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  #16 (permalink)  
Old 05-14-2004, 11:54 PM
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Quote:
I can see it's time to break out some heat transfer discussions when people continue to say the thermostat is required to slow the coolant flow in a radiator "to have enough time to transfer heat". Absolutely false!

I have to respectfully disagree. As an "old school" mechanic I believed for the longest time that if your engine was running hot, pull the thermostat and the problem would be solved. Then I started reading about "heat sink" and realized that the only way coolant could cool down would be if it spent more time in the radiator tubes and the "fins" had more time to pull away the heat. The thermostat closing, for brief periods, allows the coolant in the radiator to cool more, and then when it enters the engine block the cooler temp quickly cools the block while a portion of the heated coolant enters the radiator. Then the thermostat closes to "begin the cycle again". The end result is an engine cooling system that runs cooler than an unregulated one.

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  #17 (permalink)  
Old 05-15-2004, 03:05 AM
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32Vicky is so right! I could hardly keep my mouth shut on this topic but since Vicky brought out his points very well I will just back him up. Its simple science guys! Sure the coolant cools more in the rad witha thermostat but with more time in the rad means more time in the block to heat! We need thermostats to keep the engine operating at optimum temp (180) as much as posible. If you run too cool there is more cylinder wear. Just check the end cylinders on a sbc, they are usually worn more. Partly due to the extra heat transfer and longer warm up time by being close to the ends of the block. From a heat transfer standpoint it is impossible to have it run hotter by taking out a thermostat. The turbulance aspect does make a possible valid point tho. Just my 1 cents worth.
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  #18 (permalink)  
Old 05-15-2004, 08:34 AM
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This dead horse has been whipped , rode hard and put up in previous threads and posts. Once more, we are not running coolant thru an engine just to heat the coolant up and thru the radiator to cool it down. It is there to cool the engine, which will melt down and self destruct if un cooled. To keep the engine cool, we circulate the coolant through it at a rate that results in the best heat transfer from the cast iron, steel and aluminum to the coolant. Then we send the hot coolant to the radiator to get rid of that heat. At this point, think of an out board engine: The coolant is drawn from the lake/ocean, circulated thru the engine and ejected back into the lake/ocean. A thermostat is required to slow the water down to allow the heat transfer to take place and like our auto motors, the thermostat is where the coolant leaves the motor. The engineers design the total system to maintain that fine balance. Removing the thermostat destroys that balance. Changing to a lower than design or higher than design temp stat can change that balance. Over heating or reduced engine performance can result. This balance can also be effected by boring the cylinders, increasing compression, or replacing cast iron components with aluminum.

Internal combustion engines are mostly cooled by either liquid or air. For those of us that have had experience with both methods, we have learned to deal with the pros and cons of both methods. For years, motorcycle, lawn mowers, and aircraft engines were cooled by air. To enhance cooling, the combustion chambers and exhaust flanges were surrounded by cooling fins and cool air flowing past these fins absorbed the heat and kept the engine in the operating range. For aircraft, propellers created the air flow on the ground and cowl vents were required to be open to keep the engine from overheating. Cylinder head and oil temp gages were used to make sure you did not let the engine over heat. Once airborne, the cowl vents were slowly closed as aircraft speed sent more and cooler air over the cylinders. To keep the engine from getting too cool, the fuel air mixture was leaned out and the measure of the correct A/F mixture was the cylinder temp in the "green" range. The higher the aircraft flew, the cooler the air and the leaner the mixture. Climbing the aircraft to maximum service ceiling resulted in the greatest range. Lawn mower and motorcycle engines were not critical if they failed, so we just accepted the results of movement of air over the fins and it did not take motor cyclist long to figure out they had to get the machine moving to avoid a melt down. Now, most motorcycle engines (including snowmobiles and ATVs) have gone to liquid cooling with fans because it is more efficient/consistent than air cooling. The aircraft industry also knew liquid cooling was more efficient and made some attempts to utilize it. The most famous was the P-51. Of course, a bullet hole through the radiator or coolant line was fatal for the aircraft.

