Engine Difference Hot or Cold

[Roy_W]

I have noticed that in the morning when the air is still cold and I start the the bike, during the 10km run to work the engine runs incredibly smooth. It quite literally purrrrrrsssss. It's as if there is perfect harmony between the Air temperature, humidity and engine temperature etc..., I love it it.

[The temperature gauge is barely above the lowest mark at this point ]

In the afternoon when returning from work the engine makes a lot more noise, probably valves, timing chains or whatever and loses that lovely purring feeling.

[The temperature gauge is usually about 1/4 the way above the lowest mark at this point, which is usually its nomal position when warm and running ]

Question : Why does it purr when cold and then become clunky, chinky, metallic when warm. What would I have to do, check, tinker with, in order to retrieve that lovely purring in the afternoon when the air is warmer ?

PS : The bike runs great regardless of morning or evening.

[Simon]

you are travelling in a different direction and therefore the wind is going a different way. Would that be the reason?

[Roy_W]

you are travelling in a different direction and therefore the wind is going a different way. Would that be the reason?

I could verify that idea if only I could find the bloody reverse gear, where do they hide it ?

[faantjie]

I don't know why but have noticed the same thing on the Alp.

[captaincaveman]

ive noticed it on every vehicle ive had(bike or car) always seens to run better in cold, is it cause the air is denser and therefore more air per bang? and therefore more power? also is the smoothness down to the fact that everythings tight before the heat makes all the metal expand a bit?

[Chad]

oils cooler as well so it thicker i suppose its a little bit of all these things

[faantjie]

If only I could be so smooth in the mornings

[Dilbert]

Yes, the motor does work better in the morning because of the cooler air (up to a point) and the way it combusts and pretty soon Jenna or someone will be along to give us a dissertation on exactly why

The other thing I find is that at 6:30 am there is a lot less traffic to hold you up than at 6:30 pm so you can go at your own pace and everything just feels smoother and nicer.

[djadams]

More power cos of cold air, smoother and quieter cos of cold (thick) oil.

Most powerful when air cold (dense), coolant cold (so charge doesn't get warmed up too much) and oil up to temperature (so thin and slippy).

Quietest and "smoothest" when oil cold (so thick and gloopy), air temp not really relevant, except that it has an effect on oil temp and coolant temps, obviously.

Last of trio is:

Most economical when air warm (reduced pumping losses), oil warm (thin, slippy), coolant hot (so not much heat robbed to coolant).

[GeoBloke]

More power cos of cold air, smoother and quieter cos of cold (thick) oil.

Most powerful when air cold (dense), coolant cold (so charge doesn't get warmed up too much) and oil up to temperature (so thin and slippy).

Quietest and "smoothest" when oil cold (so thick and gloopy), air temp not really relevant, except that it has an effect on oil temp and coolant temps, obviously.

Last of trio is:

Most economical when air warm (reduced pumping losses), oil warm (thin, slippy), coolant hot (so not much heat robbed to coolant).

Now that the mornings are cooler, I've been wondering why the @ is more "up for it" those first few miles. I put it down to the denser air yielding a bigger bang. Duh. I don't think your brain is as small as your avatar lets on, professor. Get on the wiki with a course on internal combustion physics. I'll sign up!