No thermostat?

[RobJ]

Quote 3RRL: So slowing down the flow in the radiator decreases temperature in the radiator. Yes, I agree with that too, but why? It's because it has time to dissipate the heat more effectively. That is THE big reason to leave your diesel idle for several minutes before shutting down. Especially on turbo charged units. " "

So youre describing cooling less water more. This is not necessarily better than cooling more water less. Faster flow increases turbulence which aids heat transfer. Admittedly, the water would not cool quite as much during its quick pass thru the radiator but it would be passing thru more often and would more than make up for it. The "not enuf time to transfer heat effectively" is an attempt to explain what has been seen when removing thermostats and seeing a detriment. Its not a correct explanation because it does not obey physical laws governing heat flow. I suspect what really explains it is that bubbles form in the coolant under flow conditions that are caused when the thermostat is removed.

The reason for idling before shutdown is not as much related to this as it is to reducing the amount of heat being produced. It lets the hot spots cool gently while the cooling system and oil continues to distribute and remove the heat.
larry

Spydy are you just making this stuff up? Would you rather run fast over a bed of coals or walk slowly. I bet you'll get better heat transfer going slow.

 

[RobJ]

The turbo is the main (only)reason to do this. Spinning up to 100k and the heat it creates and gets to run the thing(900 degree exhaust temps) you can bake the oil in the turbo if it's not allowed to cool down. But rarely does someone go from full bore pulling a disk to off. A trip to the barn (or tent ) is usually plenty of time for the turbo and exhaust temps to come down. Take the load off the engine and the temps drop very fast to a few hundred degrees.

On my little L2500 (non turbo), if I cut the engine off after a hard workout (pulling a disk), my normal operating temp goes from 160 to about 170 (watching my mechanical gauge). This isn't anything to worry about. Actually if I just idled back to the barn it does the same thing because the thermostat is keeping the temp at 160. Oil temps are a little slower to come down but do so. But something like running a BH or doing FEL work isn't really heating up the engine that much. It's a intermitting load condition.

When I ran the diesels I rebuilt on a dyno we always watched the exhaust temps. They would react very fast to a load or unload condition.

Rob

 

[SPYDERLK]

Quote skipmarcy: "There is no air to form bubbles in a properly filled, closed cooling system. Heat transfer from the coolant to the metal surface of the tube in the radiator - the longer it stays in contact with this cooler surface, the more heat is transfered away from the coolant. Same thing with the heat transfer from the iron cylinder wall to the coolant. Pour a cup of water in a hot skillet for 5 seconds or for 15 seconds - which one will produce hotter water?"

- - Bubbles can form from coolant boiling in low pressure regions. The time in contact, unless bubbling, is 100% regardless of the flow. Faster flow just stirs itself better causing more of it to eventually touch the heat exchange surface during each pass thru the system. The stirring acts to prevent a boundary layer of heated, or cooled, fluid against the surface, and consequently maintains a greater temperature difference between the surface and the coolant touching it. This higher Delta T is why heat transfers more quickly. Theres no way around it if the fluid is touching the surface. It must be bubbles. Im guessing like this:

• 
  The fastwater cools faster but since it goes thru quickly it exits the radiator warmer than if it had gone slowly

• 
  Due to the high flow the pump is sucking harder, effectively making the radiator a restriction.

• 
  The higher suction on the warmer exiting water causes boiling and feeding a bubble slurry to the engine and inhibiting heat uptake

Chain reaction.

Lets consider boundary layers, rate of heat transfer for ambient conditions, laminar or turbulent fluid flow and its impact on rate of heat transfer to fluid mass per given unit of time!

Yup.
larry

 

[flusher]

I just read that tractors don't need thermostats. It said none of the overseas models have them, only U.S. models. I have a John Deere 950 with a diesel engine. If the thermostat is not necessary I would rather remove it. I've heard that on gasoline cars they are necessary for some reason.

A thermostat is a temperature-sensitive valve. And it's also a flow restrictor. If you don't want the first function for whatever reason (e.g. one less moving part to fail) you should still retain the second function (flow restrictor). You can remove the guts of the thermostat easily by cutting the two little support arms with a pair of dikes. Then install the remainder of the thermostat to get at least some flow restriction to increase the residence time of the coolant in the radiator to improve heat transfer. This is the advice I got from one of the parts guys at my local NAPA store.

 

[SPYDERLK]

Spydy are you just making this stuff up? Would you rather run fast over a bed of coals or walk slowly. I bet you'll get better heat transfer going slow.

Of course Im making it up. But that doesnt keep it from being true.
My feet would heat more quickly moving fast, but since time of exposure is less they would not get as hot. Then I would run thru ice water and back thru the coals repetitively. The ice would melt faster than if I did the circuit for the same amt of time and with the same length of slower steps. I would transfer more heat moving fast.

