Someones explanation of how water cools an engine - agree or not???

Phase change is irrelevant in auto cooling systems. The water remains a liquid. More important is the specific heat of water. And that water's cheap, clean, and easy to move. Specific heat is measure of the capacity to absorb and release heat. I forgot most of this, but you can google it. Water absorbs a lot of heat quickly and can release heat quickly. it's interesting to see that anti-freeze isn't as good as water in this respect, so coolant mixure can have an effect on cooling efficiency. I was looking into it once, and concluded it's best to use just enough anti-freeze to protect from freezing, with a little over on the safe side, but don't use pure coolant. Might be wrong is some regards, but that's my recollection.

--Vic

Oil does more cooling than water/water antifreeze mix.Oil also cleans and lubricates and traps crud in the filter and oil pan. cuhulin

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This is actually true (see for instance

For most people, though protection against freezing and/or boiling across the widest range is a lot more important than the modest improvement in specific heat. Also, cooling system designers, being aware of this, should increase the circulating volume and the ability to transfer the heat to the air accordingly. (Usually they succeed, but some cars *are* notorious for tender cooling systems...) The specific gravity boost of a mixture also plays a role in cooling, though, compared to pure water, as discussed on That range is an important benefit. Like most solutions, water/ ethylene glycol mix is both higher in boiling point and lower in freezing point than either component. The optimum is somewhere a bit shy of 60% glycol but unless you have to deal with extreme conditions you probably will be fine with 50-50.

The coolant also has anti-rust properties, and its viscosity might be enough different from that of straight water for some engines to care.

You're right on about (lack of) phase change, of course. The boiling point of the mixture up *quite* a lot with pressure. Of course, if you consistently *need* the ability to push the boilover limit, rather than staying in the normal range (in the 200-degree F. region these days) you're working too small (or poorly maintained) a cooling system too hard, and putting the engine at risk (especially with such widespread use of aluminum these days), but it's nice knowing that you have something in reserve when a hot summer day and a steep hill and a heavy load all team up against you. See for instance

and A pure water cooling system that did the same job would have to be larger *and* run at much higher pressures (also the reason we don't use methanol as an antifreeze anymore -- thus, AFAIK, the reason the old timers call glycol "permanent" antifreeze, because you run it year round).

Ashton Crusher wrote in news: snipped-for-privacy@4ax.com:

Oil also isn't a pure substance so doesn't have one boiling point. Butane is a gas at room temperature, but octane isn't. Oil is a mixture of hydrocarbons and other chemicals, water is *one* compound so has *one* boiling point.

The other point you don't mention which is relevant is that the water in a cars cooling system is in a closed system and is allowed to become under pressure. This raises the boiling point of the water. You get a bit of water turning to steam - 800x volume gained by the conversion to a gasous state, and the rest remains as liquid. This builds up until the safety valve on the rediator reaches it limit. At that point the pressure remains just below that limit subject to the efficiencly of the radiator to cool it unless the engine cools below the water temperature. Which would only happen once it's turned off of course. There will of course still be water temporarily turning to gas arround the cylinders, but this can be ignored as it turns back to liquid once it's heat is dissipated into the rest of the water.

****** Phase change is not the process that provides cooling in automobile systems, so while some facts are stated in this premise, the basic reasoning is false.

You CAN use phase change to take advantage of this feature in some processes.

For example, there is a polymerization reaction that is very difficult to control because of the amount of heat liberated by the process. You can dissolve the monomer in a light alcohol and kick off the process, and let the alcohol distill into the condensor to maintain the temperature in the reactor at the desired point.

This requires a lot of chilling capacity in the condensor (or radiator) but it works, so the principle is sound, but it just isnt used that way in autos.

In message , snipped-for-privacy@webtv.net writes

If so, where is the oil cooler on most cars and on the few high performance cars that do have them why are the tiny?

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If the water or other liquid in your car's cooling system actually undergoes a phase change to steam, something is horribly, horribly wrong. It makes sense to a physics student but whoever wrote that is neglecting the fact that when the water turns to steam it suddenly has far fewer molecules in contact with the iron or aluminum in the head and block therefore heat transfer from the hot parts of the engine to the cooling fluid dramatically slows, which means that if there's steam in your engine you're minutes or seconds away from a runaway overheating condition unless the engine is shut down. In fact, pressurized cooling systems are used to *raise* the boiling point of water, allowing the engine to run at higher temperatures *without* the cooling fluid undergoing a phase change.

In short, that's not the way it works at all.

nate

I dont think the basic premise is true. Lubricating oil has approximately half the specific heat of water. Most automobile oil sumps are designed to hold 5-6 litres of oil, similar to or perhaps somewhat less than the coolant volume. So the basic heat transfer ability is less with the oil.

And most cars dont have an oil cooler, using only the radiation from the oil pan and perhaps a little conduction to arrive at what little heat exchange function might be derived.

I challenge Cujo to cite his sources on this one.

