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Wife and I were arguing about the grade of gas. . . although I would never put in anything lower than premium, my argument was that one "accidental" fill up of the lesser grad would not destroy the X?

I'm right, right?!:8:
 

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Yes.

I've put a few tanks of 89 octane in the X and could not notice the difference. Did so out of necessity, not accidental.

It has been said that performance may suffer with less than premium but if so I could not tell. Perhaps with 87 octane a slight performance decrease would be noticed. I would not however use less than premium in extreme conditions, hot weather, towing, etc.
 

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I knew I was right. . . it's "five across the eyes" for the wife!:1pat:
 

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The 03' MDX brochure specifically states that 91 or higher is recommended but lower octanes can be substited with decreased performance. It does not state anywhere that lower octanes will cause damage and I would agree with that since the Pilot which essentially uses the same engine runs on 87.
 

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Hi Laborlitigator:

___I don’t know if I should even enter into this thread …

___From everything I have read, the recommendation is simply that. A recommendation. The 02/03 Ody and Pilot motors are to close to the 01/02 X’s (same HP/same Torque at the same compression ratios although slightly different RPM’s) to justify using Premium in the X. Losing HP may be something someone needs to consider if they are using the X’s accelerator like an On/Off switch but the Ody/Pilot don’t have the same recommendation for anything other than towing heavy loads (trailers) … I don’t intend to ever see 240 HP at the shaft from ours but your driving habits will probably be considerably different than ours. I said same torque although the Ody/Pilot only produce 242 Ft-lbs on Regular unleaded vs. the 01/02’s 245 Ft.-lbs in the X w/ Premium (according to the 01/02 brochures) yet in the 02/03? MDX Acuranews documents, the author mentioned the 02 X also had 242 Ft.-lbs. running Premium unleaded. Why Acura recommends Premium use or why they would have tuned the motor differently to achieve the same max torque/max HP ratings while using a more expensive fuel is anyone’s guess. Even though it may seem like a minor amount, I don’t generally pull $3.00 - $4.00 out of my wallet at the gas station and throw it into the garbage and the price for Premium over Regular unleaded is significant over the long term.

___Has anyone hooked up their laptop to the OBD-II and run the timing profiles w/ the two fuels at similar ambient temps yet? I have been waiting to see this for quite some time to put this question to bed once and for all …

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email protected]
 

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laborlitigator said:
Wife and I were arguing about the grade of gas. . .
Never argue with your wife:rolleyes: or else you'll never get to "do it" in your X!:twak:
 

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Re: Re: So what if I don't put in 91 octane?

msu79gt82 said:


Never argue with your wife:rolleyes: or else you'll never get to "do it" in your X!:twak:
Or anywhere else, for that matter. Just memorize these words and you should be OK in most situations: Yes, Dear. Whatever you say, Dear. You're absolutely right, Dear. :)
 

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Re: Re: Re: So what if I don't put in 91 octane?

mgmdx said:

Or anywhere else, for that matter. Just memorize these words and you should be OK in most situations: Yes, Dear. Whatever you say, Dear. You're absolutely right, Dear. :)
Well, who needs a wife when you've got a secretary. . . . :4:

Geez . . Just kidding guys! :14:

What's that again? "Yes dear, you're absolutely right, dear." "I should never have doubted you dear. . . "

:1zhelp: :whip:
 

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I've read all the fuel posts here, alas I gained nothing in extra knowledge.

Now, can anyone prove to us that the VTEC / engine management software on the MDX (be it the 01-02 or the 03) is the same as the one on the Pilot? This alone may decide once and for all about what gas grade to use (nevermind the "additives" being better in premium, which is STILL not proven by anyone).

About "decreased performance"...Honda is right. If you use 87 grade gas, you will lose torque output, not much, but a few lb ft, but only at high RPM. Most of you won't notice it at all. Try filling up your tank with 93 for a month, redline her pretty regularly ;) and then the following month do the same but with 87 grade. I bet you will notice a drop of 1-2 mpg very clearly. As for grocery getting and driving down the highway to see your in-laws at 60mph, nah, you won't even see 1mpg diff I bet.

