87 octane in 300SE? Problem?
 

Probably overly worried here, but I just realized the imbecile @ the gas station filled my tank with regular instead of super, which I asked for. :mad: (We can't pump our own gas here in NJ - another story)

Is this going to be a problem? Thankfully, it was only a half-tank, so I guess its like a 89 or 90 octane blend in there now. 1/2 regular, 1/2 super.

Thanks

You'll be fine. Here in TX I regularly ran 87 octane in my M103 during the cooler months with no problems. Then I would go to 89 and 93 as it gradually warmed up and I perceived slight pinging under heavy load at lower RPMs. You just have to turn the stereo off from time to time if you want to actually hear it. In NJ you can probably get away with straight 87 octane through June...

I live in oregon and I have a 89 300se. I only run 87 octane. I dont believe in cars that only run super 91. I have seen a few articles in Car and Driver and Road and Track about gas. Basically what they say is that regular vs super isnt a big deal. Arco(cheap gas) vs Chevron(top tier) is.

I run 87 in my 300SE, and my CV.

OK, thanks! No worries then.

The 103 engine does not have a knock sensor; so low octane gas can definitely be a problem - if it causes ping and detonation.
Susceptability to ping depends on the overall condition and tune of the 103 engine; and, as stated above, the ambient temp.

That being said, I always ran 93 octane in my '91 300SE. Once I tried 87, and sure enough, it pinged. But, later I discovered my EGR valve was bad.
after replacing the EGR, I have rfecently tried 87 octane, and no pinging whatsoever, yet. It's about 80 degrees here in Dallas, so, when it hits 101 degrees, I may find I need to run higher octane. Before, it never concerned me to pay 15 cents more per gallon to pamper a $56K car. Now, paying 50 cents more per gallon in my $4k car is more painful.

Anybody else have any comments on the M103 and octane requirements?

DG

I've heard a lot of things about it being bad to use 87 in the M103....they need Premium or it can damage the engine...especially with no knock sensor.

Engine: $5000

Gas: extra 15-20 cents a gallon.....the math is easy here.

Not to mention it will likely run/perform better on premium and get better mpg's.

I always wondered what harmful effects lower octane gas would have on your engine, other than poorer performance.

Octane just measures a fuel's ability to resist predetonation. That said, fuel efficiency aside, the proper octane for the M103 engine (or any other engine for that matter) is the lowest octane you can run without experiencing pinging. If your particular engine doesn't ping using 87, then 87 is fine. If it pings for whatever reason, just use the next higher-octane fuel until the pinging stops. If 89 gets the pinging to stop, 89 is fine. But you may require 91 or 93. The "premium" fuel requirement in the owner's manual is put there as a general rule for owner's who don't know the difference.

I believe the octane requirement is related to the compression ratio of the engine. So, you're saying that the higher the octane is the more likely it is to predetonate?

Higher octane fuels are more resistant to preignition which causes detonation (I may have goofed because I don't think predetonation is an actual automotive term).

That's okay. I don't know any better . . . .

Is $3-5 a fill up REALLY breaking the bank for you?

If so, maybe you should rethink driving an MB

The difference between regular and premium is usually $0.20 / gallon.

If your tank is bone dry and you put in 20 gallons, that's a total of $2.00.

I've seen people go out of their way to the cheapest gas station in town, and then run into the mini mart and buy a large Diet Coke and a package of Ding Dongs.

Duh, there goes your profit margin. :cool:

Paul's profit margins are larger than mine because of his math skills ($0.20 x 20 gal.= $4.00).

; - )