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Old 08-27-2018, 08:56 PM   #1 (permalink)
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Hot weather and poor economy

Just wondering if others are seeing very poor mileage, like 20% lower when the temps hit 100 or more? Probably from the A/C requiring more horsepower. just wondering what others are seeing.

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Old 08-27-2018, 08:59 PM   #2 (permalink)
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My car never used AC regardless of outside temps, but I did have to remove all grille blocking once outside temps reached above 90. Didn't notice any significant MPG drop other than that due to slightly poorer aero from the grille block being removed.

EDIT: The warmest weather I've driven in was 96-99 degrees Fahrenheit; nothing over 100, so I may not be experiencing what you are.
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Old 08-27-2018, 09:18 PM   #3 (permalink)
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Yeah probably retards the ignition timing.
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Old 08-27-2018, 09:26 PM   #4 (permalink)
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It's called 'heat soak', and especially noticeable on turbo cars.
The most common solution is to either fuel up higher octane fuel (89,91); fuel up with E15, or if you already fueling mid-grade, fuel up with premium.

If you're concerned about cost, the most cost efficient method is to add 1 gallon of E85 in your tank (of 87 octane fuel).
E85 isn't very fuel efficient, but it does costs less, and allows your engine to dial back on engine timing delay caused by predetonation.

A lot of cars have problems with 'pinging' or predetonation in hot climates.
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Old 08-28-2018, 01:27 PM   #5 (permalink)
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Quote:
Originally Posted by MorphDaCivic View Post
JProbably from the A/C requiring more horsepower.
Makes me wonder if it would be worth to recover the residual humidity extracted by the A/C from the cabin and use it for water injection to the engine. A former Civic owner told me he noticed an improvement of the fuel-efficiency when there was a higher humidity in the air.
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Old 08-28-2018, 05:23 PM   #6 (permalink)
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Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
Makes me wonder if it would be worth to recover the residual humidity extracted by the A/C from the cabin and use it for water injection to the engine. A former Civic owner told me he noticed an improvement of the fuel-efficiency when there was a higher humidity in the air.
I came up with that idea years ago.

Some say it works well, others say that with engine blow by, the water molecules get stuck in the oil and becomes like a gel, rather than fluid oil.

Then, some others say that the engine will be hot enough to just steam out the water, which I believe will happen at highway speeds.

The bigger issue is that AC drain hose contains bacteria, algae and fungus. Overall it's so little that it will just burn up and form carbon, that gets blown out of the tailpipe at higher speeds.
However, occasionally there are fungus parts that will come loose from the hoses, and may actually be too large to burn up, and can potentially cause engine damage. So a filter, like a gasoline filter, is needed.
Not much is known to how frequently that filter needs replacement.

Also, this won't work on turbo engines, as the turbo blades get worn out cutting drops and even water vapor!
If you can inject the water right before the intake manifold, behind the intercooler, it might actually work quite well on turbo cars.

Aside from cooling effect, adding water in your air intake adds very little to the performance. Even in USA, Chevron is known to have crappy gas (too much Ethanol), which contains a lot of water. You can often see when a car has Chevron gas, by looking at the tailpipe when he departs from a stop.
Some have what looks like 'waterfalls' coming out of their pipes!
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Old 08-30-2018, 04:56 PM   #7 (permalink)
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Quote:
Originally Posted by MorphDaCivic View Post
Just wondering if others are seeing very poor mileage, like 20% lower when the temps hit 100 or more? Probably from the A/C requiring more horsepower. just wondering what others are seeing.
The AC blowing full tilt, doubles my idle fuel burn & even city driving FE

With only 68 HP, I can really feel the power draw of the AC
If I need faster acceleration I hit the AC button to switch it off.


But on average, AC burns only 0,1 kg CNG/100km extra over my 3,7 kg/100km average - that's 2.7%
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Old 08-30-2018, 05:01 PM   #8 (permalink)
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I can't comment on your car specifically, but both my Echo and my Civic will easily account for that kind of mileage drop using a/c.

The water injection idea is awesome though! That's something I'd always be too lazy to try but it hits my sensibilities just right.
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Old 08-31-2018, 10:08 AM   #9 (permalink)
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The smaller the engine, or the bigger the ac system, the more the mpg drop.
My previous 150hp mid size sedan car had an average of 10% less mpg.
My current 200HP hot hatch car, the mpg drop from the AC is negligible
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Old 08-31-2018, 11:39 AM   #10 (permalink)
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I would suspect AC mostly too. In my wife's Subaru when we run her AC I put it on internal air recirculation and only run the AC (at or near max fan) when it is FE favorable, such as deceleration fuel cut off or downhill light cruise. When the AC is off the compressed refrigerant keeps cooling air for a bit. So in high load situations I turn AC off, keep internal air fan on, and it keeps blowing cool air for a little. Then when it is more advantageous, I click the AC back on. My wife and I both do this quite automatically now. Second nature. But there are times when my daughter or Wendy or both of them and maybe even me just wanna run the AC and so we do...

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