Why does a lower temperature thermostat make an engine run cooler?
11-29-2001, 03:21 PM
#1
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Why does a lower temperature thermostat make an engine run cooler?
OK I was just thinking about how a thermostat works...and I'm not sure I understand why anyone would bother with a low temperature thermostat.
The way I understand it, a thermostat opens at the temperature it's rated for...let's say 180 degrees. It's not uncommon for an automotive cooling system can run up as high as 200, maybe more. So both a 160 deg. thermostat and a 180 deg. thermostat will both be open before the coolant reaches peak temperature.
Once either one is open, all other things remaining equal, the amount of heat built up in the engine shouldn't change after that. Therefore, after either one is open, they are both doing the same thing...simply letting coolant into the engine.
I'm sure I'm missing something obvious here but I can't put my finger on it. Anyone?
The way I understand it, a thermostat opens at the temperature it's rated for...let's say 180 degrees. It's not uncommon for an automotive cooling system can run up as high as 200, maybe more. So both a 160 deg. thermostat and a 180 deg. thermostat will both be open before the coolant reaches peak temperature.
Once either one is open, all other things remaining equal, the amount of heat built up in the engine shouldn't change after that. Therefore, after either one is open, they are both doing the same thing...simply letting coolant into the engine.
I'm sure I'm missing something obvious here but I can't put my finger on it. Anyone?
11-29-2001, 06:31 PM
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Re: Why does a lower temperature thermostat make an engine run cooler? (krshultz)
As I understand it, the lower engagement temp allows the coolant to enter the engine sooner and do its job at a lower temp.
Say, for example, that the coolant travelling through the system is able to lower the engine temp by 20 degrees regardless of the actual temp of the engine. Therefor, if the thermostat allows coolant through the engine at 180 degrees then it will cool the engine to 160 degrees, and if at 160 degrees then cools it down to 140 degrees. I believe engine coolant will always provide a consistant drop in temp.
I also believe that it also signals radiator fan engagement.
I'm just taking a stab at this, so I am sure that someone will correct me if I am wrong.
Say, for example, that the coolant travelling through the system is able to lower the engine temp by 20 degrees regardless of the actual temp of the engine. Therefor, if the thermostat allows coolant through the engine at 180 degrees then it will cool the engine to 160 degrees, and if at 160 degrees then cools it down to 140 degrees. I believe engine coolant will always provide a consistant drop in temp.
I also believe that it also signals radiator fan engagement.
I'm just taking a stab at this, so I am sure that someone will correct me if I am wrong.
11-29-2001, 09:35 PM
#3
Honda-Tech Member
Re: Why does a lower temperature thermostat make an engine run cooler? (krshultz)
Shultz and I had a little IM discussion about this last night (apologies to shultz):
krshultz: Hey, a conversation you and I had a long time ago got me thinking.
krshultz: https://honda-tech.com/zerothread?id=95250
bmwdsp32: T-stat just keeps the coolant at the temp of the t-stat
krshultz: or higher, right?
bmwdsp32: no
bmwdsp32: if the t-stat was wide-open (stuck), the coolant temp would normally be cooler than the t-stat temp
bmwdsp32: wide open = too much cooling
krshultz: Umm...
bmwdsp32: closed = not enough cooling
bmwdsp32: somewhere inbetween = at the t-stat temp
krshultz: unless the engine was in a condition such that it was running at 200?
krshultz: Dunno...that's why I asked...
bmwdsp32: Think about it this way - cooling systems are overdesigned to be able to cool continuously under the most severe conditions -- at the revlimiter, uphill, in 1st gear, in 100 degree heat.
bmwdsp32: THEN the t-stat would stay near wide open
bmwdsp32: Every other time, the t-stat just hovers partially closed, partially open
bmwdsp32: It's an equilibrium state
krshultz: ok...
bmwdsp32: If your radiator sucks, the t-stat has to stay wider to maintain the temp. And overtemp is more likely to occur.
krshultz: OK.
krshultz: So a low temp thermostat does...what?
bmwdsp32: Low tstat maintains a lower overall coolant, and engine temp
bmwdsp32: Not neces. good
bmwdsp32: Must burn all the moisture out of the oil.
bmwdsp32: And hotter engine runs more efficiently
bmwdsp32: Want to run as hot as possible without reliability concerns.
bmwdsp32: Limited by the materials, primarilt
bmwdsp32: y
bmwdsp32: I wouldn't be surprised if F1 engines run at 240F
bmwdsp32: Intentionally.
krshultz: I knew I could count on my local giant nerd to explain.
bmwdsp32: Do you understand? I'd need a pen and paper to do it justice
krshultz: I think so...the stat isn't an on - off switch.
