Cooling Systems Questions

[dpantazis]

greeetings all-

i hope that the bearded one brought all your trucks something nice...

mine got a new 203 thermo on christmas eve. which got me thinking.
i know, when we start thinking, its a dangerous thing, but it's really a fundamentals type question.

what temperature does the cooling system run at? maybe those with real temp gauges can answer the question easiet.

when the motor is cold, the thermostat is closed and no coolant goes to the radiator.

after a while, the coolant warms up, say to 200 (simplistic), and the thermostat opens up, sending hot coolant to the radiator. but the coolant gets hotter than that right?

but the cooling system is essentialy a closed system. the motor generates heat as a byproduct of work. the radiator dissipates heat. the motor and the other components radiate excess heat as well... pressure builds up because the fluid is heating and expanding a little and the vapor pressure is building up. my cap says 16psi.

what is the 'normal' operating temperature for the motor? driving on the flats empty is propably the least taxing while towing through the mountains is propably the most demanding.

the glycol in the coolant lowers the freesing point and raises the boiling point, assumingly well beyond the limits of the operating temps.

what about the cap pressure? 15 psi for 'normal' atmospheric air. since the cooling system is closed (no openings to the outside air) does it mean that the internal pressure is actually 31 psi in the cooling system?

thanks

dennis

 

[DaveBen]

15 pounds over the atmosphere pressure, but you and the cap do not feel or see the atmoaphere pressure as we are in it. So 15 pounds over the atmosphere is 15 pounds. We do not add anything for the atmosphere. Clear???

Dave

 

[Ford_Forgotton]

Well, actually, the thermistant is not a true ON/OFF device. Its variable. It actually starts to open well before its rated temp. It should reach FULL OPEN at the rated temp.

This way, "hot" coolant is allowed to slowly start escaping the system, to be replaced by "cold" coolant from the radiator.

Putting in a "hotter" thermistat raises the overall temperature of the motor slightly, but still within operating range, just closer to Optimal than what ford decided.

The powerstroke cooling system is AMAZING! You can run in 110 degree heat with a "cold front" grille system on, and still keep cool.

Also, Diesels run best under a load. Daily driving is not what they were designed for. They were designed to GRUNT, and get HOT. a hot diesel is a happy diesel. Especially our trucks.

As for system pressure, I would assume the pressure ratings of the cabs are "sea-level" values. It is a mechanical spring inside, and atmospheric changes should have no effect on it. 15psi of pressure inside should be the same at sea-level as it as at 10,000ft. This is because the internal volume cannot change (other than some slight hose swelling). If the internal volume could change with altitude, then all bets are off!

 

[95_stroker]

Dennis,

Oh yeah, this is the good stuff now.................. I'm putting my thinking cap on here for a few minutes.

mine got a new 203 thermo on christmas eve. which got me thinking.
i know, when we start thinking, its a dangerous thing, but it's really a fundamentals type question.

what temperature does the cooling system run at?

A t-stat is a thermo-mechanical device, yours is 203°F so that means it opens up at or very near to 203°F irregardless of engine cooling system pressures. That is the temprature at which the engine will operate at. The cooling system will operate at slightly different temps than that for a few reasons. The top of the radiator will be at the 203° reading but the lower portion of the radiator that returns cooled water to the engine will be say 40° or 50° cooler than that. So to pinpoint at what temp the cooling system runs is difficult. And as you stated it will vary due to driving conditions and ambient temps. Can the coolant and engine run hotter than 203°? Yes it can. That falls back on driving conditions and ambient temps also. You touched on freezing and boiling points and the addition of glycol or ethylene glycol to the radiator. The glycol does infact increase the range of temps the "water" in our radiator can operate at without either turning into slush or vaproizing into steam. If you are pulling the living snot out of the truck across the Mojave Desert in July, there is a very good chance that your engine temp will be 250°+, thank your glycol for keeping the water in a liquid state since we all know that H2O boils at 212° @ atmoshperic pressure (sea level) which is 14.7 psig. This brings us to another question you raised........... pressures inside the system. Not only is the glycol inside your system helping to maintain a liquid state for your water at 250° so it the pressure on the system. I have a vessel outside (I am at work right now) with water in it and the temp on it is about 350° ~ 400°F, the working pressure is at 450 psig. Your cooling system is operating at 16 psig and that means that if you had pure water in there it would'nt boil until it reached approximately 215°~220°F. ( You can also boil water at 68°F if you pull a 28" hg vacuum on it,,,,,, but thats another whole conversation). So the pressure inside your cooling system is also holding the molecules of H2O from seperating and essentially boiling. The glycol changes the specific gravity which is what modifies the boiling/freezing point. The pressure inside your cooling system also increases the heat transfer from the engine block to the water and in the radiator it increases the heat transfer from the water to the air. It also aides your water pumps ability to pump water without the water cavitating on the impellar.

what about the cap pressure? 15 psi for 'normal' atmospheric air. since the cooling system is closed (no openings to the outside air) does it mean that the internal pressure is actually 31 psi in the cooling system?

