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.