Thermostat - is it necessary?

2+2GT · May 18, 2009

The high flow = improved cooling is what pump manufacturers use to sell pumps. If you want better cooling, a shroud, better fan, and bigger radiator will do it.

Hack · May 18, 2009

stonecoldtx said:
Here's the reason--it takes time to transfer the heat of the engine to the coolant, and then transfer that heat to the air via the radiator.

The restriction is required because if you allow the coolant to flow freely, it will not adequately absorb the heat from the engine, nor will it transfer that heat to the air.

How much time does it take for heat to transfer?

It's interesting to me how myths like this survive. I'm sure it's because the cooling system in a car is complicated, so it is difficult to diagnose problems. Even some "experts" believe this myth. It's possible that the water pump may cavitate if it doesn't have enough back pressure to work against, but faster flow will ALWAYS help cooling.

Imagine blowing on a hot spoonful of soup. Blowing slower will cool the soup faster, right? Of course not! So why do people think that water must move slowly in a radiator? In fact, slow laminar flow is bad for heat transfer. Just ask any turbo expert about intercooler design. You want the fluid to tumble so more of the fluid comes in contact with the hot/cold surfaces.

jlangholzj · May 18, 2009

Hack said:
How much time does it take for heat to transfer?

It's interesting to me how myths like this survive. I'm sure it's because the cooling system in a car is complicated, so it is difficult to diagnose problems. Even some "experts" believe this myth. It's possible that the water pump may cavitate if it doesn't have enough back pressure to work against, but faster flow will ALWAYS help cooling.

Imagine blowing on a hot spoonful of soup. Blowing slower will cool the soup faster, right? Of course not! So why do people think that water must move slowly in a radiator? In fact, slow laminar flow is bad for heat transfer. Just ask any turbo expert about intercooler design. You want the fluid to tumble so more of the fluid comes in contact with the hot/cold surfaces.

but nobody likes cold soup now do they????

you also forget that the thermal co-efficient of air is but ~.025 while water is ~.6. the water needs more time for the heat to transfer when compared to air, and thus it needs to travel slower to act efficiently.

Also remember that a "high flow" pump will only flow as much as the t-stat will let it. it baisically fills it up to that point, and even though its a "high flow" pump, the t-stat still will do its job. However once that t-stat opens all the way up, it'll still restrict it some, but the "high flow" pump will flow better, and yes, improve cooling, once the engine is up to temp, if it gets to cold, the t-stat closes again.

obtw...I'l be laughing my ass of when you blow too hard and "soup" goes all over your hand

2+2GT · May 18, 2009

The 289 High Performance and BOSS 302 called for different water pumps than their lower-performance brethren. The difference? The vanes in the pump were curved, which actually pumped the coolant a little slower, but prevented cavitation at high rpm.

Sadly, these pumps are long gone, although until fairly recently Ford Racing sold the special impeller.

D.Hearne · May 18, 2009

2+2GT said:
The 289 High Performance and BOSS 302 called for different water pumps than their lower-performance brethren. The difference? The vanes in the pump were curved, which actually pumped the coolant a little slower, but prevented cavitation at high rpm.

Sadly, these pumps are long gone, although until fairly recently Ford Racing sold the special impeller.

You can still get high rpm, low volume pumps at your local parts house. The pump I have on my 331, Autozone offers a "high performance" version, which is a low volume-high rpm pump. The only difference from it and the std volume pump is the impeller size. Nearly all pump applications come in three versions: low volume-high rpm, std volume and high volume. All you have to do is know what application you're looking for.

Hack · May 18, 2009

jlangholzj said:
but nobody likes cold soup now do they????

you also forget that the thermal co-efficient of air is but ~.025 while water is ~.6. the water needs more time for the heat to transfer when compared to air, and thus it needs to travel slower to act efficiently.

