# extreme heat, the engine fan and coolant temps



## CruzeEcoBlueTopaz (Jan 5, 2012)

This post is about a few observations I have made over the past year and in fact more recently the last couple weeks. 

I have noticed the normal operating coolant temp to be right around 217F degress. During increased loads such as a steep terrain increase of a few thousand feet that I encounter on a daily basis the coolant temperature reachs about 226F rather quickly with a high of about 228F and on rare occasions 232F now its about this time I reach the top and start to descend and the coolant goes back to a normal operating temp. Now these temperatures happen pretty much everyday EXCEPT when it gets to be about 95F degrees + and then the engine fan will decide to turn on depending on the engine load. By the way the engine fan does a great job of reducing the coolant temperature by about 10-15F degrees and keeping it at about 205F.

Just recently in Idaho we experinced temperatures of 110F and during cruising speeds of about 60mph with no A/C on the engine fan would stay on and keep the coolant temp at about 205F. Basically what im saying is I have noticed that most of the year the engine fan doesnt turn on until outside temps start reaching about 95F+ degress and when it does turn on it works great at keeping the coolant temperature down. 

So does the cars computer turn on the engine fan based on the outside ambient temperature because it doesnt seem to turn on based on the coolant temperature ?


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## brian v (Dec 25, 2011)

The smurfettes will be here soon enough to write all about thermal dynamics and such who knows snow man could make an appearance !


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## spacedout (Dec 7, 2010)

I noticed the fan running today in my car, 88degrees outside and no AC use. It was only running at slow/quiet speed, you should hear it when it really kicks in. This was after 1.5hrs of driving though. 

Think the thermostat might also change its rate of flow under load, have noticed 20+ degree drops in temp when climbing hills and once cresting the hill within 30seconds the car climbing back to the normal 217-225degrees. As quick as these changes happen there is no way it's the fan alone cooling things off.


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## jblackburn (Apr 14, 2012)

Intake air temps are probably taken into account. 

Mine keeps running around 208 in the 90s here. Ac is always on unless its nighttime. 


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## Hoon (Mar 18, 2012)

I'm not exactly sure what the PCMs parameters are, but it varies fan turn on temp and thermostat open temp based on conditions. 

If you beat on the car, even in the cold, it will reduce the operating temp to 200 degrees also.


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## CruzeEcoBlueTopaz (Jan 5, 2012)

The coolant temp seems to stay at a consistant 217 F all year except for the summer months when daytime highs approach 95-100 F degrees. If I recall even during winter when outside temperatures are in the single digits the coolant temp remains at 217 F which leads me to beleive the fan is almost never turning. And the reason I know this is because when the engine fan is on the coolant temps stay at 205 F. Which like I said only seems to happen during days of extreme heat. I have also noticed if its 95F degress out and im cruising on the highway the fan is not on and my coolant temp is at 217 F and then if I stop and park for a minute the engine fan will kick on. 

Anyways I was just curious about how and when the car decides to use the fan. I think on my drive I will get out the car once I reach the top of the mountain climb when my coolant temp is at 225 F and quickly check to see if the fan is on. Im sure by the time I stop and pop the hood it will kick on before I have time to check but its worth a try.


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## spacedout (Dec 7, 2010)

jblackburn said:


> Intake air temps are probably taken into account.
> 
> Mine keeps running around 208 in the 90s here. Ac is always on unless its nighttime.


Doesn't the engine fan always run with the AC on? Does on most other GM cars & trucks. Will have to check next time I use the AC.


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## Bohdan (Apr 28, 2012)

It all depends on the electronic Thermostat. This is the first car I have ever owned with such. The engine runs alot hotter at times as the Thermostat is controled as to when to fully open and remain as such. For the Cruze with the auto climate control on and the engine is cold the fan comes on and remains on.


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## jblackburn (Apr 14, 2012)

spacedout said:


> Doesn't the engine fan always run with the AC on? Does on most other GM cars & trucks. Will have to check next time I use the AC.


Yes, when the high side pressure of the system comes up to a certain point. 


