Engine damage from cheap gas?? (w211)

[700horses]

How can I inspect a w211/e320 to determine if any damage to the engine has occurred (or started to occur) from using lower octane fuel (cheaper/regular 87). As I understand it, as per the MB User's Manual, using lower octane in a w211 is only ok if it is temporary (since the engine can ping the timing to to the slower rate of burn), but it is wise to refuel with 91 as soon as possible to dilute what is in the tank, as well to try to avoid high RPMS during this temporary time. (please correct me if I'm wrong) So... I am about to purchase a 2004 e320 (build date: 04/2004) with 111k miles, and the seller has told me that one of the people who sometimes drove the car may have used Mid-grade gasoline when filling it sometimes (which could cause engine damage?) -How can I check if the engine is fully ok? -Anything I should look for? Thank you in advance for any help.

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[WEBSRFR]

Spark PLugs. I think..

Also if at that mileage the plugs have not been changed, you should change them and that might mitigate your concerns altogether.

Perhaps the experts can chime in and offer you more help...

[otto6457]

I wouldn't worry much about someone using a lower octane fuel and causing damage. The knock sensors/ecu on the engine sense any pre-ignition and retard the timing in order to prevent damage. Unless the previous owner was racing, had a reprogrammed ecu that advanced the timing beyond reasonable specs, had a turbo or supercharger installed, or towed with regular fuel for a long period of time, there won't be any damage. I've torn apart engines that specified premium fuel and had never had premium fuel in them and there was zero evidence of damage. Many people are cheap, even with expensive autos, and will only put the cheapest fuel in all of their cars no matter what the manufacturer recommends. And the manufacturers know this, so they build engines accordingly.

The worst I've seen in my career, outside of my examples, was damaged spark plug electrodes caused by the higher combustion temps from some extended pre-ignition. Most people don't understand that octane actually retards the air/fuel mixture ignition so that higher compression engines won't pre-ignite. It doesn't add horsepower or benefit an engine that isn't designed for it, and doesn't have the electronic controls that takes advantage of it. It will actually cause hard start problems in many vehicles that are designed for regular fuel.

So....in my long winded style, don't worry too much about it. If you're really concerned, inspect the plugs.

[Barry45RPM]

Do an emissions test on the car before you buy it wether or not your state requires it.

My Father had a 2000 W210 that he never put 1 single tankfull of anything other than the cheapest no brand crap he could find.

At 50k he needed all his cat converters replaced. We used OEM which included pipes, since I didn't want to weld new cats to old crappy pipes.

That being said you are looking at a high milage not recent vehicle.

[otto6457]

Low octane rating of the fuel has no bearing on catalytic converter failure. In fact, using high octane fuel in engines that aren't designed for it can cause faster catalytic converter degradation due to the fuel not burning completely and sending raw hydrocarbons into the converter which greatly raises it's operating temperature. Converter failure can be from other contaminates in cheap fuel, but not from a lack of octane. Catalytic converter chemistry is pretty simple and octane has no role in it.

[burrito_bandito]

hi guys, no need to worry. not that i recommend it, but we have been using 87 in our m112 engine for most of our daily driving since we bought our ML320 new 12 years ago. there is no way that a few instances of mid grade fuel will affect the engine. Do you get better fuel mileage and performance with high grade fuel, yes. Why do we use low grade if the high grade basically pays for itself... well idk. We also own a CLK55 AMG that we do use high octane fuel for, its not like we are just cheaping out.

besides, how often do normal people push their vehicle's over 3k anyways? of course WE do, but that's why i specified "normal" people haha. anytime we asked anything beyond the call of duty from our vehicle we have fed it properly with at least 91 (for towing, long car trips with the whole family + luggage, etc.)

Basically all i'm saying is don't worry about the fuel, if you like the car, buy it

forgot to also mention that we have about 160k miles on our ML

[700horses]

Wow thanks a lot for the input! (especially otto for the details), makes me feel a lot better about this vehicle, since it is cherry throuhgout.

From what I gathered, the plugs were last changed at 60k miles, but not yet at 100k... I will change them as soon as I get the car.

Thanks again!

[Barry45RPM]

Originally Posted by otto6457

Low octane rating of the fuel has no bearing on catalytic converter failure. In fact, using high octane fuel in engines that aren't designed for it can cause faster catalytic converter degradation due to the fuel not burning completely and sending raw hydrocarbons into the converter which greatly raises it's operating temperature. Converter failure can be from other contaminates in cheap fuel, but not from a lack of octane. Catalytic converter chemistry is pretty simple and octane has no role in it.

Cleanliness problems caused by using cheap low detergent fuel is what I was going for, as I know low octane fuel will simply cause timing to be retarded to avoid pre ignition thus avoiding engine damage. Cheap non detergent fuel can cause several other problems which an emission test will uncover.

[otto6457]

Originally Posted by Barry45RPM

Cleanliness problems caused by using cheap low detergent fuel is what I was going for, as I know low octane fuel will simply cause timing to be retarded to avoid pre ignition thus avoiding engine damage. Cheap non detergent fuel can cause several other problems which an emission test will uncover.

No doubt. Here in the high plains of Texas, farm fuel can be a major problem for us. Farmers will use this fuel in everything and a lot of it is barely gasoline. I just replaced an entire set of injectors in a 2012 truck with less than 7000 miles on it due to crap farm fuel. There was so much particulate in the fuel it clogged every injector. I had to have the tank cleaned, all the lines back flushed, and the regulator/dampers replaced. A $3700.00 repair job that warranty declined. So, we have a very mad farmer that's out $3700.00 and believes Toyota is at fault for his truck choking to death on his $3.00 a gallon "almost fuel"

We see some of this in the fuel the 7-11's and such stations sell around here, but on a much smaller scale. I always recommend to my customers that they buy fuel from name brand stations that sell a LOT of fuel. The more they sell, the fresher the fuel in their tanks, as it gets refilled more often. Especially the premium tank. Some smaller stations may not get new premium fuel but once a month, or even less often. The longer fuel sits in the ground the more likely it is to get water condensing into it.

Cheap fuel is not always cheap in the long run.

[WeathersWe]

since I didn't want to weld new cats to old crappy pipes