Premium Gas on '92 190E
 

is it absolutely important to put only premium in that tank? Thats all i've ever put in since i bought it but would it hurt it to use anything else or to mix a couple gallons with the premium?

MB suggests 91 RON octane on that & all of their gasoline cars after 1987.

we use mid grade in all three of ours. We don't run them particularly hard. Occassionally on a real hot week, I might put premium in..but only a couple of times a year.

we have 2.6 and 3.0 engines

mid grade (89) should be fine, but only you can tell whether or not there is pinging as you drive. You didn't state where you are located - local climate can be a determining factor in the type of gas you use. In my 300E I would run 87 in the winter, 89 in the spring/fall, and 91 or 93 the few weeks of the year it was very hot.

If it states to use premium, I would. The price difference isn't that horribly different that it makes a huge difference. Now if the differnce in premium and regular was a dollar, I might consider it. Would you use dexcool in your radiator when it states mercedes only coolant?

Apples and oranges. Failure to use Dexcool will result in corrosion. Failure to use 91 octane when the engine is not pinging will do absolutely no harm. The manufacturer states 91 octane as an uneducated safeguard for the drivers who don't even know what pinging is.

Who's to say his engine will not ping under use of regular fuel? Also I would call that an educated safeguard myself.

My 190E pings with 87 octane but not with 92. I also get better fuel mileage with the 92.
I would stick with minimum 91 octane to avoid pinging, as you don't hear all the pinging, and the damage is done over a long term.

This is turning into an oil thread. I'm out...

Octane rating will not affect mileage and pinging will not do any damage to your engine. Detonation will kill your engine but ping is just embarrassing. If your engine has knock sensors you probably won't even get pinging.

I just noticed my words being taken out of context:

I did not even suggest that his engine wouldn't ping with regular fuel. Read again:

Obviously if it starts pinging he should bump up the octane. Like I said, some people don't even know what pinging sounds like and wouldn't know whether or not their engine was doing it. This is why the manufacturer recommends 91 octane to be safe. But others have also stated that they run less than 91 octane and are not experiencing any maleffects.

Now its really looking like an oil thread.

Well, here's one thing I've noticed, and it DOES have to do with oil.

It is my impression that if you have one of the many 103s that burn oil because of the valve seals, you end up with some deposits in the combustion chamber that raises the compression. The car will begin to ping under load after a while, even with premium 93.

The only way to rectify the situation is to floor it and blow all the crap out of the engine. I usually wait until some jerk is behind me who won't dim his headlights, or a tail-gater. After a few hundred miles of build-up, this will put out quite a cloud of smoke but it does cure the pinging.

And remember, the 102/103s don't have knock sensors.

That's my impression. YMMV.