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## ErikBEggs (Aug 20, 2011)

I actually am taking mine in on Wednesday. I think my heat sensor is shot. The engine fan is louder than normal and is spinning on the 65F morning we had the other day when my A/C was off. The only way it shuts up is when I turn the car off


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## au201 (May 18, 2013)

ErikBEggs said:


> I actually am taking mine in on Wednesday. I think my heat sensor is shot. The engine fan is louder than normal and is spinning on the 65F morning we had the other day when my A/C was off. The only way it shuts up is when I turn the car off


Does your coolant temp gauge stay at cold?


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## CruzeEcoBlueTopaz (Jan 5, 2012)

Last week Idaho set record highs at 110F two days in a row. I do not use my a/c at all I suffer and sweat it out by rolling down the windows and using gel ice packs. Yes I know im crazy but I will tough it out this summer just as a did last summer. I would rather reduce the engine load and keep my MPG up. Because there is a noticable decrease in instant mpg by about 10-15 with the a/c on even at highway speeds. Some might argue rolling the windows down increases drag and reduces mpg but I have not seen any noticable decrease on the instant mpg from rolling the window down. I have tried using the a/c and at the end of the day driving 375 miles my mpg is reduced from 58 on the DIC to 49.

Regarding the engine fan as I was saying up until about 2 weeks ago I have never caught my coolant temp below about 215F which leads me to believe the fan has never turned on all year well up until about 2 weeks ago when I noticed my coolant temp at 205 F while cruising on the highway in 100F heat. I only know of 1 speed for the fan on and off but I could be wrong. 

Some cruze owners have even reported the engine fan starting and staying on while the car is started with the hood open. Yeah mine doesnt do that. Im not complaining about the fan at all the car does a great job at staying cool and at normal operating temperatures. Im just curious about when and how the computer decides to use it. If it depends on the air intake temp from outside or the coolant temp.

If the fan is electric and it doesnt have any impact on the engines efficiency and it does such a great job at keeping the coolant temp 10-15 degrees lower why isnt it always running ?


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## CruzeEcoBlueTopaz (Jan 5, 2012)

I also would like to note I have been running 91 octane fuel the past 4 weeks during this extreme heat and my avg MPG for the month after driving more then 7,500 miles was at 51.6 up 1mpg from this time last year. That is mainly a result of me slowing down on average about 6mph and due to better weather conditions such as warmer temperatures and much less wind. 

Plain and simple each day I do about 375 miles and on an average day will consume 7 to 7.2 gallons regardless of which octane im using wether its 91 or 87. I hate to say it I just dont see a noticable increase not even 1mpg more using 91. In fact im going to switch back to 87 non ethanol for the month of July and I guarantee my monthly mpg avg is going to be about 52mpg which will be about a 1/2 mpg increase from last month using 91 with both months being exactly the same weather conditions, speed and route. 

Im in sort of a delimmea here I would prefer to use 91 top tier non ethanol but its not available to me only 91 top tier is which is what I have been using the past month. Now the past year I have been using 87 top tier non ethanol which has been fine except im concerned about engine damage from low octane fuel. If this isnt an issue and in fact 87 octane is perfectly fine and harmless for the engine I will continue to use it because for me non ethanol and top tier are more of a priority for me then octane.


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## jblackburn (Apr 14, 2012)

Coolant temps run high for emissions purposes. I suspect it reduces temps by running the fan and regulating the thermostat when it detects knock (from high outside temps pre-igniting fuel) often. 

2 fan speeds - low speed as for the AC and then JET PLANE (usually happens when the thermostat or water pump goes bad. Or in my place, an expansion valve driving the high side AC pressure past 450 psi). 

My comfort > MPG. Forget that 110 degree crap. I've also noticed that I tend to shift a lot higher with the AC on to make up for the sapped power, so I imagine mine will take a real nosedive now that it's going to stay hot outside. 93 makes a huge difference when running the AC. It was fine on lower octane (87/89) without it. 


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## Chevy Customer Care (Oct 29, 2011)

Hi Erik

Please let me know how things go at the dealer and don't hesitate to send me an inbox message if you have any questions or need my assistance. 

