Real Story on need Premium gas please

[Robgreeneyes]

Once and for all can someone close the debat i am having on the need for Premium gas in my Mercedes ML (or all Mercedes for that matter). Do you really need to use premium or is regular good enough? what does premium actually do for the extra money? end this debat i am having with friends please

[C-Rod]

Our manuals do say to use "Premium Unleaded"....l don't know if "Pinging and Knocking", will occur with just regular unleaded....but, when you compare the extra few dollars you pay in gas as to the cost of a new engine, l think it's worth it.....[:D]

[donho]

The higher the octane, the slower the burn rate.
You get better gas mileage from premium, You get better performance from Premium since the car/truck will run full timing. When an engine detects spark knock or detonation , the ECM retards timing until it stops. This kills performance. And last but not least, Premium fuels are the only grade that contain detergents so your valves do not get buildup. For the Extra .20 a gallon, It is worth it.

[tcp_ML500]

Most basic basis for choosing octane grade is that the higher the compression ratio, the higher octane grade you will want to use. Using lower grade gasoline in a high compression ratio engine will result in early detonation and damage to the engine.

Your ML320 has been optimized for 91 octane, your engine management system will not be able to take advantage of higher octane numbers (93 won't get you more than 91 gets you, but sometimes, 93 is all that is available and it definitely won't hurt anything but your pocketbook)

Your engine management system has been programmed with provisions made to run on lower grade, if you cannot find higher grade, by affecting ignition points to compensate. Your manual, however, states that this should be done in exceptional circumstances. Typically, you will experience lower performance, although I have yet to see data on how much adversely affected the numbers would be. Personnaly, I'm to chicken to run anything but Chevron 93, so I'll never experience the performance hit of lower octane gas.

If you wish to go against the manufacturer's recommendation, you'll have to figure out the risk/reward for yourself, the valves and valve seats will be the first things to go, after that... BTW, if MB can show that the damage was caused by lower gas, none of that stuff will be cvered by original or extended warranty!

[Robgreeneyes]

It's funny. I forgot to ask for a detailed explanation, but thats what i wanted and i am grateful that that is what i got. thanks very much

[tcp_ML500]

donho - 5/17/2004 10:39 AM
And last but not least, Premium fuels are the only grade that contain detergents so your valves do not get buildup. For the Extra .20 a gallon, It is worth it.

Chevron for instance, uses Techron in all their grades.
Another, Texaco uses System3 in all their grades...

[jfday102750]

Great responses from everyone! One more little detail; if you use a 'low' octane gasoline (87 octane for example) and you continue to drive it despite the knocking in your engine, it will eventually burn a hole through something (most likely one or more of your pistons) because of the improper detonation of the fuel. Not a good plan. Pay the extra for premium gasoline.

[donho]

I was unaware that these companies use detergents in all the grades. Most companies do not. You are correct about the 91 octane. That is why software can bump up a few HP, by reprogramming to increase ignition timing for a 93 octane level. That is what my Shark Software does. Optimizes for 93 octane.

[tcp_ML500]

It's hard to find a dyno for your four wheeler, but have you, by chance, gotten numbers with and without 93 optimization, running 93 in both cases?

[bigcatny]

The full article
http://www.caranddriver.com/article.asp?section_id=4&article_id=3604&page_numb er=1

Plus

a snippet of the conclusion for the lazy among us.

"Our tests confirm that for most cars there is no compelling reason to buy more expensive fuel than the factory recommends, as any performance gain realized will surely be far less than the percentage hike in price. Cheapskates burning regular in cars designed to run on premium fuel can expect to trim performance by about the same percent they save at the pump. If the car is sufficiently new and sophisticated, it may not suffer any ill effects, but all such skinflints should be ready to switch back to premium at the first sign of knock or other drivability woes. And finally, if a car calibrated for regular fuel begins to knock on anything less than premium or midgrade, owners should invest in a tuneup, emissions-control-system repair, or detergent additives to solve, rather than bandage, the root problem. Class dismissed."