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post #21 of 47 (permalink) Old 04-16-2010, 07:19 PM
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Originally Posted by 300E91 View Post
Please explain how lower octane will "destroy" or affect the catalytic converter. Higher octane fuel simply allows higher compression levels before it explodes in the cylinder. As I understand it, that has no impact on the catalytic converter. There are other users here with extensive professional experience who have said that they never have seen a catalytic converter damaged by lower octane.
Easy. Lower octane fuel burns too hot and over time melts the converters from the the inside out. As they begin to melt, internal components start to break free and block the flow the exhaust gas. When that happens, you loose back pressure and then your engine will not run correctly. Its easy for someone to say it is alright to run 89 in a 19 year old 300E. If the cats go bad, there is no warranty coverage. You will be paying for it. When an 06 ML is under the 7 year federal mandated catalytic converter warranty, its a different story. Just because some guy who runs a repair shop told you that you could 'get away' with running 89 in a car that REQUIRES, not recommends premium, doesn't mean you should do it. I be willing to bet that he did not design the engine or exhaust system in your car or ANY MB product.
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post #22 of 47 (permalink) Old 04-16-2010, 08:43 PM Thread Starter
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Originally Posted by JoeVal View Post
MTI and SLR2098:

There is a warning in MB owner's manuals issued in countries where gas quality and availability is errant. The warning is to use an octane booster additive if no gas of the rated octane for the engine is available. It even goes further to make a point to stop using that as soon as the right gas is available.

You are the other side of the coin of those who wish to use a gas of a higher octane than specified. The difference is that in this case there is no damage to the car, while the lower octane creates combustion at the wrong temperature and has other connotations, mainly through the GRS mechanism, affecting the plugs, engine and exhaust, the injection, and the electronic feed and response action.

Excellent example of penny wise, pound foolish.
So, if I use lower octane fuel, it will "affect" the plugs, engine, exhaust, injection, electronic feed and response action? I'm not saying you're wrong, but how so?
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post #23 of 47 (permalink) Old 04-16-2010, 08:52 PM
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Just do what you want.

Ignore that big a$$ sticker inside the fuel filler door that says "use premium fuel only."

Nobody here is interested in "convincing" or "begging" you to do what the factory says. You know best. Go ahead.

Good luck with that.

"Don't pick a fight with an old man. If he is too old to fight, he'll just kill you."--John Steinbeck
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post #24 of 47 (permalink) Old 04-16-2010, 08:57 PM Thread Starter
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Just do what you want.

Ignore that big a$$ sticker inside the fuel filler door that says "use premium fuel only."

Nobody here is interested in "convincing" or "begging" you to do what the factory says. You know best. Go ahead.

Good luck with that.
Why don't you just GTFO? No one wants your negativity here. I am clearly wrong and misinformed, and am trying to learn. I want to get better gas mileage, and am trying to treat my engine better so it will live a longer life. So please, if you have nothing positive to add, just GTFO.
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post #25 of 47 (permalink) Old 04-16-2010, 09:52 PM
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Haven't seem him for a while, but in W163 is a member with handle FAR and some digits behind. I think 55.
He drives ML55 AMG in a country that doesn't have Premium available at all. Last time I read the car run just fine with it. Still he needed engine with original 314 HP to be satisfy with performance
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post #26 of 47 (permalink) Old 04-17-2010, 06:15 PM
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I don't think regular gas affects the cat converter. Leaded gas is what damages it. The only difference between the 3 grades of gasoline is the octane (anti-knock) rating, i.e.the resistance to the pre-ignition or detonation that becomes more pronounced the higher the load on the engine. Severe knocking or pinging can cause engine wear over time. In general the higher the compression ratio, the higher the octane requirement.
My '97 SL500 which I just got and have hardly driven, has a compression ratio of 10.0 which is lower than my 3.0 Subaru which also requires 91 octane (the highest) gas, but the dealer said the 89 was ok and I've yet to hear a ping even though I pull a light boat and am not hesitant about passing.
Bottom line: I'm gonna try to get by on the 89 (middle grade) simply because a gas station very nearby is the only one I can find that sells 100% gas (no alcohol) and it only has the 87 & 89.
Hope this helps.
-RB
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post #27 of 47 (permalink) Old 04-17-2010, 06:24 PM
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Originally Posted by mr.xpowerseller View Post
Easy. Lower octane fuel burns too hot and over time melts the converters from the the inside out. As they begin to melt, internal components start to break free and block the flow the exhaust gas. When that happens, you loose back pressure and then your engine will not run correctly. Its easy for someone to say it is alright to run 89 in a 19 year old 300E. If the cats go bad, there is no warranty coverage. You will be paying for it. When an 06 ML is under the 7 year federal mandated catalytic converter warranty, its a different story. Just because some guy who runs a repair shop told you that you could 'get away' with running 89 in a car that REQUIRES, not recommends premium, doesn't mean you should do it. I be willing to bet that he did not design the engine or exhaust system in your car or ANY MB product.
Knocking does raise the combustion temperature, but it's not likely to persist continuously long enough to hurt anything.
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post #28 of 47 (permalink) Old 04-17-2010, 06:32 PM
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Knocking does raise the combustion temperature, but it's not likely to persist continuously long enough to hurt anything.
This isn't just something that I read somewhere. This is real life. I've seen the dead cats come off cars where the cheap a$$ owner ran 87 thinking he or she would save money.
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post #29 of 47 (permalink) Old 04-17-2010, 06:35 PM
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Bottom line: I'm gonna try to get by on the 89 (middle grade) simply because a gas station very nearby is the only one I can find that sells 100% gas (no alcohol) and it only has the 87 & 89.
Hope this helps.
-RB
It is very doubtful that you are actually buying non ethanol fuel. Most states now have a mandate that requires it, and most gas is mixed at the refinery with ethanol so even non mandate states are getting this junk in all grades of gas. The only way to know would be to buy an ethanol test kit and sample the fuel.
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post #30 of 47 (permalink) Old 04-17-2010, 07:25 PM
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This isn't just something that I read somewhere. This is real life. I've seen the dead cats come off cars where the cheap a$$ owner ran 87 thinking he or she would save money.
I'm not trying to save money. I just don't like alcohol. There is absolutely nothing harmful that lower octane can do but cause pre-ignition which causes a ping or knock under load. EXCEPT it can also aggrevate "running on" after the ignition is turned off which is annoying but not harmful.
I repeat: the ONLY requirement or test for the octane number is the antiknock rating, i.e. a comparison between the property of n-heptane (0 octane) and that of "iso- octane" [2-2-4 trimethyl pentane (100 octane)].

But if my engine either pinged or ran on, I would use as high an octane as I could find.
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