Back to the point of hot rod engine and cooling. When we build that highly modified motor, we tend to forget we need to modify the coolant system also. Some tricks to use is bigger radiators made from aluminum that can not only transfer a lot of heat rapidly, but withstand higher pressure that raises the boiling point of our coolants, more efficient coolants, ie "water wetters", bigger and more efficient exhaust systems, more aluminum heads and intakes, and fine tuning the standard OEM thermostats that were designed for a specific engine/rad combination. We don't hesitate to re jet carbs to work better with that hopped up motor, but how many of us take the time to "tune" our thermostat by drilling small by pass holes to let just a little more coolant flow when the full open 180 degree thermostat just is not open far enough? All the fine print tells us boring a motor .030 over will make it run hotter. The writers of the fine print assume correctly we will use the same rad and thermostat. It's our job to mod our cooling system to make the motor run at desired temp.

Trees
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  #19 (permalink)  
Old 05-15-2004, 09:14 AM
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If your theory was right, we could do away with the radiator and the thermostat, and just add turbulence to the coolant.
I'm not sure how you reached that conclusion. It's a closed system. Without the radiator for heat rejection, the temperature would rise in the block until the coolant turned to a vapor and then you have disaster. Turbulence is not a method of heat rejection, therefore it alone does nothing for giving up heat.

Closed system. Closed system. Closed system. Sure the radiator gives up more heat if the coolant flows through it more slowly for that single pass. But it is also absorbing more heat from the engine at the lower flow rate. The radiator "looks" more efficient under this scenario, but the system efficiency overall goes down. Also, remember from my previous posts that the net time in the radiator is still the same even if you change the flow rate.

I think what's really happened here is that some folks have seen an improvement in the cooling system by adding a thermostat and then made a leap to assume it was flow rate related. Original equipment coolant systems are optimized so that all of the individual components work together for an efficient system. If you take the thermostat out, I would assume the system balance would be disturbed to some degree. Having a thermostat is a good thing for many reasons, but not to reduce flow rate. It helps to quickly get the engine up to operating temperature. It helps to provide back pressure to the engine and the water pump. That in turn reduces the risks of steam pockets and pump cavitation. And it also add turbulence to the coolant prior to entering the radiator.
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  #20 (permalink)  
Old 05-15-2004, 11:17 AM
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The thermostat is a valve that the temperature operates to regulate the flow of the coolant.

Anyone that has worked on cars for very long learns this very quick. It's people that don't work on cars that think you can run without a thermostat.

If your car is running the right temp, just take out the thermostat and see what happens.

About once a month someone comes up with the same silly discussion LMBO.

Troy

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  #21 (permalink)  
Old 05-15-2004, 01:48 PM
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Take a seat, pull up your socks, grab a beer and strap yourself in. Intense sarcasm to follow!

Ok. You've convinced me that slowing down the flow in the radiator is a good thing for the coolant system efficiency. Based upon that premise, I have some ideas that will revolutionize the automotive world:

1. The Detroit boys have obviously missed this one big time. They are not only robbing horsepower spinning the water pump too fast, but they are missing some cost reduction ideas.

2. Why would they put that silly restriction at the thermostat to reduce the flow when all they needed to do was reduce the horsepower robbing effort of spinning the pump too fast. So...should I tell them to change the pulley set-up or redesign the water pump? What do you guys think?

3. For all of you folks having overheating problems, don't stop by just restricting your flow from the existing thermostat, buy my new coolant efficiency disc. I haven't started production yet, but given enough orders, I could get going pretty quickly. Here's what this new disc does. The disc is a replacement for the thermostat that doubles the radiator efficiency by restricting the flow by 50%. I haven't measured the effective area on my thermostat, but I'd guess it to be about 1" diameter. So...50% of the effective area equals a diameter of .707". Any takers?

4. I wonder where the limit is of reducing the flow thereby improving the coolant system efficiency. I'm thinking that if this holds up, I could reduce the flow to where I could use the engine compartment as a frig on long trips. I could save a lot of money by not stopping at those expensive fast food joints.

5. I have e-mailed the university I graduated from and requested a partial refund on my engineering degree. It's obvious from these discussions that the physics, heat transfer and thermodynamics classes I took were in error. I knew something was wrong when the professors kept telling the earth was round.

