| 91 octane minimum??
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| Echo2625 |
Just recently got our new X and the dealer said to be sure and use only premium gas (91 octane or higher)
Is there anything to this or will the X run just fine on 87 regular?
Awesome vehicle by the way!!!! |
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| Lrpba300 |
Echo2625, do a search on octane, premium gas vs others, etc. This has been disscussed almost as much as oil!
I have used less octane rating & noticed slightly less MPG & take off power is somewhat less. |
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| DaleB |
quote:
Originally posted by Echo2625
Just recently got our new X and the dealer said to be sure and use only premium gas (91 octane or higher)
Is there anything to this or will the X run just fine on 87 regular?
Awesome vehicle by the way!!!!
Do searches on the forum. Can't speak for the latest models, but I don't believe a 'dip' down to 89 will do anything but save you money.
Latest 'tests' done to some accuracy by a couple of members seems to back this up. 91 is probably peak. Over 91 is likely throwing money away.
But some have done well with even 87. Driving style, load, climate, altitude, are all factors, most of which the engine seems to adjust to with little problem.
Read the posts and make up your own mind. By the way, I would consider the owner's manual a greater authority than the dealer. |
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| xcel |
Hi Echo2625:
___Do you normally accelerate with close to WOT (wide open throttle), tow large trailers, or large loads? If not, the highest fuel economy achieved has come from those running 87 Regular Unleaded although Octane had nothing to do with it … Your dealer is a lot less educated on the subject then what you are going to learn after reading the 100’s of pages when searching this particular forums contents. I use 87 exclusively and will never have a single problem other then saving 10% at each and every fill up.
___Good Luck
___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___Waynegerdes@earthlink.net |
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| evoge |
quote:
Originally posted by xcel
I use 87 exclusively and will never have a single problem other then saving 10% at each and every fill up.
:4: Wayne knows octane (and oil filters, too.)
I use 87 every time and recently got 22.4 mpg (24.0 for the first 2 hrs coming down out of W.Va.) on a 335 mile Labor Day weekend trip to the beach with 2 passengers, dog, and luggage. Save the 91 for extreme conditions. |
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| Echo2625 |
It's my wife's X and she drives very normal/easy 90 % of the time.
Thanks for the input! I'll give 87 octane a try.. |
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| loa3 |
| We've used 87 octane since buying our MDX in April, 04. Never a ping, plenty of power, good mileage. The key issue is whether the engine knocks. The knock sensor will adjust spark advance to prevent preignition. So far, it fully accomodates 87 octane. It's interesting that the Honda Pilot recommends 87 octane, unless pulling a trailer, then it recommends 91 octane. Not sure why Acura doesn't say the same thing. |
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| frostyra |
quote:
Originally posted by loa3
It's interesting that the Honda Pilot recommends 87 octane, unless pulling a trailer, then it recommends 91 octane. Not sure why Acura doesn't say the same thing.
I've always thought that it's because "luxury cars are more luxurious if they take hi-test," and nothing more than that. Do a search for "mogur" -- he did a very good detailed technical test on 91, 89, and 87 octanes. There was no difference in engine performance between 89 and 91, and the only reaction to 87 was that the computer would retard the spark timing slightly during WOT (wide-open-throttle, often called foot-to-the-floor) driving. That retarded timing would slightly reduce horsepower at that time. Save money with 87 -- it won't hurt your engine, and you won't notice the difference unless you drive at WOT most of the time. |
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| R Stevens |
I've been using 93 octane from the begnning with my 2002. You guys have convinced me to try lower octane. I filled the tank today with 89 octane (it was about 2/3 empty). If that works OK for a few tanks I'll go with 87.
Is there a period of adjustment for the engine? |
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| topgun_tb |
After having my '04 X for about 2 1/2 months, I must concur with the posts that indicate that the best gas mileage is achieved with 87 octane and the worst mileage with 91 octane. Here in Canada, our Xs have the fuel consumption displayed in Litres/100 km and recently I consumed an average of about 13.5 L/100 km in moderate city driving using 87 octane. Running 91 octane resulted in a fuel consumption of about 14.5 L/100km.
As many others here have mentioned, the Honda Pilot has an almost identical engine and it's recommended fuel is regular unleaded (87). Of noteworthy mention is that both the X and Pilot engines have a compression ratio of 10:1. I'm an Electrical Engineer, but in the little that I know about internal combustion engines, I believe the compression ratio is the single most important parameter that would determine the appropriate type of fuel, as it is the compression ratio of an engine that will make it more apt to knock (or pre-ignite). A higher compression engine requires higher octane to protect against premature ignition (during the compression stroke). Thus, as the Pilot and X are both 10:1 engines, I cannot see how the fuel recommendation should be different from one to the other. I'd be interested in the opinions of some Mechanical Engineering types out there.