bmwdsp32: Even if the tstat was an on-off switch, it'd still work the same.
bmwdsp32: Scenario: 180F t-stat closed, coolant at 160. No radiator cooling. Engine heats coolant to 185. Tstat opens. Surplus cooling. Coolant cools to 175. t-stat closes. No rad cooling. Engine heats coolant to 185. Tstat opens. repeat. Average engine temp = tstat temp
krshultz: OK say you're doing an extended dyno run. Engine is going to run at x degrees. So...does stat temperature matter in this case?
bmwdsp32: Dyno run = high load = tstat will be open more often (or wider) than idling.
krshultz: Ahh, I think I get it.
krshultz: But there's an assumption that the engine will run at a temperature at or close to where the stat is rated.
bmwdsp32: ??
bmwdsp32: Engines run fine when surrounded by 180, or 200, or 220F coolant
krshultz: Because taking x amount of fuel/air, and converting it to y amount of energy, results in z heat...right?
bmwdsp32: Yes
krshultz: Remember, I studied psych in college...
krshultz: So if I had a 50 degree stat my car would run at 180 (for example) regardless?
bmwdsp32: No, it'd run at 50
bmwdsp32: One un-mentioned false assumption -- the coolant around the engine will always be hotter than the coolant at the bottom of the radiator, after cooling.
bmwdsp32: Well, you'd need a giant-*** radiator and some cold outside air to run the coolant at 50
krshultz: So what happens when the z heat out of the engine outpaces the cooling system...but not by that much?
krshultz: Like the engine wants to run at 60 for example.
krshultz: Well I'm of course making huge generalizations here
bmwdsp32: Then the t-stat is wide open, all the time, the coolant temp average rises above the t-stat point, and she's gonna blow
bmwdsp32: Keep in mind -- all cars (recently) are designed with overcapacity cooling systems. Rarely gonna need more than they can do
krshultz: Shouldn't the t-stat temp be below the max. temp of the cooling system?
krshultz: I mean, you see 160 deg stats all the time...
krshultz: and 212 is boiling.
krshultz: So...What happens to those extra 52 degrees?
bmwdsp32: 212 is boiling = what do you mean?
bmwdsp32: "extra"?
krshultz: I'm being theoretical here.
bmwdsp32: None of the coolant is ever at the boiling point. It's all liquid
bmwdsp32: OK, another scenario, assuming you understand #1. Idling, say the t-stat is 25% open (or open 25% of the time) to maintain 180F. On the dyno, it might be open 75% of the time to maintain the 180F.
bmwdsp32: If the radiator's all clogged up, on the dyno it might be open 100%, and the coolant temp will begin to exceed the tstat point, cause the rad cannot take heat out as fast as the engine is putting it in.
bmwdsp32: Clear as mud?
krshultz: Getting there.
krshultz: I guess I've got the order of operations wrong...
bmwdsp32: Order?
krshultz: You seem to be saying that the stat determines (to some degree) operating temperature. I was thinking that output determined operating temperature, and that stat temps didn't matter.
krshultz: Does that make sense?
krshultz: (probably not)
bmwdsp32: You were right on the first point, absolutely -- tstat temps determine operating temps.
bmwdsp32: Of course, coolant in the engine water jacketr will be slightly warmer than right at the tstat
bmwdsp32: If you took the tstat away, then, absolutely -- output determines operating temps. Air-cooled motorcycle engines are basically like this.
krshultz: And the car would always just run real cold?
bmwdsp32: With the radiator in place and no t-stat, yes, the engine would _always_ be too cold
bmwdsp32: (unless radiator is plugged, system messed up, etc)
krshultz: This all has the underlying assumption that the cooling system is more than adequate?
bmwdsp32: Yes, cause it's a correct assumption.
bmwdsp32: If you ever hear of someone's car overheating, or their temp gauge moving above where it usually does, then the cooling system is inadequate, either by malfunction or design
krshultz: I mean...can you have a cooling system that will only cool x amount of energy to y degrees?
bmwdsp32: Yes
krshultz: So if the cooling system is inadequate, it will IMMEDIATELY move beyound stat temperature and overheat?
bmwdsp32: No, not necc.
krshultz: well not immediately, but quickly...
krshultz: Well I've read about people towing with blah truck that has a temp gauge.
krshultz: "My truck runs at 200 degrees."
krshultz: So why would it matter if it's a 160 or 180 t-stat?
bmwdsp32: OK, scenario -- cut your radiator in half and reinstal.
