Discussion: Let's talk coolant

kenchan

DE- is your car a race car? are we really the ones not understanding?

DEpointfive0

In my mind it is, it's modded in such a way that it should be, lol
I just want to see others' logic

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Mandingo

What is in the waterless coolant? The structure of a molecule means everything in chemistry. Just bear with me. I live for this stuff and I'm bored at work. *takes a deep breath*

Ethylene glycol looks like this: HO-CH2-CH2-OH. And water looks like this: H-O-H (but with a bend)

Ethylene glycol is obviously the larger molecule. It has a carbon-to-carbon bond and interaction between its two -OH groups which limits bond rotation and vibration. For these reasons, the bonds contained within the ethylene glycol molecule are not as free to vibrate/rotate as the weaker bonds in the smaller H2O molecule.

Temperature is our measure of this molecular "vibration" (also called Brownian motion). So water (a very unique molecule actually) with its bent structure and multiple ways to vibrate and rotate does a better job of "picking up" Brownian motion from the metal in one area and transferring that vibrational kinetic energy to another metal surface (the radiator).

The trade-off of course, is that water has a lower boiling point than ethylene glycol. If you're still reading you are awesome. Ethylene glycol is larger than water and has more potential for intermolecular interaction with nearby ethylene glycol molecules (due to hydrogen bonding and London dispersion forces). This makes it much harder for EG to enter the gas phase since more heat energy would be required to break those bonds/interactions with nearby molecules. Water's intermolecular interactions, while still relatively strong, are not as strong as EG's. Therefore, water is more willing to enter the gas phase with less heat energy imparted to it.

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IDZRVIT

So, at the end of the day, we're concerned about the heat transfer rate of the coolant transferred into the metal radiator and the metal radiator fins transferring its heat into the air flowing across the surface. As long as the radiator can reject the heat of the coolant to the ambient air and keep the outlet temperature from the rad below the boiling point of the coolant, then the engine won't overheat assuming its in perfect order. Steady state, steady flow. That said, why would anyone want to increase the boiling point of the coolant to 375F when it's not necessary? Nice write up, btw.

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fzgood

Thank you for posting this. Easy to understand for my chemistry-hating brain. Finished reading even though I had my Brownian motion well before the end.

Redglare

ideally you want to increase the specific heat (c) of the solution to have the best coolant possible, however ethylene glycol has a reduced specific heat, so you want to mix it with water to increase the specific heat.

also have to consider that branching lowers the BP, hence why ethylene glycol is also picked over other alternatives.

also fun fact, even though ethylene glycol doesn't have the double bond between the vicinal OH's, the name retains ethylene because it was derived from an alkene.

TerribleONE

Subd

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7419sundat

Water has a better specific heat than Evans waterless coolant thus cooling better but needs needs pressure to increase the boiling point. That stuff is also super thick so it creates more drag on the pump. There's an article on the internet where they tested an ls engine heat, power etc, Evans vs water vs 50/50. They ended up losing power with waterless coolant.