Premium Gasoline

M y '94 352s (sic) get mid-grade gas.

wrote

There have been many discussions on this subject in this group, and also IIRC in rec.autos.driving - you should google them. Basic story is: you probably can use regular without engine damage. You *will* get less power, as BMW engines are optimized for premium.

Given that, I'm not sure that the M50 engine in your car (I presume you actually have a 2.5L not 5.2L engine ;->) has as *good* a set of knock sensors and engine controller as the current crop of BMW engines do: if your car pings *at all* on regular, move up to mid-grade and then premium.

FloydR

Premium car = premium gas. If you don't want to, that's your decision. The cost over time isn't really all that much, especially when compared to out-of-warranty engine repairs.

"Toby" wrote

Being a '94 model year, I doubt he still has warranty. :)

Besides, a knock sensor would most likely pull timing and not allow the engine to get damaged. However, given the worse performance and possibly higher fuel consumption, I agree that using a low-octane gas is hardly a bargain.

Cheers,

Pete

"Pete" wrote

Nevermind that comment. Too many beers tonight...

Pete

Then I'll say it. Being a '94 model year, I doubt he still has a warranty.

I run the mid-grade in my 3 Series car and have done it for more than

120,000 miles and approaching 6 years. He won't exercise his warranty because of the gas he uses.

On 6/24/2006 7:42 PM, Jeff Strickland went clickity-clack on the keyboard and produced this interesting bit of text:

This brings up a question I've recently begun to ponder. From what I've read all the octane level means is that it changes the pressure under which the fuel will detonate. Higher octane is harder to detonate. The purpose of this is so that the fuel won't detonate early in high compression engines.

The question: What constitutes a high compression engine, low compression engine and mid-compression engine? I suspect the engines in the M cars are going to have higher compression engines, but what about the other ones? My M60 has a compression ratio of 10:1. Is this high?

"Jeff Strickland"wrote

Yeah, I think Toby realized that and that's why he wrote "out-of-warranty".

Pete

Sorta.

Your hunch is correct, higher octane will not spontaniously combust the way that low octane fuel will, this is how high octane gas prevents ping. When the car has a knock sensor (knock and ping are two words that are used interchangeably, however I've been told that they are not really interchangeable words -- but that is another post). Anyhow, if the knock sensor detects knock (as when low octane fuel is introduced) the computer can retard the timing so that the engine fires closer to TDC. This gives slightly less power because the spark comes when the piston is already on the way down, instead of just peaking over the top. A result of retarding the timing a few degrees is that the motor runs a bit cooler to avoid pre-ignition that comes from heat, but the cost of retarding the timing is a loss of power. Frankly, the average driver will not miss the lost power on his daily commute to and from the salt mine.

10:1 is on the edge of high compression. I have said several times that I use the mid-grade fuel with never a hitch.

Okay, now I get it.

Where exactly did I say that the OP had a warranty? Quit inferring. Read what is written.

Bzzzzzzzzt!! Wrong answer. But thanks for playing.

Premium gas is defined by various m,arkets around the world and varies through tme.

The 2.5L M50 engine in your 1994 325i requires 89 AKI (RON+MON/2) gasoline. That is what is meant by "premium" in the owners manual.

You can use 87 in a pinch and the knock sensors will retard the timing if/when there is pinging, but when this occurs the conventional wisdom is that the mileage will suffer.

Considering that the price of fuel in the US is about $3.00 a gallon and the difference between grades is only 10 cents, you only need to realize a 3% improvement in mileage to break even buying the 89.

My perspective is that this is a false economy. I don't know about the 1994 model, but my 2003 325i and Z4 have 14.5 gallon gas tanks, one of which I fill once a month. Going down one grade of gas will save me $2.90 per tankful at the most. Less than an espresso drink at Starbucks, an issue of Bimmer magazine, a movie rental at Blockbuster, or a pack of cigarettes. Getting a BMW and then cutting corners is like ordering custom-made dress shirts made with a cheap poly-cotton blend. epbrown

--

2003 BMW 325i Black/Black 2003 BMW Z4 Black/Black

The 2003 325i has a 16.6 gallon tank.

Anoop

Thank you all for the very helpful advice. I certainly agree that paying a few cents extra per tankful to get full performance from my

325i is well worth it. But it is also good to know that if necessary I can, > Toby wrote:

You might do that yourself. Where above does he attribute that statement to you?

-- Larry

That's why we should talk only in octane and not use uncertain adjectives.

DAS

For direct contact replace nospam with schmetterling

You're too stupid to give any more comment to.

Easy there, Fred. The "real" answer is as it frequently is in these groups - RTFM!

(That's "Read the F-ing manual, for those that don't know.)

The manual doesn't usually say "premium" for the reason that Dori mentions - different methods in different countries.