Jackie
Chevrolet Customer Care


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## GM Master Tech (Nov 11, 2012)

Are you sure you not low on coolant.Sounds like the leaking water pump problem.


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## Blue Angel (Feb 18, 2011)

The Cruze has a radiator fan, an electrically manipulated thermostat, and the Eco adds to that the lower grille shutters. Your car has three methods of controlling coolant temperature.

I don't know 100% for sure with the Cruze, mostly just because I've never actually read it somewhere, but most if not all cars with electric fans do not operate them above a certain speed. They rely solely on airflow unless coolant temps get above the high speed fan setpoint temperature. I believe this is the case even when using AC, but I don't claim to know for sure with every car. I imagine at 60 MPH the Cruze never turns the fans on unless it detects an overheating condition.

That leaves the thermostat and the shutters.

The thermostat opens and reduces coolant temperature when the engine is under a certain amount of load. It's also possible that it opens when the ambient temps exceed a certain point. I think this is what you're seeing, not the fan operating.

The shutters are also temperature controlled and will open if the coolant temps dictate more airflow is required over the rad. I don't know anything specific about when it attempts to open and close, other than the GM PR info stating that it closes at speeds above 40 MPH and will open if needed for cooling. I'm pretty sure mine stays closed almost all the time in the winter since it was always closed when the car was parked.

Regarding AC, I avoid it as much as possible also and I don't buy into the nonsense that opening windows takes more power. I'm sure if you are driving with all of the windows fully down there would be a point where at some speed the drag would cause more loss than using the AC, but who needs to drive with ALL of the windows down fully at those speeds?

I crack both passenger side windows down about 3-4 inches and leave the driver's side glass up. This makes a nice rotating breeze in the car that creates minimal drag and still keeps me cool enough unless it's really hot out (or "she" is in the car complaining about the heat). Doing the pass side windows down all the way creates quite a breeze in the car and may be even more effective than having all the windows down, with less drag.

Keeping the driver's side windows up will also protect you from hearing loss associated with wind blowing in your ears at high speed for extended periods of time... you do a LOT of driving.


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## CruzeEcoBlueTopaz (Jan 5, 2012)

I have noticed that the engine fan never turns on for me unless its like at least 90 - 95F + degrees outside and when its 95 - 100F + outside its pretty much always on. And im not talking about while the a/c is on because I do not use it. I usually can tell when the engine fan is running because pretty much any other time of the year except the hot summer weeks my coolant temp is at 217F and when the fan is on its usually at 203F.

I totally agree with everything you just typed out BlueAngel


One thing I would also like to point out is that we have had 3 days in the past 2 weeks of extreme 110F + degree weather here in Idaho and I noticed on those days my fuel efficiency was slightly reduced. So it seems that extreme cold AND heat can have similar impacts on efficiency.


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## ErikBEggs (Aug 20, 2011)

Ok. Don't mean to derail your thread CruzeEcoBlueTopaz.

I got my Cruze back today. It was a defective water pump that was leaking coolant. It caused the thermostat to go crazy. My temp gauge was always reading normal temps, yet the dealer said on their test drive they measured it at 273F (trifecta runs around 205F normally). Everything was covered under warranty. They told me that the radiator fan usually will not engage unless driver temp controls are active or temperatures are rather extreme on the hot side. The radiator fan now is back to normally and isn't on under normal driving.

CruzeEcoBlueTopaz - I understand you wanting to get better fuel economy but physics and mythbusters prove that over 50 mph lowering windows affects the aerodynamics of the car more than the additional load caused by A/C. The car doesn't use much energy at all on the highway as is so A/C won't make much difference. It makes sense to just be comfortable and not put your health at risk because you may not be saving any fuel at all. I believe there was a thread that said it takes only 10 HP to move a Cruze Eco at highway speed. Not much in the grand scheme of things.



