Just want to see how does it impact the performance and MPG.

I'm driving a 04' automatic crossfire, travel about 50 miles daily, 20% local, up and down the hill, and 80% freeway, around 70 mph.

I have been getting about 23.3 MPG, using Premium 91 octane Top tier gas (FYI, I always use Shell, occasionally 76 and Chevron). I just switched to regular 87 octane gas, probably for the next two months for a more accurate result. I expect a less MPG, but I want to see the actual "mile/$".






RESULTS (updated Feb 3, 2008):

After a few tanks of regular gas, I got some results and driving experience that I want to share with everyone who wants to know.

Gas milage:
with top tier (Shell) Premium 91 octane gas, I get average about 23.5 MPG (ranging between 22.5 - 24.5 MPG depends on driving conditions). During the 5 tanks of top tier (Shell) regular 87 octane gas, I still get average of about 23 MPG. (First tank 23.9, second 23.3, third 22.6, 22.5 and 22.7 MPG) I found the data quite interesting, I'm pretty much getting the same MPG on both premium and regular gas, difference is minimal.

Performance and driving experience:
On the first 100 to 200 miles switched to regular gas, I can feel the engine running a little rough at idle, but I don't feel that anymore after the first 200 miles, well, maybe once in a while but that's is normal. I think this is the time while the knock sensor and computer gets to work.

Regarding the horsepower, I don't have any equipment to measure, but on my regular driving experience, I don't really feel any difference, it drive the same way. But I have to point out two interesting feelings: 1, sometimes I feel the lack of power with regular gas when going on high RPM. 2, I think the up shifting is delayed with regular gas (mine is an automatic). But I don't know if this is real or just my imagination, since I know what gas I have in the tank and so my psychology may affecting my sense.

Does regular gas do any damage?:
I did some research and found there are two theories. Therory A says that low octane gas used on high conpression engines will cause early explosion causes knocking engine, the wrong timing and extra heat energy may damage the engine. Therory B suggests that new engine like ours have knock sensors to retard the timing and the engine will run with no problem. I believe in both, and my suggestion is if you drive like an old man, regular gas would works on the crossfire, but if you drive it like a sport car like wht it supposed to be, go with premium gas.

 

bad move don't do it. these are high compression engines need high octane.

 

I understand using lower octane gas may cause knock on high compression engines, but I believe the knock sensor will retard the timing of the engine and should run no problem. I just want to verify if that's true or not.

So far she is running good with no problems. I notice the engine was running a little rough at idle when I first switch to regular gas, but now seems doing better after about 100 miles on day 2.

I don't feel any difference in city driving. But when I slam the gas on highway speed, I do feel the lack of HP than before.

 

It's not about power or gas mileage. It's about detonation and damage to pistons and valves. If you don't drive it hard, you might be okay for awhile. Let's see, how long does it take at saving 20 cents a gallon to pay for a replacement MB engine ???

 

An industrial strength hard hat is supposedly effective for most construction-type head traumas, but you won't see me wearing one while purposefully firing a nail gun into my own head. :-)

Mike

 

I can't believe you only get 23 MPG? I run 93 Mobil all the time and I get at least 28 MPG. You may want to try running 93 after you finish with your regular gas experiment.

 

Holy Pistons Batman! What an idea... Jackei.

The key word here is "holes in your pistons".

 

91 is the highest I can get here in California, and I only get 23.5 MPG with 91 gas on my crossfire. No idea why the MPG is so low. Even my big old junk 96' Ford Taurus wagon v6 got 22.5 MPG on 87 gas. Any ideas?

 

Some of the 'blends' and regulated fuels in Cali are lame as far as MPG is concerned.

It seems a lot of people get poor MPG in cali compared to other parts of the US - just another way it costs more to live there!

SQ

 

Higher octane does not mean better gas mileage.


"It might seem odd that fuels with higher octane ratings explode less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation as opposed to the ability of the fuel to burn (combustion)."

