Porsche 911 SWAP Oil Temp Issue
12-21-2010, 08:42 PM
#22
TECH Senior Member
12-22-2010, 01:32 PM
#23
I forgot to add that water is actually supposed to be the most efficient medium for transferring heat, but you do need to add something to lubricate the system. I plan to run 75%/25% water to Porsche (Pink) antifreeze.
Mark
Mark
12-22-2010, 09:22 PM
#26
So Dexcool has an increased boiling point of 228, and the LS1 uses a 18PSI coolant pressure, which would give us an actual boiling point of 282... Thats even better than your spec!!!
Here is an article that explains really well why distilled water is the most efficient "Coolant"
And this is a small portion of it that explains it
Heat (or heat energy) is measure in units called British Thermal Units (or BTUs). A BTU is the amount of energy required to raise 1 pound of water 1°F.
Without knowing anything about thermodynamics, it's obvious that the best coolant is one that can absorb and give off the most heat energy per degree of temperature change it experiences - in other words it should be able to absorb and carry away a lot of heat energy without getting too hot itself. This property is called "specific heat". A liquid's specific heat is the number of BTUs it takes to raise the temperature of one pound of that liquid 1° F. In other words, the higher a liquid's specific heat, the more heat energy it can absorb per degree of temperature rise. We want the coolant to absorb a lot of heat energy while suffering the lowest temperature rise possible - that way the coolant can carry away the most heat without getting too hot itself and boiling. If the coolant boils it becomes a vapour (gas) and is now useless to us.
It turns out that plain old distilled water has the highest specific heat of all liquids commonly used for coolant. Water has a specific heat of 1 - meaning one pound of water can absorb 1 BTU for a temperature increase of 1° F.
A 50/50 Ethylene Glycol / water mix has a specific heat of 0.5, meaning it takes only 0.5 BTUs to raise the temperature of 1 pound Ethylene Glycol / water mix 1° F.
A 50/50 Propylene Glycol / water mix has a specific heat of only 0.3.
Therefore, it takes twice as much heat to raise a pound of water 1° F than a 50/50 Ethylene Glycol mix; and over three times as much heat to raise a pound of water 1° F than a 50/50 Propylene Glycol mix.
Ultimately, what this means is that straight water can carry away 50% more heat than 50/50 Ethylene Glycol mix and 70% more heat than 50/50 Propylene Glycol mix per degree per unit volume.
Of course, how much heat a liquid can absorb without boiling is also a function of the pressure acting on that that liquid. The boiling point, also called "vapour point" is that temperature where a particular liquid turns to vapour - which we don't want.
Without knowing anything about thermodynamics, it's obvious that the best coolant is one that can absorb and give off the most heat energy per degree of temperature change it experiences - in other words it should be able to absorb and carry away a lot of heat energy without getting too hot itself. This property is called "specific heat". A liquid's specific heat is the number of BTUs it takes to raise the temperature of one pound of that liquid 1° F. In other words, the higher a liquid's specific heat, the more heat energy it can absorb per degree of temperature rise. We want the coolant to absorb a lot of heat energy while suffering the lowest temperature rise possible - that way the coolant can carry away the most heat without getting too hot itself and boiling. If the coolant boils it becomes a vapour (gas) and is now useless to us.
It turns out that plain old distilled water has the highest specific heat of all liquids commonly used for coolant. Water has a specific heat of 1 - meaning one pound of water can absorb 1 BTU for a temperature increase of 1° F.
A 50/50 Ethylene Glycol / water mix has a specific heat of 0.5, meaning it takes only 0.5 BTUs to raise the temperature of 1 pound Ethylene Glycol / water mix 1° F.
A 50/50 Propylene Glycol / water mix has a specific heat of only 0.3.
Therefore, it takes twice as much heat to raise a pound of water 1° F than a 50/50 Ethylene Glycol mix; and over three times as much heat to raise a pound of water 1° F than a 50/50 Propylene Glycol mix.
Ultimately, what this means is that straight water can carry away 50% more heat than 50/50 Ethylene Glycol mix and 70% more heat than 50/50 Propylene Glycol mix per degree per unit volume.
Of course, how much heat a liquid can absorb without boiling is also a function of the pressure acting on that that liquid. The boiling point, also called "vapour point" is that temperature where a particular liquid turns to vapour - which we don't want.
Mark
12-22-2010, 09:40 PM
#27
As a side note i was partially incorrect. 
With all my training i had never heard mention of coolant actually significantly raising the boiling point, but because I found the specs for Dexcool, I wanted to find the specs for the Porsche Fluid I am going to use, as it doesnt tend to Gel like Dexcool, and I have it basically at my disposal... Well Porsche Is basically A higher quality VW G12 Spec coolant, and its boiling point is....... Greater than 320F.... Thats almost 100F higher than Dexcool... As usual its really hard to find specs on anything Porsche, but here is the Mobil one equavelent spec info
LINK
Mark
With all my training i had never heard mention of coolant actually significantly raising the boiling point, but because I found the specs for Dexcool, I wanted to find the specs for the Porsche Fluid I am going to use, as it doesnt tend to Gel like Dexcool, and I have it basically at my disposal... Well Porsche Is basically A higher quality VW G12 Spec coolant, and its boiling point is....... Greater than 320F.... Thats almost 100F higher than Dexcool... As usual its really hard to find specs on anything Porsche, but here is the Mobil one equavelent spec infoLINK
Mark
12-23-2010, 11:32 AM
#28
Definitely water will cool the best but I have always been interested in the gain/loss of using just water with an additive. Even though the engine will cool more efficiently with just distilled water it also boils at a lower temp and some have also mentions evaporation within the cylinder heads where temperatures are even greater therefor creating air and excessive pressure issues. With the use of coolant i believe you overall average temp may remain higher but overall stability of the system may outperform just water. Whats your thoughts? What are the temperature goals that are trying to be reached?
12-24-2010, 08:31 AM
#29
Getting some great feedback on this and appreciate everyone's comments, I did some more testing yesterday and here are the results:
50/50 DI Water + Dexcool + 160 T-stat
First test: 30min idle time while sitting in the garage with no incoming air (Outside Temp 70F). Fan's pulling in air and pushing over the intake and engine. Temp range after heated up was 186~190F. Average coolant temp @ 188F.
After 30min of idle time I did my last minute Christmas shopping and drove the car around town for +2hr, as you can imagine traffic was horrible but I did get a couple of open stretches and back roads where I could nail down the pedal.
During this time the engine did not exceed 220F and averaged 210F while cruzing. While in traffic at a light the temps would begin to fall under 200F.
Oil temp once engine is heat soaked is around 245F.
Overall the system is maintaining steady temps and is able to suck out the heat from the radiator when needed.
I will keep the current mixture till summer time and see how it holds up in 98F Florida weather.
50/50 DI Water + Dexcool + 160 T-stat
First test: 30min idle time while sitting in the garage with no incoming air (Outside Temp 70F). Fan's pulling in air and pushing over the intake and engine. Temp range after heated up was 186~190F. Average coolant temp @ 188F.
After 30min of idle time I did my last minute Christmas shopping and drove the car around town for +2hr, as you can imagine traffic was horrible but I did get a couple of open stretches and back roads where I could nail down the pedal.
During this time the engine did not exceed 220F and averaged 210F while cruzing. While in traffic at a light the temps would begin to fall under 200F.
Oil temp once engine is heat soaked is around 245F.
Overall the system is maintaining steady temps and is able to suck out the heat from the radiator when needed.
I will keep the current mixture till summer time and see how it holds up in 98F Florida weather.
