Running without Thermostat - Cools better?

[LeeRoy]

Pressure in a cooling system is a result of a combination of thermal expansion and the fact that the pump is moving the coolant through an engines coolant galleries/radiator which provide resistance and therefore create pressure.

A Thermostat serves many purposes mainly keeping an engine in its presdesigned operating range, which:
- Decreases the time required from startup to reach operating temp
- Reduces emmisions and produces a cleaner running engine
- Create a better idle
- Reduces engine wear

On the note of thermal expansion, an engine expands with the introduction of heat. When the engine is cold, the tolerances within it do not reach what they are designed to in order to run efficiently while minimising wear.

Oil is also selected with reference to these tolerances, with lower tolerances requiring thinner oil, and larger tolerances requiring thicker oil. Oil also thins out when heated.

Now if an engine is designed to run on thin oil (and oil is thicker when cold), and the tolerances are small and require this thin oil, by not having an engine at operating temp the friction will be increased in two ways:

1. Oil being too thick to properly lubricate and stay (or even get into) in low tolerance areas of the engine ie valves and cams, and
2. The gap or tolerance between any two surfaces is lower, making the friction between them greater.

Combine these two things and youve got yourself a recipe for short engine life and costly repairs. All for the sake of a $14 thermostat.

I know which way id be going

[mynameisrodney]

The actual issue is the water doesn't sit in the ENGINE long enough to remove hte heat from the engine.
The coolant stays cool, but the metal gets hotter.

not true. heat will be trasfered faster when the temperature difference is larger ie faster flowing coolant. if you want to test this quickly, stick an ice cube in a glass of water and another one under a running tap and see which melts faster (melting faster = more heat transfer)

[CHB]

what about this myth now? valid or busted?

[wa5]

so i suppose a turbo wont produce pressure because its an impeller? well i suppose i should get a supercharger.

a turbo impeller spinning at six thousand RPM sure wont boost a hell of a lot !

as for the supercharger, I just had a ride in a 6/71 equipped big block Chev...... you could do worse

[oldcorollas]

a turbo impeller spinning at six thousand RPM sure wont boost a hell of a lot !

as for the supercharger, I just had a ride in a 6/71 equipped big block Chev...... you could do worse

not in air it wont... but if you put the turbo in water, and then spin at 6000rpm...

actually, since water is not compressible, and gas is, it's not gonna flow as much as it could since the blades are designed for a less viscous fluid etc etc...

wa5
you cna do a test really really easily... get two lengths of tube, to make to manometers...

connect one to one side of the thermostat housing, and one to the other side (or, assuming that the thermostat is the biggest restriction, you coudl also just use the inlet/outlet of the water pump) and then see which one reads higher.
remember to block off/turn off the heater as well.

then give the engine a few revs (to say, 6000?) and see how it changes.

i haven't done it myself to give you numbers, but i am fairly comnfident you will see more than a small pressure difference..

Kyosho, you forgot the basics of heat transfer theory (yes theory ). higher temp difference = higher rate of heat transfer. faster fluid velocity = higher rate of heat transfer due to the first point.

[roadsailing]

IIRC you want higher pressure in the block to stop the formation of steam bubbles, as they dont conduct (convect to be precise as the fluid is moving) heat away from the metal bits as well as water.

the "water speed" thing is a bit of a theory that people come up with because someone said it once and it sounded right to similarly minded people.

[JoJo]

what about this myth now? valid or busted?

What are you calling a myth?

There is no myth here........

[oldcorollas]

oh the wives tale thing about speed of water...

well.. rate of heat transfer is controlled by temp difference and surfaces adn whatnot.. btu for out purposes, everything is fixed except temperature and fluid velocity.

in radiator, it will lose X amount of heat when it is Y temp.
theoretically, (and practically) having the radiator consistantly hotter will lose more energy.. ie, more joules of heat.
if you run water slowly, it cools down, so by the end of rad, it is not losing as much heat as it could.

ie, faster flowing water in radiator will lose more energy from the radiator, since more of the radiator surface is at a higher temperature, givign a higher temp differential, and increasing rate of heat loss. BUT, it also means that less heat per volume of water is lost, since it is hotter by the end of the radiator than if it was flowing slowly....

the water is hotter, BUT, for a given time period, you are rejecting more heat from the water (even tho it is hotter .. make sense?)

engine. a higher temp differential will make more heat flow from engine to water. to lose heat from the engine, a higher temperature differential is better.
hot water will not lose as much heat from the engine as cold water (assuming that the cold water doesn't overheat during it's path thru engine).
this is purely because of the temperature differential...and regardless of the flow rate.
cold water will always pick up more heat than hot water. slow cold water will pick up heat faster than fast hot water. fast cold water will pick up heat MUCH faster than slow hot water... (which is opposite of what Kyosho said )


this is where it gets complicated and i cbf calculating... (maybe later if i can find diffusion/heat flow book in library)

what you need to do is set up a balanced equation with the temp of engine (and an effective "length"), and the rate of heat tranfer to water (which is a function of temperature) from which we can work out the heat lost to water as it flows though, and the temp increase).
we need the same again with the radiator, taking into accoutn the flow path length, the rate of heat lost (as a funtion of temp) so we can work out the amoutn of heat lost and the temp decrease of the water thru the radiator...

when those two halves balance, the temp is stable. when one side puts in or takes out more heat, the temp changes.

if someone wanted to set up the equations (even just with no numbers), then we can easily see the effect of water velocity on the cooling of an engine

of course this doesn't take into account pressure, boiling and hotspots...

[MWP]

... of course this doesn't take into account pressure, boiling and hotspots...

Which faster flowing coolant/water helps prevent also.

[Grega]

of course this doesn't take into account pressure, boiling and hotspots...

need to start looking at combustion area design, water jacket placement and thickness and design as to flow of water ; plug type and range ; fuel used (some fuels burn hotter, some cooler) the list goes on and on...

in a normal day to day driving car that you use to go from home to work, stick with a thermostat.

for a drifter/track car/whatever purpose you actually want to use it for ; make up your own mind on your application based on your own test results and own experiences....

example my ae92 with 4AFC poo motor now drives absolutely wonderful with the thermostat replaced (it was previously jammed open)

[oldcorollas]

Which faster flowing coolant/water helps prevent also.

as per what grega said...

faster flowing water will not (much) prevent small areas of more concentrated heat (ie, internal corners) from occasioanlly making a bubble or two. a higher pressure (ie, both the radiator cap, and the pressure against a thermostat/restrictor) will help to close the bubbles when they form, or prevent them from forming...

it is not as simple as just flowing faster water...

otherwise... no cars would have radiator caps that pressurise the fluid

[LeeRoy]

example my ae92 with 4AFC poo motor now drives absolutely wonderful with the thermostat replaced (it was previously jammed open)

I concur, the most simple components can have the biggest influence on how a car drives

[darryl]

i've been driving around for 4 months with no thermostat. had no idea it was a bad thing. will get round to not-so-supercheap and get a new one

[LeeRoy]

A general rule with cars is that if it wasnt necessary it wouldnt there from the factory.

[kylestyleup]

A general rule with cars is that if it wasnt necessary it wouldnt there from the factory.

Isn't it for mass production? Considering it will be imported to cold countries?

I think also that is why they invented an anti-freeze coolant.
Our coolant products here at PH don't say "anti-freeze" but "anti-rust" only.

I think thermostat is important when the climate (environmental temp.) changes, like at night time.

As I analyze this conversation, with or without the thermostat, a good flowing coolant/water cools better.