imp

Even though I had already done very extensive automotive work by then in Chicago, I started hearing some things different from what I had experienced before, after I took over Dealership of an ARCO station in Las Vegas. One thing I noticed was that cooling systems seemed to react a bit differently, maybe due to the much drier air in the Desert. Boil-overs seemed rarer, for one thing. Many of my customers lived out on the west side, where the station was located, because they worked at the Nevada Test Site, over 100 miles northwest, and caught the only highway up there near my station. They commuted daily. Some took buses, some carpooled. Most bought gas from me. Many were highly educated, Engineers, Physicists, Radiological Doctors. I spoke in great detail to many of them, me being new to the West.

Everyone of course talked about the heat, Desert driving. A well-dressed man brought his big Galaxie in with 390 eng., his wife following, handed me a thermostat for his engine. Asked me to install it, we talked a bit. He was a Nuclear Scientist. Had overheating problems, so for cool months, it was perhaps October, he put the thermostat back in the engine, removed it each following Spring. Had overheating problems in Summer with thermostat installed, no problems without it. You may have heard the opposite of this story. Hear me out, first, please.

I've racked my brain for a few days trying to figure out a quite logical way to explain my own thinking on this dilemma, the belief that COOLANT CAN MOVE TOO FAST THROUGH THE RADIATOR.
Try to picture this. Typical engine cooling system, pumping water from the engine through the radiator, back to the engine. Picture a chosen hunk of this water, say a gallon, hold that gallon steady in your mind as it moves through the radiator. During it's pass, it's temperature is lowered as it loses heat to the radiator structure. Let's say it's temperature drops 10`. Next gallon loses 10`. Every gallon through loses 10`. Say the flow rate was 10 gallons per minute, not unusual for a vehicle radiator.

Now, double the flow rate to 20 gal. per min. Each gallon is now in the radiator for HALF THE TIME, and only drops HALF THE HEAT as before. But, TWICE AS MANY GALLONS are now passing through, each dropping only 5` in temp.

THE NET AMOUNT OF HEAT TRANSFERRED REMAINS THE SAME. See below, one of the many sources I've consulted having mathematical proof that FLUIDS (liquids and gases) passing through heat exchangers experience no difference in amount of heat transferred vs. mass flow rate through the radiator.

"Heat transfer rates and radiator theory
Part I.
This will be a long post that I will be working on for a while, like a build post.

There has been discussion on this forum, and others, of overheating due to the myth that coolant can move too fast through the radiator. This also applies to other fluids needing cooled. The coolant moving too fast is often associated with removal of the thermostat. I will get to the reason for this particular case later."

http://www.colorado4x4.org/vbb/showt...adiator-theory

I believe in proof over hear-say, word of mouth claims, special cases which do not apply to the concept (such as "thermo-syphon systems"). You may still not believe it. Tell me, please, if you don't, and what has prompted you to believe so: Have you driven your vehicle without a thermostat? Did it overheat then, but not WITH a thermostat? Thanks fer readin'! imp

Buck Sergeant

Through the years I have tried all the combinations you are describing.Back in the day, we would remove the stat in order to run cooler.Everything worked out fine. Yes, we would foul out a plug or two but was willing to pay the price to run cooler. (wish I knew better then)
Now today with our "Engine Management Systems." If you don't run your stat in close to factory parameters, you are looking for trouble with other systems that rely on the cooling sensor to give them instructions on their responsibilities. Not only that, if the cooling system, on engine management, vehicles is not in close proximity to OEM, the vehicle might run, but with a loss of fuel economy and who knows what else.
We tried no stat in our carbureted 331 stroker and had a nightmare of issues.
We put in a 180, with no other changes, and the car runs like a raped ape. On today's vehicles the engineers are on the money with stat temperature ratings.
I strongly recommend using a stat in domestic and race engines. If the vehicle appears to be running perfectly without a stat it is hiding a problem that could cost the owner big bucks down the road.

Derf00

In the Ford Galaxy example listed above, there are a number of variables that are unaccounted for like ambient conditions, altitude of where they lived, what PSI of radiator cap was used, size of the radiator, the size of the hoses, etc.

The thought of exponentially faster fluid rate = the same amount of heat transfer at the same exponential rate is ok in an ideal world and in an ideal cooling system but, it's a flaw in the logic for a real applicaiton. Most heat transfers do not occur in a linear fashion. Instead, they happen on a curve where, in a specific window of ideal variables. Radiator fluid can only gain/loose so much heat over a given amount of time and those rates of gain/loss may not be equal at different flow rates where residency time may be decreased.