Also remember that a "high flow" pump will only flow as much as the t-stat will let it. it baisically fills it up to that point, and even though its a "high flow" pump, the t-stat still will do its job. However once that t-stat opens all the way up, it'll still restrict it some, but the "high flow" pump will flow better, and yes, improve cooling, once the engine is up to temp, if it gets to cold, the t-stat closes again.

obtw...I'l be laughing my ass of when you blow too hard and "soup" goes all over your hand

I'm not sure what you're getting at with thermal coefficients.

Please explain what the thermal coefficient measures. What are the units? I'm sure you realize that water transfers heat much faster than air, right? Here's a layman's example for you. You feel comfortable in 70 degree air, but cold in 70 degree water, correct? That's because the water pulls heat from your body much faster than air does. You feel cold in 70 degree water even with no water movement.

Go ahead and laugh your ass "of". I got a kick out of your post.

jlangholzj · May 18, 2009

which is strange considering that 'k' values are measured in "W/(mK)" so wouldn't a higher k value suggest that it takes MORE energy to transfer the heat ???

Hack · May 18, 2009

jlangholzj said:
which is strange considering that 'k' values are measured in "W/(mK)" so wouldn't a higher k value suggest that it takes MORE energy to transfer the heat ???

I'm guessing that the k values you have given in units W/mK describe the rate of heat transfer through a material. What the number tells you is how much heat energy W (watts) will be transferred through the material if you have two plates with different temperatures (K is the temperature difference in Kelvin I assume) a certain distance apart (m) with that material filling the void between them.

I didn't look up to confirm your numbers, but a higher number will predict that more heat energy will be transferred.

D.Hearne · May 18, 2009

Are y'all also takin into account of the fact that the coolant and air are never in contact ? You've got iron, aluminum and brass to take into account too in that equation.

stonecoldtx · May 18, 2009

Hack said:
Imagine blowing on a hot spoonful of soup. Blowing slower will cool the soup faster, right? Of course not! So why do people think that water must move slowly in a radiator? In fact, slow laminar flow is bad for heat transfer. Just ask any turbo expert about intercooler design. You want the fluid to tumble so more of the fluid comes in contact with the hot/cold surfaces.

Well . . . that's not exactly how it works--but let's talk about this for a mintue, and use your soup example:

In your example, the "soup" (let's call this the coolant in the engine) is stationary--non moving; therefore, when you blow across it to cool it (airflow through the radiator), it absorbs/transfers heat of only the top layer.

This is exactly the opposite of what you are advocating with regard to cooling the engine, because you had been saying that the coolant must must faster[/Iand is not stationary!!

Regardless of whether the fluid is stationary or moving, once the heat has been transferred from the top layer, then the lower layers transfer their heat to the next higher level, etc., so if you were to continue to blow across that soup, eventually, all of the heat would be transferred away.

Compare this example to shutting off an engine and allowing an electric fan to continue running; of course, only the coolant in the radiator is cooled, and it's not instantaneouslycooled, it takes some time, and the amount of time it takes is dependent upon the temperature of the coolant, the temperature of the air flowing across the radiator fins and tubes, and the amount of coolant being cooled.

Now--when you are blowing across a MOVING stream of liquid, you only are cooling that one point at a time. Just that one small point.

So, when you pass that fluid through the radiator, you increase the surface area that is exposed to the airflow, and allow a larger amount of fluid to be cooled at once, even though it is moving--and since there is a larger amount of surface area exposed, and it is exposed for a longer amount of time, more heat can be transferred.

However--as I have mentioned above in the case where the engine is not running--it is not instantaneously cooled, and the amount of heat transferred has a limit based on several factors that are engineered into the cooling system (amount of airflow, temperature limits of that airflow, temperature of the coolant flowing through the radiator, radiator capacity, number of cooling fins per inch, etc.).

The longer the airflow passes across a section of the liquid, and/or the more liquid surface area that is exposed to that airflow, the quicker that heat will be absorbed/tranferred/dissipated.

Now, on the OTHER side of the cooling equation--the heat from the engine must be transferred to the liquid. Just as passing the liquid through the airflow too quickly will reduce the cooling effect (transfer of heat), so will passing the coolant too quickly through the water jackets and coolant passages in the cylinder head(s)--the heat cannot be effectively transferred to the coolant.

