this is what i was trying to say!!!!!!!!!! by touching the ice cube really fast you never cool down your finger and you never heat up the ice cube. i guess the way i worded it just came out wrong.

 

You all forget that a radiators capacity is measured in BTU/HR the hr part = TIM, so ALL the heat excange equations become TIME dependent -
the Greater the retention time in the Rad the more COOLING takes place (until the water temp = air temp) and the GREATER the Delta T between the ENGINE and the RADIATOR. the GREATER the the Delta the HIGHER the transfer efficency - you want the water in the block to get as HOT as possible w/o boiling and as COLD as possible in the Radiator. This is accomplished by carefully regulating the FLOW RATE through the system - the THERMOSTAT is the PRIMARY means of adjusting the flow rate in the RADIATOR.

 

Your logic is wrong. I'm not sure how to explain this any better... Jeff had a pretty good explanation for your icecube analogy. Like Jeff said, using your icecube example, you need to imagine a chain of icecubes. Let's say you drag this chain of icecubes over your hand very slowly. Your hand is ALWAYS in contact with the icecubes. Next, drag the chain of icecubes across you hand very rapidly. Again, your hand is always in contact with the ice cubes. In both examples, the transfer of heat from your hand to the icecubes will be roughly the same.

Another example. Take a large tub of water and heat it up to a boil. Place your arm in this boiling pot of water. While keeping your arm submerged in the water, move it around very rapidly. You will get burned, right? The heat transfer to your arm does not stop because you are moving it around faster. It will probably burn you worse if you move your arm around because your arm will actually cool down the water around it.

You are using time incorrectly. Also, the delta T you need to look at is between the radiator and the surrounding air, not between the engine and the radiator, since the energy is being transfered to the air.

This is getting complicated to explain, but the bottom line is that flowing faster generally accomplishes better cooling, and a more uniform coolant temperature. Residence time in the radiator is irrelevant.

 

Except for the fact paw140 was being sarcastic and saying that logic was bunk.

 

lol....guess I should read to the end of the thread before posting. DER!

 

You can only have a heat transfer if the RAD is COOLER than the Engine (rergardless of how the RAD is cooled) if the water leaves the outlet of the rad at the same temp as the water in the block the it WILL NOT cool the block (wnless the water gets hotter) as the heat transfer in the radaitor is NOT instantanious - (thermal inertia) the LONGER the water stays in the Rad the cooler it gets (untill it reaches the same temp as the heat sink ie the ambient air). But the point is MOOT since w/o a Thermostat the engine will run too COLD except at MAXIMUM output (ie WOT under LOAD) the THERMOSTAT is ther because the cooling system is designed to matain optimum temprature for ALL operating conditions - so RAD is SIZED to accomedate the heat transfer at MAX load and the the THEROMOSTAT maintains Optimum TEMP at anything LESS than MAX load by recirculating part (or MOST) of the coolant through the engine and BYPASSING the RAD (no Cooling).

 

I've got an idea. How bout we just squash it and say the official word is...

"IT IS NOT RECOMMENDED THAT THE THERMOSTAT IS REMOVED FOR ANY REASON AND DOING SO MAY CAUSE DAMAGE TO YOUR MOTOR"

 

This is incorrect and impossible. The radiator is always losing heat to the atmosphere, assuming it is above ambient temperature. And the radiator will always be cooler than the engine.

I agree that if, for some strange reason that defies the laws of thermodynamics, that if the inlet and outlet temps of the radiator are the same, then no cooling is taking place. But it is impossible for this to occur if there is a temp differential between ambient air and the coolant. By speeding up coolant flow, you are merely evening out the temperature distribution of the coolant throughout the system. For example, you can flow very slowly and have the radiator inlet temp at 250F and the outlet at 150F, or you can flow very rapidly and have the inlet at 201F and the outlet at 199F. In both cases approximately the same amount of thermal engery will be lost to the atmosphere, but you will be running much more consisent at the higher flow rate.

 

ok thanks...

I'll leave my thermostat in!

 

I'm bringing this back because I'm very surprised nobody mentioned the different heat transfer modes taking place in the cooling system.

If my memory serves me right...

