93 Octane??

I have a 1998 Jeep V8. The owners manual calls for 93 Octane.

Will using 89 hurt my vehicle and if so how?
How about 87?

I want to make sure I am not wasting my money.

 

Yes, the potential is there. The how is from detonation.

You aren't wasting your money following the manufacturer's
recommendations for your vehicle. You would waste a lot more money by
not following them.


Matt

 

Can I try 89 and just listen for detonation......or is this ridiculous???

 

Chances are that you won't hear either detonation or preignition over the
sound of the engine, unless it is a loud knock. Your engine may be equipped
with a knock sensor to retard the spark however. This should avoid damage to
the engine, but possibly cause you to lose power. If your manual calls for
93 octane, I would use it.

 

Sure, if you don't really care much about your engine. You may or may
not hear it. If you didn't want to buy high octane gas, why did you buy
an engine that requires it?

You can also not change your oil and listen for signs of mechanical
failure...


Matt

 

Matt

Give the guy a break, not everyone knows the importance of using the correct
octane fuel. All he needs to know is that he really must use the correct
octane gas. Using 89 at best would give him worse fuel economy and
performance but at worst could seriously damage his car's engine.

G.

 

i would bet it's the 5.9 engine and yes it needs the higher octane if
it's the special one i'm thinking it is

 

I, and at least one other person, told him why this was a bad idea in an
earlier post. He came back again still looking for a way to do
something stupid. I was simply making an illustration, that I hoped he
could understand as he's obviously not very mechanically literate, as to
how stupid this is. As you say, it MAY only cause him a performance
loss, but it CAN, under the right circumstances, cause him serious
engine damage.

Also, after the profane message he sent to my home email address, it is
obvious that he not only isn't too bright, he's also gutless wonder.

So, HB2, you are right, to quote from your email, misspelling and all,
"You response tells me you are an asshole.", so you'd better ignore my
advice and run the lowest octane gas you can find. Some places even
sell 86, maybe you can find some of that. Enjoy your Jeep!



Matt

 

It is ok to use higher octane fuel in a vehicle designated for use of 'cheap
stuff'.. however, it is a waste of money, as no extra performance will be
gained.. use of cheap fuel in a vehicle designated to run on higher octane
will eventually lead to problems.. if you are so cheap, you should have gone
for one of the lesser engine variants..

 

You might want to take a look at this..

http://www.omegamotors.com/enjoy/gasoline/gasoline_06.html

 

Thanks for the link. But note that it is full of very inaccurate
information. A high octane fuel in a motor not designed for it can be
harmful! It is not clear cut because the methods to achieve a high octane
number are quite varied. But some of the additives used in some of the
products can degrade performance at the least.

Richard.

 

How and why is it harmful? I've heard this claim made before, but I've
never seen any logical reason given. And I've never heard it from a
credible source such as an auto maker or gasoline maker.


Matt

 

Vehicle with knock sensor often take advantage of higher octane fuel and
advance the ignition timing. This can improve fuel economy and provide a
slight increase in power if the engine PCM has the proper programming.

However, higher octance gas when used in cars without a knock sensor is
probably at best not useful (unless you have a problem with knock). The
following is from a relatively old Ford TSB (91-8-13):

ISSUE:
Rough idle, hesitation, poor throttle response, induction backfire and
stalls during cold start/warm up may be caused by the poor volatility of
some high octane premium grade unleaded fuels (91 octane or higher
(R+M)/2). When compared to regular grade unleaded fuel (87 octane
(R+M)/2), high octane premium grade unleaded fuel may cause long crank
time.

ACTION:
Use a regular grade unleaded fuel in all vehicles, except where a
premium unleaded fuel is recommended in the Owner Guide. If lean
air-fuel type symptoms are experienced, determine the grade and brand of
fuel used and offer the following service tips.

Advise those using a higher octane grade fuel to switch to a regular
grade unleaded fuel. For those using a regular grade fuel, advise them
to try another brand. Do not advise using a higher octane unleaded fuel
than is recommended for that specific engine. Ford engines are designed
to perform best using a high quality regular grade unleaded fuel. Only
advise using a higher octane unleaded fuel to avoid potentially damaging
spark knock or ping, but do so only after mechanical fixes are
ineffective.

Ed

 

That's interesting, but as you say is pretty old. My understanding is
the vapor pressure and octane aren't necessarily correlated. For
example, in the northeast we have summer and winter gasoline. The
octane ratings are the same for both seasons, but the gasoline has a
different RVP in winter to be more volatile and thus help starting at
cold temps. Lead was one of the earliest additives to enhance octane
rating and it doesn't change the RVP. Maybe the newer octane rating
additives do have a significant affect on RVP, but since our octane
ratings don't change from summer to winter, there apparently are ways to
modify RVP independently of octane rating.


