Summer heat takes it's toll in mpg's

[GrySql]

The country has seen lots of temperature extremes in the last few years, it is happening right now.

Long winters have shown us what can happen to our FFH's mileage and some have devised ways to help optimize the mpg's, like engine block heaters, foam in the grill openings, covers in front of the grill, etc.

 

This last two weeks has been extremely hot where I live, in fact, yesterdays 'worst weather in the US' cartoon on The Weather Channel website was my small town - HOT.

Those of us in the hot areas have not written as much about our FFH's mpg's during hot weather because that threshold is pretty high.

Our HVB's are cooled by bringing cool air from the inside of the car and blowing it over the HVB.

This only helps when the car is in motion with the A/C on, parked and sitting in the sun the entire car heat sinks and the HVB gets very hot.

I saw 108F on my FFH's dash outside temp display yesterday, inside my garage it was 100F.

 

From personal experience and from other posts here the heat really starts dropping the FFH mpg's at around 95F and gets exponentially worse as the heat increases.

Yesterday's driving had the ICE running under load most of the time charging the batteries, powering the car and A/C - our 22 mile trip in the afternoon showed only 29 mpg's.

My last tank of gas netted 33 mpg's, pretty low.

 

When us early adopters first bought these cars almost two years ago that mpg range used to confuse (and irritate) me, why does it get 50 mpg sometimes and only 29 mpg's at other times?

We've learned and know the HVB is less functional in temperature extremes, it's the nature of the beast.

Now I understand why this phenomena happens and just ignore it, the weather will change.

-

Side note: My brother lives in Palm Springs where summer temperatures above 115F are not unusual, his VW Golf TDI does not get these extreme mpg ranges.

[acdii]

At least his fuel will never gel up on him there! :) I can see a drop when I have to use AC, it has been a very cold summer here, only 3 90* days, most were in the 70's(NOT complaining!!!), so I rarely had to use AC, but when I did, it was a 3-5 MPG hit depending on how hot it was. Right now I am at the point where I am just enjoying the car and anything above 42 MPG is a bonus. Since my wife drives it often and is not a tenderfoot like me(I think VROOM is her middle name), my tank averages is very inconsistent, so the giveadammer is broken.

[hybridbear]

The car will also limit HVB use in extreme heat to prevent damage to the battery. The Energi vehicles will turn on the ICE even when the battery is fully charged if the HVB exceeds a certain temp. The Tesla Model S limits power if the HVB gets too hot, and this is frequently experienced by Model S owners doing spirited driving in summer heat. The Focus Electric will send a text message and e-mail to owners if the HVB gets too hot, telling you to plug the car in so that its liquid cooling can go to work.

 

One thing I've noticed in the short time with the Energi is just how much its HVB heats up compared to the FFH. Since the Energi is using the HVB much more than the FFH it heats up more quickly. Since it's larger and has a larger thermal mass it cools down much more slowly when the car is parked.

[GrySql]

The car will also limit HVB use in extreme heat to prevent damage to the battery. The Energi vehicles will turn on the ICE even when the battery is fully charged if the HVB exceeds a certain temp.

According to this Post on the C-Max Energi Forum 115F> temperature qualifies as 'extreme heat' for the HVB and forces the ICE on.

This article was in that C-Max thread also:

http://articles.sae.org/11705/

 

I just looked at the Ford Fusion Energi Forum about this and there is a long Thread discussing heat/HVB's.

From that Thread:

The Nissan Leaf HVB's are having heat issues too.

http://www.digitaltrends.com/cars/nissan-leaf-owners-in-arizona-say-heat-is-destroying-their-cars-batteries/

 

We were out several times yesterday and the car got very hot while parked, there were times when the only propulsion option available was the ICE.

That is an odd feeling when you are doing your normal hypermiling and there is no EV.

 

BTW, the new all-windows tint is a big help with the A/C, the car cools off inside very fast now.

[Hybrider]

..., so I rarely had to use AC, but when I did, it was a 3-5 MPG hit depending on how hot it was. ...

 

Based on the A/C power draw curve below, posted by larryh in this post, and on my own prevalent use of A/C in very hot temps, the biggest hits to the MPG numbers seem to be for short trips while using the A/C, especially when there are long gaps in between where the car heats back up again. Whereas, if the trips are longer, such as in a 30-minute commute, then the use of the A/C doesn't seem to impact the MPGs nearly as much as some people have experienced, presumably when their trips were short ones.

 

 

Also, based on my experiences in high heat conditions, and others' postings in this forum on the extreme cold conditions, it seems the sweet spot for the optimum MPGs in the FFHs is in the 60° - 85° temperature range.