Many years ago, I drove a bread truck for Sunbeam Bakery.(Don't say bread, Say Sunbeam!) One time, on my way back from a little city about thirty miles distance from the Sunbeam bread relay store the fanbelt broke.I was able to to make it all the way back to the relay store from that little city without over heating the bread truck's engine too much, did not ruin the engine.Fortunately, there were some hills to coast down on that highway to help with the air flow, helping to keep the engine from getting too hot.I Guarantee you if it had been an oil leak, I would not have tried to drive that bread truck that far.

You can look in auto engineering books about oil cooling and water cooling.I will let those books cite what I say. cuhulin

In message , snipped-for-privacy@webtv.net writes

Indeed, here in England it's reckoned that once you're doing about 20mph natural air flow through the radiator is enough and fans are only needed when crawling in heavy traffic or stopped with the engine idling as in a traffic jam.

Nope. Under normal circumstances no phase change occurs. The system runs well above atmospheric pressure, and it's a sealed system so most of the fluid remains liquid during normal operation.

Now, when there is a catastrophic overheat and the system blows off steam through the radiator cap, THEN there is cooling due to the phase change and it can be very effective at cooling things down in the short term.

Also note that I don't think this applies for some earlier cars like the Model T. I think the Model T system did operate at atmospheric pressure only (our Irish friend can probably correct me on this if I am wrong) and it is designed to blow steam off periodically when stressed.

You can carry a lot more heat off with the phase change than simply by using a working fluid, but the problem is that you have to get it somewhere when you do.

--scott

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Not only did the T use an unpressurized cooling system, it used the "thermosyphon" effect to circulate the water through the radiator - no water pump. This resulted in fewer things to break (no water pump bearings to fail, seals to leak, or belts to snap) and also resulted in the "normal" flow direction of water through an engine being (relatively) cold water comes from the bottom of the radiator returns to the block, hot water exits the head and enters the top of the radiator - despite there being good arguments for *not* doing it that way on a system with a water pump (hence, you may see a modern car described as having a "reverse flow" cooling system.)

I believe water pumps were pretty mainstream shortly after the introduction of the T, but not sure when pressurized cooling systems became common, I believe that water pumps were widely adopted first. I do know that cooling system pressures have been rising over the years, with the "modern" standard of 13-14 PSI having been adopted in the mid-1950s. Lately, even higher pressure systems have been introduced.

nate

ut

true, but I'm guessing in your typical old box truck the fan is attached to the water pump snout, so his cooling system was degraded in two different respects.

nate

This is the key to the power of steam. Your A/C is the best automotive example of phase change at work. But look around. What's powering your PC, your TV, your flashlight, your garage door opener? Phase change of water/steam. Whether it's oil, gas, coal, garbage or nuke heating the water to steam, it's the phase change of steam expansion in turbines that powers the world. Used to propel most Navy ships too. I was a Boiler Tech on one. Steam turbines. Water temps about 600 degrees F since we operated at

1200 psi. Steam temp over 900 when it left the superheater. Every feed pump, which ran on the superheated steam, had a hole poked in the lagging over the powerhead. Cigarette lighter. Now I think only the nukes are steam turbine propelled. The others are diesel or gas turbine. But turbines are boring and screaming noisy. My favorites have always been the steam reciprocating. They are just fun to watch, valves popping open and closed, piston shafts moving up and down. My favorite was the engine on the Rocket, a Cleveland Tanker's Great Lakes ship I did a few tours on when I was in the Merchant Marine. Two stories high, articulated piston rods moving up and down, knuckles sliding on 8' wide, 2" thick shiny steel bars. The outside lubing was all done manually with a squirt from an oil can. Everything all shiny and oily. Smelled good. Used to go off duty in the fireroom and chat with the oilers and wipers in the engineroom. Didn't have to yell in there. There's some vids on You Tube of such engines if you want an idea. Beautiful mechanisms.

Not true. No auto engine I have seen was designed to be steam cooled. It IS possible to design steam cooled engines. It was used in some early aircraft engines. It is also possible to use oil-cooled engines. Phase change cooling systems are somewhat different in their design and particularly in operating conditions.

This explanation is way too complicated, and also, in terms of evaporation, wrong. It is the specific heat of water that is used in the normal car engine, not the latent heat of vaporization.

Inside Bruce Crower's Six Stroke Engine I Like that six stroke engine. cuhulin

So you cant, or wont, back up your post?

I am not going to spend a bunch of time looking for something to back up my post.

Heh, a few days ago, I started working on that pecan tree stump in my front yard. (I am too scared to use a chainsaw) The next day it was pouring down rain.The next day I worked on that stump again.Today it is too cold outside.That tree stump isn't going anywhere for a while. cuhulin, the stump

Watch your heart. Swinging an axe puts it to the test. You could probably have a tree man get a stump-to-chips machine in there for a c-note or less. And you get free mulch.

--Vic