Blue Angel said:


> Regarding AC, I avoid it as much as possible also and I don't buy into the nonsense that opening windows takes more power. I'm sure if you are driving with all of the windows fully down there would be a point where at some speed the drag would cause more loss than using the AC, but who needs to drive with ALL of the windows down fully at those speeds?
> 
> I crack both passenger side windows down about 3-4 inches and leave the driver's side glass up. This makes a nice rotating breeze in the car that creates minimal drag and still keeps me cool enough unless it's really hot out (or "she" is in the car complaining about the heat). Doing the pass side windows down all the way creates quite a breeze in the car and may be even more effective than having all the windows down, with less drag.
> 
> Keeping the driver's side windows up will also protect you from hearing loss associated with wind blowing in your ears at high speed for extended periods of time... you do a LOT of driving.


Cars now are meant to be driven on the highway with windows completely up. There is a very delicate slipstream that these cars go through.. which is why they spend so much time in the wind tunnel. Try this.. lower your windows on the highway a few inches at highway speeds then close them while driving at 60 mph. You should feel pressure in your ear and hear a suction sound. That is the slipstream I'm talking about.


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## CruzeEcoBlueTopaz (Jan 5, 2012)

Well thats great news. I bet you feel a bit of relief now knowing you have a new water pump doing its job and the fact that it was covered under warranty. I put my head in my engine with a flash light every weekend and check for leaks and oil and so far after 130k its still as chevy would say LIKE A ROCK.

Allright tomorrow im going to try it I will only use the a/c at highway speeds. Now if I understand correctly my efficiency will actually slightly increase because of the less drag on the car. Right now im getting between 51 and 52mpg daily. I will post friday what my mpg was for thursday.


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## ErikBEggs (Aug 20, 2011)

CruzeEcoBlueTopaz said:


> Allright tomorrow im going to try it I will only use the a/c at highway speeds. Now if I understand correctly my efficiency will actually slightly increase because of the less drag on the car. Right now im getting between 51 and 52mpg daily. I will post friday what my mpg was for thursday.


Yes give it a try. Usually 50 mph is the barrier. It is also helpful if to only use it after the car cools down a bit through the windows ya know? There is a difference between proper A/C use and excessive (where must of us screw up, lol). Also, do you have any kind of tint on your car?


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## jblackburn (Apr 14, 2012)

> The car doesn't use much energy at all on the highway as is so A/C won't make much difference. It makes sense to just be comfortable and not put your health at risk because you may not be saving any fuel at all. I believe there was a thread that said it takes only 10 HP to move a Cruze Eco at highway speed. Not much in the grand scheme of things.


My Cruze gets better MPG with AC off and windows slightly cracked. My Volvo did the same thing. 

Granted, I tend to like my AC cold, so it's on 2 or more on the highway.

This is at 65-75 MPH.


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## ErikBEggs (Aug 20, 2011)

jblackburn said:


> My Cruze gets better MPG with AC off and windows slightly cracked. My Volvo did the same thing.
> 
> Granted, I tend to like my AC cold, so it's on 2 or more on the highway.
> 
> This is at 65-75 MPH.


Well, engine load is higher at those speeds and can you tell by how much your fuel economy is increased? You would need a pretty scientific test to prove it...


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## spacedout (Dec 7, 2010)

With the automatic with 50/50 city or more I seem to loose 4-6mpg with AC use. However at speeds above 65mph It seems to be more like 2-3mpg at most. At 45-55mph the loss in MPG is much greater, because you are putting a huge load on the engine below the power curve(similar to using the AC in the city). 

58mph is 2,000RPM with the automatic, so one really should be above that RPM/speed to not put so much strain on the already hot engine. I have only been using my AC above this speed/RPM this year and have so far only lost 1-2MPG from my previous fill ups. 

Route does come into play with this loss, one interstate route I take has lots of up and downhill sections and since I am burning a ton more fuel uphill anyway the AC use makes no difference. On the downhill in DFCO the AC is free(also better compression braking with the AC on too).


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## ErikBEggs (Aug 20, 2011)

spacedout said:


> With the automatic with 50/50 city or more I seem to loose 4-6mpg with AC use. However at speeds above 65mph It seems to be more like 2-3mpg at most. At 45-55mph the loss in MPG is much greater, because you are putting a huge load on the engine below the power curve(similar to using the AC in the city).


Vs. what? No A/C at all? Bottom line is.. A/C and windows down _*both*_ decrease fuel economy. The question is how much and how comfortable you want to be.