bmwdsp32: At idle (before, the tstat was open 25%), now it's open 50%
bmwdsp32: On the dyno, (before, the tstat was open 75%), now it's ... uh-oh, overheat city
bmwdsp32: On the street at 45 MPH, before it might have been open 50% to maintain temp. Now it's open 100%
krshultz: OK OK I SEE...the thermostat isn't a "binary" device. The thermostat is a continuum.
bmwdsp32: But... it CAN be a binary device.
krshultz: So once it's open 100%...umm...
bmwdsp32: being open at 25% width is the same as it pulsating 1 cycle/second and being open 15 seconds per minute.
bmwdsp32: Or 15 times per minute.
krshultz: Is the "160 degree" rating on a thermostat at 100 percent open?
bmwdsp32: NO! AAAh! I need to be sitting in front of you to do this justice!
bmwdsp32: The 160 rating means it will start to open at 160
bmwdsp32: It's in equilibrium at 160
krshultz: Remember...psych degree, not a masters from MIT...
krshultz: I'm not very smart...
krshultz: ..we'll talk about this at the party. I need to go to bed.
bmwdsp32: Thermostats spend the vast majority of their life partially open and partially closed, or damn close to it
bmwdsp32: Hey, can I post this discussion to H-T? Might solve some confuesed posting
krshultz: Hey, a conversation you and I had a long time ago got me thinking.
krshultz: https://honda-tech.com/zerothread?id=95250
bmwdsp32: T-stat just keeps the coolant at the temp of the t-stat
krshultz: or higher, right?
bmwdsp32: no
bmwdsp32: if the t-stat was wide-open (stuck), the coolant temp would normally be cooler than the t-stat temp
bmwdsp32: wide open = too much cooling
krshultz: Umm...
bmwdsp32: closed = not enough cooling
bmwdsp32: somewhere inbetween = at the t-stat temp
krshultz: unless the engine was in a condition such that it was running at 200?
krshultz: Dunno...that's why I asked...
bmwdsp32: Think about it this way - cooling systems are overdesigned to be able to cool continuously under the most severe conditions -- at the revlimiter, uphill, in 1st gear, in 100 degree heat.
bmwdsp32: THEN the t-stat would stay near wide open
bmwdsp32: Every other time, the t-stat just hovers partially closed, partially open
bmwdsp32: It's an equilibrium state
krshultz: ok...
bmwdsp32: If your radiator sucks, the t-stat has to stay wider to maintain the temp. And overtemp is more likely to occur.
krshultz: OK.
krshultz: So a low temp thermostat does...what?
bmwdsp32: Low tstat maintains a lower overall coolant, and engine temp
bmwdsp32: Not neces. good
bmwdsp32: Must burn all the moisture out of the oil.
bmwdsp32: And hotter engine runs more efficiently
bmwdsp32: Want to run as hot as possible without reliability concerns.
bmwdsp32: Limited by the materials, primarilt
bmwdsp32: y
bmwdsp32: I wouldn't be surprised if F1 engines run at 240F
bmwdsp32: Intentionally.
krshultz: I knew I could count on my local giant nerd to explain.
bmwdsp32: Do you understand? I'd need a pen and paper to do it justice
krshultz: I think so...the stat isn't an on - off switch.
bmwdsp32: Even if the tstat was an on-off switch, it'd still work the same.
bmwdsp32: Scenario: 180F t-stat closed, coolant at 160. No radiator cooling. Engine heats coolant to 185. Tstat opens. Surplus cooling. Coolant cools to 175. t-stat closes. No rad cooling. Engine heats coolant to 185. Tstat opens. repeat. Average engine temp = tstat temp
krshultz: OK say you're doing an extended dyno run. Engine is going to run at x degrees. So...does stat temperature matter in this case?
bmwdsp32: Dyno run = high load = tstat will be open more often (or wider) than idling.
krshultz: Ahh, I think I get it.
krshultz: But there's an assumption that the engine will run at a temperature at or close to where the stat is rated.
bmwdsp32: ??
bmwdsp32: Engines run fine when surrounded by 180, or 200, or 220F coolant
krshultz: Because taking x amount of fuel/air, and converting it to y amount of energy, results in z heat...right?
bmwdsp32: Yes
krshultz: Remember, I studied psych in college...
krshultz: So if I had a 50 degree stat my car would run at 180 (for example) regardless?
bmwdsp32: No, it'd run at 50
bmwdsp32: One un-mentioned false assumption -- the coolant around the engine will always be hotter than the coolant at the bottom of the radiator, after cooling.
bmwdsp32: Well, you'd need a giant-*** radiator and some cold outside air to run the coolant at 50
krshultz: So what happens when the z heat out of the engine outpaces the cooling system...but not by that much?