A little idling before shutdown after heavy work is good for exhaust valves too.
larry

 

[RobJ]

Of course Im making it up. But that doesnt keep it from being true.
My feet would heat more quickly moving fast, but since time of exposure is less they would not get as hot. Then I would run thru ice water and back thru the coals repetitively. The ice would melt faster than if I did the circuit for the same amt of time and with the same length of slower steps. I would transfer more heat moving fast.

A little idling before shutdown after heavy work is good for exhaust valves too.
larry

See you are being cute and all and have yourself convinced...but now you are not making any sense. I guess your perception is reality, to bad that conflicts with physics...darn-it.

Since you have all these breakthroughs...I guess we'll be seeing high volume and high speed water pumps and no more thermostats...all because of a man named Larry that calls himself Spyderlk.

Who said anything about ice?

 

[SPYDERLK]

RobJ, how does my perception conflict with physics?
larry

 

[montejw]

My feet would heat more quickly moving fast, but since time of exposure is less they would not get as hot.

Just getting into this thread, but this has thrown a wrench into the whole works for me.

see ya next week.

 

[Tom_Veatch]

Lets consider boundary layers, rate of heat transfer for ambient conditions, laminar or turbulent fluid flow and its impact on rate of heat transfer to fluid mass per given unit of time!

Sorry, my heat transfer class was at 8:00am and I slept through it most days. Seem to remember the professor said something about conduction, convection, and radiation, but don't really recall what it was in reference to.

 

[Tom_Veatch]

RobJ, how does my perception conflict with physics?
larry

Yeah, I'm interested in the answer to that question, also.

I tend to agree with SPYDERLK's rather oddball explanation. The fast moving feet would, on average, have a lower temperature resulting in faster (higher average Delta-T) heat transfer. That's why counter-flow fluid/fluid heat exchangers can provide a higher heat transfer. The average temp differential between the hot and cold fluids is greater.

But the lower temperature of the feet would also decrease the rate of heat transfer to the ice, offsetting the higher rate on the coals-to-feet side of the system. But, I'd tend to move a little slower through the ice water and give the feet plenty of time to cool off - maybe that would offset the offset?

Which of the two systems would actually result in more calories being transferred to the ice water? Maybe SPYDERLK will volunteer to 'run' a few experiments and report back.

 

[RobJ]

Tom, I think you are trying to agree with Larry but your comment conflicts with that. Larry says his feet would heat up more quickly, you say the feet would have a lower temp. Maybe yall mean heat up quicker but have a lower temp??? In this example you sort of want the feet to heat up to take the heat away from the coals... Maybe try the finger over a candle trick. I'm sure my hand heats up quicker if I hold my finger over the flame for 2 seconds than quickly going over it quickly for a total of 2 seconds(see that blister)

Aren't AC systems designed to move air over the coils at a certains speed. Move the air to fast and it doesn't pick up the cold from the coils.

Funny how everything can be explained away with some sort of science. But cars and trucks still have a thermostat in them. That tell me something.

I'll let the scientist take over from here...know one? :d

 

[JSharp]

<to slow coolant down so that it spends enough time in radiator to effectively transfer liquid heat to air>

is not valid. The amount of heat removed by the air passing through the radiator is directly related to the temperature of the water in the radiator. If you slow down the flow in the radiator, you will decrease the temperature in the radiator, and you will remove less heat.

If GM taught this concept, they had poor engineers. I can believe that.

There may be reasons to keep constrictions (open thermostats) in the line. Primarily, the pump was designed with that restriction. The reason is just not this one.

Chris

Exactly. Removing the thermostat will cause many water pumps to cavitate thus reducing flow through the system.

I'm not sure how the whole "water moving too fast through the system" myth got started. I've never seen a case in industrial cooling where increasing flow didn't increase cooling...

 

[Tom_Veatch]

Tom, I think you are trying to agree with Larry but your comment conflicts with that. ...

It is quite true that each slow trip through the coals transfers more heat than each fast trip and Larry's feet reach a higher temperature on the slow trips than they do on the fast trips.

But if he runs twice as fast, he can make twice as many trips in a given period of time. Due to the physics of heat transfer, each fast trip will transfer more than half as much heat as each slow trip. The end result is that a given number of slow trips will transfer less heat than twice that number of fast trips. In either case, I expect Larry will pick up a few blisters unless he runs really fast.

If you are interested in the math, DAGS "Newton's Law of Cooling" and you'll find the basic differential equations that describe the physics. They are derived from the principle that the rate of conductive heat transfer between two bodies is proportional to the difference in temperature between the bodies.

 

[Egon]

differential equations

Now what might those be?? Or was that the time class was cut to play some pool!