Edited September 16, 2014 by Hybrider

[Hybrider]

BTW, by increasing my use of city routes versus highway routes, but still at about a 60%/40% ratio of city to highway driving, I have been slowly managing to increase my lifetime MPG average this summer, starting the summer at about 44.5 MPG lifetime average, and I am now at 45.3 MPG, even with the temps in the 95° - 110° range throughout the summer and constantly using the A/C on every trip.

 

As I do not like to be hot, and my ideal room temp is 68° - 70°, as soon as I sense I am feeling the slightest bit hot, I decrease the temp on the A/C control until I am comfortable again. So I am still able to get 45-48 MPG trip averages in high desert temps, all the while constantly running the A/C to stay very comfortable.

 

So I can't wait for the mild winters here to start soon so the temps will come down to the sweet spot temps for maximum MPGs, especially now that my FFH is becoming much more broken in too. :drool:

Edited September 16, 2014 by Hybrider

[mwr]

BTW, the new all-windows tint is a big help with the A/C, the car cools off inside very fast now.

What is the "new all-windows tint" and how does it help cool the inside of the car?

[Griswald]

It is routinely in the upper 90's to lower 100's here for days on end and I have never had an issue with excessive low MPG's. The secret is not to use AC until you get moving fast enough to suck the hot air out of the car, usually around 40 mph. I also use a sun shield in my windshield when parking into the sun, but when ambient temps are near 100, it really doesn't keep it any cooler.

 

I do see a drop, but it is only a few mpgs. I averaged 43.1 through the summer.

[hybridbear]

What is the "new all-windows tint" and how does it help cool the inside of the car?

GrySql tinted his windows recently. Check out the thread he started about it in the appropriate forum section.

[GrySql]

As we were driving today the MFT showed the outside temp @ 109F and I had no trouble using the HVB, but that was from a cool 94F start from my garage.

That trip produced 35.8 mpg.

 

An hour later a bunch of clouds from the north western tip of Hurricane Odile blew in and it started raining, which dropped the outside ambient to 82F.

Interesting weather.

 

Edit: Later, we went for a nice drive in the cooler 80-ish weather, turned the A/C off and rolled down the windows - got 47 mpg's for that trip.

My car likes moderate weather, always has.

Edited September 17, 2014 by GrySql

[nv rick]

Since I got my MKZ hybrid in the middle of summer, I really didn't expect to see very high mpg. My lifetime mpg after two months is at 37.4mpg and is slowly rising. The daily high temps here in southern NV have hit over 100 every day with a few exceptions. When going to town, about a ten mile drive, I will get anywhere from 38 to 54 mpg. I think that range depends on the SOC when I start out. I don't like to sweat, so the A/C is set on auto at anywhere from 71 to 74 degrees. When driving to Las Vegas, I generally get 38 to 42 mpg. That trip involves going up through a mountain pass.

Since my lifetime mpg is just above the "new" estimated mileage on the sticker (and slowly rising) I am completely happy. If I never left the Pahrump valley, I'm sure my lifetime mpg would be in the mid to upper 40's.

 

btw, I like to come here since the Lincoln MKZ forum is really quite dead. I appreciate the info and observations I've gotten here, and some of you gave me the advice I used to convince myself to go hybrid.

[HighwayJerk]

Desert Summer heat definitly takes it's toll on MPGs.

Here is my summer commute:

I wake up early and it's already 85 degrees out and 90+ by the time I make it to work (it's only 8AM). I have to run the AC as I don't want to arrive to work all sweaty. This leg of the trip is mostly uphill so MPGs already suffer. I take the highway in the summer as I'm able to maintain a better SoC with the AC running, (sitting at traffic lights drains the battery like crazy with the AC on) the traffic is not too bad usually, get to work and average about 39-42 MPG.

Then I leave work, my car inside is 150 degrees and it's 110 outside (but it's a dry heat right?), the AC is a must. I get on the highway where the blacktop has been exposed to nonstop sun heat and car exhaust all day, I look down and see the temperature is now 115, the AC is blowing as hard as it can draining the HVB faster then it can be charged, now the volume traffic starts on the highway, I'm sitting still, the SoC is dropping by the second, then I feel the ICE kick on and start to charge the battery, watching the dash I see the MPG start moving down rapidly, I'm not driving but my ICE is running, the enemy of MPGs. I hope this only happens once or twice today. The sun in beating down on my slowly moving car, cooking the air inside, the AC is still struggling to drop the temperature below 100 degrees, Finally, the traffic starts moving, today I was lucky and traffic started moving just as a charge cycle finished, the AC finally starts to catch up, I'm now able to keep a charge and drive, I now need to really drive for MPGs to make up for the traffic. Arrive home 35-38 MPG, today was a good day. In my old car I would have gotten 15-20.

