this arguement reminds me of the myth that a cup of warm water freezes faster then a cup of cold water when put in a freezer at the same time. i hope everyone here knows which one will freeze faster however some think that warm water cools faster then cold water and will therefor freeze first (seriously... i saw this on fox news in the morning and had to beat my head on the table for how stupid they were).

anyway, consider this: you turn a cold car on... you let the engine run 30 seconds while you slowly engage the clutch and roll back 10 feet. then you promptly shut the engine off.

your neighbor with the identical car turns his cold car on at the same time, lets it run for 15 minutes, drives it around the block, then parks it 10 feet behind where it originally was.

both you and your neighbor ran the car for at least 30 seconds cold. so whatever damage could be done was done to both your car and his. you turned your car off after 30 seconds, while his kept running. no longer was your car suspetable to further damage because it is no longer running. your neighbor on the otherhand keeps his car running for 15 more minutes meaning carbon buildup from exhaust, higher chance of getting in an accident once he leaves his driveway, more wear on the clutch from driving around, more damage to o2 sensors from exposing them to rapid head cycles, more money in gas, more miles on the car, etc. etc. etc. do what nolimit1320 said and just don't worry about it!!!!!!!!

 

Haha alright alright!!! Thanks guys I'm not going to sweat it anymore....my neighbor has an rx7 so his cars always broken but when its running it pwnsss

 

Actually, hot water does typically freeze faster than cold water... it's not as simple as you think... there's many factors when converting a substance from liquid to solid...

Cold water will form a thin layer of ice at the top of the surface fairly quickly, this thin layer of ice limits the amount of heat that can escape from the rest of the water below.

Also, hot water evaporates much much faster than cold water, so if the two amounts are the same when put into the freezer, the hot water will evaporate quickly and therefore, there will be less water to cool. Also, the engery needed in order for water molecules to evaporate into the air is released in the form of heat... so hot water looses it's heat energy much faster than cold water loses it's heat energy.

Another factor is that, hot water will bond more easily with the edges of its container... if the hot water is in 99.9999% contact with a cold container, it will be able to transmit it's heat energy into that container much more easily than the cold water, who's molecules may only be 98.88888% in contact with its container.

 

I agree with shameless to an extent. Since there is a higher 'delta-T' between the warm water temp and the ambient temp than with the cold water, heat transfer will occur more rapidly. However, as both of the cups cool, their respective delta-T's will get smaller and lessen the potential for heat transfer. It may be true that the cold water forms a film of ice on the top and that this acts as a barrier for heat transfer, but the warm will most likely do the same thing once it gets to that temperature; and it will arrive at that temperature after the cold water does because it needs to release more energy to get their. This is without taking into the effect of evaporation and the decreasing of the warm waters mass. My .02, not sure if thats exactly right tho; and it's completely off topic...

 

If you put warm and cold water in two ice cube trays and stick them in the freezer at the same time, the warm water will turn into ice cubes before the cold, but in the end, the cold ice will have more mass. Try it yourself.

 

Its the fact that there are unburnt fluids building up in various chambers of the engine that does the damage because the car never gets hot enough to burn them off

 

+1 on unburnt fluids and those side effects

 

What unburnt fluids? Like moisture? Where do you think that comes from? To save you the effort of guessing, I'll tell you.....when the car cools back down it condenses moisture. A simple "warm up" isn't likely going to evaporate that moisture, so all you're doing is creating more.