I own a “California” 94 E-320 wagon. The owner’s manual indicates that running less than a premium grade would clog/damage the catalytic converter. Does any body know if there is any truth to this? If no, has anybody noticed a significant difference in gas mileage when using regular over Premium. There was a .30 cent difference at our local gas station today. Running regular could save me (us all) some bucks..
I will tell you from experience... my 300CE had regular run through it its entire life as near as I and my indy could tell and the cats were fried because of it... and the engine was a mess, the emissions were never right on it.
I will never put anything less than premium in my car... why? Because the engineers say not to.
If you are concerned about fuel prices... drive a Honda and put the Merc. in the garage or sell it.
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2000 C230K -- Travertine Beige Metallic
2002 ML320 -- Alabaster White
2002 ML320 -- Brilliant Silver - Dad's
1991 300CE -- Blue Black Metallic -- 129,000 miles -- Sold
1981 300SD -- Classic White -- 190,000 miles -- Sold
1977 240D -- Over 300k miles (Wrecked) -- My 1st car
I once stopped at a gas station that was out of super (and subsequently mid-grade) and I put in regular. The car ran very poorly. I believe that a "knock" sensor becomes enabled and that retards the timing making the car run rich. The rich mixture would damage the catalytic converter. By the way, my mileage was terrrible also. As soon as I was down to half a tank, I filled up with super and after a brief while the car returned to normal. My car is 94 E320 so I imagine yours is the same set-up. The money you think you are saving will be wasted with the terrible mileage (due to the car sensing the detonantion of the low octane fuel and retarding the timing). Learn by my mishap - DON'T DO IT. In my case I was low on fuel so I was stuck, but next time I will out in just enought to get to the next station. It really ran poorly - No zip at all.
premium fan... never had anything less in any of my car... you win in the long run!
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300E 1993 119k MILES (MINE)
S500 2004 4 Matic 29,000 MILES (mine)
BMW 750Li 2007 8,700 MILES (Dad) (
Lexus GS460 (Mom) 5,200 MILES (too much power)
2007 E350 4 Matic (Side Car) 9900 MILES
330i 2004 Sport ZHP package STICK 32000 miles (BROTHER) Dinan everything... looks bone stock.
the knock sensors are only available on the M104 engined 124s. the M103 engined ones do not have knock sensors.
if they detect pinging they pull the timing. so your whole the fuel burned my cat tripe is just that, tripe.
as stated already, the cats will get fried if you use leaded fuel.
if your cats are gone with unleaded then you have another unresolved problem that changing fuel octane might hide, but not eliminate.
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'O=00=O' BMW 2002. long live the legend.
After reading the manual and your responses it makes sense to continue using premium (unleaded of course). The engine appears to be designed to run on higher octane fuel as indicated by the 10:1 compression. Also I understand pre ignition (“Pinging”) is often not audible and running regular can cause some serious long term problems without us even knowing about it. So I will stick with running premium and probably get better power and continue to sustain my 25MPG (actually saving money).
Thanks for all your advice
the knock sensors are only available on the M104 engined 124s. the M103 engined ones do not have knock sensors.
if they detect pinging they pull the timing. so your whole the fuel burned my cat tripe is just that, tripe.
as stated already, the cats will get fried if you use leaded fuel.
if your cats are gone with unleaded then you have another unresolved problem that changing fuel octane might hide, but not eliminate.
Believe the OP vehicle is an E320, making it an M104-24V.
Unburned hydrocarbons can and will damage a converter as they will elevate the temp in the converter possibly causing a melt down....
Premium VS Regular ?..............solved 
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