Waterless Coolant
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The table shows what would happen at 15 psi, namely that the temperature would be 129. According to the quote below (post #85 in this thread) it IS meant to happen in the car.
So, what are the facts here? Is 129 C damaging or is it not?
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The table is correct as written. There is no connection between the boiling point of coolant and the temperature that an engine runs at. The thermostat regulates coolant flow through the rad with a target of 95ish. If this set point is exceeded the fan(s) will come into play as required. If the fans are unable to control the temp, then the PCM will step in as noted above. If all that fails the coolant may rise to it's eventual boiling point, whatever that may be.
Nominal system pressure of 15 psi is induced by the expansion of the liquid coolant as it warms with the engine. No boiling has taken place. Pressure above 15psi is vented by the rad cap. All liquids expand with temperature, including waterless coolant which is why the system must be modified to avoid pressure increase.
I'm honestly baffled over the confusion.
Nominal system pressure of 15 psi is induced by the expansion of the liquid coolant as it warms with the engine. No boiling has taken place. Pressure above 15psi is vented by the rad cap. All liquids expand with temperature, including waterless coolant which is why the system must be modified to avoid pressure increase.
I'm honestly baffled over the confusion.
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Someone may have to put me straight on this. Here's my understanding:
Radiator caps increase the boiling point of coolant by about 25 C. The cap is a pressure release valve, and on cars it is usually set to 15 psi.
When the coolant heats up it expands and, together with the increasing vapor pressure of the water, causes the pressure to build up. Happily, this pressure also increases the boiling point of the coolant.
The cap is the only place where this pressure can escape. At 15 psi, the spring valve opens, allowing coolant to flow into the overflow tank. When the radiator cools back down, the vacuum that is created sucks coolant back from the overflow tank to replace the liquid that was expelled.
So, auto systems ARE designed to operate at 15psi, and this pressure raises the boiling point of coolant to 129 C. I guess that if the overflow tank fills but the pressure keeps rising, that's when the system (i.e. coolant hoses) blows. Starting with the $27 valley pipe.
If so, a pressureless system with a coolant boiling point of over 180 C seems like the answer to the maiden's prayer, especially if the maiden's name is ""STR Valley Pipe". My only concerns are that:
(a) The temp gauge does not get stuck at Max all day long, and
(b) The coolant fan never turns off unless the ECU is reprogrammed.
I'm sure that Avos will be looking at both of those possibilities.
Radiator caps increase the boiling point of coolant by about 25 C. The cap is a pressure release valve, and on cars it is usually set to 15 psi.
When the coolant heats up it expands and, together with the increasing vapor pressure of the water, causes the pressure to build up. Happily, this pressure also increases the boiling point of the coolant.
The cap is the only place where this pressure can escape. At 15 psi, the spring valve opens, allowing coolant to flow into the overflow tank. When the radiator cools back down, the vacuum that is created sucks coolant back from the overflow tank to replace the liquid that was expelled.
So, auto systems ARE designed to operate at 15psi, and this pressure raises the boiling point of coolant to 129 C. I guess that if the overflow tank fills but the pressure keeps rising, that's when the system (i.e. coolant hoses) blows. Starting with the $27 valley pipe.
If so, a pressureless system with a coolant boiling point of over 180 C seems like the answer to the maiden's prayer, especially if the maiden's name is ""STR Valley Pipe". My only concerns are that:
(a) The temp gauge does not get stuck at Max all day long, and
(b) The coolant fan never turns off unless the ECU is reprogrammed.
I'm sure that Avos will be looking at both of those possibilities.
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Why would either of these occur?
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It is said that Evans runs at a higher temp than regular coolant. If this higher temp exceeds manufacturer expectations, it may cause the ECU to assume that the max has been reached, and send a message to the gauge, which seems to be stuck at Normal until it's too late. For the same reason, the ECU may decide that not enough cooling is being achieved, and keep the fan going.
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I'm sorry, but no, that's not what the table shows. It shows that if you increased the pressure to 15psi you would have to heat the fluid to 129 degrees to make it boil, not that raising the pressure would cause the temperature to rise to that. Your car should be running at the normal operating temperature which is usually around 90 degrees. If I saw anything approaching 130 degrees on my temperature guage I'd be parked at the side of the road waiting for the very nice man.
Last edited by Jerakeen; 11-25-2014 at 01:44 AM.
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Jumpin' Jag Flash (12-24-2014)
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In the case of our cars there is no air space in the cooling system to accommodate the expanding coolant. Were there no pressure release device (ex. a rad cap) the weakest link in the system would soon burst, most likely long before the engine attained normal operating temps. The weakest link might be a hose but could also be something far more expensive.
Here is a list of coefficients of expansion for common liquids
Volumetric - Cubical - Expansion Coefficients of some common Liquids
and a calculator
Volumetric - Cubic - Thermal Expansion
which indicates that plain water would increase in volume by a factor of 0.000214 for each degree C. Multiply this by the volume of liquid in the cooling system, times the difference in inital and final temps. That's how much coolant is vented by the rad cap into the reservoir each time the engine is brought up to temp. No boiling or steam involved.
The answer to Robin's statement If the answer is "in part due to expanding coolant", that might well explain the puzzle."
is 'all of it is due to expanding coolant.' The system achieves rated pressure 15 psi during normal warm up and maintains this level until shutdown and subsequent cool down.
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Jumpin' Jag Flash (12-24-2014)
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I'm surprised it is meant to run at 15psi. I thought that would be a max with normal pressure way below it (say half).
I also didn't know about any radiator cap; I just knew of the expansion (header) tank cap and that's a safety feature not expected to do anything in normal use AFAIK.
Seems to me that 15psi will gradually balloon aging hoses, which is what we see, and in due course failure, which again is what we see. So it all fits and reinforces my desire to get rid of the pressurised system or reduce the pressure as far as practicable.
I also didn't know about any radiator cap; I just knew of the expansion (header) tank cap and that's a safety feature not expected to do anything in normal use AFAIK.
Seems to me that 15psi will gradually balloon aging hoses, which is what we see, and in due course failure, which again is what we see. So it all fits and reinforces my desire to get rid of the pressurised system or reduce the pressure as far as practicable.
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One of my other car hobbies is old Corvettes. It's not rare to see a 40-50 year old example show up with an original hose or two still in place. Occasionally, we see an absolutely unused original spare tire that's never been removed from the holding tray under the gas tank. Although it may still hold pressure of 20-30psi, the external deterioration from heat, ozone, oxygen etc. makes it no longer safe to use. The insides of the tire are like new. Pressure is NOT the prime or exclusive cause of failure.
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As it happens I've seen ballooned hoses on other cars with pressurised cooling systems. I just replaced them as it was easy. It's not easy on the STR.