By this point you will have noticed me typing psi as psig. These are the units in which viturally all pressure readings are interperted.

PSIG = Pounds per Sqaure Inch Guage, which means if you have a guage laying on your desk it will read "0" at atmospheric pressures.

PSIA = Pounds per Square Inch Absolute, this takes into account the 14.7 pounds of atmospheric pressure put on us by the earths gravitational pull or the weight of our atmosphere. PSIA is very rarely used in common every day applications. Your analogy of "if my cap says 16 psi then my radiator is at 31 psi" is an example (albiet incorrect) of PSIA. PSIA is used primarily in industrial process conditions. Basically, unless a gauge or instrument is specifically marked PSIA then assume it is PSIG such as our cooling systems.

Did I really just type all that?

Mike...............out

 

[DaveBen]

Good one Mike.

Dave

 

[Ford_Forgotton]

Just for point of reference. Our MAP sensors on our trucks (and I think the Exhaust backpressure sensor too) is calibrated for psiA. You'll notice that if you hook a scan tool to the truck with the engine off, the sensors read about 14.7psi

 

[95_stroker]

Just for point of reference. Our MAP sensors on our trucks (and I think the Exhaust backpressure sensor too) is calibrated for psiA. You'll notice that if you hook a scan tool to the truck with the engine off, the sensors read about 14.7psi

Excellent point Daryl..... MAP = Manifold Absolute Pressure.


I believe the EBPV is PSIG...... could be wrong though.

 

[Glassdude]

Nice explanation Mike. Now my head hurts but I think I got it

Mike

 

[dpantazis]

Thanks!

Mike-

Thank you for your explaination! It does help me understand things.

Does any one have a temp gauge that can post some example values of what the coolant temp is under certain circumstances?

I guess the other thing I am trying to find is the phase diagram for coolant. I have found plenty for plain water, solder, etc... but not for anything that is coolant related.

This weekend the truck is getting its coolant filter finished up and its first SCA test! Starting of the new year right...

Thanks again!

Dennis

 

[Tennessee Titan]

Dennis,

Oh yeah, this is the good stuff now.................. I'm putting my thinking cap on here for a few minutes.




A t-stat is a thermo-mechanical device, yours is 203°F so that means it opens up at or very near to 203°F irregardless of engine cooling system pressures. That is the temprature at which the engine will operate at. The cooling system will operate at slightly different temps than that for a few reasons. The top of the radiator will be at the 203° reading but the lower portion of the radiator that returns cooled water to the engine will be say 40° or 50° cooler than that. So to pinpoint at what temp the cooling system runs is difficult. And as you stated it will vary due to driving conditions and ambient temps. Can the coolant and engine run hotter than 203°? Yes it can. That falls back on driving conditions and ambient temps also. You touched on freezing and boiling points and the addition of glycol or ethylene glycol to the radiator. The glycol does infact increase the range of temps the "water" in our radiator can operate at without either turning into slush or vaproizing into steam. If you are pulling the living snot out of the truck across the Mojave Desert in July, there is a very good chance that your engine temp will be 250°+, thank your glycol for keeping the water in a liquid state since we all know that H2O boils at 212° @ atmoshperic pressure (sea level) which is 14.7 psig. This brings us to another question you raised........... pressures inside the system. Not only is the glycol inside your system helping to maintain a liquid state for your water at 250° so it the pressure on the system. I have a vessel outside (I am at work right now) with water in it and the temp on it is about 350° ~ 400°F, the working pressure is at 450 psig. Your cooling system is operating at 16 psig and that means that if you had pure water in there it would'nt boil until it reached approximately 215°~220°F. ( You can also boil water at 68°F if you pull a 28" hg vacuum on it,,,,,, but thats another whole conversation). So the pressure inside your cooling system is also holding the molecules of H2O from seperating and essentially boiling. The glycol changes the specific gravity which is what modifies the boiling/freezing point. The pressure inside your cooling system also increases the heat transfer from the engine block to the water and in the radiator it increases the heat transfer from the water to the air. It also aides your water pumps ability to pump water without the water cavitating on the impellar.



By this point you will have noticed me typing psi as psig. These are the units in which viturally all pressure readings are interperted.

PSIG = Pounds per Sqaure Inch Guage, which means if you have a guage laying on your desk it will read "0" at atmospheric pressures.

PSIA = Pounds per Square Inch Absolute, this takes into account the 14.7 pounds of atmospheric pressure put on us by the earths gravitational pull or the weight of our atmosphere. PSIA is very rarely used in common every day applications. Your analogy of "if my cap says 16 psi then my radiator is at 31 psi" is an example (albiet incorrect) of PSIA. PSIA is used primarily in industrial process conditions. Basically, unless a gauge or instrument is specifically marked PSIA then assume it is PSIG such as our cooling systems.

Did I really just type all that?

Mike...............out

Very nice write up, 'Stroker. If I may ask, why not just change your coolant over to Evans NPG and not have to worry anymore about SCA's, boiling/freezing point, green or gold coolant,etc? Just curious.