Heater costs 2 mpg?
 

Going into work today I had the heater on and was getting far worse mpg then I was several days ago.
Temps had droped from being in the 60's and 70's to being in the 30's and 40's with a cold front that moved in causing my super awesome tank average of 58 mpg to plummet.

On my trip to work I have several flat stretches so I held the car at 45 mph to get a level mpg reading and then turn on the heat and my mpg would drop by 2 (4% loss).

Even though I did this test 20 times (16 of 20 lost 2 mpg, 4 of 20 lost 1 mpg) I know it's far from being a scientific set of A-B-A tests.

Frostbite is not sexy so I'll still be using the heater, I was just wondering if anyone else noticed lost fuel economy due to turning on their heater.

Heaters are known to use a lot of energy. my small space heater i use in the garage uses 1500 watts the only thing is, i thought the heaters in the car only use a fan because the heat is from the engine coolant?

Thats what I thought also.
My coolant temp was above 180F so it was plenty hot enough.

I did not notice any increased revs like I would with running my A/C but that was almost certainly a drop in mpg.

its the increase of electrical load on the alternator.

My heater fan on the highest setting is drawing over 80 watts, so not quite as much as the head lights but it's getting close, also some cars do turn on the A/C at least for defrost to help dry the air.
Was the drop instant? if it was then I would think that the drop would be from an electrical load, but if there is a lag time then it's from the fact that it's pulling heat from the engine, the jump back up with an electrical load should also be instant where a cooler engine again will have a slight lag time, maybe 30 seconds or so?

Drop only took 1 or 2 seconds I would guess it took about 4-8 seconds to come back up after I turned it off.

Was only turning heater fan to 2.

what were your other electrical loads at the time? do you have a scan gauge or some other way to see what your battery voltage is? I'm guessing that your alternator is either turned off or putting out just an amp or two and when you turn the heater fan on it's energizing the whole alternator, I haven't checked to see what kind of alternator controls your car has but I would guess that is what is happening.
Another way to test is to leave the fan on but to turn the heat down as that should turn the valve to the heater core off.

Modern heater fans draw close to the same wattage whether they're set to their lowest or highest setting. All they do is bridge different resistors at their lower speeds. I'm thinking your AC is running when your heater is, to dehumidify the cabin air. It's not logical for just the heater and fan to draw 2 mpg.

yah, I unclip the lead on the compressor in the winter (and usually leave it unclipped for the summer). My defrost turns on the compressor to dry the air and I usually just need some airflow (a towel and/or fog-x are good options too).

hmm.... will have to figure out how to do that.
Air is dry enough as is during the winter around here.

You have to love the old fashioned button on the dash in my 99 Maxima. Kill the compressor and just let the high pressure push the air through the heater core. If that still costs you mileage block off some of the radiator.

Plenty of free waste heat.

regards
Mech

Already running a 60% grill block.
May put some time aside to look into this.

I leave my heater blower speed on position 1 most all winter, at which speed it draws about 40 watts. That's not enough power draw to measureably affect my MPG. That blower speed is good down to about 0 deg F.

Occasionally, in mild weather, I can shut the blower off and let ram air do its thing.

I pull the AC compressor fuse whenever I don't need AC to allow me to use defrost without running the AC.

Its not the heater causing the drop, or the electrical load. Its the cold air thats going into your engine, its alot more dense so the ecm has to add more fuel to maintain the proper air/fuel mixture. The way to get around this is to preheat the incoming air to around 100*. The trick is to get the ducting off the the exhaust manifold & feed it to the air filter.

Yeah, for the sake of Pete People.....Have you all taken leave of your senses???

I mean, if you were to drive off a cliff and your windshield wipers were on, would you assume the flapping of the wipers was making you fall to the ground?

You lose a crap load of MPG's when the temperature drops for many reasons, heater load is a very small part of the cause. Check out this old thread for good stuff.


MetroMPG's list of reasons why your winter mileage is so bad

Heater indeed....no more talk of this!

Seems like some did not read the original post, or does winter strike the instant he turns on the heater ;).

regards
Mech

The higher your mileage, the greater (worse, actually) the effects of your auxiliaries. Your fan, your headlights, they all consume fuel (via the added engine power to drive the alternator harder to produce the extra amps) at a fairly steady rate (when they're on).

