BIG MPG increase!

[Titan]

I've been getting 28.5-29.5 mpg on highway trips at speeds of 68-74 mph the past month. I drained/filled my Subaru transmission with some ATF/Power steering all-purpose fluid from the Subaru dealership. Shifted a little more abruptly, but, not too much that it feels like a problem. Found out it must be some VERY old stuff, as the Subaru techline can't match the part numbers to anything on their current list. Anyway, Tuesday, on my usual 340 mile trip, the MPG jumped to 33.9 mpg. Why? The fluid change? I sincerely doubt it. The real difference is the temperature was in the mid-50's, instead of the mid-teens. So, the take-home message is: don't drive so much when it's really cold.

 

[Dave Hess]

Maybe they changed the formula of gas in your area??

Does SC get 'winter' gas ?

 

[arkainzeye]

i would point more towards temps and the Efi not having to add as much fuel for the same distance your driving. my suzuki was real touchy with cold temps. i would drop from 26 to 21 mpg like nothing...this wasall due to colder temps, (more dense air) so the efi had to matchthe air by adding more fuel..

 

[unDummy]

Yep, warm weather does that! Warm up is quicker, all fluids are warmer and thinner, less enrichment for cold driving, tire PSI is higher, .... lead to better MPG.

I gained a solid 1 MPG from replacing a thermostat. I'm also considering 'hot air' intake plumbing.

I know some that got an MPG improvement when switching ALL fluids over to higher end synthetics.

There is plenty of MPG hidden in a vehicle. Too bad automakers are tuning for emissions and power. MPG tuning is all but gone!

 

[Doc8404]

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Yep, warm weather does that! Warm up is quicker, all fluids are warmer and thinner, less enrichment for cold driving, tire PSI is higher, .... lead to better MPG.

I gained a solid 1 MPG from replacing a thermostat. I'm also considering 'hot air' intake plumbing.

I know some that got an MPG improvement when switching ALL fluids over to higher end synthetics.

There is plenty of MPG hidden in a vehicle. Too bad automakers are tuning for emissions and power. MPG tuning is all but gone!

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then why is it that everyone is sold on the fact that "cold" air intakes increase MPG?
well, if that's the case, everyone bags on my K&N Series 77 for sucking "hot engine compartment air"...guess that's a good thing now!

 

[LouDawg]

I wouldn't put a whole lot of faith in only one tankful of gas that seemed to get better mpg. There a lot of unseen variables that can affect it from one tank to the next. If you see it consistently over the next 5 tankfuls, then I'd celebrate.

 

[BillionPa]

you want the air entering the cylinder head to be about 104F for optimal fuel vaporization. any higher, risk knock, any lower, poorer economy.

the cold air intakes are great for forced induction cars, where the compression naturally heats up the air. on most other cars, they only help in the higher RPM range, but reduce encomony and power in the lower RPMs.

 

[Duffman77]

BillionPa

What is your source, I only ask becuase I am very interested in this kind of stuff, & not because I dont believe you.

 

[BillionPa]

i think i got that from something regarding naturally aspirated Honda race engines.

 

[mechtech2]

Cold intake air increases HP, not MPG.

 

[nascarnation]

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then why is it that everyone is sold on the fact that "cold" air intakes increase MPG?

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marketers for cold air intakes might be saying that
folks who understand the system aren't
when the engine management senses warmer air, it will lean out the mixture, not richen it up

 

[Titan]

mechtech2 nailed it. Colder air is more dense, and more fuel can then be added to the mixture, so you get more power. More power doesn't equate to higher economy. I used to have several turbo engines...they all ran much stronger at cooler temps...but, the MPG dropped like a rock then, too.

 

[pidster]

Colder intake air = more O2 per volume. ECU will add more fuel, even when engine temp is high, to maintain correct air:fuel ratio. Winter fuel, warm up time, gelled gear oil etc compound the problem but there's no getting around it. Anyone with an economy car with less than 100HP like me can surely feel some difference in how sluggish the car is on a hot summer day and (comparatively) quick it is on a nice cool night.

And any manufacturer that says a cold air intake increases MPG is full of it.

 

[Doc8404]

well, i will tell you from REAL WORLD experience, not speculation and what you've read, my series 77 actually increased MPG, but ONLY when i'm very light on the right pedal....FACT!

 

[mdv]

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And any manufacturer that says a cold air intake increases MPG is full of it.

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You're forgetting that an MPG increase can come from eliminating the restriction that can be found in aome stock intake systems. If you look at it from that standpoint and not from a temperature standpoint, I can see how this is possible.

 

[Doc8404]

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And any manufacturer that says a cold air intake increases MPG is full of it.

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You're forgetting that an MPG increase can come from eliminating the restriction that can be found in aome stock intake systems. If you look at it from that standpoint and not from a temperature standpoint, I can see how this is possible.

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that's correct, great point...why disect it and look at it in pieces instead of the system as a hole...

 

[Leo]

This sounds a bit ridiculous but I always got much better highway economy when it was hot, even with the A/C on. I always presumed that the hotter air atomises the fuel better as well as lowered wind resistance due to decreased air density.