Or used better gas. Lower octane fuel cause valves to vibrate in seats
> when it knocks even below a audible level. This leads to erosion and
> togehter with higher exhaust temps from retarded spark timing needed
> with lower octane fuel, leads to eventual burning of valves. They do
> not tell you that though.
Regular fuel is fine if the engine is designed for it. I notice some engines with a CR too high for regular octane specify regular can be used. Sure let it knock so we can adjust it, a sure way to the troubles you mention. IMO Toyota's Camry 3.5L V6 has too high a CR for the specified regular fuel. I Emailed Toyota about this and they said premium fuel is needed for best performance. We could add for longer engine life eh!
I doubt if using premium fuel in modern engines with knock sensors has a significant effect on engine life (assuming the PCM has enough adjustment range to compensate for the use of regular fuel). With the knock sensor strategy, the PCM adjusts the timing until knock is detected and then adjusts it back down to the point that the knock is eliminated - BUT - for this sort of strategy to work it has to occasionally (based on some sort of algorithm) advance the timing until knock is detected. I suppose it might be that with premium fuel the engine never knocks under any allowed ignition advance but I doubt it. Ford did recommend premium fuel for the 32V Navigator, but the knock sensors do protect the engine when regular is used. The 2V Expedition version of the engine was specified to run on regular fuel, but the PCM would adjust the timing if you used premium fuel and increase the performance slightly. I owned two Expedition, and in over 250k miles of driving I never had a problem with spark knock. I did try running premium for multiple tank fulls in my 1997 Expedition but I could never detect any difference in performance or fuel economy. At least as far as I was concerned, running premium was just a way to give the oil companies another $0.20 per gallon.
I have noticed that many of the Japanese companies are now specifying premium fuel but allowing the use of regular fuel. I think this is done for two reasons - 1) By making premium fuel the primary specified fuel they can advertise the slightly higher HP numbers achieved when using premium fuel and 2) by specifying premium fuel in the manuals, the EPA will use premium fuel when conducting the emission and fuel mileage tests. When using premium fuel the cars get slightly better fuel economy. This is good for the CAFE game but not really detectable in real world driving. I have seen it claimed that for engines that have knock sensors, using premium will increase fuel economy by 3% to 5%. I don't think must people keep careful enough records to detect a .6 to 1.2 mpg increase. Companies that follow this strategy (specifying premium fuel for mundane cars) are doing a disservice to many of their Customers. The slight fuel economy improvements associated with the use of premium fuel will not offset the much higher cost of premium fuel. I doubt if the typical Camry driver can detect the difference in performance. I doubt an "expert" could detect the difference without a dyno or a stopwatch. So in the end, by specifying premium fuel Toyota, is screwing the little blue haired little old ladies who are the primary Camry buyers. I suppose if economy was the primary goal, they wouldn't be driving a Camry (and for sure not a 3.5L Camry).
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