Look At My Temperature!
07-13-2011, 03:39 AM
#46
I think we need a clarification here-
If there is a leak then lower pressure can make the water hotter. It's not that water leaks out but the lower pessure that causes trouble.
Lower pressure will not make the car hotter. The inablility of the cooling system to reject the heat that is generated in the engine makes the car hotter. A lower pressure from a leak or compromised water pump will bring down the boiling point of coolant. This will cause problems because the coolant is more likely to flash and not be as effective since the heat transfer rate of a gas is only a fraction of that of a liquid on the same surface area. The boiling point of pure water is 212 F at atmospheric pressure (most 50/50 mixes boil around 220 F at atmospheric pressure). You can also add about 3 degrees F for every psi. It is unlikely that flashing of coolant is causing reduced efficiency and elevating your temperatures unless you have blocked passages.
If there is a leak then lower pressure can make the water hotter. It's not that water leaks out but the lower pessure that causes trouble.
Lower pressure will not make the car hotter. The inablility of the cooling system to reject the heat that is generated in the engine makes the car hotter. A lower pressure from a leak or compromised water pump will bring down the boiling point of coolant. This will cause problems because the coolant is more likely to flash and not be as effective since the heat transfer rate of a gas is only a fraction of that of a liquid on the same surface area. The boiling point of pure water is 212 F at atmospheric pressure (most 50/50 mixes boil around 220 F at atmospheric pressure). You can also add about 3 degrees F for every psi. It is unlikely that flashing of coolant is causing reduced efficiency and elevating your temperatures unless you have blocked passages.
Here is my observation from only 42 years of driving and fixing cars. Reduced pressure in the cooling system gets a car in trouble. Be it the fluid can escape which is why the pressure wont build up or reduced pressure doesn't allow the radiator and its flow rate to throw off the heat. Some cars removing the thermostat will doom the car to running hotter. A removed thermostat car doesn't warm up as fast and all dont run hotter while some might run cooler. 6 of 1 and half a dozen of another but when the pressure is low through the whole range of operating temp the cars headed to a high heat. Oh my could this be why the radiator caps and over pressures have a set range for bleeding off pressure?
Anyway a quick check of my seat of the pants theory is either remove the cap or leave it loose and hit the hwy like I have tried in emergencies running with a hole in the radiator. It keeps the pressure down so that the water doesn't jet out the hole as fast but..........emmm be ready for a boiling cooling system when the system isn't pressurized.
07-14-2011, 11:12 AM
#49
Pac 996- I am nto saying you are wrong. Actually you are correct in many of your observations.
Heat transfer in an engine is a function of flow of a fluid across the internal heated surface area of the engine. Flow is a function of a difference of pressures so if you are not producing pressure (such as having the cap off) there is may not be enough flow in some internal passages that require more pressure to produce adequate flow.
Heat transfer in an engine is a function of flow of a fluid across the internal heated surface area of the engine. Flow is a function of a difference of pressures so if you are not producing pressure (such as having the cap off) there is may not be enough flow in some internal passages that require more pressure to produce adequate flow.
07-14-2011, 09:38 PM
#50
Race Director
If the coolant temp continues to rise when it reaches 216F (102C) the fans are switched to high speed. They remain in high speed mode until the coolant temp drops to 205F. (I have observed this behavior in my 02 Boxster and my 03 Turbo using real time OBD data monitoring device connected to the OBD2 port.)
If the A/C is on the fans run all the time at low speed unless the coolant temp climbs to 216F at which time the fan speed switches to high speed.
Also, if the A/C is on the fan speed can switch to high if the A/C system obtains some high internal pressure threshold that arises I think when it is called upon to satisfy extraordinary cabin cooling demand.
Sincerely,
Macster.
