Will a Car Run Hotter Without a Thermostat? (1 Viewer)

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I see this question come up repeatedly. I think it belongs in tech because its pertinent when diagnosing a cooling problem, but if mods think its chat, then I apologize and please move it.

I've heard the argument that when coolant flows too fast it doesn't have a enough time to dump heat through the radiator. I believe coolant will dissipate heat at the same rate regardless of how fast it moving. When the coolant runs faster, more coolant will spend less time in the radiator, but net heat dump will be constant.

Image a toy train with 10 cars running on a circular track. Image each car carries a toy man who throws a piece of toy coal once per second. Image a toy coal bin along side the track.

A piece of coal is analogous to a packet of heat.

If it takes 10 seconds for each car to pass the coal bin, and one complete revolution of the train takes 100 seconds, then after 100 seconds the coal bin will contain 100 pieces of coal. If the train speeds up so it only takes 5 seconds for each car to pass the coal bin, after one revolution, the coal bin will have 50 pieces of coal, but after 100 seconds it will still have 100 pieces.

I'd like to hear other's opinions.
 
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I'm taking a long shot here but,

The engine may not even get to temp with out a thermostat. A thermostat opens only when the coolant gets above a set temp and then closes again when the coolant drops below that temp. Up here in the winter, if you don't have a thermostat you won't get heat from the heater.
 
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I'd say no, it will not run hotter without the stat. The bottleneck in the cooling system is the stat so without it, it would run even cooler than it would if stat was wide open.
 
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Coolant is usually a combination of anti-boil/antifreeze and rust inhibitor and of course water.

Note anti-boil/antifreeze is around 30% less efficient at transferring heat than water so I have been told by numerous people.

If you live in a region where it does not freeze and your cooling system is in good order and you don't have a heating issue I would just run corrosion inhibitor.

Removing the thermostat will only take longer for the truck to warm up from cold and usually makes little difference to overall temp once up to normal. But be aware of this, a truck that takes longer to warm up does more damage to it's engine during this period. Hence a thermostat.
 

rover67

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i've experienced in multiple cars that no thermostat makes a car run hotter. everybody has always told me this is because the coolant flows through the radiator too quickly, which makes sense.

think about th ehot water pipes in your house. when it is flowing fast you've got hot water at the tap. if you let it slow to a trickle, it gets cold.
 

brian

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i've experienced in multiple cars that no thermostat makes a car run hotter. everybody has always told me this is because the coolant flows through the radiator too quickly, which makes sense.

this is the correct answer.

with out a thermo the coolant flows too quick, both through the motor where it will not pick heat as well, and through the rad, where it will not dump the heat as well.
that is the job of the thermostat, to restrict and control the flow.
true that it will take longer to heat up, but given the chance, it will run hotter.
 

Elbert

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in the winter the truck will not get up to normal operating temperature during normal driving. So in the winter its going to run cooler....how cool is that...depends on where you live.

In the summer the thermostat does act as restictor to the coolant flow, so running without it could allow the truck to run a little hotter.

Absolutly no reason to not run a thermostat....the bad issues of not running one far outweight any perceived good "issues"...

Never run pure water, unless you want to have your freeze plugs rust out and deal with a serious corrorision problem with your entire engine and coolant system.

Don't get talked into any "magic ideas".... all liquid cooled engines that I know of have thermostats..... that must be for a reason!
 

3_puppies

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in your anology, you didn't mention that the engine can produce more heat at times, pulling a hill, lugging, ect.
so the heat output of the engine is not constant
 
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stolen from texican's wright up on pirate

"I've seen some advocate hi performance W pumps, my thinking......the coolant must stay in the radiator long enough for the heat transfer to happen, one reason you must run a thermostat or restictor so it will not flow thru too fast...most hi performance pumps are for cars that turn 6000-9000 RPM's and actually have fewer blades on the impellors"


makes sense to me. The radiator cools the water by heat transfer and you have to give it time to do it.
 
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its needs that stat to run cooler.

otherwise it does not enough time to transfer heat to the radiator. you would be correct on the fact that the coolant would disipate the same amount of heat over the same time. but you are bot running the coolant through open air but though another object to no mater how fast the coolant cn disipate heat it will rely on the radiator it passes through to cool it. just like an alum. rad cools better than a metal rad. if it has more time in the rad. then it will have more time to loose the built up heat.
 
