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1994 E-320 Wagon
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Discussion Starter · #1 ·
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..
 

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2003 C320 Coupe\71 220 gas, 4-speed\95 Talon TSi AWD\97 J30\79 GS1000S\80 SR500\'69 Datsun 2000
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Cataclysmic diverters only care about lead in the gasoline's makeup. So long as it's unleaded, the octane rating won't matter a whit.
 

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2002 ML320
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1,951 Posts
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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94 E320
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209 Posts
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.
 

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1976 BMW 2002. 1991 250TD. 1995 E320. 2018 Honda Africa Twin
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some of you are posting doo doo.

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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1994 E-320 Wagon
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4 Posts
Discussion Starter · #8 ·
Premium VS Regular ?..............solved

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
 

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95 S320; 99 E3204M
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While not worth it to me, a compromise is to buy 1/2 93 octane and 1/2 89 octane. This will give you 91 octane, which is what the manual calls for.
 

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99-C43, 05-G55K, 71-280SL, 94-E320 CAB
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some of you are posting doo doo.

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....
 

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Mercedes Benz forever. :)
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Doo doo or no, my car runs terrible on regular. It pings when under full load, is slow on the get go and runs a little rougher at idle. The 5 bucks extra per tank is worth it to me!
 

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While not worth it to me, a compromise is to buy 1/2 93 octane and 1/2 89 octane. This will give you 91 octane, which is what the manual calls for.
You know, that is not a bad idea.
 

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93 300E 2.8, 79 450 SLC
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Engine with high compression ratio requires high octane gas. I'm not sure if 300e's engine has high compression ratio.

BTW, Higher octane gas is not better than lower octane gas. It's just higher octane gas explodes in higher compression. My friend use 91 octane gas in his 91 Honda Civic which is completely waste of money. He insists his car runs better with 91 gas. Actually, what he need is a tune up and adjust the timing, etc.
 

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1976 BMW 2002. 1991 250TD. 1995 E320. 2018 Honda Africa Twin
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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....
but arent unburned hydrocarbons the result of poor ignition, rather than fuel?
 

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1995 E420, 2002 C320 Wagon, 1964 Lincoln Convertible
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Last week I was involved in an accident and totalled my 400E. But when I was driving my 400E I always used premium and never thought twice about the extra $4.00 everytime I filled up. What the heck, forget your latte for the day if it bothers you that much. On one occasion I was in the boonies of Alabama and stopped to filled up finding out that I had a choice between diesel and regular. I filled with regular and the car ran like garbage; missing, lack of power and guzzled the fuel. When down to 1/2 tank of fuel (not very long) I filled up with premium and noticed a difference within miles. As I recall it took another tank to get my mileage and performance back to where it should be. So for me, if you own a Mercedes you need to treat it like the quality vehicle that it indeed is. Don't scrimp on fuel.
 

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99-C43, 05-G55K, 71-280SL, 94-E320 CAB
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but arent unburned hydrocarbons the result of poor ignition, rather than fuel?

Overly rich condition is not caused by ignition....

Either case, poor tune or too rich can cause the unburned portion to ignite in the cat, potentially causing damage.

How do I know?
We rattled the bricks loose on two brand new 5.0L Merc cats on the dyno, while setting the fuel maps for the twin turbos.
Perfect ignition, just a bit too rich for the stock cat.

Didn't have a problem after we installed a newer technology spun metal cat.....
 

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94 E320
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209 Posts
some of you are posting doo doo.

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.
Well, Let me say this about that. I am telling you what happen when I put regular in my 94 E320 which is a M104 engine and when timong retards to prevent detonation it leaves unburned gas behind which then tends to overheat the catalytic converters. I don't know how sensitive the Mercedes cats are to this but there have been problems in other cars when this condition happens. I think it is you who is posting Doo Doo, my friend.
 

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94 E320
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Oh just to let the first post guy know. I didn't experience any problem with the catalytic converters as a result of this brief encounter with regular fuel. But then again I was very careful to drive it conservatively because I could tell it wasn't like the regular fuel. Whether or not extended use of regular will damage the cats used on these cars - I don't know and I don't want to find out. The first point I was trying to make was that the is no economy in using the regular gas because you lose the cost savings in less miles per gallon. I do like the cocktail (Mixture) idea that somebody else posted since these gas prices are going wild. If the car requires 91 then putting in 93 isn't giving you anymore. I guess you also do 2/3 of 93 octane and 1/3 of 87 octane - correct? Kind of hard to justify the extra hassle though, but gas prices being what they are - It is starting to look more attractive all the time.
 

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R129 SL 500 97, W124 E320 Coupé 96, W124 300E twin turbo 90, W126 300 SE 91, Ford Capri 2.8i 84
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The compression ratio is 10 in the M104 and 9.2 in the M103, but it's 8 in the low-compression M103 (.94, .981, .983, .985). Source: MB's Technical data passenger cars (Oct. 93).
 

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2003 C320 Coupe\71 220 gas, 4-speed\95 Talon TSi AWD\97 J30\79 GS1000S\80 SR500\'69 Datsun 2000
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While not worth it to me, a compromise is to buy 1/2 93 octane and 1/2 89 octane. This will give you 91 octane, which is what the manual calls for.
Um... unfortunately, chemistry does not equal "math"; your concoction isn't yielding 91.

Unburned fuel will overheat a cataclysmic diverter. How much, over how long will "depend". What kills them is leaded gasoline: the lead coats the catalyst, and insulates it from operating. Often, reverting to unleaded will clean them back to functioning over time.
 
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