Well, hope these are not too stupid questions....., and not off topic.

My friend leases a 2004 BMW 330Ci. This car *requires* premium unleaded gasoline. However, the 91 is around $2.6 here, so my friend just pumps 87 into the car. I don't feel too comfortable with this but he said: "it's a lease car......."

1. what could happen if you don't use the premium gas for those car state require it?

2. On my 2003 C4S gas lid, it states Minimum 93 octane..... but I can only find 91 at the gas station. I assume this is ok, right?

Thanks.

 

All that happens is the engine timing is retarded by the ecu...this results in lower performance. In an extreme condition, and if the ecu doesn't catch it, then you may damage the catalytic converter. 91 is ok....the car was designed for 93. So performance will be slightly reduced.

 

Not a stupid question at all, but doesn't it say 93 RON (Research Octane Rating)?

The premium gas we have here in california is 91 octane, which equates to 93 RON, I believe. Our cars can compensate if a lower octane is used by electronic adjustment, not sure if BMW has this feature. If it doesn't, undo wear on the engine would probably take place, not a good thing. The price difference in my area between a tank of regular unleaded to premium is $4.00. Is it really worth it to him, lease or no lease?

(Found this...)
"To obtain the maximum energy from the gasoline, the compressed fuel-air mixture inside the combustion chamber needs to burn evenly, propagating out from the spark plug until all the fuel is consumed. This would deliver an optimum power stroke. In real life, a series of pre-flame reactions will occur in the unburnt "end gases" in the combustion chamber before the flame
front arrives. If these reactions form molecules or species that can autoignite before the flame front arrives, knock will occur.

Simply put, the octane rating of the fuel reflects the ability of the
unburnt end gases to resist spontaneous autoignition under the engine testconditions used. If autoignition occurs, it results in an extremely rapid pressure rise, as both the desired spark-initiated flame front, and the undesired autoignited end gas flames are expanding. The combined pressure peak arrives slightly ahead of the normal operating pressure peak, leading to a loss of power and eventual overheating. The end gas pressure waves are
superimposed on the main pressure wave, leading to a sawtooth pattern of pressure oscillations that create the "knocking" sound.

The combination of intense pressure waves and overheating can induce piston failure in a few minutes. Knock and preignition are both favoured by high temperatures, so one may lead to the other. Under high-speed conditions knock can lead to preignition, which then accelerates engine destruction."

 

Robyn is a geek...

 

Don't be a hater my wingless friend!

(I'm in a spicy mood today...be vewwy vewwy careful!

 

She sure is a geek. Can you explain all that in 6th grade english, Robyn? Isn't all that amounts to spontaneous combustion?

 

Sure!!

"Don't do it you bonehead...it's only $4!!!" How's that?

Of course, what can we expect from a BMW owner? HAHA

Kidding, I'm kidding!!!!! Honest, really, just kidding!! I like BMW's...they are very nice cars...for old people! hehehe Really really, I'm only teasing, honest!

(I knew I had the Halloween costume all WRONG...I went has a catholic student...should have gone as the geek! )

 

What we're getting at is this: When the air/fuel mixture goes into the cylinder, it's at something close to ambient temperature. When the mixture is compressed prior to combustion, it heats up. Depending on a bunch of factors (outside temperature, compression ratio and amount of crud inside the engine, the compressed gas may have the tendency to ignite before the spark from the spark plug. This is bad. Also, think of it in super slo-mo. The air/fuel mix doesn't explode all at once. The gas nearest the spark plug goes first, then the 'front' expands from there. If there's crud in the plugs, and the mixture doesn't fill properly, you get local hotspots that ignite before they're supposed to. This is bad, too.

Octane is put into gas to reduce its tendency to do this. Some cars need more (usually high compression ratio/ turbo- or supercharged cars) than others. If the put in the crappy gas, the engine will see that pre-ignotion is occurring and sort it out.

Long story short - if you're driving on the track in 110 degree temperatures, you'll notice a loss of power. In other conditions, it might happen, but you might not notice. You're really really unlikely to do any damage, and besides, it's a lease. Skimp away.

 

I think he's got it now. Thanks to you Robyn, he'll lease a prius next time instead

 

$5.80 / gallon within a year.

 

Thanks for the tip. I'm going to ask Alex@Akkurat to put an electric motor in the useless trunk.

 

Pictures?

 

Not the mechanic this year Robyn?

 

I was hoping there is a good reason to tell him not to use the cheap gas on the brand new Bimmer. It is somehow hurting me to see him feeding crappy gas into that car. It's his choice and money, though.

Anyway, I guess the verdict is:
Due to the high oil price, be careful when buying a lease-returned car..... even they are high end cars.....

 

yea. i saw a guy pumping gas into his ferrari at Rotten Robbie the other day.