Theory on heater and mpg

[dochawk]

Edit: It's one of the reasons the old vehicles had quarter windows.

Those were awesome for those first few minutes of driving in the cold! You adjusted the angle to control the flow.

Historically Ford typically runs the ac compressor when defrost is on to further dehumidify the air and provide better defrosting.

Long ago, a service advisor told me that it was important to not wait until the hot season to service something on the compressor on my '83 Cougar, as it was run every time (the engine came on?) to lubricate its seals. Supposedly, it could move from whatever service I needed to needing to replace the compressor if I put it off.

true, I don't know. . . .

Sponsored

 

[Ozarkbeard]

MAX runs the motor all the time.

MAX. aka HI temp heat setting runs the resistance heat, too, draining the HV battery and in turn, makes the gas engine run.

 

[Glen Baker LLC]

MAX. aka HI temp heat setting runs the resistance heat, too, draining the HV battery and in turn, makes the gas engine run.

In truly cold weather. Max/Hi temperature 85+ The electric heater also puts out warm air before the engine coolant gets warm. Heating the cabin up faster.

 

[MakinDoForNow]

You can feel the engine slow down from drag when the AC or Defrost is on

Not in the hybrid... Engine may not even be on....

 

[CD_SM]

Defrost doesn’t use AC. It uses heat.

It uses both. The AC drys the air, and then the heater, well, heats it. Been that way for literally decades.

 

[dochawk]

You can feel the engine slow down from drag when the AC or Defrost is on

I still recall an upperclassman driving us than after school event in a foreign car in the late 7s.

To accelerate to pass, he flipped off the AC . . .

 

[dewmeister2000]

Been interesting reading all these. Took a 1200 mile trip. Couldn’t keep windows from fogging up. Read a forum on it. Now I run with ac on. But now I get 6 miles less. Stop at gas station more often or run over someone because of fog. Go figure. dewmeister2000

 

[Lennox]

With winter fuel blends I lost 10% mpg with my hybrid.

 

[Master Blaster]

Been interesting reading all these. Took a 1200 mile trip. Couldn’t keep windows from fogging up. Read a forum on it. Now I run with ac on. But now I get 6 miles less. Stop at gas station more often or run over someone because of fog. Go figure. dewmeister2000

Just open the back window a bit.

 

[rlhdweman]

My last car ran the compressor whenever set to defrost, so in fall after the hot weather I pulled out the a/c compressor relay until spring, was good for 3mpg increase, cleared the windshield fine in the winter without the compressor running.

 

[HughdMan]

There have been some recent threads here about how the heater significantly drops mpg, even more than AC.

In my fiddling around and experimenting with my new 2025, it seems that whenever the windshield defroster is on, the drop in mpg is the greatest. Even if you keep the fan speed and temp setting the same, just turning off the windshield defroster seems to keep my mpg higher.

I know it seems counter intuitive- using the defroster should only use heat. However, as I recall, most vehicles rung the A/C to dehumidify the air that then goes thru the heater coils. I too watch defrost cut MPG.

 

[HeyBales]

I still recall an upperclassman driving us than after school event in a foreign car in the late 7s.

To accelerate to pass, he flipped off the AC . . .

Had to do that in the Rav4, also going up the Ozark hills heading south into Branson, MO.
Or the cruise would end up in 3rd gear sounding like it was going to blow.
With no AC there was enough power in 4th to just barely make it.
For winter camping it wasn't AC for cooling - it was the AC on with defrost purely to get heat to the windshield. Very annoying as I'd forget for huge stretches when I was done with heat there, but impacting my MPG.

 

[BradH]

I still recall an upperclassman driving us than after school event in a foreign car in the late 7s.

To accelerate to pass, he flipped off the AC . . .

Used to do that on my '85 Escort in college. My buddy called the A/C button the "turbo boost" (aka "Knight Rider")

Sponsored