Way more info here:

http://en.wikipedia.org/wiki/Octane_rating

It's not worth saving a few dollars per fill-up, and risk damaging your engine.

 

Agree about the gas blends in California. When I moved from California to North Carolina; my Nissan Maxima's gas mileage did improve quite a bit. I burned 87 octane in both California and North Carolina and saw about a 3 mpg difference in my Maxima in North Carolina.

As for the Crossfire I wouldn't mess around with regular unleaded in it. The owner's manual says a minimum of 91 octane and I get to burn 93 octane here in North Carolina.

Did a lot of highway driving last week with cruise control on and got exactly 30 miles per gallon in my Crossfire.

 

It has been my experience that lower octane in higher compression engines produce more carbon build up and ends up fouling the O2 sensors. I can only get away with 85 & 87 octane in my four cylinder Escort and six cylinder Jeep without issues. The other cars get 91 or higher from Tier 1 stations only.

 

Very bad idea. Engines with forced induction need higher octane to prevent detonation. Detonation is bad. Switch to 91+ before you blow a ring land.

 

I think most people here would concede that's it's a bad idea to use regular gas in a Crossfire when the owners manual clearly states that you need Premium.
It's not that your car won't run on it, it just will not run the way it was designed to.
If the few dollars you feel you're saving at the pump by doing so, can offset any future repairs that may occur, then good luck.
But I would think that any damage that might happen to your engine by using regular fuel would make it necessary for the dealer to remove the heads from your engine, and once that's done, they will be able to identify the tell tale signs of low octane fuel usage. And then it's goodbye warranty.

 

yes, yes... what everyone is saying is true. Its not a good idea to run the car on regular. Obviously people though come on. Its not as if "jackei" doesn't know this, its just an interesting experiment. It caught my attention and I am interested to know the results! Odd gimicks and posts such as this are what makes the forum interesting.

 

Why does the word "guinea pig" come to mind.

 

In regards to low MPGs, I'm on the east coast and run nothing but 93 octane, 60 miles a day of interstate driving and I get 20-21 mpgs tops. Weird their is such a large gap in the reported MPGs people get with these cars.

 

DAY 3 - 150 miles

Looks like many people get upset because I put regular gas in my crossfire. Forgive me please, but I do want to see how it affect the performance and MPG. However, in my point of view, if a few tanks of regular gas is enough to do any damage to this beautiful engine, than Mercedes is really sucks! (of course I won't put coke into the fuel tank for experiment)

From my understanding, premium gas is required because this is a high compression engine. using lower octane gas will cause knocks. but I've read many articles that the knock sensor will retard the timing of the engine and should not have any problems. This is another reason why I'm doing this.

Findings: Yes you guys are right, the engine ran kinda rough on the first day after I switched to 87 octane gas. But the knock sensor and computer are doing their job, and she is running so smooth again on day 3. I don't feel any different under normal driving condition, although it does lack of some HP on freeway speed.

My question is: Although it is not doing what it supposed to do, lack of power, not firing at the ideal timing, if it is able to do the adjustment and compensate the timing error, and it is running very smooth in fact (I'm talking about normal city driving, not racing) does it really cause any damage? (Just a though, I will go back to premium gas after the test)

 

If i would need to worry about saving .25 to .30 a gallon i would sell my car and ride my bike.
It is your money and your car so do what ever makes you happy.

 

As Guy III pointed out in another thread, regular fuel runs "hotter" than Premium, thus over time it could eventually burn a hole in your piston.
How long, probably depends on the type of driving you normally do, how fast, and the type of terrain you're driving over.
If you're only going to experiment with it for awhile, you probably won't do any long term harm.
I don't doubt that thanks to the higher fuel cost that we've seen this past year, that alot of people have tried, and still use lower octane fuel on a regular basis in their Crossfires, and just don't tell anybody (here on the forum about it) since they may want to try selling it here at some future date.
That's one of the reasons I prefer to purchase most of my cars brand new. You just never know what you might wind up with.