End of sarcasm

trees - Nice support of my point when you described drilling holes in the thermostat to increase the flow to improve the cooling system efficiency. I couldn't have made the point better myself.
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  #22 (permalink)  
Old 05-15-2004, 03:02 PM
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Sarcasm belongs in the hotrodders lounge, not in this forum where someone could mistake it for useful information.
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  #23 (permalink)  
Old 05-15-2004, 03:20 PM
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Sorry 32, but the discs have been on the market for 50 years
with a 5/8ths hole. I think they went broke.

Troy

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  #24 (permalink)  
Old 05-15-2004, 03:55 PM
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Gee guys I'm sorry for the sarcasm.

How about if I make it up to you? The 1st five orders for my coolant system efficiency disc gets them at half price.

Yep. Those discs have been around a long time. If flow reduction improves coolant system efficiency, I wonder why they went broke? Hmmmm...any ideas guys? You're making this too easy.
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  #25 (permalink)  
Old 05-15-2004, 04:43 PM
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32, your posts should be in the lounge like about 150 of your previous ones. And not do your trolling here.

Troy
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  #26 (permalink)  
Old 05-15-2004, 05:41 PM
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oh yeah...and my mother wears combat boots, too.

Call me a troll if you wish, but I've given plenty of technical reasons as to the fallacy of flow reduction making a coolant system more efficient. When will someone provide something technical in rebuttal.

I've agreed that slower flow in the radiator allows more heat rejection for that one pass. But I've also demonstrated that the net time in the radiator is the same regardless of the flow rate for the system. So...explain in technical terms how slowing the flow gets you more time in the radiator. Where did my calculation go awry? I've also agreed that on some systems, adding a thermostat can make an engine run cooler. What I have disagreed with is the explanation as to why it sometimes helps.

Stop the name calling and provide something substantial. As for which forum this belongs in, it should stay in the "engine" section as this is where all of the folks look for answers to engine cooling issues.
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  #27 (permalink)  
Old 05-15-2004, 06:42 PM
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There is nothing technical about installing a thermostat, like I've said it's like a valve in the system to control the rate of flow of the coolant so it will stay in the radiator long enough to cool before it recirculates to pick up heat and return to the radiator to radiate more heat.

Net time in the radiator? In that case you could run the coolant through as fast as you want to. Defeating the purpose of the thermostat.

Class dismissed.

Troy

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  #28 (permalink)  
Old 05-15-2004, 07:59 PM
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Hey vicky i really dislike everything you have to say, mostly because the tone you've decided to use in saying it.

This is a great forum full of very knowledgeable people, just as highly educated as you are... they all have useful information to share with you, you just have to not take things personally when someone else disagrees with you.

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  #29 (permalink)  
Old 05-15-2004, 08:17 PM
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This is my understanding of the reasoning for reducing the flow at the outlet (whether it be a thermostat, or a 'washer'), so please feel free to correct me:

Water (including coolant mixed in) has a set boiling point. To raise that boiling point, increase pressure (on a linear scale, I believe). So, by resticting flow at the outlet, it creates a pressure build behind it. Pressure is also increase to a certain extent by the expansion of the coolant in a finite space. This increase in pressure reduces/eliminates hot spots around the bores. Without the restriction by a thermostat or washer, the pressure build is not enough to eliminate the steam pockets/hot spots, thus increasing the likelyhood of detonation.


Tim
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  #30 (permalink)  
Old 05-15-2004, 08:30 PM
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I reluctantly reenter this furball for a little more pontification. Think of the thermostat as a flow valve, which it really is. The binarry valve action makes it automatic and it is predicated on maintaining the coolant at a selected level. It can go from most all the way closed to wide open, a setting that was designed by the thermo engineers for a specific engine and a large range of operating conditions such as 40 below 0 F to 130 F and air conditioning going and stop and go traffic. Now we highly modify that motor and put the same rad and thermostat in it and the wide open hole in the little thermostat is just too small to allow enough coolant flow and most likeky if you put in a larger thermostat , the rad will not effectively transfer enough heat. The method of drilling the small holes I mentioned earlier is a cheap way of increasing the wide open flow capacity of the themostat and couple this with a big aluminum rad, then that big fire breathing monster will be tamed.

32, I also have one of those worthless pieces of paper that says I studied thermo and fluid dynamics. That and a buck twenty five will buy me a cup of coffee most any where!

Trees
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