Thanks,
Ed |
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| frostyra |
quote:
Originally posted by R Stevens
Is there a period of adjustment for the engine?
No. The "knock sensor", aka "ping sensor", aka "detonation sensor", is in the timing control system. It will cause the ignition timing to be retarded when detonation is heard, and I believe it will add more retard with more detonation -- i.e., the timing would be retarded more with Wide Open Throttle on 87 octane, and less with Almost Wide Open Throttle. |
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| frostyra |
quote:
Originally posted by topgun_tb
I'm an Electrical Engineer, but in the little that I know about internal combustion engines, I believe the compression ratio is the single most important parameter that would determine the appropriate type of fuel, as it is the compression ratio of an engine that will make it more apt to knock (or pre-ignite). A higher compression engine requires higher octane to protect against premature ignition (during the compression stroke). Thus, as the Pilot and X are both 10:1 engines, I cannot see how the fuel recommendation should be different from one to the other. I'd be interested in the opinions of some Mechanical Engineering types out there.
'Nuther EE here. I would say that it is a combination of compression ratio and ignition timing that determines aptness for knocking. The more the timing is "advanced", the more likely that the engine will knock, and thus need higher-octane fuel. With the knock sensor retarding the ignition timing whenever knock occurs, you can run almost any octane without the engine knocking. And as others have attested, the only noticeable ignition retardation seems to occur with 87 at or near Wide Open Throttle. |
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| DaleB |
There could be some finite differents in advance curves, etc. between the 2 engines, but to what purpose, I am not sure.
For MOST engines, if you look at various models of cars, 10 to 1 compression ratio is really on the fence as to octane ratings.
MOST over 10 to 1 have premium fuel recommendations, and MOST under have regular fuel recommendations.
I don't think it is a coincidence that many 'mainstream' autos have compression ratios of around 9.75 to 1, as exhibited by many GM V6s.
And they have regular fuel recommendations.
Of course, depending on the internal design of the combustion chamber, some are by design more or less suspectible to preignition.
There are always exceptions, but when the Pilot manual says premium fuel might be advisable when driving with heavy loads, that is a pretty good indication it is not a solid recommendation.
Maybe Honda does think Acura MDX drivers will be more agressive in their driving, or that we expect a 'luxury' vehicle to run on premium. |
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| TheWorm |
While on the subject of timing advance, etc and the X vs. Pilot, keep in mind the 03+ X has 20 or 25 more horses than the Pilot.
The 01/02 X and the Pilots are rated the same @ 240 (and peak torque is the same, too).
Keeping this discussion based on the same engine (rating, anyway -- the 01/02 X vs 03/04 Pilot): the HP and torque curves on the X are broader/flatter (i.e., peak available across a wider RPM band). IIRC it was a significantly flatter curve, too. That difference alone would seem to indicate the timing advance is probably different betw the two cars in that range. Of course, HP and torque curves are generated @ WOT, in a 1:1 gear ratio.
The 01/02 X has 3 VTEC cam profiles vs the Pilot's 2. I'm not really sure what that means (whether the camshafts are different physical profiles, or whether the ECU has different software profiles), but it was another notable difference.
I realize Mogur's earlier study w/the Davis carchip is the basis for comments on the differences in timing advance based on octane ratings. However, IMO the Davis Carchip lacks the resolution to make any significant conclusions. The resolution of that unit is 5 seconds, and the few times I've looked @ timing advance on my unit, it's all over the place, like -10 to +25 (making those up, but you get the idea...every 5 second "snapshot" had wildly different numbers). Of course, my driving was in the city...perhaps at steady-state on the highway there'd be less variance.
I can't remember how many datapoints the unit can store; we have a long highway trip coming in a couple of weeks. Maybe I'll do one way w/89 and the other w/91 and record the timing advance along with the overall mileage. The problem is that it'll be on highway 5 and prevailing wind can be a factor.
FWIW we're using 89 pretty much all the time. I actually notice a bigger SOTP difference between brands of gas than 91 vs 89. Our X is a pig w/76 gas. Just horrible. |
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| DaleB |
I find interesting that 'topgun' gets worse mileage with higher octane. At best I would expect no big difference between 87 and 91, and if anything, a little more efficiency with higher octane.
