I plan on giving several posts about how higher altitudes effect your truck, including the cooling system discussed here, and future posts covering the turbo, engine, exhaust, and tires. Pic #1 is from my recent viewing of Old Faithful, and that's what started me thinking about boil over at higher altitudes. I asked our tour bus driver, and he said that during the summer months he see's several boil over's on the higher altitude passes every week. The quote below shows that boil over can happen to a PSD. Unfortunately, I never got any follow up on this event as it seems the truck driver boiled over as well, and hasn't been heard from since.

Ok, here's a quick overview of the other 5 pics, then comes the math and science behind them because this is very interesting stuff. Pic #2 gives boiling temps, Pic #3 gives RAM air pressure, which pushes an air flow through the radiator, Pic #4 gives air density, Pic #5 combines volume air flow and air density to give mass air flow through the radiator, and also gives RAM air pressure, and finally, Pic #6 gives heat removal by the radiator in terms of how much waste HP heat can be removed by the RAM air flow through the radiator.

Those who read my post about how you can breathe in outer space might recall that at sea level atmospheric air pressure of 14.7 psi, there's about 7.6 X 10^23 air molecules in each cubic foot (ft3) of volume. If you consider a cubic foot box of air, open at the top, this 14.7 psi in the box is caused by the combined weight of the entire column of air above the box. There are two competing forces which work in a balance to exactly maintain this 14.7 psi at sea level. Gravity is trying to cram as many molecules into the box as it can, and the thermal kinetic energy of the molecules makes them buzz around like a swarm of angry bees, and as many bees as possible are trying to get out of the box. These forces balance to the point where the bees that are trapped in the box have an average random velocity so that as they bang into the sides of the box, they exert an average force of 14.7 lbs on each square inch of surface area.

Now if you heat the box, the bees fly around faster, and some more manage to get out, so now there's fewer bees in the box, but the ones that remain are flying faster. The net result is that the faster aspect exactly balances the fewer aspect, so that as the bees bang into the sides of the box each one hits it with more force so that the bees collectively still exert exactly 14.7 psi of pressure. The only thing increasing the temp did was to reduce the density of the bees, not the pressure they exert. Now if your engine HP was determined by bee pressure instead of the number of bees, sucking in a fewer number of hot bees from under your hood wouldn't be a problem, oops, I'm not supposed to talk about that anymore. If you put a lid on the box, and kick it with some more heat, the bees can't get out, and they fly around even faster, and the pressure in the box increases to more than the 14.7 psi outside the box. But that's a subject for another post!

So what does a box of angry bees have to do with boil over? Well a box of hot water approaching the boiling point temp works kind of the same way. The atmospheric pressure (due to gravity) on the surface of the water is trying to keep the H20 molecules in the box, and their ever increasing thermal velocity is trying to let them escape at the surface. A more scientific definition of boiling point is that it's the temp at which the vapor pressure of the water is equal to the external pressure. In this example, the external pressure is the 14.7 psi of atmospheric pressure. As you go up in altitude to say 10 K ft, the 14.7 psi is reduced to only 10.1 psi because there's now much less weight of air above the box, and since the external force stopping the H20 molecules from escaping is less, the temp at which the water boils is also reduced. You also need to know about the bees, because as they swarm through your radiator core they absorb a lot of heat, and carry it away with them.

Now water doesn't just sit there nice and quiet until its boiling temp is reached, and then go crazy, water starts doing things that have adverse impacts on cooling your engine at temps well below its boiling point. Here's some benchmarks, where all reference temps apply at sea level, and are even lower at higher altitudes.

Poach - 160 to 180°F. The water is beginning to move, to shiver.

Simmer - 185 to 200°F. There is movement, and little bubbles appear in the water.

Slow boil - 205°F. There is more movement and noticeably larger bubbles.

Real boil - 212°F. The water is rolling, vigorously bubbling, and steaming.

When bubbles start to form, heat conduction is reduced, and the coolant can't transfer waste heat from the engine as well, and can't shed the waste heat in the radiator core as well. If your coolant starts forming bubbles, and you don't do something to reduce the waste heat load on your cooling system, like shut off the A/C, let off the throttle some, shift to a lower gear, etc.., it's a rapid downhill cascade of the bubbles reducing cooling efficiency, this increases coolant temp and larger bubbles form which further reduces cooling, and then comes the steam, etc... and eventually boiling.