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## spacedout (Dec 7, 2010)

ErikBEggs said:


> Vs. what? No A/C at all? Bottom line is.. A/C and windows down _*both*_ decrease fuel economy. The question is how much and how comfortable you want to be.


VS no AC and a few windows cracked. The decrease in MPG with AC use is much greater than the windows cracked. Aerodynamics only start to come to play at speeds above 50mph, so if one typically drives 15-60mph there is definitely more of a MPG decrease with the AC compressor vs windows down.


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## CruzeEcoBlueTopaz (Jan 5, 2012)

Yes my windows are tinted to legal. I mean I will try using the a/c tomorrow only at highway speeds of 50 to 55mph and not during any acceleration from a stop just because im curious what the difference will be. I just know its going to reduce my mpg by about 3 or 4 at least. It bothers me to get any less then 50mpg actual but im willing to try it 1 day just to see what the difference is. Even if using the a/c reduced my mpg by only 1mpg I still wouldnt want to use it. 

I have noticed that on the dic my instant mpg is reduced by about 10 to 15 mpg instantly after turning on the a/c and yet after rolling down the windows 1/2 , 3/4 or even all the way there is no difference on the dic showing instant mpg except for the normal fluctuation due to terrain or wind.


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## spacedout (Dec 7, 2010)

CruzeEcoBlueTopaz said:


> I will try using the a/c tomorrow only at highway speeds of 50 to 55mph and not during any acceleration from a stop just because im curious what the difference will be.


At those speeds you might be correct at 3-4mpg loss. Like I said I see much more loss in MPG when used below 2,000RPM & in the city(more times on the gas, more load). Will be interesting to see your difference. 

If my automatic cruze is only at 1,850RPM at 55mph were torque is just peaking, I can imagine with the ECO gearing your RPM is much lower and below the 2500RPM torque peak of the manual transmission cruze. I suspect one would need to drive faster to see less loss from AC use in the ECO. My 2012 automatic seems to like to run between 2,000-2,500RPM 58mph-75mph with the AC on for the least loss in MPG.


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## Blue Angel (Feb 18, 2011)

I will stand by my previous statement that cracking the passenger side windows a few inches keeps the cabin tolerable as long as it isn't too hot out, and doing this wastes FAR less fuel than using AC.

The REAL answer to this debate is always going to vary based on which car is being considered, how efficient/powerful the AC is, how much AC is used, how hot it is outside, how many windows are put down, how far the windows are put down, how fast the car is driven, the driver's tolerance to heat, etc. etc. etc.

There's no cookie cutter answer that will be true for all people and with all cars, simple as that. But the data TREND will definitely show that the slower you drive the less aerodynamics come into play and the less affect having the windows open will have. This cannot be debated. And once again, the trending data will be different for every car based on how aerodynamic it is, how efficient it is, whether it's a 2 or 4 door (my 2 door Saturn had poor interior circulation with the windows open compared to my 4 door Saturn), etc. etc., and the FACT is that most people will hang their hat on the BS Mythbusters testing that only duplicates ONE possible scenario using very inefficient vehicles.

My Corvette has the AC on all the time when I'm driving it because A) I don't care much about mileage in that car, B) the car is so powerful I can't even tell the AC is running, and C) it's not an overly efficient car to start with so the impact of running the AC is far less %-wise than it is on a more efficient car.

In a 50+ MPG Cruze Eco on the highway, AC use will have a significant impact. Cracking only the passenger side windows four inches will not. Whether or not this solution is acceptable will vary with the driver. CruzeEcoBlueTopaz, I anxiously await your results. Of anyone on this forum I think you are the best person to report on their findings.


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## jblackburn (Apr 14, 2012)

As I recall that Mythbusters test did the test with the windows ALL the way down. 

In my old car, if I rolled all windows and the sunroof down, even pedal to the floor, it had trouble getting over 85-90 to pass. You could feel it just being held back. Windows up, it had no problem doing 135. 


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## Blue Angel (Feb 18, 2011)

jblackburn said:


> Windows up, it had no problem doing 135.