Matt

 

It is from the post lead era, but from a time when many Fords used speed
density (no MAF) / bank fire injection systems. I think these were less
tolerant of less than ideal gasoline.

Chevron has an interesting web site if you want to read up on gasoline:

http://www.chevron.com/prodserv/fuels/bulletin/motorgas/
http://www.chevron.com/prodserv/fuels/gas_qanda/api_octane.shtml

Mobil also has some good information (although a little more pro premium
than Chevron):

http://www.mobil.com/USA-English/GFM/Products_Services/Fuels/Gasoline_FAQ.asp

Ed

 

I have never heard a credible source warn against using higher octane
fuel in a car designed to use a lower octane fuel. Octane is simply a
measure of the volatility of the fuel. Higher octane = less volatility
and slower/cooler burn with more energy per molecule of fuel. Higher
octane is also more resistant to pre-ignition/detonation than "the cheap
stuff." The net effect is that combustion chamber temperatures are
lower with higher octane fuel. Another benefit is that more air/fuel
can be mixed in the chamber (under higher compression) resulting in
higher power output for a given combustion chamber volume. That's why
most forced induction applications (turbocharged/supercharged) tend to
spec high octane fuel.

As for the methods of raising octane, there really are only 2 that are
widely used for unleaded fuel. You can add MTBE (methyl tertiary-butyl
ether) or alcohol. In many states (like NY as of the end of the month)
MTBE has been banned so chances are that your fuel is a mix of petroleum
distillates and ethanol to achieve the desired octane.

Other than unecessarily lightening your wallet, there should not be any
reason to avoid higher octane fuel if your car doesn't call for it.

Cheers,

C

 

That WAS a problem at one time, when alternatives to lead were first
being experimented with to obtain higher octane ratings than 85-87
(R+M)/2. I would date this to probably the mid to late 1980s, just guessing.

The fact that early "high octane" (what a joke!) unleaded fuels had this
problem has in fact lead to a wide-spread misconception that "octane"
and "volatility" are related, and that "high octane" fuel is "less
volatile" than low octane fuel. In general, that is NOT true at all.
Octane rating is a measure of resistance to self-ignition, that is all.
Volatility has no fundamental bearing on the matter. If you were to take
two gasoline base stocks and raise the octane of one sample by using,
say, tetraethyl lead or MMT and leave a second sample alone, the two
samples would have the same volatility (propensity to vaporize at a
given temperature and pressure). However, if gasoline makers use
aromatic hydrocarbons (or non-hydrocarbons for that matter) to increase
the octane rating instead of lead or manganese, then the volatility may
be adversely affected, as it was in 80s era fuels. Today, most gasolines
except the EPA-mandated special brews seem to be very well compensated
for volatility and octane. Using a higher octane rating might be a waste
of money, but with modern fuels it is harmless. And in fact *some*
makers put other goodies like detergent and lubricant additives in their
higher octane fuels, so there may be some advantage to the fuel system
even if the octane rating is of no benefit.

 

No. Octane is simply a measure of a fuel's resistance to spontaneous,
uncontrolled ignition under specific conditions. The measure of fuel
volatility is called Reid Vapor Pressure (RVP).

No. RVP (i.e. volatility) and octane do not have a causal relationship
with each other in either direction. There are plenty of low-volatility,
high-octane fuels, and there are plenty of high-volatility, low-octane
fuels.

No. High-octane gasoline burns at the same speed as low-octane gasoline,
as long as preignition ("ping", "knock", the uncontrolled spontaneous
ignition referred to above) is not encountered. And the burn is at the
same temperature, not "cooler".

This is not an "also", it is the defining characteristic of high-octane
fuel.

This is only the case if preignition is encountered in a particular
combustion chamber with lower octane fuel. If it is not, then this
statement is false.

No. The octane rating of the fuel does not affect the amount of air/fuel
mixture that can be introduced into the cylinder. This is a function of
engine and induction system design.

No. There are a great many refining techniques and chemicals that are used
to increase the octane rating of unleaded fuel. The addition of MTBE and
"alcohol" (ethanol) are only two of them.

Chris, you *really* need to read the Gasoline FAQ.

DS

 

<blush>

Apparently so.

</blush>

 

Is this the Gasoline FAQ you mentioned -
http://www.repairfaq.org/filipg/AUTO/F_Gasoline6.html#GASOLINE_001 ?

Ed