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-   -   V8 --- what grade of gas to use? (http://www.jeepgarage.org/f73/v8-what-grade-of-gas-to-use-19009.html)

Dan JGC 02-17-2011 01:06 PM

V8 --- what grade of gas to use?
 
Just curious...what grade of gas is listed for the V8?

I have always used the regular unleaded gas in my 2005 V8 Hemi....then a few weeks ago Costco was out of it so I filled up with high grade (they only carry regular and high grade, no mid-grade). I quickly noticed a difference in engine performance...I was surprised at how noticeable it was. Runs a but smoother and seems quieter along with more power.

When I get my new WK2....finally....I want to use the right fuel from the start.

JTS97Z28 02-17-2011 01:10 PM

Re: V8 --- what grade of gas to use?
 
The 5.7 Hemi uses recommended mid grade 89 octane. Do not burn premium in the car is its not designed to run on that nor will it benefit anything. It can run on 87 and shouldnt cause any problems, but since mid grade is usually only 10 cents more than regular theres no reason not to just use what it recommends.

Answer: Mid grade 89 octane and if 89 is not available burn regular 87. If anyone says anything different its all in their head and nothing more than personal opinion.

James

Technosavant 02-17-2011 01:20 PM

Re: V8 --- what grade of gas to use?
 
The "do not burn premium" isn't so much a warning as much as a recommendation; there's just no point to it- you're only spending more for no additional benefit. Running regular (87 octane) will result in the engine de-tuning itself to prevent knock (since blowing holes in pistons is generally A Bad Thing), which is why you felt more power when you used a higher grade of gas- the engine could advance timing a bit for more power.

Nouveau Redneck 02-17-2011 01:23 PM

Re: V8 --- what grade of gas to use?
 
The only thing that higher octane gasoline does is help prevent pre-detonation (knocking) in higher compression engines. If the manufacturer says that it can run fine on 87 octane, then even 89 is a waste of money. Simply using higher octane gasoline will not change the performance of the engine. It is probable that the higher octane at your local pump also has less ethanol in it than the regular, and decreasing the amount of ethanol will definitely increase the performance of the engine.

Dan JGC 02-17-2011 01:26 PM

Re: V8 --- what grade of gas to use?
 
James --- When you refer to the 5.7 Hemi are you referring to the V8 in the 2011 or to my 2005?

Dan JGC 02-17-2011 01:27 PM

Re: V8 --- what grade of gas to use?
 
Just saw this online...I'm going to use whatever the manual says....that's mid-grade 89 octane in the 2011 V8 correct?

http://www.ftc.gov/bcp/edu/pubs/cons...tos/aut12.shtm

The Low-Down on High Octane Gasoline
Are you tempted to buy a high octane gasoline for your car because you want to improve its performance? If so, take note: the recommended gasoline for most cars is regular octane. In fact, in most cases, using a higher octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner. Your best bet: listen to your owner's manual.

The only time you might need to switch to a higher octane level is if your car engine knocks when you use the recommended fuel. This happens to a small percentage of cars.

Unless your engine is knocking, buying higher octane gasoline is a waste of money, too. Premium gas costs 15 to 20 cents per gallon more than regular. That can add up to $100 or more a year in extra costs. Studies indicate that altogether, drivers may be spending hundreds of millions of dollars each year for higher octane gas than they need.

What are octane ratings?

Octane ratings measure a gasoline's ability to resist engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders. Most gas stations offer three octane grades: regular (usually 87 octane), mid-grade (usually 89 octane) and premium (usually 92 or 93). The ratings must be posted on bright yellow stickers on each gasoline pump.

What's the right octane level for your car?

Check your owner's manual to determine the right octane level for your car. Regular octane is recommended for most cars. However, some cars with high compression engines, like sports cars and certain luxury cars, need mid-grade or premium gasoline to prevent knock.

How can you tell if you're using the right octane level? Listen to your car's engine. If it doesn't knock when you use the recommended octane, you're using the right grade of gasoline.

Will higher octane gasoline clean your engine better?

As a rule, high octane gasoline does not outperform regular octane in preventing engine deposits from forming, in removing them, or in cleaning your car's engine. In fact, the U.S. Environmental Protection Agency requires that all octane grades of all brands of gasoline contain engine cleaning detergent additives to protect against the build-up of harmful levels of engine deposits during the expected life of your car.

Should you ever switch to a higher octane gasoline?

A few car engines may knock or ping - even if you use the recommended octane. If this happens, try switching to the next highest octane grade. In many cases, switching to the mid-grade or premium-grade gasoline will eliminate the knock. If the knocking or pinging continues after one or two fill-ups, you may need a tune-up or some other repair. After that work is done, go back to the lowest octane grade at which your engine runs without knocking.

Is knocking harmful?

Occasional light knocking or pinging won't harm your engine, and doesn't indicate a need for higher octane. But don't ignore severe knocking. A heavy or persistent knock can lead to engine damage.

