What are the ill effects of using mid grade gas in my E320? Will this cause the O2 sensor to fault? (or cause a fault in any other anti pollution system

There's lots of opinions regarding premium fuel vs. less expensive alternatives. Here's mine.

If the lower quality fuel results in detonation/pinging, the knock sensors will retard the ignition timing to prevent engine damage. Under normal driving conditions I doubt most people would notice the decrease in power.

I'd be more concerned about carbon build-up. You can avoid this problem by periodically using one of several fuel additives, but you'll probably still end up putting the same amount of money into the tank either way.

I have 3 vehicles, all requesting the use of premium fuel, 96 S-320, 97 SL-320 and 98 volvo S-90. All have over 75,000 miles on them, I never use anything but REGULAR fuel, they all still run fine with no ill effects i can detect. Good luck on your decision...

Ron

Subjective, for sure - but I really do believe I get better overall performance (idle, acceleration, etc.) with Chevron premium fuel (93 octane) in my gassers. Over the years, I've tried both Chevron regular (87 octane) and mid-range (89 octane) and just don't seem to get the same performance. I suffered no ill effects, except a 'feeling' of less-than-peak performance.

There is one exception - my '96 SL600 would not pass smog in California due to the ECU's 'Not Ready'... until I moved to Texas and used one tankful of Chevron premium (93 octane). In California, the highest, readily available was 92 octane. After only one tankful, the computers all came up 'Ready'. Can't explain it; neither can Mercedes.

Regardless of all that, good luck.

Cheers,
Jeff

__________________
MBCA Member #B012089 (Lone Star Section)
OBK Member #47 (W123 Division)
'96 SL600 (105K) Triple Black - Mein über-Fräulein
'79 240D (292K) Yellow/Saddle - Mein Spielzeug
'01 ML430 (123K) Black/Saddle - Wife's Ride
'94 SL500 (164K) Green/Champagne - Daughter's Dream
'73 450SL - RIP
'86 300E - RIP
'88 420SEL - SOLD
'94 S320 - SOLD

Here's the story from Mercedes:
https://www.mbwholesaleparts.com/StarTuned/pdfs/LiquidJune06Star.pdf

Seems to me if you believe in the car, you believe the requirements, even if they're not what you want to hear.

__________________
Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

I don't try to backyard engineer things, I do what the FSM and service literature recomend.

Besides its a freaken $50k++ car, who gives a crap about saving .10 cents on a gallon of fuel?

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

If anyone owns one of these cars, do you use super all the time or do you use plus aka 89 unleaded. The car has "Use Premium Unleaded" on gas gauge. But my question is do you ever cheat? The reference resistor is supposed to allow for this since it retards the time by 5 degrees I believe.

I use 91. Only Sunoco in my area has it. The pumps in Europe give out 95 RON as their regular gas which is what the cars are rated for and that translates to our 91 octane.
http://www2.mercedes-benz.co.uk/content/unitedkingdom/mpc/mpc_unitedkingdom_website/en/home_mpc/passenger_cars/home/products/new_cars/eclass_saloon/technical_data/petrol_models.0006.html


In Europe the only Mercedes rated for our 93 octane are the AMG's which take 98 RON.
http://www2.mercedes-benz.co.uk/content/unitedkingdom/mpc/mpc_unitedkingdom_website/en/home_mpc/passenger_cars/home/products/new_cars/eclass_saloon/technical_data/petrol_models.0008.html


93 Octane is recommended because chances are thats the only thing your local gas station in the US is going to have available.

Now that gas prices are so high, the differential in 87 to 93 isn't that much. I agree with what others say- pony up to get the best gas your car was designed to use. The lower octane is meant to be used temporarily and the knock sensor will decrease the timing. As these cars age it's even more important to use the proper gas.

My mother in law's 1995 525i was pinging on 87 and she was told to use higher octane given the higher mileage of her car and chance of detonation damage. Granted that car probably doesn't have knock sensors, but still....why keep the car in more or less a limp mode. If you want to save gas $ and don't car about performance, the diesels are probably more suited to you (with added benefit of the even longer longevity of those cars)