Big cloud of smoke at start up

My tank was half full of 89 octane which I had mistakenly pumped a tank of, and I refilled it with 91 octane gas. Now at startup there's a huge plume of smoke... I mean a big *** cloud~! What's going on? Any advice? I have noticed the difference in power... how much more power is there to gain by going with half a tank of 91 octane and half a tank of 100 octane 76 gas?

I cannot give you the technical explanation but white smoke at start up is normal. It has to do with the flat six motor, and usually you may see it crop up more often (at least it does on mine) when the car has sat for several days since being ran. Accidentally fueling with 89 octane would not cause that (in fact, one time I accidentally used 87 octane--being tired at the lunch break of a DE, I picked the wrong nozzle--I went back to the track and the car ran fine). I would not worry about your gas--the knock sensor will do its job and you should not have problems. I use 93 octane (I'm in Texas where its plentiful)--you should be fine with 91. I don't think you're going to really notice a performance lift by mixing 91 with 100, except in your wallet (which will be lighter) or your fuel economy (which would be a little better but not enough to offset the cost of the 100 octane, if you care about such things).

I agree with the above post. Additionally, I had white smoke on start-up after driving my 2001 996 C4 on the track during a PCA driver education event. Apparently it is caused by driving vigorously which causes oil to leak past the valves. It is then burnt off on start up. It is a common problem with the 996 and a technical service bulletin was issued concerning it. The fix is simple and involved having a slightly longer dip stick installed and having the dash oil level gauge reprogrammed. This serves to reduce the amount of oil by about one quart, which eleminates the problem. It cost about $15.00 for the new dip stick. Since then I have driven at several other DE's and no white smoke. Check it out. Best of luck.

Maybe it is me or maybe it's the fact that I have a 99 no e gas, but when I do 4 gal. 100 to the rest 91 it does run better. It doesn't pull the timing back as it is supposed to run on 93ron anywayz. I feel it mainly in the mid rpm, and it "seems" that it goes a little better a little earlier where the torque is concerned. I do it almost everytime, unless I am going on a roadtrip type of drive,and yeah it's not cheap

Same here with my 99 and no e-gas. I normally do 50% 91 and 50% 100. Also, I don't get any smoke on startup. Dont think that is normal. One last thing... how could you MISTAKENLY put 89 Octane? Must have been a rough day!

I just back from an afternoon run in the Sepulveda twistis with the top down, and literally "smoked" a VR6 that was trying to follow... with a downshift from 3rd to 2nd, a huge plume of white smoke shot out. Is this signs of the problem related to the oil leak past the valves?

White smoke is usually a sign of coolant getting in the combustion chamber..Bluish smoke is oil related.

huh that is weird, yes my car does not blow smoke either, however I was following my friend's new c4s and between shifts there was a little puff from the right exhaust pipe. I would tend to agree with Jim, if it's white then it's water or coolant, if it is bluish and stinky then it's oilly fun.

i too get the big cloud when I start up my 02 after having run some laps. I was advised to run a little less oil and that helped. But is that really a good idea? So far the dip stick change and reprogramming sounds like the answer

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Cydog: <strong>... how much more power is there to gain by going with half a tank of 91 octane and half a tank of 100 octane 76 gas?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Your car's ECU was programmed to achieve optimum performance with 98 octane European standards which equates to 93 octane USA. The car can run on minimum 91 octane USA. At least, that's what the manual specifies. <img border="0" title="" alt="[Wink]" src="wink.gif" /> BTW, as mentioned above, white smoke on startup (especially when the car has been sitting for a few days) is a relatively common occurrence.