Hi All,

Just got back from Yuma, Arizona and glad to be back in 98 degree Reno. While in Yuma, I drove from Yuma to Phoenix one day and only got 29mpg!!! Never had such bad mileage. From Phoenix back to Yuma in the evening, got 35mpg - also not good for me.

Next day I took it to dealer and they said "everything was OK." Is that much mileage drop to be expected in highway driving in high temps? My TCH is an 07 with 45K miles and I've driven in Arizona before during summer but never got that poor of mileage. In fact, driving from Reno to Yuma got 40mpg.

So, is it the heat or possibly something else? I'm flying back down next week and driving the car back.

FYI - I typically get 36mpg around town and 40+ on the highway even with heavy loads.

Thanks

John

 

It has been my experience that my mileage will drop also in hot weather. I believe it has to do with the thinner air.

 

The Ford Escape seems to use the A/C compressor running FULL TIME to cool the hybrid battery pack if the OAT is elevated, above 95F.

 

This is not a true statement for my 2005 Escape Hybrid.

 

My experience is that mileage improves as temperature increases up to the point that I turn on the A/C. At that point it drops. I suspect that at 110F, the A/C is working fairly hard which drops your mpg.

 

Mrs Scooters has been getting about 38 combined MPG. It has been over 100 here in TX for the past Month. She should be back up over 40 when it cools off and the AC doesn't run so much.

 

The TCH will pull plenty of amps from the battery when the temperature is about 98 degrees on up. The generator is pulling on the engine some to help supply those amps and keep the traction battery charged. Try pressing the ECO button to the right of the fuel door button. When the ECO is activated you will see ECO shown in the center of the AC window. I'm in southern new mexico and can run the cabin temperature around 78 degrees. I can get by on 2 notches of fan, use 3 on a really hot day. 105 degrees is our peak so far.

I don't think the traction battery cooling requires any direct AC cooling. The cool air from the cabin is drawn in by a fan though the scoop that's located inside the the rear window.

 

It might be that if this one tank (or trip) was so far off (and if the mileage was calculated manually instead of relying on the onscreen display), the cause might be a mistake in the calculation or a combination of a series of other factors.
Possible situations...

• What if driver, inadvertently reset the mileage counter amidst the trip, thus recording fewer miles per tank than actually driven?
• What if the recorded amount of gas used was mistaken. I usually rely on the onscreen display (since it's always withing 1-1.5 mpg of the manual calculations). When I refuel, occasionally I will glance at the gallons purchased and 'remember' the amount. Later on I'll either write it down and calculate it, or if I'm feeling smart, I'll calculate it in my head while driving. What if driver purchased 13.5 gallons, but 'remembered' 15.3? Or if driver was Roger Clemens, what if he "mis-remembered"?
• What if the tank before the trip wasn't completely filled (fuel shut off early) and then the tank after the trip was filled to the rim (with Brim!....sorry, I watched a lot of television in the 70's), thus recording far more fuel for the one trip than actual.
• What if there was a significant difference in the factors relating to the cars performance in this one tank (or trip)? For example, if driver, weighing 140 pounds, typically drives alone with an empty trunk. What if driver traveled with four passengers each weighing 250 pounds and the trunk was full, adding an additional 250 pounds. In this situation, the extra 1250 pounds will cause the mileage to suffer. *
• What if driver typically purchases gas without ethanol, but for this trip, got some of the 'good stuff' (10% ethanol) for this one tank?
• What if tires were under inflated before the trip, but were filled up after the trip?
• What if there was a head wind during the trip?
• What if trip included a few stops, whereas driver typically drives long stretches without stopping?

In either case, I think it's not meaningful to record mileage on a tank or trip basis, since (IMHO) the goal is to find one's average MPG and one trip can have too many variables to provide an accurate reading. Better to average it across a few tanks to get the 'true' mileage...again IMHO.
I'd say there was cause for concern that the temperature was the culprit if this trip could be repeated with similar conditions (weather, etc.) and if the results were similarly poor.
Not saying driver was at fault, but at least, the possibility of user error has to be considered.


* Supposedly, each 100 pounds reduces mileage by 2%, so could 1250 extra pounds reduce it by 25%?

 

I have a Ford Escape Hybrid.

Part of this picture is that as heat rejection temp (simplistically ambient air temperature) rises the IC engine gets less and less efficient.

Similarly for the A/C as outside air temp rises the amount of power needed to produce a given amount of cooling rises.

If you are running A/C (and who wouldn't with an air temp of 110º) the combined effect of these on the car has to result in poorer mileage.

With a smaller engine (relative to big V-8s for example) this effect will have a greater impact on mileage.

As Isaac Asimov once wrote about heat engines, in the world of energy you can't even break even.

 

I gave up on the calculated mpg method a year ago. Too many unlevel driveways in front of the pumps. When using the low nozzle setting, the gas pressure would vary, some slow, others were to fast.

I prefer the mfd readout for the average gas mileage. It's simple, subtract about 1 1/2 mpg which would usually match my average calculated figures. I trust the ecu readings as it don't vary as much. I am careful to press the Trip reset when I refill the tank.