Mid Grade Gas

[RedRT]

The owners manual for my RT says that mid-grade gas is recommended. I have been putting regular rather than mid-grade in the car and it seems to run fine. Why is mid-grade recommended?

[sdeveau]

For optimal performance, I believe.

Our SXT recommends the same, we always put 89 in, every now and then we'll give her a treat and put in some 91.

My old dodge preferred higher octane gas, the manual recommended 87, but the engine growled with its use.

[jaymista]

I use the mid-grade only because the manufacturer recommends it in the manual.. From what I understand, unless you live in higher elevations, you really don't need to use the mid-grade. I decided with gasoline prices being as high as they are, I could spare the extra two bucks or so it takes to fill up with mid-grade. I used the lower grade for a month or so and I don't see any performance difference. I just thought it was meant to burn cleaner.

[wyoram]

Mid grade for me too. With today's electronics I really don't think using a lower octane fuel will permantley damage the motor. I am not a mechanic, but this is how I understand how it works.

I think most if not all modern engines (especialy high performance) have a knock sensor installed. It will prevent premature detenation and pinging in the cylinder. Detonation is very bad. It causes more heat and could result in the rod punching a hole in your block. Otherwise known as a window in your block. Detonation is caused by improper fuel octane or poorly tuned engine (air fuel ratio). I am sure there are probably other things too. These appear to be the major causes.

The knock sensor will pull timing or fuel or both from the motor to prevent premature detonation. Again this is my best understanding of this. Maybe someone with more knowledge on the matter can chime in and agree or correct me on the matter.

Using a lower grade should not be a problem. But I would prefer to use the manufactures recomendation. It really is not that big of a difference on cost. I can't quite remember the fuel tank capacity. I think it is 21 gallons. Gas price difference is around .10 cents per gallon. Current gas prices for me are $2.39 for the cheap stuff and $2.49 for mid-grade. For 21 gallons of fuel to fill up is $50.19 and $52.19 respectfully. If you drive 10K miles @ 20 mpg consumption the cost difference is $50 dollars.

Not worth the cost for me to use the cheap stuff.

[Remline]

Since 87 is allowed it will not damage the motor. I found that 87 was causing a rough idle. I also noticed less fuel economy. I get about 1.5mpg more with midgrade. That is a wash at an extra .15 per gal. But the rough idle is gone.

[kchillh]

Have a trip comming up from GA to NY...will use mid-grade in hopes of better MPG. I had her up to 28 MPG *say's EVIC* in the past so let's see if we can do 30 with a 6cyl. on the road...what crusing speed should I set it at....I love to do no less than 70mph.

[JourneyMan71]

I started a small experiment to see if 89 was better than 87. I drove to Kentucky from my home in Northwest Ohio. I got 21.1 going down and 22 coming back. I have under 5,000 miles on it now. I had 5 passengers and luggage. It is not that bad in my opinion. Kentucky is very hilly anyways. I do not guess anyone gets the sticker MPG down there,lol.

[RedRT]

I started a small experiment to see if 89 was better than 87. I drove to Kentucky from my home in Northwest Ohio. I got 21.1 going down and 22 coming back. I have under 5,000 miles on it now. I had 5 passengers and luggage. It is not that bad in my opinion. Kentucky is very hilly anyways. I do not guess anyone gets the sticker MPG down there,lol.

Did you use mid grade one way and regular another? If so, which provided the best mpg?

[crunkfrunk]

Posted May 28 2009, 08:12 PM

Mid grade for me too. With today's electronics I really don't think using a lower octane fuel will permantley damage the motor. I am not a mechanic, but this is how I understand how it works.

I think most if not all modern engines (especialy high performance) have a knock sensor installed. It will prevent premature detenation and pinging in the cylinder. Detonation is very bad. It causes more heat and could result in the rod punching a hole in your block. Otherwise known as a window in your block. Detonation is caused by improper fuel octane or poorly tuned engine (air fuel ratio). I am sure there are probably other things too. These appear to be the major causes.

The knock sensor will pull timing or fuel or both from the motor to prevent premature detonation. Again this is my best understanding of this. Maybe someone with more knowledge on the matter can chime in and agree or correct me on the matter.

Using a lower grade should not be a problem. But I would prefer to use the manufactures recomendation. It really is not that big of a difference on cost. I can't quite remember the fuel tank capacity. I think it is 21 gallons. Gas price difference is around .10 cents per gallon. Current gas prices for me are $2.39 for the cheap stuff and $2.49 for mid-grade. For 21 gallons of fuel to fill up is $50.19 and $52.19 respectfully. If you drive 10K miles @ 20 mpg consumption the cost difference is $50 dollars.

Not worth the cost for me to use the cheap stuff.

Thats correct in how the ECU will work with the car, the difference in 87 gas and 89 is that the 89 is HARDER to ignite so it is less likely to predetonate, I'm familiar with all the knock talk because I do tuning with supercharged cars

How about a Journey with a supercharger :rolleyes:

[JourneyMan71]

Posted May 28 2009, 08:12 PM

Mid grade for me too. With today's electronics I really don't think using a lower octane fuel will permantley damage the motor. I am not a mechanic, but this is how I understand how it works.

I think most if not all modern engines (especialy high performance) have a knock sensor installed. It will prevent premature detenation and pinging in the cylinder. Detonation is very bad. It causes more heat and could result in the rod punching a hole in your block. Otherwise known as a window in your block. Detonation is caused by improper fuel octane or poorly tuned engine (air fuel ratio). I am sure there are probably other things too. These appear to be the major causes.

The knock sensor will pull timing or fuel or both from the motor to prevent premature detonation. Again this is my best understanding of this. Maybe someone with more knowledge on the matter can chime in and agree or correct me on the matter.

Using a lower grade should not be a problem. But I would prefer to use the manufactures recomendation. It really is not that big of a difference on cost. I can't quite remember the fuel tank capacity. I think it is 21 gallons. Gas price difference is around .10 cents per gallon. Current gas prices for me are $2.39 for the cheap stuff and $2.49 for mid-grade. For 21 gallons of fuel to fill up is $50.19 and $52.19 respectfully. If you drive 10K miles @ 20 mpg consumption the cost difference is $50 dollars.

Not worth the cost for me to use the cheap stuff.

Thats correct in how the ECU will work with the car, the difference in 87 gas and 89 is that the 89 is HARDER to ignite so it is less likely to predetonate, I'm familiar with all the knock talk because I do tuning with supercharged cars

How about a Journey with a supercharger :rolleyes:

Well, when I was on my trip I only used 89, I started 89 a few fill ups before that. I keep track of all and every fill up. I know how good or bad I will get on my MPG's. I keep track on gas buddy I enter in every time I get gas. I have gained a 1 mile per gallon up from 15.5 mpg, to 16.5 mpg on my trip. I drive alot in the city, and I am guilty of being a spirited driver from time to time. I have a bit over 4,700 miles. It is not broke in yet,so I expect to gain. I use Shell gas except for the few times the dealer put Sunoco gas in it and I did fill up with Chevron one time on my trip. I think a good quality 87 octane gas such as Shell and or Chevron gas. It should be as good as other 89 octane gas from others.