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so I am over here in kuwait and Iraq running convoys with different trucks. Most of them are 6.5 turbo humvees and besides these trucks needing a real engine in them they need a new cooling system. we are always overheating when we drive around during the day. what I am wondering is if anyone knows the best mix for the antifreeze when you are in a desert environment and don't need to worry about freezing. I think the increased boiling point made by higher mixes of anifreeze while making sense doesn't hold up in this kind of situation. would running straight water actually work better. all the rest of the mechanics still want to go with 50/50 mix and I think that is causing alot of our probs.
.... what I am wondering is if anyone knows the best mix for the antifreeze when you are in a desert environment and don't need to worry about freezing.
Go by the boiling point chart on the back of the jug of antifreeze. If you're using green antifreeze with a supplemental coolant additive, then the jug probably says:
40% = 259º boiling point
50% = 265º
60% = 270º
70% = 276º
more than 70% = don't do it. More than 70% and the boiling point begins falling like a rock. Sorta like a horsepower curve - more RPM than the red line and the horses all head for the barn.
So 70 percent antifreeze is probably best for your conditions.
If you are having boil-over problems using 50% antifreeze and 50% distilled water, then you probably have a bad batch of radiator caps. When you have a good 15-PSI radiator cap, the boiling point of the 50% solution should go way above the 265º on the bottle. If you're not using distilled water mixed with the antifreeze in your radiators, then your chief of maintenance should have his hiney kicked.
And yes, the driver needs to be sure the engine fan is working right to suck air through the radiator. And if the humvees have junk mounted in front of the radiator, move the junk. You must have air flowing through the radiator so the radiator can do it's job as a heat exchanger.
I don't claim to know anything about Army procedures, but with 30 years experience on the periphery of aircraft maintenance in the Air Force, I know the maintenance techs had Air Force "tech specs" they were supposed to follow for things like mixing antifreeze and water. If you have such tech specs, then the IG will be unhappy if you don't follow them. But in the absense of tech specs, I'd use 70% antifreeze and 30% distilled water in those humvees - unless your antifreeze has different boiling points than plain ole green ethlene glycol.
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I think the increased boiling point made by higher mixes of anifreeze while making sense doesn't hold up in this kind of situation.
The experts disagree with your thinking.
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...would running straight water actually work better.
Heck no. Pure water has a boiling point of only 212º at sea level, and even less as you climb up the mountain. Plus pure water will corrode the inside of your water jackets and cooling system in a heartbeat.
One of your problems might be that the troops have added tap water to the radiator, diluting the antifreeze to less than 50/50 concentration and adding hard-water minerals which decrease the efficiency of the coolant. You should have a refractometer in the shop and use it often to check the antifreeze and maintain the antifreeze at the max concentration allowed in every cooling system on the post. If the Army is too cheap to provide you with a refractometer, a cheap version for shade-tree mechanics is called a hydrometer, or simply "antifreeze tester".
And you didn't ask, but you also need to worry about cavitation. If the antifreeze you are using is the plain old green ethlene glycol, then you need to properly maintain the level of supplemental coolant additive (SCA). If you are using GM DEXCOOL or other extended life coolant (ELC), then you probably don't need to add SCA to it. But again, your antifreeze tech specs should explain that.
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Last edited by SmokeyWren : 09-13-2008 at 01:16 PM.
I do demolition derbies where cooling the engine and keeping it from boiling over is a high priority, i run an additive called "marvel mystery" and it raises the boiling point up considerably.
I ran around 15 mins at full throttle w/o hardly any air getting through the radiator, and i did NOT boil over by using this additive. Right before i got to the track i was running the engine at my shop w/o the additive in and it was boiling over in a matter of a few minutes,(even quicker when i would use any throttle) thats some great stuff!
Boiling point is less than half of the story.
As you add more glycol to a glycol/water solution, three things happen:
The boiling point rises.
The viscosity increases.
The specific heat (thermal capacity of the solution) decreases.
The last two mean that the engine is more likely to overheat, not less, and their effect is a lot stronger than the boiling-point increase. Increasing viscosity means that there will be less coolant flowing and decreasing specific heat means that each gram of coolant flowing will carry less heat away from the engine.
Reducing the amount of glycol in the mix will reduce the risk of boil over. If it were only a question of glycol and water concentrations, the best heat transfer is with pure water.
I assume you've already done all the normal maintenance - cleaned everything, checked the thermostats & radiator caps, and that's not the problem. I also assume this isn't the first time the army's seen this. Don't they have some sort of desert-operations field manual?
Failing that, you'll have to decide how important preventing boilovers is vs. preventing corrosion. Pure water will best prevent boilovers but offers no corrosion protection. Running pure water with SCA might work; I don't know enough about radiator chemistry to say. Otherwise, run the leanest solution which offers acceptable corrosion protection.
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Last edited by drcampbell : 09-15-2008 at 06:40 PM.
