fatt-dad

Dear Forum:

I know what the mfg wants - 91 octane. I'm just trying to figure out what's the history of this group running on 89 or even for more adventure - 87 octane? I put in a tank of 89 and the car (2001 E320 4-matic wagon) seems to run great - no knocking or performance problems.

Comments?

f-d

CLS550

ive been running 87 since it was new and its been fine.

Untertürkheim

You should not notice any immediate problems because the engine has the ability to temporarily compensate for lower quality fuel. There is a reason that there is a minimum octane specification on the cars. Prolonged use will result in engine damage, and carbon buildup at the very least. Car manufacturers have to reason to make you waste money on more expensive fuel, but there is an expectation that when you buy a car like this you will use the proper products.

fatt-dad

Dear Untertürkheim,

Thanks for the reply, but I guess I look at this somewhat different. I don't look at regular, mid or high test fuel as an indicator of "quality". I'd say that they may all have the same quality (i.e., as in manufacturing quality), but high-test is less explosive than regular gas (i.e., high-test with greater octane). As far as I'm concered, if there's no knocking they'll both burn clean. (I may be off on this, but that's what I "think".)

Don't get me wrong, if the car just won't hold up under regular gas, I'm sticking with the higher octane. MB specs 91, which just isn't available in the U.S. (one of their bigger or biggest markets). We have 89 or 93 to chooe from. I guess I could do a 50-50, but often wonder whether how the rest of the MB drivers feel (at least those with the 320 motor).

CLS550, You may be my inspiration - first I'll await further comment; however. . . . .

f-d

Bossman123

Lower octane will cause the cats to fail prematurely. If you have ever paid to have one replaced, that will surely justify the higher octane purchase at the pump. The engine is designed to run on higher octane gas due to the higher compression ratio. Why would you risk costly repairs to save a few dollars a month.

CLS550

When my parents first go the e320 they proboblay used 91 or w/e for a whiel but as long as i can remember and as long as i have been driving it i have been using 87. In our newer cars high octane is used though. I am having some problems with my cats recently.

lexrex

87 octane won't damage the engine. The engine has knock sensors, which signal the ECU to retard the ignition timing. Retarded ignition timing saves the engine from damage at the expense of power and gas mileage. The reduction in gas mileage on low octane more than offsets the lower fuel cost. Running lower octane than recommended is false economy. (Higher octane than recommended is also a waste of money.)