Quote:
Originally Posted by TexasCotton
I put some Wetter Wet coolant additive with my Zerex 50/50. I guess I was a sucker for slick marketing...
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There's no slick marketing involved here, just a suboptimal application. I've used Water Wetter, Redline's product, in an RV when we went West, so I researched it at that time.
It starts with Thermodynamics, so I understand the reticence to dive in, but perhaps I can explain.
It starts with "heat capacity" defined as the "energy required to change a object's temperature." It's usually called "specific heat" as the amount of mass being heated matters, so we express it as energy/(mass x degree) or
Joules/(gram Kelvin). It's also calories and BTUs, although those terms have disappeared from technical usage,.
Water has a heat capacity of about 4 J/gK.
Propylene glycol is more like 2.5 J/gK, roughly 60% that of water
Mix the two and you get three things
- higher boiling point
- lower freezing point
- specific heat that's inbetween; 50/50 would be ~3.2 J/gK
You also get lubricants and anticorrosives in coolant to improve the reliability of the cooling system, but we'll assume those are unrelated to heat transfer in a new, clean system.
So a pure water cooling system has 25% greater heat transfer capability per gram than a 50/50 mix, but a narrower temperature operating range. So far, so good.
How does Water Wetter help? It decreases surface tension, so the resulting mix can't support bubbles as well.
That's important when you get water close to its boiling point, as boiling always starts as bubbles of steam that expand. That's really bad because steam has lower specific heat than coolant alone, so a steam bubble at a hot spot reduces heat transfer where it's most needed. It's not hard to see why that's a bad thing. Prevent bubbles from forming and the hot spot stays cooler, preventing bubbles from forming.
So why set up a cooling system like this? Weight and size.
Given the same radiator efficiency, a wetted-water engine cooling system needs a smaller radiator, a lower volume of liquid in the cooling system, and lower flow rates to transfer the same amount of heat. Plus all the positive benefits of pressurization remain, negating much of the boiling point elevation advantage of a mix.
Think RACE CAR; lighter weight, with less parasitic drain on engine power with nearly the same temperature gradient.
Also think LOW DRAG AERODYNAMICS.
Grill blocks reduce drag, but they also reduce radiator air flow and so thermal efficiency. Hucho shows how radiator air flow optimization can be a powerful tool for optimizing a body for low drag, and smaller give you more options. As a guy on the Corvette forum put it:
"Water cools WAY better than antifreeze. School of hard knox has let me master the auto cooling system,flow rate,rad thickness, copper,aluminum,flue width,airflow,and so on.As ive said in other posts I cooled a 575HP smallblock on a GM v6 radiator 1"1/2 inches thick. This thing wouldnt hit 200 for nothing."
If this all makes sense, you can see how there's no magic or snake oil involved, just as there's little to be gained unless you're re-optimizing your entire bodywork and cooling system, you rebuild the engine regularly, and it never gets cold where you live.
And it's not a panacea; our radiator still sprung a leak driving the RV up Rabbit Ears Pass!
Have fun,
Frank