As others have said, just play it safe, spend the extra $200 a year on the premium stuff. Especially if you have an 03 'X. Unless you never get the tach above 3000rpm like many people do. :eek:
 

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The reason for higher octane fuel is to retard preignition.
Octane rating by defination is the amount of resistance that a fuel has to detonation. The higher the number, the less likely it is that a particular fuel will detonate under pressure.

The Octane rating is from the refrence fuel Isooctane (C8C18) which is assigned a knock resistance value of 100 RON.
N-heptane (C7C16) is the low value reference fuel. It is very prone to knock and has a value for 0 RON. The octane rating is determined by the mix of these fuels. However today other additives ae used to give an effective octane rating (And thus octane can be rated above 100 or 100% Isooctane)

The MDX has a higher compression engine and this requires a fuel that will not diesel or ignite prior to spark. Lower octane can cause knocking and pinging which is an indication of preignition which can damage the engine.
 

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whynotmdx said:
The reason for higher octane fuel is to retard preignition.
Octane rating by defination is the amount of resistance that a fuel has to detonation. The higher the number, the less likely it is that a particular fuel will detonate under pressure.

The Octane rating is from the refrence fuel Isooctane (C8C18) which is assigned a knock resistance value of 100 RON.
N-heptane (C7C16) is the low value reference fuel. It is very prone to knock and has a value for 0 RON. The octane rating is determined by the mix of these fuels. However today other additives ae used to give an effective octane rating (And thus octane can be rated above 100 or 100% Isooctane)

The MDX has a higher compression engine and this requires a fuel that will not diesel or ignite prior to spark. Lower octane can cause knocking and pinging which is an indication of preignition which can damage the engine.
Thanks for that explanation -- can you tell us more? What kind of damage, how long will it take to damage the engine, what if any repair costs will there be, and how is the damage or amount of damage or extent of the damage related to the 'drop' or 'decrease' in octane? You see, there seems to be a theme in these 'gas threads' that can be summed up as 'if it only hurts it a little, I'll do it' and this seems to relate to mpg as well as engine damage -- in other words, most people that use the lower octane gas seem to care little about loss of mpg or 'some' engine damage. I, on the other hand, use the expensive stuff because that's what I was told to do! Lemmings aren't always right!
 

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Modern cars (starting in the early 80's) have knock sensors. Their function is to hear the knocking and retard the ignition timing to prevent any damage to the engine. Retarding the ignition timing will reduce horsepower slightly. The engine makes the most power when the timing is advanced to the point where it is on the verge of knocking, which is what all those expensive computers in the cars are for. Different manufacturers use different types of knock sensors in different locations on the engine.

The first 800 miles on my '03 have been on regular unleaded and I have not heard a single knock. Many things can effect knocking including air temperature and altitude. For example when I lived in Phoenix, there was a noticeable difference in engine performance between racing in the evening and during the day. The hot air during the day would cause the engine to begin knocking earlier, causing the computer to retard the timing, hence less horsepower. For example on my '94 300 HP stock Corvette, it would mean the difference between a 14.0 quarter mile in the evening and a 14.3 or so quarter mile during the heat of the afternoon. That equated to about 3 car lengths at the end of the quarter mile at about 100 MPH.

Hope this helps.
 

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Type and severity of damage, I would say don't expect much under normal driving conditions. But at 20,000 per year, $0.10 upcharge for higher octane, and avg of 20mpg you are only talking $100 for the entire year.

As far as drop in MPG, you can get that from using too high of an octane as well. A low compression engine can not fully detonate the fuel in a high octane gas.

Trust the governemnt?

Here is their view on octane...

http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm

And here is a decent description based on airplane engines.

http://link.sandiego.com/scripts/wheelbase/message.idc?passin=297
 

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Hi Whynotmdx:

___Welcome to the Acura MDX forum … The one point you seem to be missing is that the Pilot uses the same compression ratio, Bore/Stroke, and block as the X yet runs on Regular Unleaded just as fine as does the X.

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email protected]
 

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Thanks, I checked the web sites and you are correct. When I asked the dealer about differences in the Pilot and MDX one of the things I was told was that the MDX had a higher compression engine. I failed to verify this response...
 
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