Decreased Gas Mileage Due to Temperature

[llll1l1ll]

Hey Mafia,

I'm curious: now that summer's here to stay for several months, is anyone experiencing a significant decrease in gas mileage? I've noticed that I've gotten about 70 miles less out my tank the past two fill ups.

The first instance was likely because I had three others in the car in stop and go for about two hours in the heat with the a/c on. That's clearly the cause of that. However, this time around I didn't do much stop and go and kept the a/c off unless I was cruising. Despite that, the gas mileage has suffered once again.

I was thinking: since the Cessna I fly will perform poorly in hot weather, perhaps my car is doing the same. It's either that, or the O2 sensors are on their way out. I gotta go to Advance Auto to pick up an oil filter this weekend. I'll read the codes there.

Anybody else experience this?

For reference: I can average about 410-430 miles out of one tank. I squeezed 435 out of a tank on a drive from NC to MD with the a/c on the whole way. My gas light is on (I fill up when it comes on) and there's about 360 on the trip.

[danewilson77]

I have not noticed a difference.

http://i1015.photobucket.com/albums/af278/nicee46/IMAG1555.jpg

The only thing I can think of...is at higher temps...the gas is less dense....therefore you can't get as much in your tank. I think this would be somewhat insignificant however.

[M3TA5IN]

I'm getting about .5 mpg less since I've been back from Arizona. This could be attributed to many things though.

[telijah]

Could be your local stations have not switched to their summer mix yet. Gas suppliers refine their gas mixes each season... I think...

[Ryans323i]

Wait, you came to NC and didn't stop and say "hi"!?!?

[llll1l1ll]

Hmmm all very plausible things. I'll keep an eye on this round and see what happens.



Wait, you came to NC and didn't stop and say "hi"!?!?

Hahahah I was on a short hop to NC to go to a wedding about 15 miles west of Winston Salem in a town whose name slips my mind. They have an arboretum there.

[328ioc]

Mine has dropped a little. From 23.1 to 22.9.

Not to side track but holy crap Dane. How do you get 28?

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[danewilson77]

Mine has dropped a little. From 23.1 to 22.9.

Not to side track but holy crap Dane. How do you get 28?

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Proper care and feeding of ZHP. I talk really nice to it, and do all of the preventative maintenance required. I don't drive like it, like I stole it either.

[llll1l1ll]

I usually get around 28, too.

[M3TA5IN]

I get 27 and I drive it like I stole and am running from the cops.

[328ioc]

Hmmm mine is more or less up to date except for the vanos. I do take on ramps kind of spiritedly though.

Oh well

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[llll1l1ll]

Vanos might be doing it. I noticed a bit of improvement after I did the Vanos.

[webster]

i get 20mpg but i drive 85% city M-F. weekends is more highway/freeway, but still in a week i average right at 20mpg.

if i take a road trip i usually average over 25. i believe my underdrive pulleys sap MPG some, not sure...

...and honestly i don't care. if i cared about MPGs i'd buy a honda. anything in the 20+ ballpark and i'm fine.

[M3TA5IN]

...and honestly i don't care. if i cared about MPGs i'd buy a honda. anything in the 20+ ballpark and i'm fine.

QFT

This is the first vehicle I have owned that has gotten over 20! I'm extatic

[328ioc]

...and honestly i don't care. if i cared about MPGs i'd buy a honda. anything in the 20+ ballpark and i'm fine.

I agree. I was just amazed at what Dane was getting.

I am totally fine getting 350 to a tank in mixed driving and on road trips I get closer to 450.


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[Newjack]

I usually average about 21mpg. I do a lot of city driving and tend to have my revs a little higher for a little longer for engine braking in traffic and for quick acceleration.

Revo + TT

[telijah]

I usually average about 21mpg. I do a lot of city driving and tend to have my revs a little higher for a little longer for engine braking in traffic and for quick acceleration.

Revo + TT

Just so you know, engine braking actually saves you gas versus going into neutral. It might be quite minimal, but most modern cars now know to cutoff fuel when in gear and throttle is at 0%, except when at idle, then of course you can idle in low gear like when in bumper to bumper traffic.

[Ryans323i]

..........

Hahahah I was on a short hop to NC to go to a wedding about 15 miles west of Winston Salem in a town whose name slips my mind. They have an arboretum there.

Pfft. We have a arboretum. :biggrin Just giving a little hard time.


I get 27 and I drive it like I stole and am running from the cops.

Me too, but I'm around the 21-24mpg. And I have to do the math!

[danewilson77]

Tires are stickier when the roads are hotter....therefore more rolling resistance.

:shifty

Sent from Williamsburg, VA USA

[M0nk3y]

Depending on ambient temperature...extreme hot air can cause heat soaking to the engine, which in turn causes poor combustion and loss of power

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[edlvrt]

I would have thought that all things being equal, you should get better MPG in the summer as the aerodynamic drag is lower due to the less dense air.:dunno

[danewilson77]

I would have thought that all things being equal, you should get better MPG in the summer as the aerodynamic drag is lower due to the less dense air.:dunno

......and the fact that the viscosity of the wheel bearing grease is lower. :shifty

[llll1l1ll]

Just so you know, engine braking actually saves you gas versus going into neutral. It might be quite minimal, but most modern cars now know to cutoff fuel when in gear and throttle is at 0%, except when at idle, then of course you can idle in low gear like when in bumper to bumper traffic.