Reason: obsessive compulsion
Regardless of boiling points.............. Overheating is overheating.
Stated in an above post. Get the stuff out from in front of the radiator, get a larger radiator, or make sure the fans are oving enough air.
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UPDATED 8/1/08 Replace so far. 1 LUK flywheel+clutch, 2 thermostats, 2 set of brakes, 1 set of calipers, 5 CPS, 3 sets of tires, 2 Transfer pumps, 1 Injector modual, 1 Computer, 2 Alt, 2 sets of batteries, 1 Water pump, 6 Belts, 1 PS hose, 2 Sets ball joints, 2 set u-joints, 2 carrier bearing, 2 Speed sensors, 1 oil pres sender, 1 temp sender, 4 sets of e-break cables, 1 front fuel tank, 2 rear fuel tanks, 2 set of glow plugs, 6 Glow plug relays, Oil galley o-rings, Turbo pedistal o-rings, EBPV o-rings, 3 sets of Injector O-rings, 1 Vac-pump, 1 new carpet.Total $$$ in repairs v/s miles driven = 3.0 cents per mile. Add fuel to that it jumps to 14.8 cents per mile over the life of the truck.
Some coolants do transfer heat better than others.
Propylene glycol-based coolants will not transfer heat as well as ethylene glycol-based coolants. So make sure you're not using propylene glycol...it is popular over-seas.
Conventional "green" coolants, G-05 "gold" coolants, and other traditional coolants contain anti-corrosion additives like silicate, phosphate, borate, amines, and so on. These additives form a chalky or slimy, white or green, barrier layer on the metal. This coating creates a thermal barrier that prevents coolant from pulling heat away, especially in critial areas like the combustion chamber. Heavy Duty Extended Life Coolants are free of these components, and thus have been shown to provide up to 10% better heat transfer.
Increasing the concentration of antifreeze will raise the boiling point, but it will also decrease the fluids ability to remove heat. A 50/50 mix with a 15 lb cap should get you to 265 degrees. If you're exceeding that, then you have cooling system problems that go beyond the coolant. Sufficants can be added to help transfer heat, but they won't reduce the boiling point.
For boil-over (and associated top-offs), I would suggest a 60% concentration of a silicate-free HD ELC coolant, 40% distilled water, and the addition of a sufficant, like Water Wetter. JMO.
Boiling point is less than half of the story.
As you add more glycol to a glycol/water solution, three things happen:
The boiling point rises.
The viscosity increases.
The specific heat (thermal capacity of the solution) decreases.
The last two mean that the engine is more likely to overheat, not less, and their effect is a lot stronger than the boiling-point increase. Increasing viscosity means that there will be less coolant flowing and decreasing specific heat means that each gram of coolant flowing will carry less heat away from the engine.
Reducing the amount of glycol in the mix will reduce the risk of boil over. If it were only a question of glycol and water concentrations, the best heat transfer is with pure water.
I assume you've already done all the normal maintenance - cleaned everything, checked the thermostats & radiator caps, and that's not the problem. I also assume this isn't the first time the army's seen this. Don't they have some sort of desert-operations field manual?
Failing that, you'll have to decide how important preventing boil-overs is vs. preventing corrosion. Pure water will best prevent boil-overs but offers no corrosion protection. Running pure water with SCA might work; I don't know enough about radiator chemistry to say. Otherwise, run the leanest solution which offers acceptable corrosion protection.
Adding glycol will reduce cooling "power". Adding glycol will raise "boiling point". Boiling and cooling are two different things.
In large diesels (like ships) we ran pure water with Zinc Chromate.
Once it gets real hot like 120 or 130 outside, blowing hot air across a hot heat exchanger may just not do it. More Air or bigger exchanger may be needed.
Silly as this may sound turning of the HVAC which puts a lot of additional heat load may be one of the answers.
Aircraft answer.
In large aircraft, the turbine makes power to make thrust to push the aircraft forward. I know brilliant!
The compressor of the turbine also makes compression to the power turbine. I know brilliant.
On very hot days or in very high altitude airports the compressor is maxed out because of air density and as the compressor maxes out the TIT (Turbine Inter Temperature) and EGT starts to go off scale in the red. NOT GOOD.
On hot days we need all available power because the air is thin.
On take off much of the turbine compressor air is also being used to run the HVAC system and the pressurization system.
What to do: Just before roll out, turn off HVAC and turn off pressurization which gives much more power. At 3,000 (AGT) turn on the HVAC and pressurization. Passengers don't like this much. But hey it gets you off the ground.
Conversely on a very cold DRY day like 20 below the compressor is so efficient that the engine is making too much power, in some instances way too much.
I've seen a full gross Boeing use 7,000 feet to just get the front tire up and on very cold days I've seen it up in less than 1500 feet.
Back on topic. More air (fans) bigger cooler, and turn off AC.
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