Which grade of gas are you using?
 

Hi All,

I just completed the break in for our ML350. I'm curious to see how much power it has when I stomp it... so far we love it, its not flashy and is bigger than it looks.

Just curious what octane gas are you using for your MLs? I've been using 91 since we've gotten it but just wondering if it really needs those extra octanes..

Thanks,
03ML350

Yep - I've always used 93 octane (we have that here in Texas).

Supposedly it will run on lower gas (I think we had to put some sort of nasty stuff in it once in Wyoming) but I don't want to mess it up, so I try to always run the good stuff.

Thanks jswedberg,

that's what I'm thinking too, but my buddy thinks I'm nuts because its a "truck"

BTW I'm looking at getting either a new M3 with SMGII or a C32, how do you like your C32? Any truth to the rumors of a C35, should I wait?

Thanks,
03ML350

Yeah, it's a truck, but it's a truck with a high-compression alloy engine it, not the traditional American truck engine!

I am very happy with my C32 - it fits my purposes perfectly. I traded in a 993 to get it, and was looking for more room, creature features, and (gasp!) an automatic.

M3s are good cars - there are several threads discussing the pros and cons on th C32 forum. An M3 (even with SMG) is going to be stiffer and smaller feeling. Many people say the SMG shifts very abruptly. It is more of a sports car - I would place it closer to my old 993, in fact.

It makes sense that they will move to the new 3.7 liter engine. As to when, who knows? Maybe for 2004, maybe not. It will probably bring the horsepower up to 370 or 380.

Owners manual recommends putting in a minimum 91 OCT rating
 

but do not go any lower.

In an emergency (or if nothing else is available) you can put in lower octane - the knock sensors will retard the engine timing. But as soon as you can, refuel with the proper octane.

hey i live in mass most typical gas stations have 97-93 for octane ratings...at this sunoco right by my house they have a diffrent nozzle that has 94octane. i use that sometimes if i can fill it up full with the 94. and it could just be me trying to notice something positive but i swear, it runs a little more powerful with 94, any other opinions?

I'm pretty sure all Mercedes are optimized for 91 RON.

The only reason it should give you more power is if you chipped the car or mucked with the timing in some other way.

i heard the computer can tell or in some way take advantage of the higher octane gas, probably wrong whatever
-steve

I started using 87 octane over a month ago with no ill-effects...yet:rolleyes:

All Sunocos have that 94 octane nozzle and in my opinion, it's a waste of money - I should know 'cause I use to be part of a team that designed the system. The mix ratio for the 94 doesn't justify the price difference - then again, is there ever any justification for gas prices???

Thanks for letting me know. I didnt think it was justified either. The diffrence in price is like going from 87-91 octane but your only going from 93-94. So screw it no more 94 for me.
Does anyone use any type of fuel additives?
-Steve

me too
:(
started using 87 almost 2 monthes ago

My dad has been using 89 (Plus) in our ML since the day we got it...no problems so far. :)

i have been using 91 octane since i got it. I just follow what it says in the manual book 91 is the requirement octane.

Plan on having valve problems down the road. Probably just after the factory warenty runs out. Be sure and post your VIN number so no one buys it after you trade it in. You might as well just not do any more oil changes and for that matter don't bother washing and waxing it anymore either. The engine was designed for 91 so there is no need to pay more to go above that and it is not good long term to go below that. The ML320 has had the same engine as the E320, C320 and the CLK320 but you don't here anyone else bragging that they use less than 91 in their cars. :hammer:

My sentiments exactly.........you spend 35G+ for a vehicle and then are too cheap to pay what averages $2-3 more for a tank of gas. I just cannot understand it or see the logic in it. Bottom line....pay now or pay later.

PS......not singling anyone on this board out, but, when problems do occur down the road or the warranty works is denied because of improper fuel.........this type of person will scream and slam MB the loudest!!

Why would using a lower grade of fuel affect the engine valves over time ?...
 

just wondering

Re: Why would using a lower grade of fuel affect the engine valves over time ?...
 

LOL.

Loaded question of the day award...

Doh, you saw right thru' me Pete....
 

of course I know the answer about lower octane fuel and 'valve trouble'. Just interested to hear the logic behind such a statement - if there is any ;-)

Hey what about those poor people at high altitudes who can't easily get any octane higher than 87 - guess their ML's are going to have valve trouble....

Higher octane fuel has a slower ignition time than does regular 87 octane. This way it can be compressed more without preigniting. Because the Mercedes engine is designed to have higher compression than a standard engine, the ignition of the fuel needs to be delayed. Compression alone can cause ignition as in a diesel engine where no spark is used. The lower octane fuel can preignite before the engine timing is ready for it and tear the engine apart. The engine timing retards to try to compensate for the preignition but is only meant to do this temporarily. Over time there is more stress put on the engine and it doesn't have as much power output as well. Why lose power and slowly tear the engine apart just to save a couple of bucks. I feel sorry for people who can't get higher octane fuel, but not for those who choose to use what is lower than recommended.

Actually even with high octane fuel.....
 

the engine management is still 'doing its thing' with regard to timing also - such that under heavy load the ignition gets retarded to prevent detonation. With lower octanes it just retards it a few more degrees.

