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Why would BMW want the engine to run hotter?? eom (archive)

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Posted by Andy K. on August 03, 2001 at 12:54:00:

In Reply to: actually let me rephrase.. posted by Ox///M on August 03, 2001 at 10:44:01:

replace density with viscosity.. since I just remembered that density is not related to heat. actually strike all I just said.. I just had an epiphany. I was on the right track.. but not entirely. Because I thought of Aero Gel. It can hold ALOT of heat energy, but it is one of the least dense substances on earth. So lets think again.. The substance may be harder to heat and cool, not because of the density, but because of the viscosity. I think they test oil weight by heating it up, and then letting it run out a hole in a test device. Since oil thins when heat is applied, the rate of flow changes. So if the oil runs out of the hole fast, it gets a lower rating. (ugg, here is where I wish I took more advanced physics and chem classes) So.. we have a substance that is more viscous. Perhaps the density is that same, but the bonds are able to take more infrared energy, aka heat. I am also going to make the assumtion that it takes X amount of energy to move an electron to a higher level, and each level after, it takes (x)2 amount of heat... sorta like dB. It takes twice as much energy to go from 100 dB to 101 dB. (sheesh I'm really bsing now) So if the makeup of the oil allows for X amount of energy (X ends up being 260) then perhaps it takes twice as much energy to get to Y aka 270.

Also.. when I said friction, I didn't mean between engine parts.. I doubt there is more friction between engine parts.. But keep in mind, internal viscosity of the higher weight oil is greater.

Ok.. so I'm most likely wrong on 99% of this.. but I'm just trying to think this through..

Who is the chemist out there that can help?

Well, let's think here. 10w-60 is a thicker oil which has a greater density. So my thinking is that the density of the oil would make it more difficult to lose heat. Since heat is just energy then you would have to lose twice as much heat since you have twice as many molecules (lets just say that for this example). But in fact I wouldn't worry about it. Because to raise the temperature further, it would take much more energy.

I wouldn't be surprised if it runs hot since it's harder to cool, but I betcha it will not get much hotter... Also, I bet it takes more time to heat the oil than the 5w-30. I also don't think it means more friction.

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