I've personally seen vehicles overheat specifically because of this issue, and installation of a thermostat resolved the issue.

This is basic thermal dynamics, and it's a fact, not a "myth"; you can read all about it in any book on the subject, at just about any library . . . but--if you feel that it's all just a myth, then as I've mentioned before, by golly all you have to do is remove the thermostat in your own vehicle(s), and see what the effects are after driving at highway speeds for 20 miles or so . . .

Platonic Solid · May 18, 2009

So since my thermostat is the slightly cooler 180° version, rather than the standard 192° one, I assume I'd be wise to stick with SAE 30 weight oil for proper lubrication.

santeechris · May 18, 2009

Hack is crazy. Lets take his soup example. Start pouring soup through a straw, now as it is pouring blow on the straw. If it only takes half a second for the soup to pass through the only cooling source how cool has it gotten? now if you reduce the flow and it takes 2 seconds to get through the straw how cool is it? that is the effect of a reducer. it slows the flow of the soup through the straw, and remember essentially thats all a radiator is. A tank with a bunch of finned straws. A stat takes that one step further. When the bowl of soup reaches a set temp, like 192 degrees it opens a valve, pushing the soup from the bowl (engine) into the straw (radiator). The soup that was in the straw (radiator), now having a chance to cool returns to the bowl (engine) and cools it. it remains until it reaches the temp where it again rotates. As for the reason race cars use restrictors, its simple. Their engines run at such a level that a stat would remain open virtually constantly, BUT full open would not allow the coolant to cool in the radiator at all. To solve this they limit the flow.

woodsnake · May 18, 2009

Here's another take on the whole thermostat thing.

It acts as a restrictor, to hold water in the block UNTIL it reaches what ever operating temp. In this case, 180 deg.

The radiator cap, maintains PRESSURE on the coolant in the radiator. Engine coolant boils at a different temperature than water does. This is a very important point to remember.

The radiator holds the coolant/water mix long enough for the heat to be exchanged from the mix to the air, so that the pump can pull in cooler mix, so the whole cycle can start over again.

Read up on it all here:

HowStuffWorks "How Car Cooling Systems Work"

40oz · May 18, 2009

whether flow rates affect cooling in an engine is immaterial. The thermostat is used to maintain a constant operating temperature regardless of flow rates.

Water is always circulating in your engine. The thermostat just sends it to the radiator when it gets to a set temperature, pumping in cooler water.

Without a thermostat there is no regulation of the water flow. And so there is no control over engine temperatures. It might overheat on cool days and run fine when it's hot and humid. Or it might randomly overheat or run rough. Since your engine generates varying amounts of heat and the water flows wherever it can, there is no consistency.

If you rig it so the water is always pumped through the radiator, you still have no control over engine temps because radiator cooling depends on atmospheric conditions and your engine is still making various amounts of heat depending on how you are driving it. Some days it will cool better and some kinds of driving will fare better or worse.

Basically, people have been forever "proving" an engine will still function without a thermostat. That was never a question.

A better question is why you would ever prefer to not have one? In my climate people have one in every house. They don't just turn on the furnace and leave it. And that's with a furnace that always puts out the same amuont of heat. It makes even less sense if the heat source was always fluctuating.

Hack · May 19, 2009

I agree that you always want to run a thermostat and it is somewhat immaterial why removing the thermostat could possibly cause some systems to run warmer (most will run cooler).

I'm not going to fight about it any more. Too many incorrect theories to refute. Everyone have a great day.

Platonic: I run 5W-30 in my cars in Minnesota. In a very hot climate I would probably run 10W-40. I also run synthetic in the motors that I want to last a good long time. Its benefits may be debateable for engines that don't get run as often, but it's still not much money compared to the cost of building an engine. I would never run straight 30 weight in a car. The multi-viscosity oils are better.

Thermostat - is it necessary?

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