Heat transfer due to a fluid (coolant or air) on a surface (engine, rad) is mostly due to convection, and the faster the flow the higher the heat transferred between the fluid and the surface. That's why higher flowing fans cool a radiator faster.

Now there's also a combination of conduction and convection there, maybe here lies the confusion many seem to have. The faster the fluid moves the better the convection but the lower the conduction of heat between the molecules as they don't have as long time together to transfer the heat. (Of course there's also radiation and natural convection involved but I won't go there) This is also true backwards, a still fluid in contact with a different temperature surface will conduct the heat better thru the molecules but will have minimal convection (some natural convection will still be there)...

So the question would be, which is the highest operating mode of heat transfer in the car's cooling system?

My perspective is something like this: (this is my opinion, I may be wrong)

Engine to coolant:
Mostly convective heat transfer; why? Because if it was conduction we would use a highly conductive solid connected to a radiator to shed the heat to ambient air and no fluid in the engine internals or rad except for the ambient air cooling it.

coolant to radiator: same as above

radiator to ambient:
Mostly convection as well but with a higher degree of radiation than the others, thus the name "radiator". The rad will radiate heat away even with no fans but at a far less rate not sufficient for proper operation of the car.

As far as heat transfer rates go I think (correct me if I'm wrong) that

convection > conduction > radiation

So after this half asleep dissertation going back to my college years I conclude that the better the flow the more the heat is transferred... as long as the coolant stays liquid and the pump doesn't cavitate.

Discuss?

I also wanted to add that I agree with this:

With the slower flow half the engine will be cooler than the other as well. With the faster flow the temperatures tend to even out, which is better for the engine.

 

Just leave the stock one on, like I said on the other thread when I bought my car the previous owner had drilled 6 holes throught the t-stat which caused my "cooling problem" my car would never reach operating temps, it would always stay at 74c and sometimes drop down to 69c which really sucked, I could not go WOT since engine was still too cold.

I reaplaced it, now no more problem....

 

I love these discussions!

Quotes from my thermodynamics book:
"Conduction is the transfer of energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interactions between the particles. In gases and liquids, conduction is due to the collisions of the molecules during their random motion. In solids, it is due to the combination of vibrations of the molecules in a lattice and the energy transport by free electrons."

"Convection is the mode of energy transfer between a solid surface and the adjacent liquid or gas which is in motion, and it involves the combined effects of conduction and fluid motion. The faster the flulid motion, the greater the convection heat transfer. In the absence of any bulk fluid motion, heat transfer between a solid surface and the adjacent fluid is by pure conduction. The presence of bulk motion of the fluid enhances the heat transfer between the solid surface and fluid, but it also complicates the determination of heat tranfer rates."

(Cengel, Y. Introduction to Thermodynamics and Heat Transfer, McGraw-Hill, 1997)

So, yes, I would say you are right.

 

When water pumps have no pressure behind them, the pumps produce more heat. Just dremel out the wax and spring and leave everything else in... if you completely remove the thermostat you will have little to no pressure at high rpm and the pump will add heat to the water.

Your guys theory on water heat transfer is just plain stupid. It's the same as running a turbo at full flow with no pressure, it overheats...

 

Reviving a 21 year old thread with so much new information is just brilliant

this thread is old enough to drink.

 

Absolutely moronic comments. You clearly haven't done any actual thermodynamics engineering study or calculations on heat transfer in fluid systems. Or use control systems with temperature and flow monitoring.

So many muppets still stuck in the fact that when manufacturers started running bypass ports on thermostat housings you had to block them when removing the thermostat, unlike the older, simpler cooling systems. This gave rise to the moronic "the coolant is going too fast to transfer heat", ah yes, that bane of heat exchanger efficiency, additional turbulent flow to surface.... oh wait, isn't that why PWR introduced dimpled cores. No window lickers, what you are experiencing is the radiator being bypassed.


Bonus points for trying to conflate an effectively closed, fix mass system with one with variable mass flow and numerous other effects.

 

I came here to say the same thing, removing or gutting the thermostat without plugging the bypass port would yield less flow through the radiator when the engine gets warm. I'm not a fluid or thermo expert, but a physics professor once claimed that the thermostat's restriction near the end of the system helps increase pressure of the coolant inside the engine (due to Bernoulli's principle) which helps avoid localized boiling.

