Ok, I know some of you must be having the same shock everytime you go to the pump and fill up. I've been religious about using only Premium Unleaded since I picked up my RL back in '05. I have never attempted to use Regular in my car. If I were to consider changing from Regular, what might I notice from the car?

 

these engine is made for high grade fuel. sell the car if you can not give it what is needs.

 

Chris:

Thanks for your update, but it still doesn't answer the question.

G

 

I'm sure someone more techcical than I about this will answer, but I think you are mainly risking pre-ingnition (pinging) which can damage the valves. However, the engine has sensors to prevent pinging, so its unclear if you would actually experience it.
I have always wondered about the mpg difference between using regular versus premium as on a % basis, premium is only about 5% more than regular these days.
From my old days of car DYI, I recall advancing the timing to the limits of pinging to get the best fuel economy. If the engine sensors retard the timing to reduce pinging, would not that reduce gas mileage. I have read on this subject and the chemists claim that premium gas does not deliver better mileage. However, I wonder if they are factoring in the impact of changes to ignition timing in response to reducing pre-ignition.

 

I believe most newer car engines have knock sensors in them that can detect the lower octane of non-premium blends. They then retard the ignition timing to compensate. The result is poorer performance from the engine, which ultimately gives you poorer gas mileage, thus negating most of the savings from switching from premium in the first place.

 

Alright I actually ran the numbers for this.

Take these stats:
10,000 miles a year
avg 20 MPG
.20 cents more for super

With those stats you would use 500 gallons of gas a year. Times that by .20 cents more per gallon and thats only a $100 more a year. Now $100 is a lot of money in general but not when your talking about a 50K car.

 

Here's an old thread with a good explanation of fuel requirements.

https://acurazine.com/forums/showthread.php?t=637

HTH.

 

i have twice filled up with regular by accident. Neither time did I notice any knocking, nor a loss of performance or MPG. Though this is not a scientific study. By practice, I spring for premium and don't worry about the fuel cost difference.

 

I agree with Christopher1, sell the car if you are not going to use the correct fuel. In that same light to save money, you could extend oil changes, use really cheap oil, and buy cheap junk tires, never wax it, etc.
It is $100 per year and should never become a question IMO.

 

No need to beat up on him, he just had a question, and now he has the answer, which is "yes, you can use regular on the short term, but expect a decrease in mileage and performance".

 

Thanks for pointing to that older post. That's exactly what I've read elsewhere over the years regarding this question about octane-game-playing.

Bottom line; don't think you're saving anything by using regular. Even if you only lease the car and don't care about long term potential damage, the immediate 1mpg lower fuel economy will almost completely negate the 5% pump price savings.

 

So curiosity prompts me to ask the reverse.

If you have a car tuned for regular, will the reverse happen? Does feeding the car premium cause the knock sensor to advance the timing with a corresponding efficiency/power increase?

When the minivan is fully loaded for a vacation, it might be nice to know that premium gives you 10-15 extra horses (say in a 215 hp 3.0 V-6 tuned for a fatter torque curve.) to give it some extra get up and go.

 

Generally using premium on a regular designed car gives no difference in almost any area, they are not designed to advance timing on premium gas, so it is wasted money.

 

My RL knocks and pings on super unleaded (93 octane) I poured 2.5 gallons of xylene in the tank bringing the octane up to 97 (that's what the TL-S owners on the TL forum learned was the lowest octane to avoid knocking and pinging). Let me tell you, the car is running unbelievably well. The power increase in amazingly noticeable and the engine is running extremely smooth. On top of that, I'm getting 2.1 more mpg (mostly city). Factoring the cost of the xylene and the $3.75/gal for super unleaded, I'm paying $4.50 per gallon total but I think the cost evens-out with the increase mileage and the better performance makes it worth it.

I'm still finding it hard to believe that so many TL-S owners are complaining about pinging and hardly any RL owners (see TL forum under "valve chatter" thread...20+ pages of discussion). We have the same exact engine as the TL-S. I'm starting to think that the RL is just more isolated from the engine and that it's not as noticeable. I hear it every day (exept for now that I have 97 octane). It is definitely subtle. If you really listen, I would bet you could hear it, especially on regular gas.

 

I've never had any pings with 93 gas. However, as explained above regular can be used since the computer will retard ignition to compensate, the difference in performance will be slight and certainly not detectable in day to day driving. However, chronic use of regular gas will affect engine longevity in the long run since the engine is not operating to its design parameters. One option, if gas prices are killing you, is to alternate premium and regular. My solution is that the RL is parked and my s2000 (30mpg highway) is my summer daily runner It also serves as a compensator for our MDX which sucks gas with gusto

 

Is there any chance that the 93 octane gas is not really 93? Is your gas the summer reformulated?
Can you try gas in another state?

