Driving up hill and MPG

How much is your altitude change?
You have to consume a certain amount fuel to gain your "potential energy". It's 106 mL per 100m or 0.085 gallon per 1000 feet.
http://priuschat.com/forums/gen-iii...ll-makes-biggest-difference-3.html#post948346

Ken@Japan

 

You should also gain some back on the downhill drive home.

Your main "problem" is your short drive to work. Seven miles is short enough that you take a major hit warming up the engine each time. On the other hand it's great to have a short commute.

Tom

 

Qbee is right. An EBH would prewarm the engine for the morning commute; grill blocking might keep the engine warmer than not by the time to go home.

 

You might treat this as an experiment and start gathering some data and comparing the results:

• temperature and tripmeter to work - all three variables, distance, MPG, average speed

A ) No warm-up - get three samples

B ) Warm-up in driveway to engine off (make sure car in ECO and heater is off during warm-up) - get three samples

C ) Alternate route(s) to work - three samples

D ) Alternate max speeds to work - three samples

You'll have the car for a long time so experimentation is good. Better still, share your results.

Bob Wilson

 

You can't do a simple mpg averaging here.

It looks a little inconsistency in your numbers, but if numbers like this, it is not 45mpg average.

	miles	mpg	gallons	average-mpg
1	7.0	25mpg	0.280
2	7.0	65mpg	0.108
3	14.0		0.388	36.1mpg

If you saw these numbers on your commute, you consume extra 0.086 gallons for uphill and you gain 0.086 gallons for downhill.
Reflecting the 0.085 gallons per 1000ft rule, I can guess your altitude change is 1013ft.

Ken@Japan

 

Yup, they covered the calculations for you.

I used to routinely avg. 52mpg when I had a normal highway commute on flat ground but once I switched jobs and went from a 76mile commute (flat ground) to a 13mile commute (over 1,000ft. elevation gain) I dropped down to mid-high 40s.

 

I bet it's caused by 7 miles short commute.

Ken@Japan

 

I have an 8 mile commute going from 40m to 110m altitude, and have found that blocking the grill does give me 3mpg UK better results during the winter months, that said it isn't so cold here (8C today) and I can cycle two or three days each week so avoiding the short journey completely. I get 45 to 50mpg UK inbound and 65 to 70 outbound. I do like the information given by Ken about the fuel needed to gain altitude, very nice, thanks Ken. Anyone have any thoughts of trying to get back, being downhill, on the battery alone, but then the cabin will be a bit too cold? I wonder if the downhill stretch will yield more improvement.

 

KV55, I love the combination of Miles traveled, Meters of altitude, Celcius temperatures and UK gallons in your post.

For the whole gang, especially the techies,
My father told me that accellerating up hills was bad for mileage. Is this true?
Now, Ken tells us that a certain amount of gas is required to lift a given weight a given amount--i.e., to increase its potential energy. I take it that this reasonably disregards the higher amount of the vertical component of wind resistance on the car when the slope is steeper or the speed is higher.
When the weight drives back down, some of the potential energy is lost, again to wind resistance, which is one reason why regen on downhill doesn't capture all the additional energy used to drive uphill.
So, obviously, I'm forgetting some basic physics formulas about the energy use of uphill accelleration???

And my ultimate question is this: better for gas economy given the toyota hybrid system to accellerate uphill, go at a steady pace uphill, or slow down uphill?
Where should I try to keep the hybrid system indicator (if that is relevant at all)?

 

No because it puts the engine in higher power, regions, decreased engine efficiency. It isn't as bad with the 1.8L engine due to cooled exhaust gas recirculation compared to the 1.5L Prius but it is observable. This is especially true if running 87 octane and not 89:

Ok but still tends to get in the higher power regions and can 'over drive' the gasoline octane.

Depends on traffic. If you can use a truck as your pacing vehicle, DO NOT TAILGATE, you'll be in good company going up the hill.

Hills come in many grades and weather conditions are often different. The cooled exhaust gas recirculation has made things less bad but my personal experience is once the HSI is 'pegged', engine rpm is the only indicator left. I agree with Hobbit that a little gap on the end of the HSI "PWR" bar makes sense but mostly I like to either keep the speed constant or let it bleed off say 5 mph or just use a truck as the pacing vehicle up the grade.

If you're driving often in hilly areas, try 89 octane. The 1.8L engine can exploit the higher octane to improve climb efficiency.

GOOD LUCK!
Bob Wilson

 

Hills with stops and short commutes are a tough combination. You don't recoup the potential energy on the downhill because of the stops. The ICE will run needelessly going downhill while the engine is warming. Plus each of the stops results in inefficient transfers back and forth to the battery.

Add in cold weather and you really take a hit.

About the only advantage of hill climbs is that one during the warmup will bring the ICE to temperature quickly.

 

I agree mostly Shawn. I have a short 13mile commute starting at approx. 200ft elevation and I drive less than 1 mile to the freeway and only 3/4 of a mile off the freeway till I get to work which is at approx 1,220ft. elevation. I watch my Scangauge and on cold days (40deg or less) I do not reach full operating temperature till I'm nearly at work (70mph avg.).

On the way home I try to coast as much as possible while maintaining 70mph avg. and I find that the car doesn't reach operating temperature until I'm back off the freeway and go through a couple stop lights but then I'm home. lol

Like you stated though, I never recover the mileage I lost from going uphill. I tested this the other day get about 55-60mpg downhill and about 25-28mpg uphill (27deg uphill, 38deg downhill). I'll test this out in the really hot summer months since this will add about 60-70deg to ambient temperature.

 

I need to remind myself that if I go up and then down a hill using the same route my overall mileage will always be less than twice what I got going up.