Found discussions going back to at least 2006. Second, it isn’t limited to V10s. Ford has it in many of their manuals, if not all.

My Jeep and Canyon ( GMC) also emphasize using 87 octane, but make no mention of the 85 or 86 octane offered as regular in higher elevation.

There might be a technical reason brought on by more sophisticated computer controlled fuel injection systems. They can measure ambient air pressure and adjust spark delay and fuel/air mix. But I don’t see why they can’t then adjust for using 85 octane at higher elevation because the physical facts haven’t changed.

Although they claim engine damage can result I suspect you’d hear some serious knocking or pinging before it began to burn valves. I certainly cannot hear any with either of my V10s.

It isn’t trivial where I travel. 87 octane is priced 30 to 50 cents per gallon higher in the areas that offer 85 octane. With an 80 gallon tank and 7 mpg that can make a significant cost.

I wonder if it actually has to do with federal regulations. The testing they have to do to meet air quality requirements is likely expensive. They may not want to do it over simulating high altitude operation with 85 octane.
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Old 02-20-2020, 02:24 PM   #6
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In my experience, Ford engines in general are more prone to ping or knock. This is not a scientific observation...just a casual one. I've owned quite a few Fords, and, in hot weather especially, they tended to knock...and older ones were notorious for "run on".

Higher octane is a defense against that knock.

With an engine that is highly stressed essentially all the time as it would be in a motorhome application, better safe than sorry.

You don't say what year the engine is. Older ones were known for blowing the spark plugs right out of the head.

And for the record, it appears that F53 is a chassis number and has nothing to do with the engine other than the engine pairing with that bare motorhome chassis.

This might open the door to some insights about your V-10. More exploration may reveal inherent vulnerabilities in your particular engine that warrant relying on higher octane fuels to avoid unusual damage that might result from engine knock. Certainly knock in a 2005 and earlier V-10 would be a culprit in blowing the plugs out of the head.

https://lasmotorhomes.co.uk/case-stu...gine-problems/
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Old 02-20-2020, 05:09 PM   #7
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Pre-ignition

Quote:
Originally Posted by jimmoore13 View Post
This might open the door to some insights about your V-10. More exploration may reveal inherent vulnerabilities in your particular engine that warrant relying on higher octane fuels to avoid unusual damage that might result from engine knock. Certainly knock in a 2005 and earlier V-10 would be a culprit in blowing the plugs out of the head.

https://lasmotorhomes.co.uk/case-stu...gine-problems/
Pre-ignition is certainly hard on the pistons/rod/crankshaft, as the fuel-air combusts before the piston reached Top Dead Center, essentially trying to turn the crankshaft backwards.

But I don't believe the peak explosive force in the cylinder would be any higher with pre-ignition than with normal combustion, so I can't see a relationship between pre-ignition and "blowing the plugs out of the head."
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Old 02-20-2020, 05:19 PM   #8
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...I can't see a relationship between pre-ignition and "blowing the plugs out of the head."
What you said is true. I think Mr. Moore was exercising poetic license more than critical analysis.
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Old 02-21-2020, 12:17 AM   #9
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Some facts.
Engine Basics: Detonation and Pre-Ignition by Allen W. Cline

It appears that detonation, i.e. ping or knock, does raise pressure. I didnít mention pre-ignition.

Whether the engine in question is old enough to have the short plug threads is still unknown. That wasnít really the point anyway. While that surely would be a problem, the goal of the fuel octane spec is largely to prevent detonation and the associated shock waves we experience as ping.
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Old 02-21-2020, 12:28 PM   #10
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On my second motorhome with the Ford V10. Always use regular and never had a problem at sea level or where I live in the mountains.
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Old 02-21-2020, 12:59 PM   #11
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On my second motorhome with the Ford V10. Always use regular and never had a problem at sea level or where I live in the mountains.
I don’t recall seeing 85 Octane regular in Cascade although the elevation might justify it.

Answer to another question: my V10s are 2017 and 2019. I traded the 2017 in on the 2019. It had 35,000 miles with maybe 10,000 w 85 octane. The latter is the three valve version. I don’t know if the 2016 was.

Blowing out spark plugs is a new one on me. I suspected the concern is excessive knocking can burn valves.
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Old 02-21-2020, 03:09 PM   #12
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I don’t recall seeing 85 Octane regular in Cascade although the elevation might justify it.
Almost all highways in Western States are far lower then highways in the areas where "85 Octane" regular is available.

When you are driving in places like Colorado and other Rocky Mountain States the average altitude is up in the 6,000 foot or more range. In contrast the highest highway pass in WA State is 5800 ft. That's only ONE highway and it's closed half the year. I lived in Colorado for 10 years down on the "flat lands" and my house was at 6300 feet. Everything went up from there.

Several things work in the favor of the lower 85 octane number.

First off all it's cheaper to produce.

Second, as mentioned less oxygen in high altitudes so it has the same effect as lowering compression, lessening the tendency to pre-ignite/detonate.

Third, for the same as above the lower oxygen content also creates a more rich mixture which also has a tendency to reduce "pinging". Yes, Oxygen sensors regulate fuel mixture but they do so within a range. The higher altitude pushes the mixture to the upper limits of rich which testing has shown to make the fuel perform as well as 87 Octane when used at high altitude. Any power loss is the result of the altitude, not lower Octane.

A note, if one has a huge fuel tank, or carries extra fuel in cans or aux tank, then fills up in a place selling 85 Octane, they might encounter issues if they are still burning it when they get down to sea level. This is more likely if a vehicle is towed from high altitude to low altitude with a tank filled up before towing.
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Old 03-03-2020, 07:36 PM   #13
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Apparently no one on this forum has a clue as to why Ford takes their anti-physics position.

I’m betting it has to more to do with lawyers and Federal Regulations than physics.

Anyhow, thanks for your inputs. I’m giving up here.
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Old 03-04-2020, 08:12 PM   #14
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Pre-ignition takes place when temps and pressure in the combustion head are very high. Pre-ignition does and can cause piston ring and valve damage.

In post #1, you cited that Ford prefers premium at sea level, but requires 87 octane minimum. That tells me that Ford envisions the POSSIBILITY of temperatures and pressures in the engine under heavy loads that could cause pre-ignition on 87 octane (at sea level). It would follow, that at altitude, you COULD run into heavy loads causing internal temps and pressures to be high enough to cause pre-ignition when using 85 octane.

Whether or not YOU will encounter temps and pressures high enough to require more than regular octane gas is an open question. A lot has to do with engine cooling, RPM the engine is running at (too low an RPM for the load is much more likely to cause pre-ignition than a higher RPM, and how lean the computer tries to run the mixture. I would guess that IF your cooling keeps the engine temp steady under all conditions, you could use 85 octane at altitude without problem. But if your temp gauge rises as you climb a grade, you probably would be safer with the 87 octane. Just my guidance from my flying days.

In flying piston engine airplanes with pilot-controlled mixture, we would set the mixture rich when requiring full power from the engine, and set the cowl flaps for maximum cooling. In reduced power settings (cruise), we would lean the engine for better fuel economy using the cylinder head temp gauge as the guide for peak engine efficiency. Cowl flaps would be closed during descents to keep the engine warm enough.

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