krshultz: Like the engine wants to run at 60 for example.
krshultz: Well I'm of course making huge generalizations here
bmwdsp32: Then the t-stat is wide open, all the time, the coolant temp average rises above the t-stat point, and she's gonna blow
bmwdsp32: Keep in mind -- all cars (recently) are designed with overcapacity cooling systems. Rarely gonna need more than they can do
krshultz: Shouldn't the t-stat temp be below the max. temp of the cooling system?
krshultz: I mean, you see 160 deg stats all the time...
krshultz: and 212 is boiling.
krshultz: So...What happens to those extra 52 degrees?
bmwdsp32: 212 is boiling = what do you mean?
bmwdsp32: "extra"?
krshultz: I'm being theoretical here.
bmwdsp32: None of the coolant is ever at the boiling point. It's all liquid
bmwdsp32: OK, another scenario, assuming you understand #1. Idling, say the t-stat is 25% open (or open 25% of the time) to maintain 180F. On the dyno, it might be open 75% of the time to maintain the 180F.
bmwdsp32: If the radiator's all clogged up, on the dyno it might be open 100%, and the coolant temp will begin to exceed the tstat point, cause the rad cannot take heat out as fast as the engine is putting it in.
bmwdsp32: Clear as mud?
krshultz: Getting there.
krshultz: I guess I've got the order of operations wrong...
bmwdsp32: Order?
krshultz: You seem to be saying that the stat determines (to some degree) operating temperature. I was thinking that output determined operating temperature, and that stat temps didn't matter.
krshultz: Does that make sense?
krshultz: (probably not)
bmwdsp32: You were right on the first point, absolutely -- tstat temps determine operating temps.
bmwdsp32: Of course, coolant in the engine water jacketr will be slightly warmer than right at the tstat
bmwdsp32: If you took the tstat away, then, absolutely -- output determines operating temps. Air-cooled motorcycle engines are basically like this.
krshultz: And the car would always just run real cold?
bmwdsp32: With the radiator in place and no t-stat, yes, the engine would _always_ be too cold
bmwdsp32: (unless radiator is plugged, system messed up, etc)
krshultz: This all has the underlying assumption that the cooling system is more than adequate?
bmwdsp32: Yes, cause it's a correct assumption.
bmwdsp32: If you ever hear of someone's car overheating, or their temp gauge moving above where it usually does, then the cooling system is inadequate, either by malfunction or design
krshultz: I mean...can you have a cooling system that will only cool x amount of energy to y degrees?
bmwdsp32: Yes
krshultz: So if the cooling system is inadequate, it will IMMEDIATELY move beyound stat temperature and overheat?
bmwdsp32: No, not necc.
krshultz: well not immediately, but quickly...
krshultz: Well I've read about people towing with blah truck that has a temp gauge.
krshultz: "My truck runs at 200 degrees."
krshultz: So why would it matter if it's a 160 or 180 t-stat?
bmwdsp32: OK, scenario -- cut your radiator in half and reinstal.
bmwdsp32: At idle (before, the tstat was open 25%), now it's open 50%
bmwdsp32: On the dyno, (before, the tstat was open 75%), now it's ... uh-oh, overheat city
bmwdsp32: On the street at 45 MPH, before it might have been open 50% to maintain temp. Now it's open 100%
krshultz: OK OK I SEE...the thermostat isn't a "binary" device. The thermostat is a continuum.
bmwdsp32: But... it CAN be a binary device.
krshultz: So once it's open 100%...umm...
bmwdsp32: being open at 25% width is the same as it pulsating 1 cycle/second and being open 15 seconds per minute.
bmwdsp32: Or 15 times per minute.
krshultz: Is the "160 degree" rating on a thermostat at 100 percent open?
bmwdsp32: NO! AAAh! I need to be sitting in front of you to do this justice!
bmwdsp32: The 160 rating means it will start to open at 160
bmwdsp32: It's in equilibrium at 160
krshultz: Remember...psych degree, not a masters from MIT...
krshultz: I'm not very smart...
krshultz: ..we'll talk about this at the party. I need to go to bed.
bmwdsp32: Thermostats spend the vast majority of their life partially open and partially closed, or damn close to it
bmwdsp32: Hey, can I post this discussion to H-T? Might solve some confuesed posting
11-29-2001, 11:12 PM
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Re: Why does a lower temperature thermostat make an engine run cooler? (whitney)
Very very good food for thought. Does anyone know the best operating temp for the GSR and Type R engines? Mugen makes a thermosatat for the Integra is it worth the price?
11-30-2001, 10:58 AM
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Re: Why does a lower temperature thermostat make an engine run cooler? (Kelvin96GSR)
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