Last post on Jan 20, 2013 at 2:20 PM
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Engine, Fuel System
#291 of 297 Re: BMW X3 and "regular fuel" [Mr_Shiftright]
Jan 18, 2013 (4:48 am)
octane is by-definition a measure of: resistance to detonation. a measure of the resistance to the initial ignition. ...as far as i understand it...
also iirc, independent of top-tier or bottom-tier gas, it's been decades since there were different additives in different grades of fuel - except for variations required to change octane & maintain the govt-mandated oxygenation.
Clearly BMW has a 'bug' to fix with the vehicle and a TSB may be appropriate if the issue is common.
Owners who prefer to spend more per gallon to get identical winter performance by running premium fuel should be forewarned that the x3 may not be the right vehicle for them.
i wonder if the BMW does better with unoxygenated/minimally-oxygenated 91+ octane? (you may have to drive >500 or >1000 miles to find any, maybe not worth it just to find out :| .
#292 of 297 Re: BMW X3 and "regular fuel" [elias]
Jan 18, 2013 (8:19 am)
octane is by-definition a measure of: resistance to detonation. a measure of the resistance to the initial ignition. ...
Your first statement is correct, but not the second. There is no difference that I know of in the ease with which 87 octane gas ignites in the presence of a spark verses 91 octane.
So I don't understand why using 87 octane in the BMW would solve the problem she mentioned. Unless it's related to the winter time formulation of the gas where she lives - which is what I think you were getting at.
#293 of 297 Re: BMW X3 and "regular fuel" [srs_49]
by Mr_Shiftright HOST
Jan 18, 2013 (9:28 am)
Exactly. My personal opinion is that the explanation given by BMW is, as we used to say, "the sunshine treatment". We park your car for a day, tell you it's all better, and hope you go away.
#294 of 297 Re: BMW X3 and "regular fuel" [Mr_Shiftright]
Jan 19, 2013 (7:58 am)
regular fuel fixed the problem with the BMW, if i read the initial post.
so the techs did in fact fix the problem. if not then its gotta be fuelpump or injector issue?
assuming i read correctly that the original problem was actually solved by using the supported 87 octane, it can addressed by adding 4 words to the owners manual:
"premium fuel is recommended, EXCEPT IN FREEZING WEATHER".
some time maybe you will encounter non-start situation in frigid weather with whatever engine and if you have lower-octane fuel available, maybe you'll see it work...
(btw, so i see your point correctly that the octane measures the resistance to pressure-induced ignition, not sparked ignition?!)
in any case, i'm wishing to go back to a diesel engine, so looking forward to our ongoing different stylings regarding CETANE . never mind all this octane stuff.
one of the automags years ago (before oxygenated gas became required in USA) put a big v8 crate engine on a bench and tested it with the various octanes, as well as precisely measuring the tiny octane differences in the gasolihe. it was amazing how little difference the octane was, and how little difference in performance actually resulted.
#295 of 297 Re: BMW X3 and "regular fuel" [elias]
by Mr_Shiftright HOST
Jan 19, 2013 (8:31 am)
yes but that's anecdotal, and anecdotes are not evidence. Stalling can be caused by so many factors that we have to be careful, if we wish to be good diagnosticians, --we have to be careful not to confuse causation with correlation.
chances are pretty good that someone else with a similar problem will not find regular gas to be a solution.
I suppose it would be fair, at least at this point, to say that using regular gas does not "cure" cold start stalling in an X3, but that it may, under certain circumstances, alleviate it in certain cars?
The bench test with the big V-8 would be meaningless if the engine didn't have computer controls for timing I think, because all they had to do was set the timing to just short of the ping point on regular fuel---and then yeah, sure, using higher octane wouldn't matter much at all. There isn't any more "power" in high octane gas.
#296 of 297 Re: BMW X3 and "regular fuel" [Mr_Shiftright]
Jan 20, 2013 (9:38 am)
yeah... it was a racer-type magazine that tested those V8s, i'm sure they did not omit the knock sensors... pretty sure knock sensors are 'standard' on GM V8s for decades.
anyway, "YMMV" ! speaking of BMWs and fuel types, I've been seeing so many X5d lately! must be nice to drive one of those ....
#297 of 297 Re: BMW X3 and "regular fuel" [elias]
by Mr_Shiftright HOST
Jan 20, 2013 (2:20 pm)
I think knock sensors came out in 1981 or so.