 

Exactly my plan. I drive the S whenever the weather permits, and I'm currently getting 25 mpg as I occasionally, ahum, rev to 9k rpm (sheepish grin).

and would you PLEASE talk to my wife about that? I've been trying to convince her for YEARS that she was wasting her money by putting premium in a car rated for regular. Total waste of money. Maybe $4 a gallon gas will make her change her mind.

On another point, I filled my RL this morning on my way in to the hospital. $4.112 for premium!!!!!!! In Cleveland!!!! First time for me over $4 and it was a nearly $80 fillup.

 

Tough crowd!! I personally appreciate the superb engineering that goes into my RL(as do all), so I am usually obedient when it comes to manufacturers recommendations, and follow them blindly, for better or for worse. All things being equal, they should know best, and have the vehicle's interest in mind. Interesting question, nonetheless.

 

While most of these cars have lower miles, keep this in mind for future reference. As the rings and valves wear over time, your static compression measurement will inevitably drop. This results in a lower effective compression ratio over time. Lower CR=lower energy generated AND lower cylinder temps. The lower temps reduce the propensity for pre-ignition and detonation. I tracked my mileage religously on my 94 legend, and found that once I hit 100k miles, there was no performance or mileage difference between 89 and 91 octane.

 

From Consumer Reports:

"Many people use premium gasoline in the belief that it's better for engines than regular. That can be a costly mistake, especially during times of high fuel prices. Octane grades don't represent a “good, better, best” choice; they simply measure the resistance of fuel to knocking or pinging, a condition in which gasoline burns uncontrollably in the engine's combustion chambers. Knocking and pinging can damage an engine.

While high-octane formulations resist knocking better than lower octanes, most engines are designed to take regular gas, which has an octane rating of about 87. Engines requiring premium gas are typically the more powerful ones found in sports and luxury vehicles. Those engines use a very high compression ratio, making them more vulnerable to knocking, so recommended fuels have octane ratings of 91 or higher. Using premium gas in an engine designed to run on regular doesn't improve performance.

Some engines for which premium gasoline is recommended can run on regular without problems. That's because the engine's knock-sensor system detects the presence of uncontrolled burning in the chambers. When it does, the engine's computer-control system retards engine timing, eliminating the knock but slightly reducing power. If you don't mind giving up some performance, you can run these engines on less-expensive regular gasoline. To check whether your engine is capable of running on regular gas, read your owner's manual or ask your dealership's service department."

AND...

"In a December report on "60 Minutes," Andy Rooney said, "There are a lot of things I'd do if I was rich... I'd fill up with high-test gas instead of the 89-octane I usually buy now."

I don't know what kind of car he drives, but if it's one that doesn't require premium, he'd be wasting his money.

And "89 octane?" If he drives, say, a Lexus or BMW (which require premium - at least 91 octane), he's likely to void his engine's warranty if something goes wrong. And if he drives something that only requires regular, well, he's pouring money down the drain.

We've always said that if your car specifies regular fuel (87 octane), don't buy premium under the mistaken belief that your engine will run better. Most cars are designed to run just fine on regular gasoline. Furthermore, many cars that recommend premium fuel also run well on regular.

What should you do - even if you are "rich?" Check your car's owner's manual to find out if your engine is designed to handle either grade. Think twice about using the more expensive gas even if your owner's manual suggests "for optimum performance use premium." We have found that the differences aren't perceivable during normal driving. However, if your car "pings" or knocks with lower grade fuel, buy premium.

Again, for all models where premium fuel is not required, buying the high-grade gas is simply a waste of money... even if you have it to burn."

LL

 

As somebody said before, if I were worried about regular vs premium (~$120 a YEAR difference, ymmv -negligible-) I probably wouldn't be driving a >$45K car. I see it as part of the cost of owning a luxury car. Worst case scenario I would drive it less but I would not put in something less than it was designed for, regardless what "experts" say.

 

Is this the net/net:
Engines designed for premium will get lower performance AND lower mpg with Regular
Engines designed for regular will NOT get better performance or better mpg with Premium

In case 1 (and not accounting for potential for engine damage) if lower mpg greater than X% with regular, than buy premium if premium less than X% more costly.

 

I just did a quick check and for the first quarter 08 vs 07 it cost me about 30% more for the 08MDX and 06Rl in fuel costs. Over a year it is over 1000 bucks more

 

If you have a few hours to read through the TL forum, you'll see that people connected laptops to their TL and saw the the timing is being retarded 15-degrees by the knock sensor and it's still pinging. I don't think timing will fix the problem. The thought is that 11:1 compression is pushing the limits of pump gas and the ULEV runs lean which adds to the problem. Once you get a little carbon which further increases the compression ratio and the pinging can cause chips in the pistons which become hot-spots that can also cause detonation. This is a bad situation and one in which I'm not sure what I'm going to do.

 

My car has been pinging for over a year (it's only 18 months old). I've tried every brand of gas and I ALWAYS use 93 octane. It's running wonderfully on 97 octane but buying a 5 gallon drum of xylene every-other tankful (2.5 gallons per tank) is very inconvenient. For now, it might be worth it but I'm sure I'll get tired of it very soon and probably get rid of the car. I'm going to give the dealer a chance to fix it but, after reading the TL-S owner's experience with dealers around the county, the prognosis is not good.

