- Messages
- 4,790
- Location
- Houston, TX
Here's a post from 2001 to the Supra community:
Why isn't it recommended to run 50/50 water/glycol ratios?
You only have to understand a little about heat transfer. It's basic algebra... and won't hurt a bit....promise. I've even left most of the units out to make things more readable.
Here's the simplified heat transfer equation for water based cooling systems:
GPM * deltaT * SH * 500 = BTU/hr
where:
GPM = gallons per minute of coolant flow
deltaT = the difference in temperature across your radiator
SH = the specific heat capacity of the cooling fluid.
Pure water has a specific heat of 1.0
Pure ethylene glycol has a specific heat of about 0.6
A 50/50 mix has a specific heat of about 0.75-0.80
500 = a constant to convert mass flow of water to volumetric flow
Btu/Hr = the rate that heat is removed from the engine and transferred to the environment via the radiator.
For our purposes, we have to remove heat (BTU's) from our engine to keep it from overheating and the water pump, radiator and fan do this for us. The pump circulates a certain GPM (gallons per minute), and the radiator and fan transfer the heat to the environment and gives us a certain deltaT between the hot water coming into the radiator and cooler water leaving. (The thermostat is in this loop and regulates the whole process to keep the engine from being cooled too much on cold days)
Now, if we used pure water in our cooling system, and the pump (for example only) circulates 100 GPM, and the radiator gives us 10 degrees deltaT, we'd have:
100*10*1.0*500 = 500,000 BTU/Hr
If we used pure ethylene glycol, instead of water, we'd have:
100*10*0.6*500 = 300,000 BTU/Hr
What's this mean? In real life, it means a pure glycol solution isn't going to remove nearly as much heat, as fast, from the engine as pure water and the engine will run hotter. As it runs hotter, (particularly the cylinder head) it will be more prone to detonation, and the end result will be that the ECU pulls the timing.
Result is reduced power, poor gas mileage, etc. This becomes more and more important as you modify your engine and produce more power. More output means more heat into the cooling system. Eventually you HAVE to increase the size of the radiator....
Bottom line(s):
1) Run as much pure water in your system as you can.
2) Run just enough glycol in your system, for your climate, to avoid boilover/freezing.
3) Be sure to use a corrosion inhibitor and water pump lubricant, as pure water has neither of these qualities, and glycol is deficient in both.
Redline claim their Water Wetter has sufficient corrosion inhibitor and water pump lubricant to protect the cooling system, although it does not offer any protection against boilover/freezeups.
Why isn't it recommended to run 50/50 water/glycol ratios?
You only have to understand a little about heat transfer. It's basic algebra... and won't hurt a bit....promise. I've even left most of the units out to make things more readable.
Here's the simplified heat transfer equation for water based cooling systems:
GPM * deltaT * SH * 500 = BTU/hr
where:
GPM = gallons per minute of coolant flow
deltaT = the difference in temperature across your radiator
SH = the specific heat capacity of the cooling fluid.
Pure water has a specific heat of 1.0
Pure ethylene glycol has a specific heat of about 0.6
A 50/50 mix has a specific heat of about 0.75-0.80
500 = a constant to convert mass flow of water to volumetric flow
Btu/Hr = the rate that heat is removed from the engine and transferred to the environment via the radiator.
For our purposes, we have to remove heat (BTU's) from our engine to keep it from overheating and the water pump, radiator and fan do this for us. The pump circulates a certain GPM (gallons per minute), and the radiator and fan transfer the heat to the environment and gives us a certain deltaT between the hot water coming into the radiator and cooler water leaving. (The thermostat is in this loop and regulates the whole process to keep the engine from being cooled too much on cold days)
Now, if we used pure water in our cooling system, and the pump (for example only) circulates 100 GPM, and the radiator gives us 10 degrees deltaT, we'd have:
100*10*1.0*500 = 500,000 BTU/Hr
If we used pure ethylene glycol, instead of water, we'd have:
100*10*0.6*500 = 300,000 BTU/Hr
What's this mean? In real life, it means a pure glycol solution isn't going to remove nearly as much heat, as fast, from the engine as pure water and the engine will run hotter. As it runs hotter, (particularly the cylinder head) it will be more prone to detonation, and the end result will be that the ECU pulls the timing.
Result is reduced power, poor gas mileage, etc. This becomes more and more important as you modify your engine and produce more power. More output means more heat into the cooling system. Eventually you HAVE to increase the size of the radiator....
Bottom line(s):
1) Run as much pure water in your system as you can.
2) Run just enough glycol in your system, for your climate, to avoid boilover/freezing.
3) Be sure to use a corrosion inhibitor and water pump lubricant, as pure water has neither of these qualities, and glycol is deficient in both.
Redline claim their Water Wetter has sufficient corrosion inhibitor and water pump lubricant to protect the cooling system, although it does not offer any protection against boilover/freezeups.