All the curves in pic #2 are the temps for a full blown rolling boil, and as discussed above, bad things can start to happen at temps 20 degrees or lower than for a full boil. Plain water would just barely avoid these effects at 0 K ft, and at 7K ft would come to a full boil at less than 200 F.

The next curve up (green) is for a 50% mix of water and the green Ethylene Glycol coolant that I use in my early 99. Now this is interesting, because alcohol has a lower boiling point than plain water, at sea level, about 175° F for alcohol compared to 212° F for water. But if you mix them you get a higher boiling temp for the mix, as is shown in the table below.

Boiling Point Ethylene Glycol Solution

<TABLE class=large><TBODY><TR><TD colSpan=9>Boiling Point</TD></TR><TR><TD bgColor=#ffffcc colSpan=2>Ethylene Glycol Solution


(% by volume)

</TD><TD bgColor=#ffffcc>0</TD><TD bgColor=#ffffcc>10</TD><TD bgColor=#ffffcc>20</TD><TD bgColor=#ffffcc>30</TD><TD bgColor=#ffffcc>40</TD><TD bgColor=#ffffcc>50</TD><TD bgColor=#ffffcc>60</TD></TR><TR><TD bgColor=#99ff99 rowSpan=2>Temperature</TD><TD width="10%" bgColor=#99ff99>(<SUP>o</SUP>F)</TD><TD width="10%">212</TD><TD width="10%">214</TD><TD width="10%">216</TD><TD width="10%">220</TD><TD width="10%">220</TD><TD width="10%">225</TD><TD width="10%">232</TD></TR><TR><TD width="10%" bgColor=#99ff99>(<SUP>o</SUP>C)</TD><TD width="10%">100</TD><TD width="10%">101.1</TD><TD width="10%">102.2</TD><TD width="10%">104.4</TD><TD width="10%">104.4</TD><TD width="10%">107.2</TD><TD width="10%">111.1</TD></TR></TBODY></TABLE>

It's a long complicated story why this happens, involving molecular effects at the surface, depression of vapor pressures, etc..., but lets just say that it's kind of like putting a piece of 1/4" mesh on the top of the box. The bees cans still get out, but you have to heat them a little more to get them riled up and flying a little faster before they can get through the mesh.

It's also of interest that the specific heat capacity of an ethylene glycol water solution is less than that of plain water. Therefore, to maintain a given amount of heat transfer capacity, the circulated volume of coolant must be increased. In a 50% solution the specific heat capacity is decreased by about 15% to 20%, and this must be compensated by circulating more fluid. This is shown in the table below.

Flow Increase Needed for 50% Ethylene Glycol Solution

Flow increase for 50% ethylene glycol solution compared with water is indicated in the table below:

<TABLE class=large><TBODY><TR><TD bgColor=#99ff99 colSpan=2>Fluid Temperature</TD><TD bgColor=#ffffcc rowSpan=2>Flow Increase


(%)

</TD></TR><TR><TD bgColor=#99ff99>(<SUP>o</SUP>F)</TD><TD bgColor=#99ff99>(<SUP>o</SUP>C)</TD></TR><TR><TD width="33%">40</TD><TD width="33%">4.4</TD><TD width="33%">22</TD></TR><TR><TD>100</TD><TD>37.8</TD><TD>16</TD></TR><TR><TD>140</TD><TD>60.0</TD><TD>15</TD></TR><TR><TD>180</TD><TD>82.2</TD><TD>14</TD></TR><TR><TD>220</TD><TD>104.4</TD><TD>14</TD></TR></TBODY></TABLE>

By adding a 5 psi pressure cap, water boils at about 16 F higher than it naturally would at a given altitude, for a 10 psi cap it boils at 28 F higher, and for the 15 psi cap shown in the pic, water boils at a 38°F higher temp. To avoid the potential for getting bubbles in your coolant, it's best to stay 25 F below the top line, which at 10 K ft is a max coolant temp of about 220 F.

Pic #3 gives the RAM air pressure at the front of the A/C condenser for a 70 MPH speed. As can be seen, hotter ambient air temps and higher altitudes result in less RAM pressure, and this in turn results in less volume flow through the radiator. The lime curve that slopes to the right, gives the % reduction in RAM air pressure as one moves up in altitude at a constant ambient temp. At 6 K ft, for example, the pressure is reduced by about 20% from its sea level value.

