Might be a crazy question but . . . .
I got my 1990 Grand Marquis 5.0 EFI when it had around 50,000 miles on it.
Now there are 145,000.
I knew the previous owner well and he told me that he had used high test
gas from the day he bought the car so I continued the same.
Now with the gas rip-off going on, one day I had put AMOCO Silver in
instead of Gold and I might be nuts but to me the car seems to be running
better. Idling, acceleration and more, they all seem better and I know this
car like the back of my hand.
Is this in my mind or is it possible that a lower octane gas can make these
changes for the better in my car?
Still scared to use regular though.
All of the post 1985 Fords I have had liked 87 octane better
than anything else. I have had better performance and
better mileage. Another problem with the hiogher octane is
the tendency to produce a bit more carbon contrary to what
the ad folks would like you to believe. Ford recommends
that you do not use higher octane. The only thing you get
with higher octane if the engine doesn't need it is a
If you do not have a high compression engine, you are probably getting worse
performance from running the higher octane gas.
The octane rating is actually a knock rating, "The ability of a fuel to
resist knock is specified by the fuel's octane number. A fuel with a high
octane number is more knock resistant". Higher octane burns slower not
This may SOMETIMES be true, but it is not necessarily so. A hightest
fuel can provide the same BTUs as regular - and in many cases it can
convert more of it, not less, to useable power.
On an engine that does not require higher octane, in most cases it
will have no detrimental effect to the vehicle, but no improvement
either unless you get better gas mileage because your wallet is
Over the years I have owned numerous vehicles that got enough better
mileage running on premium to MORE than make up for the difference in
price. And this was in the days before electronic engine controls.
Your previous owner friend is an idiot.
I have only had one Ford that called for reg in which I had to run high
test because it ran better on it. Well it was my wife's van with a 351,
and she used Sohio (Standard) gas, later BP. Or "Amoco" if you wish...
Turned out that when I finally convinced her to stop using that crap, it
ran just fine on regular gas from anywhere else.
(Note that BP recently started using the Amoco blend instead of its
"own" and I have used it several times since with good luck, or no BAD
luck. Before that, I would have had to run out of gas with no choice
before I let it in my tank)
Buy the most popular brand, from an always busy station. I can vouch for
Speedway/Marathon if it's popular in your area.. if not, dont use it.
I have had injectors checked at 150kmiles and they were almost whistle
clean, required one cleaning pass, only. And never had a filter clog...
even at over 75kmiles.
The octane rating is the number given for the resistance of the gasoline
to ignite. The higher the rating, the harder it is for the gasoline to burn.
Your engine may knock if you are using a lower octane rating than is
recommended by the manufacturer. Also, as an engine ages carbon tends to
build up within the combustion chamber to the point that it increases the
compression ratio. Therefore, older engines sometimes have a tendency to
knock when burning the recommended fuel octane. The reason for the knocking
is that the fuel/air mixture is igniting too EARLY. Engines are designed
(compression ratio/timing) for a specific octane rating - it is typically a
HUGE waste of money to use a higher than recommended octane rated fuel.
Therefore, the easiest answer to your question regarding the proper octane
fuel to use is to use the octane rating as close as possible to what the
manufacturer suggests for the engine. This mindset assumes you have not made
major modifications to the engine (compression ratio/timing).
Yet another $.02 worth from a proud owner of a 1970 Mach 1 351C (searches
for the highest octane I can find) @
On Tue, 23 Aug 2005 10:23:58 -0400, "Grover C. McCoury III"
You have it close, but not QUITE accurate.
Octane is not specifically related to how easy fuel lights or burns.
It has to do with how easily it "detonates" - or auto-ignites.
Volatility and flashpoint, although peripherally related, do not
AKI, or Octane, has more to do with the hydrocarbon makup of the fuel
and the chemistry involved in combustion - things like free radicals
etc which cause UNEVEN burning of the fuel under high pressure and
temperature, AFTER it has ignited.
The carbon buildup causes problems for 2 reasons - increased
compression pressure, which requires higher AKI (anti knock index - or
octane) to prevent detonation, and pre-ignition due to hot spots on
the carbon lighting the fuel before the spark fires.
First, thanks for all the replies. Even though my friend was called an
idiot, it is what I expect from some NG poster's, I guess for some it is
too easy just to post the info without flaming, no matter.
I admit I was using high test because of "my" lack of knowledge and it is a
shame that it took me all this time to finally wake up.
I have been using regular now, 87 octane rating, and I am having no
problems. No pre/post-ignition, whatever it is called, good acceleration
and fine idling. Matter of fact it seems to be runnng better, if that's
possible. As far as gas mileage goes, I have been getting 23 in the city
and expect that to stay the same.
So, thanks again for the replies and good information.
Meaning your friend fell for the marketing hype, of course.
Whatever your opinion of this 62 yo geezer's comments, take it to the bank
that my other anecdoatal advice is on the level.
And yes, I am still learning new tricks, as well.
I still know people who will not buy anything but Shell or BP because they
are the national brands, and thus must be 'better'
Of course they ALSO use Pennzoil and Fram... search around on the net for
opinions on THOSE big names! I mean by people who actually KNOW something.
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