Different cam profiles would certainly explain some differences in the torque curves between the Pilot and MDX.
I am not sure that 20 more HP makes much difference either. Espeically if it is the result of better breathing.
I wonder what the fuel recommendaton of the latest Saturn VUE is?
I notice the latest models are advertising 250 hp, maybe an 03 engine or just one taliored specifically for that model. |
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| Mr_MDX |
hmmmm, i just picked up my 04 MDX last week and I asked my sales person the same question... his comment was premium octane is suggested but not required. The dealer said they fill new cars up with mid-grade and I could run normal unleaded with no problems @ all.
he said most of the newer gases pretty much contain the detergants in all grades unlike the old days where the premium gas were the only ones that did.
I met them half way and use only Shell mid-grade gas. I figure with the quality of gas (i.e. price) being much more than fina, race track, diamond shamrock, I would be pretty much safe with a mid-grade gas from Chevron or Shell
but who knows :8: i've only filled up 2x so far so i don't have a baseline anyway |
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| Frumious |
| Not much choice for me: The highest octane available in my town is 90. Used to have 92 here until about two months ago. 90 is priced as premium; 89 and 88 as "plus"; 87 as regular. I might try the 87 to see if my gas mileage improves. That would be slick: lower price AND better mileage. |
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| presten |
| There really should be no reason why 87 Octane gas would improve fuel mileage...All gasoline has the same (within a couple of percent) heat capacity in BTU's per pound. The main differences and reason between the octane ratings is the resistance to "spontaneous combustion of the end gasses" or detonation, as it is commonly known. Normal combustion in the combustion chamber is a flame front that originates at the spark plug and moves rapidly across the chamber to consume the entire air/fuel charge. As this burning occurs, the pressure and temperature within the chamber rises rapidly. If it rises to a high enough temperature to spontaneously ignite the remaining air/fuel mixture...you have detonation! The purpose of octane enhancement additives (such as the old tetra-ethyl lead) or selective refining methods is to raise that spontaneous combustion temperature to a much higher number. With higher octane fuel, the compression ratio can be raised (along with corresponding combustion temperatures) and the spark timing optimized for best power. Modern "knock sensors" sense the presence of "Knock" and retard spark timing to reduce the combustion pressures. Now the end result of that timing change is some loss of power and economy...but, generally that timing change occurs only at WOT (wide open throttle) or very nearly that, since that is the only time when combustion pressures and temperatures (remember Boyles law, all you engineering types) rise to the design peak values. All other operating conditions keep things well under critical values and do just fine with the lower octane ratings. Having said that, there is certainly some justification to use the higher octane fuel for pulling a trailer, sustained high speed freeway driving in hot conditions, pulling long grades or any other use that puts you in that WOT situation. For local driving and light use, the 87 fuel should work just fine. By the way, those of you who live at higher altitude (2000 ft or more) should never bother to buy 91 octane fuel. The thinner air at altitude acts in the same way as lowering the compression ratio of the engine. In fact, in most of the high altitude Western states such as Utah and Wyoming, it is hard to find 91 octane fuel at all. Many stations start at 89 octane and go down to 85. Now having said all of the above, let me go back to my original statement...87 octane fuel will not give better fuel mileage all other things being equal. One other little known fact is the source of supply for much gasoline is the same for many brands. Here in the Bay Area, over 50% of the fuel comes from the Shell refinery in Martinez, CA. As the various tanker trucks from Chevron, Mobil, Shell, Texaco, etc. pull up to the terminal, the fuel loaded is the same but an additive package as specified by their company is blended in as the fuel is loaded. With most major companies, the additive package is now the same for all octane grades. This final company additive package does not effect octane...refining methods and additives during the refining process determine the octane rating. |
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| highcountrymdx |
In order to comply with EPA certification rules, an automobile manufacture must require that the automobile be maintained as it was originally presented for certification. This means, in the case of the MDX, that the crankcase oil must be 5w-20, and the fuel must be 91 octane.
Acura was able to squeeze a bit more power (and EPA mileage) by using a very thin oil viscosity, and high octane gas.
In all but extreme conditions, high ambient temps (over 90F), or extreme engine loading, for example, you will never call on the engine to develop full rated power that was certified with 91 octane and 5w-20 oil.
It is interesting to note that if Honda/Acura wanted to go to the limit, they would have presented the engine to the EPA with a synthetic oil in the crankcase (like Mobil 1 0w-20). Of course the owner's manual would have had to require full synthetics to be used.
As far as engine longevity goes, 87 octane and 10w-30 will work just fine, with no durability issues noted. |
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