...on a closed course, I'm sure. 

That's exactly the issue with this topic; how many windows and how far down to keep you acceptably comfortable? Everyone seems to first assume that "open windows" means all of them all the way down.

My method of opening just the passenger side windows a few inches probably increases the car's drag less than holding your hand out in the wind.


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## jblackburn (Apr 14, 2012)

Haha of course...abandoned county airport. Watching out for potholes at that speed is real fun. 


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## Aussie (Sep 16, 2012)

This thread made me curious as all my cars with a/c have had 2 engine fans, 1 comes on when air is turned on and the other with engine temp. Went outside and popped my Cruze diesel hood and guess what 2 fans. Maybe the Eco has a 2 stage fan, low speed with air and high speed when needed? Just a thought.


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## jblackburn (Apr 14, 2012)

Aussie said:


> This thread made me curious as all my cars with a/c have had 2 engine fans, 1 comes on when air is turned on and the other with engine temp. Went outside and popped my Cruze diesel hood and guess what 2 fans. Maybe the Eco has a 2 stage fan, low speed with air and high speed when needed? Just a thought.


Exactly how it works. 

Last car I had with 2 fans was an 85 Saab. Thing was ALWAYS overheating. 

Maybe the Australian Cruze runs a differently sized radiator. 


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## Aussie (Sep 16, 2012)

jblackburn said:


> Exactly how it works.
> 
> Last car I had with 2 fans was an 85 Saab. Thing was ALWAYS overheating.
> 
> ...


117F 68mph air, on cruise on, temp completely normal at 89C. 4 adults and luggage on board, with tinted windows and auto climate control car was really comfortable inside.


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## CruzeEcoBlueTopaz (Jan 5, 2012)

Allright so I was planning on testing out the effects of a/c use on the cars efficiency Thursday but the weather turned out to be an anomaly. So I waited for Friday and calm 95F degree weather. Now I wont have my receipt until Monday when I fuel up so I dont have the actual fuel used but right away I noticed a 4-6mpg decrease on the DIC compared to my normal daily average mpg over about 350 miles. So the decrease was less then I was expecting but im fairly certain and predicting there will be a noticable 3 mpg actuall decrease from my daily normal 51.5 to about 48 to 49mpg which isnt bad considering I was cool and comfortable. I dont mind sweating it out to keep my mpg's up and decrease the load on the engine which I noticed makes much more noise with the a/c on coming from the fan, vibration and a buzzing sound from under the hood. 

It is safe to say and I know quite a few members on this forum have said and others will agree myself included that for the eco at a 1500(50mph) to 2000 rpm range the effects of a/c use on the engine are minimal its only during acceleration and possibly lower and/or higher speeds that the drag of a/c is noticable.

So basically yes there was a decrease of about 3mpg actual for me with the use of the a/c under ideal conditions.


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## Blue Angel (Feb 18, 2011)

CruzeEcoBlueTopaz said:


> So basically yes there was a decrease of about 3mpg actual for me with the use of the a/c under ideal conditions.


I did some steady state economy testing yesterday afternoon. I'd been wanting to do it for some time but it was the first chance I'd had some spare time and decent weather. It got up to 90F on the temp display and winds were low. I tested at 62 MPH (100 km/h), so a little higher speed than you were doing. My AC-off runs were made with the passenger side windows down about 3"-4", AC-on runs with all windows up and a fan speed of 2/4 (this would have kept the cabin comfy).

This is two-way average mileage off the DIC, averaged over the same stretch of highway with the cruise control set.

Average with no AC = 57.6 MPG
Average with AC = 52.6 MPG

There was a little more inconsistency between my two way runs with AC-on, so I'd be OK with adding 1 MPG to that average. That would bring the average up to 53.6 MPG for AC-on, making the difference 4.0 MPG.

I usually correct my DIC by 7% as it is usually about that amount high, so real results would have been closer to 53.8 MPG without AC, and 50.1 MPG with AC, for a difference of 3.7 MPG or 7.4%.

The difference may have been higher if I was driving with the pass side windows up, but I doubt that has any significant effect on the car's mileage at that speed.


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