So, I went to test drive the Pontiac Vibe GT that the dealer obtained for me to buy. It has about 350 miles on it and as I drove it I could clearly hear the engine knocking away. The cheap ***** had obviously put 87 octane in it instead of the required 92. My question is, could they have damaged the car by running it 350 miles with the 87 octane gas?
It’s pretty hard to do any significant damage caused by pinging in only 350 miles. Sure sounds stupid, though.
Well, the knocking you heard was premature detonation (insert your own off-color joke here), which is essentially a whole lot of little explosions happening in the cylinders, instead of a nice clean burn. It’s possible that this may have done some damage, IF it was severe enough, and/or IF it actually was going on for the entire 350 miles the car has been driven. I think the latter is unlikely. Most people, regardless of how cheap they are, will not tolerate severe knocking for very long.
Which brings me to my question for you. Why is this car available, with only 350 miles on it? It sounds like too many for a car that has only been test driven a few times. It also sounds like too few for a salesman’s car. I’d run it through CarFax.com before I plunked down any money for it. This situation is setting off alarms in my mind.
On the other hand, it’s quite likely that the dealer is the first one to put the cheap gas in it, and it has never knocked, before. In that case, and assuming there isn’t something else funky about this deal, you’re fine. Knocking is usually caused by too low an octane, but can also be caused by the engine being out of tune, as well as other, more serious, problems. If CarFax.com gives it a clean history, make the dealer resolve the knocking issue, and give you another test drive to confirm that they have, before you buy it.
It is a new, previously untitled car. According to the dealer I am planning to buy it from it was originally at a third dealer, driven to the second where the buyer decided not to purchase it, and then driven to the third and present dealer, which added to the mere test drive miles. I am assuming the worse which is that it has had the wrong gas for the entire time, but it doesn’t sound like it would cause any permanent damage, and the knocking isn’t all that bad, you have to listen pretty carefully when it was being driven uphill. At idle it sounds fine.
Why is a new car knocking anyway? I was under the impression that modern cars (say, within the last 10 years) had knock sensors that would advance or retard the spark to adjust for variations in octane, and that running a lower octane than recommended would result only in reduced power, not knocking. My '93 Volvo’s manual recommends at least mid grade gas, but I run 87 octane all the time, with no knocking.
My warning sensor says “beware”.
The 2zz engine in the Vibe requires the higher octane because of a high compression ratio. Like I said, it was very mild. On the other hand, maybe I’ll just have them get me another new car with less miles on it.