It's also important to note that RAM air pressure is proportional to MPH^2 so that if you gear down to pull a grade at 35 MPH the pressure is reduced by a X4 which drastically reduces the RAM air flow, and this heats up the engine compartment to 205 F and makes the fan clutch lock up to provide forced air flow.

 

The RAM air pressure effects the CFM volume flow of air through the radiator, and pic #4 gives the air density, and both of these combine to determine the mass air flow (MAF) which determines the net RAM air heat removal capability of the radiator. As can be seen in pic #5, at 60 MPH the MAF varies from about 700 lb/min at 0 K ft to about 460 lb/min at 10 K, which is more than a 30% reduction in RAM air heat removal capacity.

The heat capacity of air is 1J/g/K=0.2388 Btu/lb/F. For example, if 100 lbs of air flows through the radiator, and it undergoes a temp rise of 50 F, that 100 lb mass of air removed 1,194 Btu of waste heat from the radiator. If 100 lb/min flows through with a 50 F temp rise 1,194 Btu/min of waste heat is being removed, and since 1 HP=42.167 Btu/min, this is 28.3 HP of waste heat is being removed.

It's more convenient to measure the waste heat removal in HP, because as I've already discussed in the unmentionable Intake CFM shootout thread, an engine puts out a lot of HP waste heat which makes the engine compartment air very hot. Typically for every 1-HP at the flywheel, an engine puts out another 1-HP of waste heat into the coolant, and yet another 1-HP of waste heat into the exhaust. Of course a lot of the exhaust waste heat is radiated back into the engine compartment from the turbo case and exhaust manifolds, and then there's also the waste heat from the A/C condenser when you run it, and from the IC when you're pushing the turbo hard to pull a grade.

Pic #6 gives an estimate of the waste heat removal HP due to RAM air flow only for the conditions shown in the inset, a 1.8 ft2 effective grill capture area which I measured for my truck, an ambient air temp of 80 F which is typical when I tow, and an estimated 50 F temp rise as the RAM air flows through the radiator core. At 62 MPH and 0 K ft the curve indicates a 200 HP heat removal capacity which is sufficient for 200 HP at the flywheel. At 7.5 K ft where I was at Yellowstone, that's down to 150 HP, and if you push the engine harder than that the cooling fan has to make up the difference. That's why the cooling fan runs more at altitude, and that's why I did the Genedad 2 mod before I left Yellowstone to get more pure RAM air cooling so that darn fan doesn't run as much.

It would be nice if someone could provide the CFM flow spec for the radiator cooling fan under various conditions, like when it's fully locked up vs RPM or whatever anyone can find out about it. Then I can add the forced CFM air flow to the RAM air flow and have a more complete model of the PSD cooling system.

In closing I'll just point out another of life's little quirks, like mixing a lower boiling point liquid with water to increase its boiling point! Consider that the heat capacity of air is X2.65 times higher than that of copper, but only 25% that of liquid water. Hydrogen has a heat capacity that's more than X14 higher than for air! I could probably explain all this with bees if asked, but it would take some time to do it.

 

Gene, not sure how far you want to go with the CFm measurement, but in the Grainger catalog, you can pick up a digital vane meter with rs232 cable+software for 210.00. If you choose to go to the Electronic catalog, part number is 4gu19. I would volunter, but I am with out the lap top, nor the funds LOL. Good Luck!

 

I looked into that, but my HP laptop doesn't have a serial port. I'm thinking about finding a Venturi like the plastic ones I've seen on black tank roof vents on RV's, and using my dual port gauge to calibrate it for CFM by hanging it out the window at different road speeds. What do you think of that idea? I might have to duct tape it to a rod to get it far enough away from the truck to get into clean air.

 

I've been running Evan's coolant and a 0 psi system for 3 yrs now. Towed a 15,000 lb 5th wheel from sea leval to 9000 ft passes. Never over heated, never boiled and with the 0 pressure I don't have to worry about blowing a hose. don't have all the engineering behind it. just know it works for me.Barney

 

I believe I know what you are talking about, I guess what I am wondering is, are you going to use a DC tach, a voltmeter, then do the math, knowng the diameter, then knowing the speed? I just dont rcall any way to monitor the RPM on that type fan? Unless you set a tach generator into the center of the fan blade....

 

Sorry Gene, I forgot, the motor would create the voltage..... Yeah, I guess I was running in the wrong direction. I thought about it after i sent the thread.. I then grabbed a 6" fan, started spinning it wiht a meter set on AC. I dont know how you would get the CFM though, with out know the actual RPM of the fan blade..