My headlights burn roughly a sixth of a horsepower's worth of electricity, I'd guess it's a quarter horse when alternator efficiency and mechanical losses (belt slip and flex) are included...it could be more, but a quarter horse at the crankshaft costs me 2 to 2-1/2 ounces of fuel per hour. At cruise MAX burns about 60 ounces an hour (and gets about 100 mpg) so turning on my headlights knocks me down about 4%, or 4 mpg. So yeah, if you're getting better than 50 mpg normally, turning on your heater fan is going to cost you a mpg or two.

Now if I'm driving my 20 mpg van at 60 mph, I'm burning 3 x 128 fluid ounces of fuel an hour, so its headlights are roughly 1/2% of its fuel consumption, roughly 1/10 of an mpg. Barely detectable. But in MAX, if I'm going 55 with the lights off I get better than 100 mpg and with the lights on, worse than 100 mpg.

The more you improve your mileage, the more you'll notice the little powersuckers.

This is so true, but very rarely mentioned or talked about.

The better your mpg gets, the more traps lurk in the shadowy areas of your commute - or they just hurt more when they get you.

Examples:

- hills you barely noticed before hypermyling look like the Alps when looking at the SG

- drivers forcing you to brake and re-accelerate get promoted from 'idiots' to major felons

- slight headwinds make you grind your teeth

and so on...

Sorry for the OT - could not resist

tinduck

I consider hills as an opportunity to store energy with less fuel. I live at the edge of the Piedmont area of eastern Virginia. East of my home the grades are very slight, not enough to maintain speed coasting. West of my home they become more significant allowing coasting at speeds as high as 65 MPH.

Climbing grades of this type allows higher BSFC operation and the increase in altitude allows the vehicle to become a storage device. On the shallow grades to the east climbing the grade makes a small difference in instantaneous mileage, while coasting down the grades allows the energy stored in the mass of the vehicle to be utilized for astounding moments of mileage. The averages obtained in my CVT Insight, using this knowledge made it possible to average mileages of close to 80 MPG on my local favorite route. The thing that caused me to "grind my teeth" was poorly timed traffic lights. I always considered timing the lights as the most important factor in my average mileage.

When I was lucky I could miss 42 of 44 lights, and almost reach the magic 80 MPG number. I would get 83 on the inward leg of the trip of 20 miles, but invariably the return trip from sea level to an elevation of 75 feet would reduce my average to just below 80 for 40 miles. When you get to this level of mileage, ANY electrical load, of ANY type was directly attributable to lower mileage. It boils down to energy accounting to the most precise degree.

While many might consider electrical accessories as insignificant, when you get close to 80 MPG average over literally hundreds of trips down the exact same route, you will find that even the radio has a cost, as well as every other load, however insignificant, of which the cumulative effects can become very significant, to the tune of several MPG combined. Adding the AC made 65 MPG the reality.

On exactly the same route on my Honda CBR250R motorcycle, my average is 84 MPG, which makes the Insight mileage that much more significant. Of course on the bike the effort required is only a fraction of that required when driving the Insight, which demanded absolute concentration. Average speed on this route, depending on the lights caught was always between 37-39 MPH, not crawling at 22 MPG, the route would not allow lower speeds or you would catch almost every one of 44 lights.

Maybe OT, but the OP might find a way to mitigate his mileage loss through finding what is the real source of the loss. If the AC compressor is working, then it would be the primary cause. After that the blower motor. Fresh air, warmed through unaided flow (not blower) would be the least cost, energy wise, and thus the least consumer of fuel. My cars stay in my garage when no in use, so that gives me the advantage of never having to scrape ice or wait for the defroster to work. They also are about 50 degrees when started on even the coldest winter days. The pait on my 13 year old Maxima still looks like new, with no sum damage to the interior.


regards
Mech

Try to run the car without using the heater until the engine is up to operating temperature.

Import tuner did some testing in their Fact or Fiction tech section back in August 2010. They dynoed a Subaru Impreza to find the power loss due to parasitic drag from the engine accessories. First getting a baseline, then with all the electronics on, then with the A/C going. The electronics (lights, radio, fan, etc) showed about a 2% loss in power. The A/C was about 10%. The URL is below. This was, to me, one of the best sections of the magazine, it's a real shame they've stopped doing it.

Fact Or Fiction: Do Electrical Systems Decrease Power? - Import Tuner Magazine