# What's the theory behind the computer controlled thermostat?



## Dale_K (Jul 16, 2011)

I don't understand the reasoning behind the computer controlled thermostat. Sometimes I've heard people say it allows the motor to warm up faster but I don't see any difference between my Cruze and my GMC pickup with an old-fashioned mechanical thermostat. The Cruze doesn't warm up any faster and it's hard for me to imagine how a smart thermostat can close the flow any better than a mechanical stat. They're both going to be solidly closed until the temp comes up.

I don't doubt there's something going on with these smart thermostats since I see they're on plenty of new generation motors but I don't understand why they're better.


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## StoneCrab (Sep 14, 2011)

Good question. In theory the computer could more tightly control the coolant temp than a mechanical open/closed thermostat. But practically speaking I'm not sure how much different it is. In my 2012 I watch the coolant temp on the DIC, it always rises to 225F, thermostat opens and it drops to about 214, then is regulated up to 217 and stays exactly at 217 as long as I have some air flow across the radiator. Maybe the computer is adjusting the thermostat to stay precisely at 217F.


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## maven (Feb 27, 2011)

The thermostat starts to open at 221°F naturally and with ECM help as early 176°F. It is fully open naturally at 248°F. They do this just so the ECM can have a broader range of control over coolant temps. this is for fuel efficiency and emissions.

With a standard thermostat the ECM cant control engine coolant temps other than by using the fans.


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## 70AARCUDA (Nov 14, 2010)

...what *maven said*. Also, when cruising under *light load*, the computer runs the thermostat at a _*higher* temperature _for better fuel economy. But, when running under a *heavy power load*, the computer runs the thermostat back down at a _*lower* temperature _for less heat-strain on both the engine AND the turbocharger--remember, it too is being "cooled" by the engine coolant.

...and, when the engine is under heavy load, with maxmium turbo spool happening, there's heat being dissipated from the intercooler, which is physically sandwiched _between_ the A/C- and engine-radiators. That's _additional_ heat being put into the engine radiator, so lowering the coolant temperature, means a slightly smaller engine radiator is needed (because of the back down in coolant temp at higher engine loads).


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## montgom626 (Jan 16, 2011)

StoneCrab said:


> In my 2012 I watch the coolant temp on the DIC,


You can read the temp in the DIC on a 2012????? Cool


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## GoldenCruze (Dec 18, 2011)

70AARCUDA said:


> ...what *maven said*. Also, when cruising under *light load*, the computer runs the thermostat at a _*higher* temperature _for better fuel economy. But, when running under a *heavy power load*, the computer runs the thermostat back down at a _*lower* temperature _for less heat-strain on both the engine AND the turbocharger--remember, it too is being "cooled" by the engine coolant.
> 
> ...and, when the engine is under heavy load, with maxmium turbo spool happening, there's heat being dissipated from the intercooler, which is physically sandwiched _between_ the A/C- and engine-radiators. That's _additional_ heat being put into the engine radiator, so lowering the coolant temperature, means a slightly smaller engine radiator is needed (because of the back down in coolant temp at higher engine loads).


I have to agree, and that explains what I observed during a 500 mile trip today. The coolant usually runs at 224 degrees. During some climbs up 6% and 7% grades at 75mph on cruise control, I saw the temp drop to 204 degrees while the engine was working harder. It then climbed back to 225 degrees going down the other side of the mountain.


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## 70AARCUDA (Nov 14, 2010)

...reading the *GM Service Manuals *has a _few_ benefits.


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## DrVette (Dec 6, 2011)

Quote;
"reading the GM Service Manuals has a few benefits"

I totally agree, however some owners struggle with 
the payment, 
the $75+ monthly insurance payment and 
a $200+ ad-valorem tax. 

Not to mention service costs.

Rusty Wrench


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## montgom626 (Jan 16, 2011)

70AARCUDA said:


> ...what *maven said*. Also, when cruising under *light load*, the computer runs the thermostat at a _*higher* temperature _for better fuel economy. But, when running under a *heavy power load*, the computer runs the thermostat back down at a _*lower* temperature _for less heat-strain on both the engine AND the turbocharger--remember, it too is being "cooled" by the engine coolant.
> .


cuda, you are the best!


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