 

All right, yes, It can be done, I was just playing, i used a strobe light, a 6" fan, a shop fan. What I got was at 1146RPM, .9043 vlt ac... Yeah, you could definatly do it...

 

I think what you're doing is a very bad idea, and is possibly doing damage to your engine. 1) Your concern about "blowing a hose" is off the mark. Most of the hose failures occur on the lower hose due to road debris, not due to the 15 psi from the radiator pressure cap. 2) I'm not sure what kind of coolant you're using, but my boiling point analysis gives the exact boiling temp vs altitude for a 50% mix of the green coolant, and I gave the reasons why you want to stay 20F lower than those temps. 3) By running your cooling system at 0 psi you have a smaller volume of coolant circulating, and as I discussed, for a 50% ethylene glycol solution you need 15% to 20% more flow, not less which is the case for a 0 psi cap. 4) Having your cooling system pressured to 15 psi has other benefits in addition to depressing the boiling temp. It aids the heat transfer between the block and the coolant by pressing the coolant against the block, and It helps to avoid air pockets that might cause hot spots. It also helps push the coolant through the radiator core from the hot higher pressure top, through the core, to the bottom reservoir. 5) Have you considered that running unpressurized might be increasing cavitation. The 15 psi might be very important for ensuring that the FW-16 SCA gets pressed up against the cylinder walls to break up the micro bubbles.

 

gene, do a search for Evans coolant. It has a boiling point of 375 at 0 pressure and a freezing point of -60. It has enhanced cavitation properties and better cooling properties than 50/50 coolants. don't dicount it until you've tried it,or at least studied what it is and how it workes.

 

[QUOTE=ernesteugene]I looked into that, but my HP laptop doesn't have a serial port.QUOTE]

a serial port is easy to install,just a slip in card think mine was about $40

 

Ok I did the search as you suggested, and now I feel qualified to state without any reservation whatsoever that I would NEVER put that stuff in my truck!

At 50F Evans NPG is X23 times MORE viscous than a 50% mix of EG, at 25F the NPG viscosity increases by a X3.2 compared to its viscosity at 50F, at 0F it's a X12.4 higher viscosity than at 50F, and at -25F it's X69.7 more viscous than at 50F. To me these viscosity comparisons make NPG sound like it's thicker than molasses at these temps, but I haven't yet found a viscosity number for molasses to confirm this!

NPG also has 16% LESS heat capacity than a 50% mix of EG, which is consistent with their claim that your engine heats up faster with their NPG product than with a 50% EG mix, as their web site puts it "FASTER ENGINE METAL WARM - UP". The Evans web site states that "the coolant will run hotter but the cooling system will not fail and metal temperatures will remain under control." Whatever that's intended to mean, it doesn't sound like something I'd want in my truck, as I've being tearing it apart piece by piece trying to get MORE cooling, not LESS! The last thing I need is a HOTTER engine, even if it can get to 375F before the NPG boils out.

Below is a post from an apparently satisfied user of the newer Evans NPG+ coolant!

"As the beta tester for the Evans NPG+ lifetime coolant, I was struck with a dilemma today. Jinking around through traffic and stop lights the high temp. idiot light came on. Not a problem with the evans since it boils at 375F but, at what temps do other engine problems develop? How do I know when the engine is too hot to run when I'm already off the scale?? Seems like 300+ degrees would at least fry the plastic cooling fan if not something more important.

While this is not an issue on my highway comute to work, it will certainly be on hot summer days in traffic because today wasn't even a hot day by florida standards. What do you guys think is the upper limit in terms of running temperatures?? And I'm open to suggestions on how to monitor these higher temps."

The suggested solution on this forum was to "Add Water Wetter to your Evans coolant.". This sounds like the doc prescribing a second pill to help with the side effects from the first pill, that wasn't even necessary to be taking to begin with!

Well Evans is supposed to be safe for dogs to drink, but I'm not sure if that's true if you add the "Water Wetter" to it? I'll be sticking with the tried and true 50% mix of EG + FW-16, and try not to harm any dogs while using it.

 

Ok Gene. Thats what these forums are all about. we are all entitled to our opinions. I've never have had a cooling issue. It always runs perfect and yes I use my heat gun to measure temps when we stop along the road. I too pull a 15000 lb 5th wheel. so I do work the truck. It works for me. I was just stating my facts as related to my experience,and my opinion. so I'll go with what works for me. Barney