ok,

My car is a 2004 E320. It says Premium Unleaded only. does that mean Super Unleaded ONly? Can I use the regular gas in it?

what damage might result from using regular gas? Any body use regular and not have problems???

thnx

As long as you can find a minimum of 91 octane, you're fine.

Last time i read the owners-manual, it stated that regular gas could be used if premium was not available, but to avoid full throttle accelerarion and to fill-up with premium ASAP...

But it is available. They mean if you are running low and the only gas around is regular. You would also be expected to buy as little as you can get away with, and fill it with premium as soon as possible to raise the octane level of whats in the tank.

What is your goal?

$4 a tank savings

$4 x 52 weeks = $208 per year...

And lower gas mileage with less performance, WHAT A GREAT DEAL!!!!!!!!!!!!!!!

And a great way to kill the life of your car. Engine knock will lead to engine failure at some point down the road.

All the posts above = don't do it.

I do not disagree with any advice here. These cars are expensive to operate and maintain. $6.00 / quart oil, tires at $600 set and up, premium gasoline, $50windshield wipers, the list goes on. I run 93 octane gasoline because it exceeds the factory recommended fuel. I don't think that was arbitrary. I will bet that you could use 89 octane fuel if you are willing to:
1. Reduce throttle demand to 50% of available power , less if pinging occurs
2. Minimize vehicle gross weight
3. Avoid high engine temperatures.

I do not agree that the motor will automatically disentigrate.
The knock sensors will retard the timing as much as the ECU will allow.
The available power will be reduced and the mileage should decrease as well.

I cannot back up those claims with personal M-B experience but I have with other vehicles. The choice is yours. Personally, I believe you can dumb the car down with inferior parts, lubricants and accessories till one has to wonder why it was chosen over a cheaper model. No one here bought the thing because it was a bargain. Give it a chance to perform as it was intended. They do get under your skin.

not worth it

Mr Horn is right. When I was driving a 540i and surfing the discussion boards, there was evidence that running these cars at less than 91 octane is a net wash between the per gallon savings vs. decreased fuel economy. So from a pure fuel savings/fuel economy savings, you are going nowhere. Then there is the potential engine and emission problems running at lower than 91 octane. Stay with the recommended octane.

thats what i said

It works the opposite of what you may think. Higher octane gas (91,92,93) does not ignite as easily as lower octane gas (87,89, etc), and cars that use lower octane tend to have lower compression levels therefore needing a fuel that ignites easier. Putting low octane gas in a high compression motor like in the Eclass causes knocking/pinging because the high compression of the motor causes the gas to explode before the piston reaches top dead center and causes the piston to slap against the cylinder wall better known as knocking/pinging. Now the computer in the Eclass can and tries to adjust to this, and you may get away with it for a long while, but in the end you'll end up with a motor that has cylinder wall damage, smokes, and has less power, and burns oil. Not worth saving $2.00 at the pump

Not always Barry, if you've ever drivin in Colorado there premium is only 89 octane (i believe because of the high altitude) and the vehicles don't run as strong in the evironment

Its true that Colorado has lower octane available for the regular (85) and mid-grade (87), but from my experience premium is generally 91 here. Has to do with the higher altitude, cooler and less dense air.