Is all "premium" or "regular" gasoline the same?

The octane rating of gasoline marked "premium" or "regular" is not consistent across the country. One state may require a minimum octane rating of 92 for all premium gasoline, while another may allow 90 octane to be called premium. To make sure you know what you're buying, check the octane rating on the yellow sticker on the gas pump instead of relying on the name "premium" or "regular."

Technosavant 02-17-2011 01:49 PM

Re: V8 --- what grade of gas to use?
 
Quote:

Originally Posted by Dan JGC (Post 358127)
Is all "premium" or "regular" gasoline the same?

The octane rating of gasoline marked "premium" or "regular" is not consistent across the country. One state may require a minimum octane rating of 92 for all premium gasoline, while another may allow 90 octane to be called premium. To make sure you know what you're buying, check the octane rating on the yellow sticker on the gas pump instead of relying on the name "premium" or "regular."

One additional item they don't say: the octane rating is a measurement of resistance to preignition (it isn't so much a measurement of the existence of the hydrocarbon molecule octane expressed as a percentage of the whole). At higher altitudes, in less dense air, fuel is less likely to preignite. Therefore, if you're in Denver, you may notice that the octane ratings on the fuels aren't what they are closer to sea level. They aren't cheating you; the fuel just doesn't preignite as readily.

Nouveau Redneck 02-17-2011 02:10 PM

Re: V8 --- what grade of gas to use?
 
I wasn't aware that the manual recommends 89 octane. I just bought my Overland a couple of weeks ago. I have only filled it once so far, and with 87 octane. I'll wait until it's close to empty before filling it next time and go with 89 to see if I notice any difference.

J13ntv 02-17-2011 02:44 PM

Re: V8 --- what grade of gas to use?
 
I fill it with 89. As per recommendations of the manual, and its usually only 5-10 cents more a gallon, so at an expense of ~$2.00 at most per fill up, I'd say why not. Considering my gas mileage is a lame 11-13 mpg usually, I guess $2 x 3 or 4 fill ups is 6 or 8 bucks more a month but still not a killer.

JTS97Z28 02-17-2011 04:10 PM

Re: V8 --- what grade of gas to use?
 
Quote:

Originally Posted by Dan JGC (Post 358126)
James --- When you refer to the 5.7 Hemi are you referring to the V8 in the 2011 or to my 2005?

Well I was only really referring to the 2011, but the same holds true for the WK V8 as well. That's a mid grade 89 burner as well.

Breitling65 02-17-2011 09:09 PM

Re: V8 --- what grade of gas to use?
 
I would say - try 93 and see yourself. Nothing will happen to your engine with this action. In general I would expect slightly better performance and as result less pressings on gas pedal/better millage per gallon. 90% of my time I am in stop-go traffic with max 40mil/h and would be no point to burn expensive gasoline driving like this. Also don’t listen comments “car not designed…”, there is no such thing that car is not designed for higher octane gasoline. Also there is no design, it is ignition adjustments which are computerized these days, however I use to do them manually long ago on my first car (fiat) to prevent knocks.

Technosavant 02-17-2011 09:31 PM

Re: V8 --- what grade of gas to use?
 
Quote:

Originally Posted by Breitling65 (Post 358548)
Also don’t listen comments “car not designed…”, there is no such thing that car is not designed for higher octane gasoline. Also there is no design, it is ignition adjustments which are computerized these days, .

Not correct. The engine itself can be designed to require higher grades of fuel. It comes down to the amount of compression in the engine- the more the volume of air in the cylinder is compressed, the more prone to preignition it is. Boyle's Law and all that- temperature and pressure are the same thing; compress a mixture, you will raise the temperature. More volatile fuels (lower octane) WILL preignite in very high compression engines. There's a reason many forced induction engines require premium fuel- high compression.

The more compression, the more efficient the engine, but that comes at a price. You can squeeze a few more HP out of an engine by increasing the compression, but that will result in preignition with low grades of fuel. This is why race engines generally require VERY high octane (100+) fuel; they're set up to get the most power possible out of a given engine size.

You are correct that the electronic engine controls can adjust timing on the fly to reduce preignition or to take advantage of less volatile fuel, but that isn't the full story. Usually the engine computer will dial things back to prevent damage. However, if the manufacturer intended for lower grades to be used to give maximum performance out of the engine, a higher grade of fuel will NOT give more power. The engine controller is not capable of just cranking things up like that. It will go to what it is designed (both the engine combustion chamber and the computer) and no more.

Putting a higher grade of fuel into a vehicle than it is intended to require is wasting money; anywhere from ten to thirty cents per gallon, depending on the grades involved and the price differentials. If you're putting premium into a Grand Cherokee on a 20 gallon fill-up (I'm assuming you don't run it all the way dry), that's somewhere between $2 and $6 every tankful. Not going to break you, but it adds up.


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