Questions

[theholycow]

Originally Posted by bobc455

p.s. one important followup point: most OEM ECMs run their timing too far advanced IMO, and rely too heavily on the knock sensor to tweak the timing to the correct point. This system works by retarding the timing after it hears knock. This is fine in the short term, but over 100,000 miles these occasional knocks will have an accumulative affect and you could ruin your head gasket.

Wouldn't that point support the practice of using higher octane ratings than specified?

Also, your theory sounds ok but in practice we have the longest lasting engines ever. 181,000 miles on my GMC engine, never had the heads off...should I be looking for signs of cumulative occasional knock damage?

[bobc455]

Originally Posted by theholycow

Wouldn't that point support the practice of using higher octane ratings than specified?

Yup - unfortunately, though, it is difficult to tell what's going on with the knock sensor unless you have a scan tool that can give you a KR readout. And even then, most knock is transitional (i.e. during quick throttle changes or shifts).

Also, your theory sounds ok but in practice we have the longest lasting engines ever. 181,000 miles on my GMC engine, never had the heads off...should I be looking for signs of cumulative occasional knock damage?

One more benefit of hypermiling! Since we are generally much lighter on the throttle than the average driver, we tend to stay out of the "transitional" areas where average drivers see the most knock.

For my family's cars (my Saturn and the wife's Taurus), we both use 89 octane under most circumstances. We do this because I can hear the occasional knock when using 87 octane fuels. (I am lucky to have a trained ear that can hear that occasional knock, most drivers will never pick up on it). The 89 octane fuel gives that extra safety cushion to stay out of the knock zone.

-BC

[Jay2TheRescue]

I don't know. My 98 GMC pickup has 160,000 miles on it. It had 109,000 on it when I bought it. Absolutely no problems with the engine at all. I've always gotten better than average mileage in my vehicles, but i've only been actively hypermiling for about a year. Even at that I still occasionally open up the throttle and let the horses out for a run. I think if you're having head gaskets blow at 100,000 miles its not due to a knock sensor, its more likely due to poor vehicle maintenance or poor engine design.

Even running hard the gaskets hold up a long time. I remember at the rescue squad we had an old 86 Caprice with the police package and a 350. It was a Sheriff's car, and the Sheriff's dept gave us the car when they retired it (after 5 years and 110,000 miles) Then the squad had the car for another 5 or 6 years and the car had well in excess of 170,000 miles on it when the head gasket blew.

No civillian in their normal driving could be as hard on their vehicles as a Sheriff's dept and a rescue squad. The car lasted over 10 years and 170,000 miles. The county was a large county, and the squad cars got a workout.