 

There may be edge cases where this is true, but changing coolant medium, relief pressure or significantly increasing flow or porting the gallery is almost certainly a better control measure.

 

I just re-read all the posts in this thread FMD it's stuff like that which poisons LLMs for your magic "AI google search". So much idiocy.

iF yOU tOUCh aN IcE cUbE

Short and dirty explanation, removing the thermostat works like it does through it's normal operating range, just with more flow, with bonus additional turbulence from increased velocity improving the temperature distribution/profile in the flow anywhere it may have been laminar. Provided all the flow is going to the radiator because you have blocked the bypass. Again for street cars you are better off leaving it in, endurance racer the reliability/ultimate heat transfer capacity benefits outweight the downsides.

Even if the top and bottom hose temperatures are closer together with higher flow, the additional mass and heat flow outweights the lower temperature gradient, bonus points, more consistent temperatures throughout the block than lower flows, which is why they went to thermostat bypass circuits in the first place for warm up.


A/C is a compressible gas and relies on a phase change so it's not entirely equivalent but there is a reason you cabin gets colder inside when you drop a gear and increase pump speed and hence mass flow in the transfer media. Or perhaps someone wants to argue it works better with the pump declutched

 

A caveat to the above is reduced internal pressure in the block. Higher coolant pressure due to thermostat (or other) exit restriction helps prevent cavitation and boiling at hot spots. Otherwise, increased flow velocity and more constant coolant temperature, etc., are all beneficial. Obviously, this all applies to cars using their cooling systems near their max capacity for long periods of time.

 

If you are concerned with pump cavitation the inlet side pressure is far, far more important, that's why bulk water pumps have a rated suction lift pressure at sea level. So cap pressure and vapour pressure of the fluid are your defining limits. Likewise with block hot spots, the restriction of the radiator in the circuit should still be more than the thermostat, I'm yet to hear of an application where a simplified system with the bypass blocked/removed has generated hot spots in a pressurised system.

There is a reason you trim DOL fixed speed pump flows with outlet side not inlet side valves to reduce cycling frequency on staged dam/tank systems even with 150m of head (or only 1m ejecting to an open drain) pressure on outlet side, dropping pump inlet pressure is what kills them, they are far less sensitive to changes in outlet pressure, it just reduces mass flow. The only way you might damage them with outlet valving is to literally dead head them until the the shear friction cooks the seals and causes super heated steam pressures to generate bubbles.


For automotive applications the quality of the impeller design and drive speed are more important than slight changes in system pressure.

 

You are obviously well-versed in cooling system requirements. So, having said that...
I was not talking about pump cavitation although that is also an issue that internal boiling point affects - I was talking about the localized cavitation/boiling that occurs on the downstream side of asperities/hot-spots in the flow path within the block. In that case, the main thing that prevents that is increasing the boiling point of the coolant, either with coolant properties or increasing pressure within the block. So I'm not arguing - we're talking about 2 somewhat different issues.

Obviously, increasing cap pressure helps control both issues, but too much pressure can cause leakage at any marginal connection or seal.

And then there is coolant heat capacity and heat-transfer coefficient...

 

For track applications it seems like a small portion of water wetter added to distilled water (I'm assuming it significantly surfactant so bubbles are less likely to get stuck in cavities) with reasonable cap pressure is the best overall combination due to the specific heat of water being significantly higher than glycol type mixes. Obviously antifreeze properties are important in street vehicles in many places.

 

In my racecar I'm using Valvoline Super Coolant (10% VSC, 90% distilled water), which, unfortunately, seems to be discontinued. It is/was the best coolant additive I have found, similar to your opinion on W-W. Luckily I bought a case of the VSC 10+ years ago so I still have some. When I tried Water-Wetter (powdered version) many years back, I didn't like it because it left hard deposits in the cooling system. IIRC, WW now has a liquid version that probably doesn't have that issue.

 

It always seems to be the best products are significantly carcinogenic or far more expensive to produce.

 

FYI

Water Wetter Information:
https://www.redlineoil.com/content/f...ech%20Info.pdf