[s-cars] Wet Engine

[Cody Forbes]

I'll add to Bretts comments.

Work creates heat. An engine idling is barely working at all, maybe  
using 2% of it work capacity. An engine under load from driving gently  
during warmup uses a totally guestimated 40% of it's work capacity.  
More work, more heat. Until the thermostat opens you are heating a  
mass of metal and coolant with basically the same cooling capacity  
(airflow through the radiator doesn't matter until the thermostat  
opens) but by creating more heat by driving you heat that mass faster.

Besides increased wear from the bits not being at operating dimensions  
you have a lower oil pressure at idle than at... more than idle ;-).  
Also when an engine is cold it burns rich (adds excess fuel) because  
the fuel doesn't burn as well in a cold chamber as in a hot chamber  
(simplified, there are other reasons). This increases emissions of  
green house gasses. Making it even worse is the fact that the  
catalytic converter doesn't work cold so the extra greenhouse gasses  
just pass right on through. The ONLY way to warm up the cat is by  
increasing the exhaust gas temperature, which will NEVER happen at  
idle. Even sitting still in a traffic jam your cat will cool down  
below it's op temp.



-Cody (mobile)