 

Is Xylene available to consumers? It appears to be in the benzene family, which I don't think is available to shade tree mechanics. I think Xylene is already present in most high octane gas, so I assume that it doesn't have any negative effects on the catalytic converter or the O2 sensor.

 

no 93 octane available in CA only 87, 89, and 91.
Or is it measured displayed differently here?

 

wiki, always a good source for info:
http://en.wikipedia.org/wiki/Octane_rating

 

Thanks Bob, it's most appreciated. And you are right, I just wanted to get the specifics on using a lower grade of fuel in the RL.

 

Only put premium in the RL. The Santa Fe and RX300 run fine on regular. I'll echo what everybody else has said here. Three or so years ago I put a tank of premium in the Santa Fe (when it was $2.25 for premium) just as an experiment; not worth it and I haven't done it since.

 

Yesterday, after reading a few threads here and on TL section, I thought I would give it a try, listen carefully while going WOT on empty roads. 2nd gear run up to 60 mph or so.

I always put 93. I always have Auto climate set at 72. When I punched it, I did hear what sounded like valve chatter at last a few hundred RPMs. For the next run, I turned off climate control, and did not hear anything all the way to rev-limit. Ran another, same thing, no noise at all with climate control off. I then turned on the climate control, and I did not hear anything either.

I just thought it was interesting that I actually heard it at least once. I "DRIVE" this car and never heard it before.

 

It seems to happen mostly at light throttle but the theory is that you can hear it batter at light throttle because the engine isn't as loud. The best way to hear it, at least in my RL, is to shift manually and if you shift a little early, listen as soon as it shifts and you'll hear the pinging. Mine does it more easily than that but to be able to hear it, that's the best way.

 

Sherwin-Williams paint stores sell a 5-gallon drum of it. It's some kind of solvent. I've also heard that gas companies use xylene as their octane booster. It is 117 octane so if you do the math, 1 gallon of xylene to 5 gallons of 93 gives you 97 octane.

117(octance of xylene) x (1/6) = 19.5

93 x (5/6) = 77.5


19.5 + 77.5 = 97

The RL runs incredibly well at 97 octane. Definitely not a waste of money in my opinion. The problem is that it shouldn't need that high of an octane to run properly. That's my complaint.

 

Thanks for info. I am not worried about the engine. After having driven highly modified BMW with all kinds of worries, driving this car with factory backed warranty is least of my worries.

As far as people saying how TL and RL's 11:1 ratio is pushing the limit and how that relates to pinging, etc. I do not buy it. I do think the compression ratio is higher than regular low rate motors on economy cars, but it is not pushing the limit, it is just failing to perform properly, is all.

My previous M Roadster, when it was near stock (S54 motor with 11.5:1 Comp Ratio), never had a hint of pinging, all the way to 8000 rpm. Current BMW M5s have 12:1 compression ratio and they don't have any hint of pinging as far as I know.

In my mind, if TLs & RLs & odysseys do experience pinging with only 11.0:1 ratio that revs only up to less than 7000 rpm, it is just poorly engineered or put together, regardless of if it's software related or hardware related.

 

My personal experience is using regular (87 octane) will have no real impact on MPG.

I bought a 96 RL in 2000 w/ 67K and started with premium fuel for first 6 months to get a good feel for mileage. I then switched to regular and checked MPG for next year and no difference. That car now has 177k and has been run exclusively on reg fuel. The engine is rock solid with no problems whatsoever.

I did the same experiment on 04 TL and found little difference in MPG. I can't speak to long term damage on that vehicle because it was traded on 05RL.

I've been running premium in 05RL for several months, but I have put a couple of tanks of regular in it just to see if I noticed any performance issues. I haven't done a MPG comparison check yet, but I may just stick w/ premium for now.

I can't disagree that the annual cost difference isn't significant, but I just didn't see the point of buying something that I didn't need. Maybe it was more the fact that we had 5 cars for 6 drivers and I didn't want to spend more for gas than necessary.

 

3.95 yesterday in Columbus for regular
4.15 for premium.....

 

Where do you live Gavine? Some states are doing 10% ethanol mixes in ALL fuel now. Not a pump choice thing. Could you be using a E10 mix and not know it?

I notice some pinging when I've used Ethanol mixed fuels

 

I live in NJ. I'm not sure what the Ethanol percentage is here. If Ethanol affects the octane, then they should account for that in the measurements, right?

 

You would think so, but what if there are other properties of the ethanol that affect ignition timing? I don't know, but I never had pinging problems myself until recently when some brands started converting all their stations to E10. In Florida, all stations are mandated to be converted to E10 by 2010. I know ethanol doesn't have as much energy in it per gallon, therefore we will expect to see a slight drop in mpg with this mix.

 

read the wiki link. Ethanol has higher octane, but less energy