Even my old E30 cut the gas when coasting in gear.

[telijah]

The suspension temperature sending unit also notices the higher temps, causing the rotator cam pulley to run less efficiently.

[danewilson77]

The suspension temperature sending unit also notices the higher temps, causing the rotator cam pulley to run less efficiently.

:scratchhead

Sent from Williamsburg, VA USA

[BimmerWill]

Not surprised by 28...I squeezed out 33 driving to myrtle beach about a month ago..interstate most of the way also a/c was off but was fairly happy



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[telijah]

:scratchhead

Sent from Williamsburg, VA USA

Don't worry, tis a joke :) "Suspension temperature sending unit"... come on!

[Johal E32]

i get 26.7 out of the 323it/5.

and around 26-27 out of the 530i/5

not really driven fast. Mostly freeway, a bit of city. Rarely are they in traffic.

[danewilson77]

Don't worry, tis a joke :) "Suspension temperature sending unit"... come on!

I know.

Sent from Williamsburg, VA USA

[az3579]

On the highway I'm not noticing a difference. I have been driving faster recently, so the hit from the usual 32 or so mpg down to 30-31 is expected. When I'm cruising, I can still hit 33mpg depending on what interstate I'm on.

On the track day, high 90's temps, I averaged around the same mpg, around 11.2mpg.


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[Johnmadd]

E30 mpg has gone from 24.5 to 25.0 with the hot weather, pretty weird. Zhp gets 28mpg like Dane's,

[Johnmadd]

Depending on ambient temperature...extreme hot air can cause heat soaking to the engine, which in turn causes poor combustion and loss of power

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Fyi to everyone, your engine gets the hottest when you shut it off after it is fully warmed up because it has no wind moving through the grill and engine fan is inoperable.

[Rovert]

The main thing I can see with hotter ambient temperatures are air density. The engine should still run at the same temperature if your cooling system works which in most cars..it does! :) I feel I roll better in hot air when I'm on the highway but there are cold nights where I feel the same. I think a lot of factors come into play. I got the best mileage when the weather was 85-90F on the highway. Coming back on the same route at night when it was probably 60F I couldn't get the same but a tad worse mileage.

So if the air is hotter there is less drag from less dense air but marginally less oxygen per stroke into the engine. When it's cold there is more drag with more dense air but marginally more oxygen going into the engine. It comes out to be the same! Haha...just drive the car and fill her when she drinks it up. At least she's cheaper per gallon than going to the bar. :P

[M0nk3y]

Fyi to everyone, your engine gets the hottest when you shut it off after it is fully warmed up because it has no wind moving through the grill and engine fan is inoperable.

True...sometimes my fan is still cycling to cool down the block....especially after auto-x when i shut the car down.

As far less drag....that's hard to believe.

Laminar flow of a car is about 1/4 of a inch on the hood...everything else is turbulent flow.

Basically...every car sucks at eliminating wind resistance. Although the coefficient of drag is less for you than I. You dont have a huge front flat bumper

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[Ryans323i]

Let's just get it out there, the flux capacitor heats up the space time continuum and air density changes the viscosity of liquid movement and the gas evaporates. Period.

[brettbimmer]

Let's just get it out there, the flux capacitor heats up the space time continuum and air density changes the viscosity of liquid movement and the gas evaporates. Period.

DANG! I KNEW it! :D:thumbup:

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[M0nk3y]

AC load can contribute to loss of MPG.

[llll1l1ll]

I think my increased a/c usage is contributing to my lower gas mileage.

[danewilson77]

AC load can contribute to loss of MPG.


I think my increased a/c usage is contributing to my lower gas mileage.

Negligible on E46.

[M0nk3y]

Negligible on E46.

I dont think it should be dismissed.

On my E46...it clearly needed more gas to get the car moving at full AC versus part-load

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[danewilson77]

I dont think it should be dismissed.

On my E46...it clearly needed more gas to get the car moving at full AC versus part-load

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Yup. Start-stop is a good point and I completely agree. Silly me only thinking about all the highway miles I drive.

I will tell you...I noticed more bog on the 2001 325i, than I do on the 2004 ZHP.

[M0nk3y]

I will tell you...I noticed more bog on the 2001 325i, than I do on the 2004 ZHP.

That makes sense

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[llll1l1ll]

I try not to use the a/c in stop and go; but, if it's just a day around town, I'm cranking that.

[Ryans323i]

That makes sense

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Just curious, why?

[M3TA5IN]

Just curious, why?

Older cars the A/C pulls on the engine more or "bogs" it down.

[M0nk3y]

Just curious, why?

Smaller displacement engine....effects it more

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[llll1l1ll]

Update - maybe I did get a couple bad batches of gas. I've noticed that my mileage today and yesterday on the highway, both with ac on and off, was significantly better than my last tank which was 318 miles. The needle has barely moved from the full mark and I've already squeezed almost 60 miles out of the tank. Plus, it is so much cooler now, so I think that's part of the cause, too.

[WOLFN8TR]

Older cars the A/C pulls on the engine more or "bogs" it down.

This is true. I had an old Chevy truck with a clutch driven cooling fan, no seperate electric AC fan like on the ZHP's. That thing was a PIG with the AC on. I put dual Flex A Lite electric fans in place of the stock clutch fan and what a difference! Not only did I pickup 1.5 mpg more but I could idle all day with the AC on in the desert heat.

Makes a difference when it's this hot!
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