# cold start vs warm start for cars **URL:** \ **Category:** Factual Questions\ **Created:** [November 22, 2013, 7:36pm UTC](https://boards.straightdope.com/t/cold-start-vs-warm-start-for-cars/674556 "2013-11-22T19:36:21Z")\ **Posts on this page:** 1\ **Showing post:** 7
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [November 23, 2013, 3:39am UTC](https://boards.straightdope.com/t/cold-start-vs-warm-start-for-cars/674556/7 "2013-11-23T03:39:27Z")
> [@Crafter\_Man](#): > > At startup, and for a few minutes afterwards, the cylinder walls are cold. Some of the fuel condenses onto the cylinder walls and runs down into the oil pan via gravity. It doesn’t _condense_ on the cylinder walls - it never evaporated in the first place. Gasoline is a blend of many different hydrocarbons that evaporate over a range of temperatures. When you inject it into the intake port of a hot engine, all of it evaporates quite readily and burns completely; you only need to inject exactly the amount that’s going to burn. When an engine is cold, only the lighter hydrocarbons evaporate, leaving the heavier ones to remain as a liquid. You have to inject extra fuel so that you can evaporate enough of the light hydrocarbons to form a combustible mixture, and the heavier hydrocarbons get drawn into the combustion chamber in liquid form and splatter against the cylinder walls. Then the piston moves upward, and those HC’s collect at the piston rings, diluting the tiny amount of oil that’s there, reducing its ability to lubricate the rings and prevent wear. If you subject the engine to heavy loads (i.e. stomp on the gas) during this period of time, you may cause metal-to-metal contact between the rings and the cylinder bore, causing wear. --- _[View the full topic](https://boards.straightdope.com/t/cold-start-vs-warm-start-for-cars/674556)._