Cold weather and engine detonation? (1 Viewer)

[Bob Friend]

Can anyone tell me if cold weather is more or less likely to affect engine knock?

I use 87 octane (as prescribed by the owners manual) in my '05 Honda CBR600RR (motorcycle) and noticed a lot of knocking on the way to work this morning. I've been using the 87 octane for months and have never noticed this before (even in the hottest days of summer).

 

[Scott L]

I think it's the cold. Auto engines can have similar problems. Not sure what the answer is but I think it has something to do with the oil.

 

[Steve Schaffer]

Engine knock or ping are terms for a phenomenon called "pre-ignition" in which the fuel ignites before the sparkplug is energized by the ignition system. The compression and heat in the cylinder can cause the gasoline to explode prematurely, just as diesel fuel ignites due to compression alone (diesel engines don't have sparkplugs--just glowplugs to heat the combustion chamber for cold starts.

This is why lower octane fuel tends to make ping more prevalent, and why most modern cars have knock sensors which detect the ping and prompt the engine computer to retard timing so the plugs ignite before the fuel does.

So in actuality, all other things being equal, this knock should be less, not more likely during cold weather.

In my experience with older cars without knock sensors here in Fresno (average summer temp 95-105 from mid May to late Sept.) ping is much less prevalent in cold weather.

That being said, fuel refiners now often use different blends of additives in the summer vs winter. Here in CA we get "oxygenated" fuel from mid fall to early spring which cuts fuel economy so much that in the hot parts of the state we get the same mpg in the winter with no AC use as we do in the summer with AC running max at all times.

 

[Bob Friend]

May have been bad gas. I ran it dry and filled up with 93 Octane from a different station and all seems to be well. The engine has a fairly high compression ratio (13.5:1) but Honda says it'll run fine on 87. I'll stick to the super to be on the safe side.

 

[Scott L]

oops forget it was a moto, that 13.5:1 psyched me out for a sec