 

So when you are in the cold of your winter thinking about how your MPGs are suffering, remember us deset dwellers in the Summer.

Edited September 20, 2014 by HighwayJerk

[acdii]

But its a dry heat! I would rather deal with your 110* heat than 90* HUMID heat here. YUCK!

[HighwayJerk]

But its a dry heat! I would rather deal with your 110* heat than 90* HUMID heat here. YUCK!

 

I'm not going to mention the temp and humidity level we get when the Monsoon season is in full force and god forbid if a hurricane is off the coast.

Unfortunately we all can't live and afford to be in San Diego where it is 75 degrees every day.

[lolder]

The "ICE running" is not the "enemy" of mpg. The ICE running inefficiently is. The ICE has to run as all the energy comes from gasoline and at highway speeds the ICE should run all the time. The raising of the max EV speed in the 2013+ was a mistake. Cycling of EV at highway speeds is a mistake by Ford.

Try a solar ventilation system to lower the heat soaking if you can't park in the shade or vent your windows while parked. Drive a few blocks with all windows and roofs open.

Edited September 21, 2014 by lolder

[Griswald]

The "ICE running" is not the "enemy" of mpg. The ICE running inefficiently is. The ICE has to run as all the energy comes from gasoline and at highway speeds the ICE should run all the time. The raising of the max EV speed in the 2013+ was a mistake. Cycling of EV at highway speeds is a mistake by Ford.

Try a solar ventilation system to lower the heat soaking if you can't park in the shade or vent your windows while parked. Drive a few blocks with all windows and roofs open.

So using gasoline is more efficient than not using gasoline...I don't understand. I do everything in my control NOT to use gasoline, no matter what the conditions. My ICE never shows above 40 MPG, but when on EV, it shows way over 100, sometimes ad high as 500 MPG (on my OBD fuel consumption gauge). Seems to me that I want to be closer to the 500 number than the 40 number.

[acdii]

It takes gasoline to charge the HVB. In reality the EV should only be used for coasting, cruising, and assist. Drain the HVB, then look at your instant, its 20 MPG or less until you get above 50% SOC, then in the 30's until you reach 70%, once above 70% then you get above 40 MPG. If you go a mile on EV, then take 4 miles to recharge back to full and cycle that way, you will use more fuel than if you maintain a steady 70-80% charge and run on just the ICE.

 

Good example is this morning. I normally drive so that I use 100% ICE on the highways(55MPH Rural ones), and can see about 46-50 MPG depending on weather, traffic, and lights. This morning the sun was at a bad angle and I could not see my dash, so I slipped into EV too many times without knowing it until the spots went away and I could focus on the dash. End result was 43 MPG. With the temps and traffic today it would have normally been 48 MPG.

 

In City traffic, mixing ICE and EV is the most efficient. Accelerate on ICE, back off and coast/cruise on EV, anything under 40 MPH this works best and quite easy to get 50+ MPG all day long. If you were to see my daily drive graph, where its highway for 2/3rds and city for the last, you will see a block of around 40 MPG and the ending block maxed out.

[talmy]

It's really short trips that hurt mileage, the temperature extremes just exaggerate it -- heavy AC load in hot weather to get the interior cooled down and in the winter get the engine warmed up (made worse by heating the interior). The HVB is less efficient when cold (but warms up when driving) but also must be kept relatively cool in hot weather. Long drives seem to stabilize all of this. The only unsurmountable weather factor I've seen is rain and snow which drastically increase rolling resistance.

 

These factors also affect conventional gasoline cars, but it seems that only hybrid drivers get paranoid about gas mileage. :)

[darrelld]

So using gasoline is more efficient than not using gasoline...I don't understand. I do everything in my control NOT to use gasoline, no matter what the conditions. My ICE never shows above 40 MPG, but when on EV, it shows way over 100, sometimes ad high as 500 MPG (on my OBD fuel consumption gauge). Seems to me that I want to be closer to the 500 number than the 40 number.

 

The FFH uses an Atkinson cycle engine with thermal efficiencies approaching that of diesel engines under certain conditions. The downside of Atkinson on a gas engine is little low end torque which the electric traction motors provide when needed to assist the Atkinson gas engine reach its optimum.

 

http://en.wikipedia.org/wiki/Atkinson_cycle

[hybridbear]

These factors also affect conventional gasoline cars, but it seems that only hybrid drivers get paranoid about gas mileage. :)

Combine that with the fact that when your car uses less overall energy you have larger swings in energy consumption as a percent of expected when anything changes.