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In a nutshell- the temperature difference (delta T) influences the rate of energy transfer.

If you allow the radiator to run hot (because the thermostat is controlling coolant flow)- it will dissipate heat faster than flowing more coolant at a lower temperature.

Then, if that coolant, after having released some energy from the radiator into the surrounding air, is cooler, it can go back into the engine block and pick up more energy. (Again delta T).

If however, the entire system is running at the same temperature. Block, radiator, water pump etc are all at 215*. There is no energy movement because there is no temperature difference (No delta T).
 
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2mbb

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I have a hard time with the argument that the faster flowing water doesn't have the time to transfer heat out the radiator. While this is a correct statement in itself, this statement does not account for the fact that the coolant system in an automobile is a circulating closed loop. That same packet of water that can't get cool in the radiator is also traveling faster through the engine, so it won't get as hot in the engine, either, so using the same argument, wouldn't the water entering the radiator be cooler? LukeZero is correct that the temperature difference drives the heat transfer, but when dealing with fluids (both liquid and gas) the heat transfer is also influenced by the heat transfer coefficient which is related to how fast the fluid is flowing. Faster fluid flow gives a higher heat transfer coefficient, which means more heat can be transferred. I am not convinced that the engine will run hotter just because the flow is higher. If there is a correlation between the thermostat and engine temperature, it must be due to some other reason (better flow distribution, higher pressure preventing localized boiling,...)
 
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I service and install hot water heating systems. Everything boils down (no pun intended) to delta T and delta P. The flow rates involved with a conventional water pump on an engine are really beside the point. The real problem is not allowing the temperature difference in different parts of the system. You can move all the water you want, but you won't move any energy until there is a difference in temperature.
 
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Thermostats are designed to let your engine run at optimum operating temperature as fast as possible to minimize wear and tear.

As for the above post don't forget your assuming the water pump is in good condition and the radiator core is free flowing. All these things need to be taken into account. As they too will effect the result of removing a thermostat it could go either way in an old FJ40 but then again I guess that why this is such a HOT topic LOL
 
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One of the rules to remember w/ thermodynamics is that heat moves to cold. Never the other way around. You can produce all the heat you want, but you can not produce cold. You can only create a condition that has less heat.

The air passing over/through the radiator removes the heat from the water at a lesser rate than the direct contact of the metal transfers heat to the water. ( not a very good explanation, but I did not go to school to be a teacher)

If the water does not spend enough time in the radiator to remove enough heat, then the head builds up in the water (and the engine). If the change in temperature is enough, the balance of heat transfer keeps the engine (and water) at an acceptable level. (Like a said, I did not go to school to be a teacher)
 
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I've had a thermo fail open. The engine ran cooler.

Simple fact is without a thermostat more of the water will spend more of its time in the radiator than it would with a working thermostat.
 
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I've had a thermo fail open. The engine ran cooler.

Simple fact is without a thermostat more of the water will spend more of its time in the radiator than it would with a working thermostat.

The important part of your statement is that you had a thermostat in, so the flow was restricted. There is a big difference between a stuck open thermostat and none at all.
 
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I unknowingly drove my 60 from Las Vegas to Boise without a thermostat and the temp indicator never once got above around 30%. Installing a thermostat actually brought my temp up a little.
 
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The important part of your statement is that you had a thermostat in, so the flow was restricted. There is a big difference between a stuck open thermostat and none at all.

Flow restriction is not about slowing the water down in the radiator, it is about raising the water pressure in the engine block. If the pressure in the engine block is not high enough a steam pocket can form and that will lead to overheating the block as direct water to metal contact is lost.

If you radiator cap were set to a high enough pressure (and the radiator could handle the pressure) then any boiling in the engine could be avoided. Water changes its temperature in a very consistent and predictable manner.

1 cal of energy to raise 1 ml of water 1 deg Celsius.

No scientific or engineering book anywhere says anything about how fast the waster is flowing. The amount of energy absorbed or released by a single molecule of water is not important. What is important is how much energy is absorbed and released by the entire system.

Without a thermostat the system will run cooler as a whole. That is the way chemistry and physics work.
 

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