Anti-Freeze Question
Anti-Freeze Question
(OP)
Does anybody know where I can obtain the curve for pressure vs. boiling temperature of ethylene glycol at various concentrations? I am trying to determine the effect that putting a higher-pressure cap will have on the system's cooling capacity.
Thanks You.
-Reidh
Thanks You.
-Reidh





RE: Anti-Freeze Question
The manufacturer will most likely be a very large multinational petrochemical company.
They will probably have the info on their web site.
Regards
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RE: Anti-Freeze Question
I always attempt to do my due dilligence before posting so as not to waste other's time.
Thank you.
-Reidh
RE: Anti-Freeze Question
You could always set up a pressure cooker and a thermometer, a pressure gauge, and an adjustable pressure relief valve, then read the pressure and temperature as the valve cracked for various loads on the valve. A few points should soon make a curve obvious.
A bit of a hassle, but maybe quicker than further searches.
Regards
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RE: Anti-Freeze Question
If I can make time to set up that experiment, I will post the results here once I have completed.
Thanks again.
-Reidh
RE: Anti-Freeze Question
RE: Anti-Freeze Question
From Bosch handbook:
glycol %by vol. Boiling Pt. deg. C
0 100
10 101
20 102
30 104
40 106
50 108
Pressure effect (H2O only)
PSI Boiling Pt. deg. C
14.7 100
17.8 107
22.1 116
26 124
30 132
35 142
39.4 152
RE: Anti-Freeze Question
RE: Anti-Freeze Question
I am curious if I can extrapolate between these two tables? That is, if a 50% mix of water/coolant yields an 8% gain in boiling temperature, can I assume for example that at 22.1 inches of H2O the boiling point is approximately 125 C (116*1.08) for a 50/50 mix?
-Reidh
RE: Anti-Freeze Question
Here are two good charts that show boil and freeze performance with a 14-15psi cap. (Note that manufacturers do not recommend >70% glycol)
As for the pressure relationship, I have seen values from 0.5-3.25°F increase in the boiling point for every psi increase. Most are in the 2.5-3.25 range, but unfortunately none of them specified the exact conditions (H2O only, ethylene glycol/water mix, etc) A good rule of thumb seems to be ~3°F/psi.
Hope this helps. IceStationZebra
RE: Anti-Freeze Question
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Radiator Caps: In a cooling system, a higher pressure equates to a higher boiling point for the coolant. Higher coolant pressures also transfer heat from the cylinder heads more efficiently. We recommend using a radiator cap with the highest pressure rating that the radiator is designed to accept. In general, performance radiators will accept 22-24 PSI, and professional racing radiators will accept a 29-31 PSI.
The coolant will typically only build to 16-18 PSI, due to expansion up to 200°F. However, if the engine does overheat due to external factors, the pressure inside the cooling system could reach as high as 28 PSI. Once the radiator cap has opened and vented coolant, the engine will not cool down until it has been turned off. The radiator cap is basically a "safety valve", so always use the highest pressure radiator cap that the radiator will tolerate. If you are unsure of the pressure rating for your radiator, check with the manufacturer for the maximum recommended operating pressure.
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Summary
1. Higher pressure will help increase your boiling point as long as the cap doesn't open.
2. A higher pressure can not decrease your operating temp - provided your not currently experiencing boiling over :)
3. Most sites seem to indicate that the radiator is the weak link, though I would also be worried about the hose connections.
RE: Anti-Freeze Question
PSIG DEG F
0 224
1 228
2 231
3 234
4 237
5 240
6 243
8 248
10 253
12 258
14 262
16 266
18 270
20 274
22 277
24 280
25 282
RE: Anti-Freeze Question
Also, a couple more points
1. I noticed that the first chart has a slight error. The red line should start at 32deg-F with a 0% propylene glycol concentration (i.e. 100% water).
2. If you are working with a diesel engine with wet liners, higher pressure should help suppress the localized boiling and resulting cavitation erosion.
3. FYI - Water has a higher specific heat than an ethylene glycol or propylene glycol coolant mix. Therefore, it provides the best heat transfer performance in a cooling system. Glycol solutions are used to raise the boiling point (especially important for water pockets around the exhaust valves), provide anti-freeze protection, corrosion inhibitors to protect the metals in the cooling system, and a lubricant for the water pump. In terms of the relative heat transfer performance of ethylene glycol versus propylene glycol coolant bases, they are pretty much equal when mixes according to the manufacturers’ recommendations, usually a 50/50 water to glycol mix. Ethylene glycol coolant solutions provide slightly higher heat transfer performance over propylene glycol solutions at low coolant flow rates.
So....
- For maximum heat transfer performance in non-freezing climates (or racing) use water as a coolant with an additive to provide a corrosion inhibitor and water pump lubricant.
- For street vehicles use 30-50% ethylene glycol depending on lowest expected temperature. >30% will provided the needed corrosion protection and water pump lubrication. If a cooling system is marginal, only overheating on the hottest of days or while towing, increasing the proportion of water in the coolant or running straight water with an additive during the summer may solve the problem. Remember to run a standard 50/50 solution during the rest of the year.
- For extreme winter service use a 50-70% ethylene glycol coolant solution. Remember that the lower percentage of water will reduce the cooling capacity during warm weather.
IceStationZebra
RE: Anti-Freeze Question
This means a higher coolant temperature, but more boil over protection. A very slight power and fuel economy improvement might be a side benefit as the engine will have slightly better thermal efficiency.
Regards
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RE: Anti-Freeze Question
RE: Anti-Freeze Question
I was trying to reason in my head if there is an optimum coolant ratio for the best cooling - but my educated guess is that it depends on several variables. Its a balance between boiling point and heat transfer. I suspect the NASCAR boys run a 29-31psi cap to get a higher boiling point while running mostly water. On one coolant supplier's web site (I forget which) they were touting their super racing "coolant" which was really just an anti-corrosion/lubricant package - it didn't even affect the freeze point!
ICZ
RE: Anti-Freeze Question
RE: Anti-Freeze Question
I think it works. By lowering the surface tension, this should allow an infentesmal amount of better contact btw the coolant and the surfaces inside the cooling system. Hence incresing the heat transfer by conduction.
It made my daily driver coolant, (50/50 premix), get kinda gunky after 30,000mi. I quit using it.
Note the second paragraph is just a SWAG, it might mean nothing.
nick
RE: Anti-Freeze Question
I think you are correct.
Better heat transfer allows more cooling of the coolant in the radiator, but causes more heat to be transfered from the head and block. Result, similar final coolant temperature, but lower thermodynamic efficiency of the engine.
Just as well it makes negligible difference as water already has very good heat transfer.
Corrosion inhibitor and lubrication are certainly worthwhile attributes.
Regards
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RE: Anti-Freeze Question
RE: Anti-Freeze Question
http://www.evanscooling.com/main21.htm
Alternative to WW
http://www.thethirsks.co.uk/motormax/racing.php
RE: Anti-Freeze Question
RE: Anti-Freeze Question
RE: Anti-Freeze Question
Regards
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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.