froggy47

I was doing a radiator dump/refill on one of the trucks last week & got to reading the label on the Prestone antifreeze/coolant.

50/50 blend raises boil protection to 265F

70/30 blend raises boil protection to 276F (70 prestone/30 water)

Straight water (and a splash of water wetter) as we know boils at 212F.

So why do a lot of people on the forum claim that straight water cools better?

Leave out of the discussion the part where someone posts how dumping water on a track is better than dumping antifreeze/coolant on a track. Let's just talk about cooling.

Something about better heat transfer vs. the ultimate (boiling) failure of the coolant. I know steam (or super heated water vapor) doesn't conduct/transfer heat very well.

Educate me.

Scooter70

The boiling point of water increases when under pressure. I'm not positive as to the pressure of the C5's radiator cap, but 15psi is typical.

According to the chart below, 30psia (~15psig) pure water boils at 250*F.

http://www.engineeringtoolbox.com/bo...ter-d_926.html

brkntrxn

http://www.e30m3project.com/e30m3per...ter_wetter.htm


Seems to be a good explanation.

brkntrxn

This one makes my brain hurt.

http://www.dual-star.com/index2/Serv..._tech_info.htm

froggy47

Mostly about water wetter, but this section gets to my question.

It's a matter of "heat transfer" vs. "boiling point" being two different areas of importance in the overall cooling system function.

Thank you.

An additional benefit of using "Water Wetter" (in conjunction with 100% water) in you cooling system is that water has an extremely high heat capacity. Thus a gallon of 100% water can carry more heat away from you engine than an equivalent gallon of 50/50 water and coolant. Water also has a high thermal conductivity which increases the convection of heat away from the coolant passage walls and into the free stream of the liquid flowing through the passages.

"Water Wetter" does not increase the boiling point of water. Standard automotive coolant does increase the boiling point of the mixture above that of 100% water. But remember that if your cooling system is operating properly, it should never get hot enough to boil (I mean BOIL, not just localized boiling). Raising the boiling point of the coolant in passenger cars is primarily a safety measure, so that if the cooling system is over stressed (climbing a hill on a hot day with AC on), it will not boil over. On performance cars the primary duty of the cooling system is to keep the engine in its optimum temperature range. This is best accomplished with 100% water, because its high heat capacity makes it very efficient at transferring heat.

Performance cars often run relatively high cooling system pressures. This also raises the boiling point of the coolant. But the high system pressure is not used to avoid boiling so much as to allow the engine to operate at a higher temperature for reasons of efficiency. A higher cooling system bulk temperature also allows the use of a smaller radiator (there is a greater driving force to transfer heat from the coolant to the free stream air). Take a look at the E30 M3's "tiny" radiator and you will see what I mean.



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froggy47

Thanks!

crease-guard

http://en.wikipedia.org/wiki/Boiling-point_elevation

You also have to take into account PV=nRT for the steam portion of the contained system.

kverges

I am fairly confident water has a higher (like twice) heat capacity than ethylene glycol and is therefore better at absorbing heat per unit change in temperature. Boiling point is not a factor unless, at the operating pressure of the system, you are exceeding the boiling point of the coolant and then there are a host of other problems.

db2xpert

Certainly explains why we would like to use only water with water wetter from a cooling perspective.

So, if we live where we don't have to be concerned with freezing temps, what should be added to the coolant to provide the necessary corrosion resistance for the aluminum block and heads?
How much, and how does that affect cooling ability versus plain water + water wetter?

jlutherva

I was told by my friendly NAPA guy that Water Wetter has additives to protect against corrosion. In addition, I flushed and refilled w/ distilled water rather than tap water.

It's very time consuming to flush all of the antifreeze out of a C6Z

Jim

Maynor29

Worth a read and it's LSx specific.

http://www.pirate4x4.com/tech/billavista/Cooling/

You can jump down to the water section if you don't feel like reading the entire cooling system tutorial. Hint: it's all about specific heat capacity.