Likewise altitude (effective compression ratio) also affects timing automatically - hence the guys at high altitudes have no problem.

FYI All modern engines operate on the verge of detonation for best fuel efficiency and power output all the time when under heavy load.

A lower octane fuel reduces power output and that's all, further in real life the average 'butt dyno' will not be able to even detect the reduction in power.

Coming from an ECU design back ground for a major US motor company I fully understand the implications of running a lower octane fuel - ie it affects power output / torque and to a lesser extent emmissions. But does not affect engine life / valve damage.

Please feel free to explain why it should damage valve gear.

Interestingly this topic crops up every few months - maybe it should be in the FAQ.

Bottom line - you pays your money and takes your choice...

Judge for your self, It's your Engine...
 

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, old cars and certain luxury cars, need mid-grade or premium gasoline to prevent knock.

Listen to your car’s engine. Knock occurs when cylinder pressures are high. It is normal for an engine to ping a little at full throttle because cylinder pressures are very high at full throttle. Engine knock, however, should not be ignored since it can result in serious damage to the engine. High octane gasoline burns slower than low octane gasoline. The slow burn prevents engine knock when cylinder pressures are high. Persistent knock can lead to engine damage and carbon buildup.

Some things to note: Damage can occur during heavy load situation like climbing hills, pulling loads, racing or most Under wide-open-throttle (WOT) conditions. The EEC is not looking at the knock sensor because the engine is simply making too much noise for the knock detection strategy to filter out the knock signal from the noise. Timing and fuel for WOT is derived from lookup tables that are vectored primarily by crankshaft RPM and engine coolant temperature, and to a much lessor degree by the mass air signal.

One web site puts it this way:
Octane Rating - A number that represents the resistance of gasoline to premature detonation when exposed to heat and pressure in the combustion chamber. Such detonation is wasteful of the energy in the fuel and potentially damaging to the engine.

Engine designers assign an octane number rating (ONR) to the engines they design and it is the octane number at which at engine will run without knocking. Many factors affect the ONR, including compression ratio, ignition timing, fuel/air ratios, cylinder head temperatures, and combustion chamber design.

Compression ratio has the largest impact on both ONR and engine efficiency… higher compression results in a more efficient engine and a higher ONR. Retarding the engine timing, running either rich or lean, reducing cylinder head temperatures, and using swirl type combustion chambers all reduce ONR.

Octane below ORN causes pre ignition. Pre ignition occurs too soon before the piston is at top dead center, you place a tremendous strain on the engine… the forces of burning happen too early and press against the piston while it is still traveling up. Third, hot spots develop in the engine. The cylinder head is designed to take maximum heat, and maximum flame duration.

The pistons normally have the shortest period of contact with the flame front, but if the gasoline ignites close to the piston, say, due to a carbon deposit, then the piston is subject to temperatures for which it was not designed.

I Like the way this Engineer puts it when asked about octane:
"If the fuel is too low octane, it may spontaneously ignite before the spark plug fires due to thermal rises from the heat of compression or from hot spots in the cylinder itself. This kind of ignition is called pre-ignition (as opposed to knocking) and is a pathological case which will just turn an engine to scrap.

Pre-ignition can damage an engine before you finish reading this sentence. To reiterate, what we're really concerned with is called "knock" and that's the spontaneous ignition of the fuel-air mixure ahead of the flame-front as a result of the rise in cylinder pressure caused by the onset of ignition (caused by the firing of the spark plug).

An engine's efficiency is in direct proportion to its compression ratio. Unfortunately, raising the compression ratio means we need to protect against knock/detonation. How do we do this? Use higher octane fuel! "

Thats exactly why at WOT the knock sensors..
 

are critical to preventing detonation. FYI they actually work all the time - particularily under full load and WOT. Engine noise at full throttle any other point has no effec they still work.

All the other stuff you post about detonation being a bad thing is absolutely correct - but the fact is the ECU can detect knocking on a cylinder by cylinder basis under all conx.

As I stated before even running 91 octane your engine is on the verge of knocking anyway - no different to running a lower octane.

On your logic we shouldn't be able to drive our ML's at over 10,000 ft asl as we likely can't get hi octane fuel to re-fill the tank !

Try this simple test - encourage your ML on 91 octane to knock, then repeat same test later with 87 octance. Not a nice test I know, but you'll likely discover no difference in the level or severity of knocking - the ECU will take care of it :-)

My ML has been running for nearly 4 years on either 87 or 89 (mostly 89) and I really can't tell the difference and the engine is still running fine. (All the warranty issues in my sig were not engine related.)

My 996 TT however because its turbo charged and thus at a much greater risk of detonation always gets 91 octane.

Like I said before 'you pays your money and takes your choice'.

I'd wager my ML running on 89 octane will last just as long as any other running on 91 as many other factors are far more important such as regular oil changes & routine maintenance etc. come into play.

I suspect we might just have to agree to differ on this one :)

Higher altitudes cause compression to go down so you can get away with lower octane more than at sea level. You must live on a mountain top.

Your ML will last in spite of you because it's a Benz.

It's your engine. :hammer: