Author Topic: Hypermiling question  (Read 6083 times)

chops

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Hypermiling question
« on: February 23, 2014, 11:18:16 AM »
It had been COLD in NE until recently and I was wondering if any of the hypermilers on here could tell me if using heat actually decreases MPG performance? 

My thought is that it doesn't affect it if you can wait to turn on the heat until the car warms up (maybe 5-10 minutes after starting.)  Am I right?

Emg03063

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Re: Hypermiling question
« Reply #1 on: February 23, 2014, 01:21:06 PM »
I wouldn't expect any measurable impact regardless of wait time, as you are simply redirecting engine cooling air to inside the cabin instead of outside it.  You're not changing the load on the engine, or the cooling airflow, to my knowledge, but I'm not a mechanic.

Greg

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Re: Hypermiling question
« Reply #2 on: February 23, 2014, 03:24:40 PM »
You're right.  The difference between using the heater (causing coolant flow through the heater core) and not using the heater (coolant only circulating through the engine until the thermostat opens) probably isn't that great.  But to a hypermiler, it could matter.  Make sure your thermostat is good, and that other intake preheater ducting and stock airbox are intact for best effect.

the fixer

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Re: Hypermiling question
« Reply #3 on: February 23, 2014, 03:38:50 PM »
That excess heat would exist no matter what, it's a byproduct of running the engine. So whether or not the coolant carrying that heat energy gets routed into the passenger compartment or to the radiator makes no difference MPG-wise.

chops

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Re: Hypermiling question
« Reply #4 on: February 26, 2014, 06:46:25 PM »
Thanks all!

dragoncar

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Re: Hypermiling question
« Reply #5 on: February 26, 2014, 07:36:34 PM »
Cold air is denser increasing combustion efficiency

loki

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Re: Hypermiling question
« Reply #6 on: February 27, 2014, 07:04:09 PM »
It definitely doesn't; I checked with my Ultraguage on two different cars and there weren't any instantaneous differences with heat on vs off.

ThermionicScott

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Re: Hypermiling question
« Reply #7 on: March 03, 2014, 10:47:59 AM »
Cold air is denser increasing combustion efficiency

I thought it was the opposite -- the FI system must inject additional fuel to balance out the extra oxygen, and the denser air increases pumping losses.

At any rate, one thing that has helped my car this winter (and I wish I had done it much sooner) is to install a cardboard grille block over the upper grille on my '96 Outback.  The car warms up much faster (allowing me to use the cabin heater sooner) and the car is running much nicer by the time I get to my destination.  Since I've made other mods and changes to my driving habits at the same time, it's hard to tell if the grille block alone is helping my MPG.

P.S.  Anyone considering this mod should keep an eye on their temperature gauge to make sure they don't overheat.

wtjbatman

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Re: Hypermiling question
« Reply #8 on: March 03, 2014, 07:44:47 PM »
Cold air is denser increasing combustion efficiency

I thought it was the opposite -- the FI system must inject additional fuel to balance out the extra oxygen, and the denser air increases pumping losses.


There's a reason one of the most common and easiest engine mods is a cold air intake.  You want to increase that flow of cooler air to the engine. Installing the intake in the fender is, I believe, the preferred method.

k-vette

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Re: Hypermiling question
« Reply #9 on: March 03, 2014, 07:59:23 PM »
Just don't confuse performance with high mpg...  mpg goes down in cold weather considerably. Ecomodder.com is a good hypermiling community.
« Last Edit: March 03, 2014, 09:41:57 PM by k-vette »

Greg

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Re: Hypermiling question
« Reply #10 on: March 03, 2014, 08:16:29 PM »
Back to the original question:  Does using the heater decrease mileage.  The answer is yes.  The heater uses coolant heat that would otherwise help warm up the engine, and the engine uses up tot 2x the fuel while warming up.  Once the thermostat opens (or if, in really cold weather) the heater circuit is "free" heat but until the thermostat opens using the heater will slow engine warm up.

ThermionicScott

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Re: Hypermiling question
« Reply #11 on: March 04, 2014, 02:42:25 PM »
There's a reason one of the most common and easiest engine mods is a cold air intake.  You want to increase that flow of cooler air to the engine. Installing the intake in the fender is, I believe, the preferred method.

It's a common and easy performance mod, yes.  It gets a little more oxygen (and fuel, due to the action of the EFI) into the cylinders for a little more power.

I guess where we're in the weeds a little is that while it does help the engine efficiency slightly, it doesn't necessarily improve overall MPG, which is generally the thrust of hypermiling.  Hypermilers often report better MPG by using a warm air intake.

theSchmett

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Re: Hypermiling question
« Reply #12 on: March 04, 2014, 08:29:32 PM »
And it might not be much, but the fan runs on electricity, so the alternator has to work more, placing some drag on the engine. Like I said not much... but there it is. 

I suppose that cold tires are also a change, as is thicker colder air... but we're really splitting hairs here.

schimt

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Re: Hypermiling question
« Reply #13 on: March 06, 2014, 07:06:01 AM »
Cold air is denser increasing combustion efficiency

As already stated, cold air is denser allowing more oxygen molecules into the cylinders on each stroke. Modern electronic fuel injection systems are efficient with the use of mass air flow sensors (feed forward system) and o2 sensors (feedback system) to adjust the amount of fuel injected to burn as close to 100% of the oxygen in combustion chamber.

Hence the reason, more oxygen = more fuel = more powerful combustion. Sooo slight increase in power and decrease in efficiency.

Someone spoke about forced induction such as a turbo engine. This is more efficient because you can greatly undersize the engine for the weight of a vehicle, when you need the power to accelerate, the turbo spools up and compresses the air, increasing o2 and fuel and ultimate power, but at cruising speeds, the engine is running at atmospheric pressure.

On the original question, i agree, there is no effect on MPG after the engine is warm (except the slight increase in draw on the alternator to run the fan), cold engines are less efficient (increase blow by from pistons that have not experienced thermal expansion to properly fit the cylinders, thicker engine oil, ect) The motor has a thermostat that does not allow coolant to reach the radiator until the engine is warm, but when you turn the heat on before the engine is up to the appropriate running temp it is keeping the engine cold longer. So if you suffer through the cold until the engine is close warm, you will have no effect on MPG. This is a big deal if you mostly take short trips.

Since that has all be explained a few times, if you engine is ever overheating due to a potentially failed thermostat, turn your heat to full blast, even if it is hot outside, this will pull heat from the engine.

ketchup

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Re: Hypermiling question
« Reply #14 on: March 06, 2014, 08:19:07 AM »
Since that has all be explained a few times, if you engine is ever overheating due to a potentially failed thermostat, turn your heat to full blast, even if it is hot outside, this will pull heat from the engine.
Always a tip to keep in mind.  My uncle drove from Connecticut to Missouri for training one August in a car that he had to do that in.  I'm sure that was fun.

schimt

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Re: Hypermiling question
« Reply #15 on: March 06, 2014, 08:55:30 AM »
Since that has all be explained a few times, if you engine is ever overheating due to a potentially failed thermostat, turn your heat to full blast, even if it is hot outside, this will pull heat from the engine.
Always a tip to keep in mind.  My uncle drove from Connecticut to Missouri for training one August in a car that he had to do that in.  I'm sure that was fun.

I did it midsummer in my old VW from Myrtle Beach SC to Jersey and it sucked! But it did the trick.