 

[larso1]

About many import tractors not having a T-stat, that is the case with my Japanese grey-market Iseki TS-1610-F. Did not come with one, has no provision for one, and there is no restrictor in the cooling system. However, the USA model Bolens G-194 which is almost identical to mine, same sheet metal, same Isuzu motor, does have one. It's a separate bolted on casting at the outlet from the block that conatains the T-stat and also by-passes a small amount around the radiator through a small separate line. So to me, that indicates they may not be particularly necessary unless you live in cold climates and don't want to wait a long time for the motor to heat up. I don't think it's very cold in Japan during the early and late crop seasons when they're being used there.

The tiny bubbles being talked about are actually steam, produced on the back side of the pump's impeller in a zone of low pressure, created by the spinning impeller, AKA cavitation. If you pulled a sufficient vacuum on the radiator with 70-deg.F. water in it, it would all flash to steam. When the water bursts into steam bubbles on the surface of the impeller, pitting and a reduction of material thickness of the impeller blades is what results, and over time the impeller needs to be replaced. Normally, higher system pressure (via the radiator pressure cap) eliminates this effect of cavitation on the pump when the water temp is high.

On the liquid flowing too fast thru the system, as has been mentioned above, liquid turbulance increases as the velocity increases and actually makes heat transfer more efficient. It eliminates or reduces the skin effect (a resistance to heat flow, common in a laminar flow situation) on the interior surface of the radiator tubes. In heating boilers, some have spiral inserts in the water tubes called, surprisingly, "turbulators" that enhance liquid turbulance and thus heat transfer. The liquid going thru the radiator may not lose as much heat in one pass when the flow rate (velocity) is increased, but it will make more passes thru it in a given time and should all average out. Or, I could be wrong....just show me;o)

Bill

 

[Soundguy]

I didn't mean to imply that you may be mistaken about the part you were looing at.. what I was getting at was, Is it possible the unit could have originally been thermosyphon.. and then been upgraded to the water pump. If so.. I'd think that'd be why it may not have a provision for a thermostat. Just a guess on my part.

Soundguy

Nope that is DEFINITELY a water pump. But it is curious as the Hoye parts manual does not show a thermostat anywhere. Guess some rumors are right. I wonder how they planned on getting the thing to normal temp in the winter? cover the rad I suppose, but they you need a gauge so that you know when it is time to open it a bit.

Hoye has a sale on the pumps right now for $116.
Mike

 

[Soundguy]

That statement is sufficently vauge as to nearly rener it void. I can show you many OEM presurized cooling systems with air space inthe top tank.

Also.. any time you have a pump and fluid.. you can get cavitation.. if you can get cavitation.. you can have bubbles in a fluid... it's a simple vapor pressur issue.. ( cavitation pinholes in diesel sleaves aren't cause by entrained air.. but rather by micro bubbles forming and then imploding ont he sleave surface causing pitting... the vibration / expansion / contraction from the cyl is what changes the local vapor pressure properties of the coolant around the sleaves. Thus the various addatives to prevent cavitation and electrolysis.. etc.. )

Soundguy

There is no air to form bubbles in a properly filled, closed cooling system. Heat transfer from the coolant to the metal surface of the tube in the radiator - the longer it stays in contact with this cooler surface, the more heat is transfered away from the coolant. Same thing with the heat transfer from the iron cylinder wall to the coolant. Pour a cup of water in a hot skillet for 5 seconds or for 15 seconds - which one will produce hotter water? It's pretty basic. In the case of removing a thermostat in an engine, some systems can handle it better than others, depending on alot of factors, but in most automotive engines you will definitely see some sort of increase in operating temp. at higher rpms, some to the point of overheating especially if the radiator isn't 100% clean or a soft lower hose trying to suck shut etc. etc. It's still a good idea to gut a bad thermostat as opposed to removing it completely to get you by until a replacement can be installed.

 

[Soundguy]

No, it is not true. The YM2220, which is definitely a Japanese rather than an U.S. model, does have a thermostat. Or at least the one I own does.

(And as other's have indicated, physics is no respector of national origin. Physical principles are the same regardless of the language printed on the warning decals.)

Most of the grey models under the 2000 were sans water pump... there are exceptions..

Soundguy

 

[Soundguy]

Lets consider boundary layers, rate of heat transfer for ambient conditions, laminar or turbulent fluid flow and its impact on rate of heat transfer to fluid mass per given unit of time!

Might as well throw in open channel flow when looking at the top rad hose as well..

Soundguy

 

[Egon]

Bill, did you turn on a light switch and put some illumination on the topic???

Are there not some types of graphs that show the fluid state versus pressure versus temperature???

Do you wish a v-notched weir or just a plain old square gate one Soundguy?? Probably could not see it just looking at the top radiator hose!