Example. At a flow rate of 10gps the Fluid can lose/gain 10F. But depending on many variables, at a higher flow rate it still gains 10F but can only lose 5F due to an undersized cooling system. Or it may happen the other way if the cooling system is over sized for the application. That's just an example.

Things like ambient temperatures, driving conditions, altitude, condition of flow path (oxidation, gunk, etc), pressure differential between the hot/cold side...can all affect both sides of that curve. Is it possible to have a free flowing system be as or more efficient than one gated by a thermostat? Absolutely, but it's just not practical for the real world. There are too many environmental and cooling system variables to consider a one-case-fits-all solution.

No, I haven't run my car without a thermostat before so I have no anecdotal experience but think about it... if it were that simple as to run a free flowing system, why hasn't it been adopted by ANY car manufacturers? My guess, is that in order to create a free flowing system that would provide a large enough surface area to cool the system properly in the environments, it would need a huge radiator and other considerations for the variables mentioned above. Also, whatever system is designed, would only work in certain ambient conditions and altitudes.

So, while I have no doubt that under the right conditions most cars (like the galaxy example above) could run and cool efficiently without a thermostat, the window of environmental and driving conditions is so narrow that it just doesn't make sense for a real world application?

imp

Here is a thought for you. BTW, thank you for contributing a response. Evidently, my nut-case ideas are easily ignored.


The classical heat transfer equation is Q = M C Delta t, where Q = the amount of heat transferred in nominal units (calories, BTUs, etc.), M = the mass of the medium transferring heat, C = the Coefficient of Latent Heat of the Medium, and Delta t = the temperature difference between input and out.


In our meanderings here, AIR is the medium to which heat is transferred. Thus, if M increases, that is MORE air flows through the radiator, more heat is transferred to the air. C is a fixed constant dependent on the medium, and does not cause variation in heat transferred, and Delta t is the temperature difference between inlet and outlet (of the radiator).


So, the bigger the radiator, the bigger the area exposed to transfer heat, or the LONGER the tubes, or greater number of them, the more heat transferred (Delta t). M increases via a bigger fan, or higher vehicle speed, etc. C varies only a little bit with relative humidity.


Notice that the amount of heat transferred from the COOLANT to the AIR passing through the radiator is INDEPENDENT of the state of the coolant, be it moving fast, slow, or standing still.


How can we refute the classical physics of it? imp

Buck Sergeant

IMP, I like your style. The key to proper engine cooling is the amount of time it takes the coolant to get to the radiator. If the coolant takes to much time the engine overheats. If the coolant is flowing to fast, the engine overheats. Now, the rate of coolant FLOW is determined by two major components; the thermostat and water pump rotational speed. That's why in racing applications the water pump can be very critical. I notice your equations omit the influence of the water pump. If you want to get very trick, check your equations with different water pump rotational speeds. I went crazy matching the water pump with the radiator and thermostat. But it had to be done so my race cars would operate at their maximum performance level .

Derf00

Not ignoring or trying to refute classic physics, just pointing out that certain physical calculations presume certain variables or are calculated using certain assumptions. In the thermal transference what was the chemical makeup of the radiator fluid used? While the metal of the radiator will retain it's properties independently of the type of fluid used, the type of fluid will impact the efficiency of that transference...

Remember in physics questions in school that sometimes started the question with , Assume this or that when determining a particular answer? Assume gravity is standard? Assume that the thermal coefficient of this metal is standard for this heat difussion problem etc...it's because if they didn't say that, the answers are infinite or highly variable and there would be no one single right answer. It's the same thing with the cooling system. The fundamentals are fixed but with so many external variables you have to take them into account or the basic principle will appear to not work.

EPA and MPG is a huge example. For decades the EPA was lauded because they used a laboratory setting where the vehicle was driven steadily at a specific speed or speeds for a specific amount of time, no braking, no hills, no nothing. So of course the numbers were inflated, in the real world, no one drives a fixed 35 or 50 mph in a straight line. There's also idling time, fuel quality, engine maintenance etc etc. I always laugh when I hear people complain about MPG and the first thing out of their mouths are things like, I've never had to service the car (and it's got 30K+ on the Odo) or, it was great up until I got new gears a performance tune etc, or my favorite recently on another forum, I got this Ford Escape and I drive in rush hour traffic a lot and idle for hours sometimes and my gas mileage seem to be nowhere near where I was told it should be (it's like 17 mpg vs the 21 stated on the tag). People look at the answer for what they should expect (in a perfect world) and completely ignore the reality.

Buck sums it up nicely indirectly. Every system is different so while the classic physics of it still applicable, they system will never be at tip-top performance if you don't take the variables into account.