John

Screamin Z

Plus.. If you blow a radiatior hose on the track, your friends on track would much rather run through water instead of antifreeze!

froggy47

Great link.

froggy47

I did actually cover this in the original post. I went back and put it in bold.

rfn026

Here's an article I did on cooling systems a few months back. I was sort of surprised to see how hot race cars are running today. They run a lot of pressure and a few chemicals that act as a surfactant. Keep in mind that anti-freeze already has some surfactant.

Most folks seem to feel you need to be in the 210-degree range to make power. Some are running at 240-degrees but that's really pushing the envelope.

Richard Newton

FASTFATBOY

Always put water pump conditioner in a straight water system. Prestone makes it, cuts down on corrosion and lubes the water pump seals. It's kinda white and milky looking.

Bill Dearborn

Best information I have is from this Wikipedia write up: http://en.wikipedia.org/wiki/Ethylene_glycol . The pertinent section says:

Coolant and heat transfer agent

The major use of ethylene glycol is as a medium for http://en.wikipedia.org/wiki/Convective_heat_transfer in, for example, automobiles and liquid cooled computers. Ethylene glycol is also commonly used in chilled water http://en.wikipedia.org/wiki/Air_conditioning systems that place either the chiller or air handlers outside, or systems that must cool below the freezing temperature of water. In http://en.wikipedia.org/wiki/Geothermal_heating/cooling systems, ethylene glycol is the http://en.wikipedia.org/wiki/Fluid that transports heat through the use of a http://en.wikipedia.org/wiki/Geothermal_heat_pump. The ethylene glycol either gains energy from the source (lake, ocean, http://en.wikipedia.org/wiki/Water_well) or dissipates heat to the source, depending if the system is being used for heating or cooling.
Pure ethylene glycol has a specific http://en.wikipedia.org/wiki/Heat_capacity about one half that of water. So, while providing freeze protection and an increased boiling point, ethylene glycol lowers the specific heat capacity of water mixtures relative to pure water. A 50/50 mix by mass has a specific heat capacity of about 3140 J/Kg C (0.75 BTU/lb F) three quarters that of pure water, thus requiring increased flow rates in same system comparisons with water. Additionally, the increase in boiling point over pure water inhibits nucleate boiling on heat transfer surfaces thus reducing heat transfer efficiency in some cases, such as gasoline engine cylinder walls. Therefore, pure ethylene glycol should not be used as an engine coolant in most cases.

I had personal experience with this about 30 years ago. My wife had an 81 VW Rabbit Diesel that had to have the two year coolant change that is required with standard antifreeze. To get a 50/50 mix required less than a jug of antifreeze but I just dumped the whole thing into the radiator before I added water. Didn't really notice anything right away but the next winter the heater wouldn't work. Those small 4 cylinder diesels didn't produce much heat (especially when idling in -10 degree weather while waiting to pick up my daughter from her weekly ski club trip) so it was very noticeable when the heater stopped working altogether when idling in really cold temps. After checking everything several times I took it to the dealer. Mechanic tested the coolant and found the freeze point was somewhere around -50 and the boiling point was much higher than required. He drained some coolant added water to bring the mix to 50/50 (-34 degree freeze point) and the heater started working again.

Bill

froggy47

Great example of vw heater not working.

FASTFATBOY

You also have to consider local hotspots on cylinder walls running straight water, straight water will boil itself away from the cylinder wall quicker than when it's mixed with coolant.

This will cause detonation.

TripleAstyle123

If you live in an area that freezing conditions are not possible then you should run 100% water. Add the "water wetter" to prevent corrosion, which is the 2nd goal of anti-freeze after preventing "freezing" of the fluid. This will give the best heat transfer of fluid. Anti-freeze does exactly that, prevents freezing at less than 32F (pure water), but at the cost of heat capacity of the fluid. Essentially pure water can absorb more heat than a water/glycol/antifreeze mix but pure water lacks the benefits of your home water softener preventing build-up of minerals in your engine(water wetter supposedly makes up for this). I am in MN so I stick to 50/50 and run fine temps but pure southern track cars make no sense in running anti-freeze unless GM motor seals require it?!!?