mileage just disappearing
 

well winter gas is upon us here in Ontario and my MPGs have suffered a good kick in the a$*. getting 19mpg now, down from 23mpg (all city). i would not mind if it wasn't for the fact that i did lot of coasting, driving without brakes, no idling (no remote start), and driving with load. just crazy how sensitive my car is to winter gas. it seems to just run so rich now that it's cold and for some reason when i drop to neutral going downhill my rpms climb to ~1300rpm instead of staying at 800. this only happens below 45mph & when Not stopped, and makes coasting in neutral completely pointless.

I'm sure the cold itself is doing you no favors either. You could try more thoroughly sealing your engine bay perhaps?

Winter MPGs will also drop with increased air density, primarily due to increased air drag but also due to increased throttle loss. 10% summer-winter variation is normal. (I'm not familiar with your vehicles though, no idea whether your results are normal.) However:

This symptom makes it sound like your engine temperature is cooling excessively. (Do you have a temperature gauge?) Toronto weather is just dropping below freezing now? I wonder if your thermostat is broken. First thing in the morning you can start it and open the radiator cap. If the coolant is still, it's okay, if you can see it circulating, the thermostat is stuck open. (At least on my Corolla, it's really obvious.)

Ecky may also have a point, grille blocking to increase engine bay temperature may be in order.

(Being where you live, do you have / use block heaters?)

Block heater (if you have access to a plug) and a grille block.

And as has been pointed out, the winter fuel formulation is just one factor in many that is lowering everybody's fuel economy:

http://ecomodder.com/forum/showthrea...leage-220.html

Yep, was at 42 mpg, now struggling to maintain 38. Though less EOC due to a desire for heat. Do what you can but grin and bear it:) Some cars will idle higher in colder temps for some reason. I suspect more load on the alt due to heater fan on high, and perhaps emissions (more exhaust gasses to keep the cat warm?)

actually i removed hood insulation pad because it increase my intake temp and because my engine gets hot. in about 5min my car reaches 70'c coolant temp, which is what subaru claims to be fully warm engine. 7-10min until the highest 88'c temp. so im not sure if heat is an issue here.

my afr map is fuel friendly 16:1 cruising under 55mph and 14.7:1 idle. i get 0.23gph according to SG2 warm idle. cold idle 0.6gph. under no circumstances afr goes under 14:1 unless over 4000rpm. throttle response seems excellent. my only issue is as though the gas is evaporating in there. i had to calibrate my sg2 to +10% as it was showing consumption to be too low! its usually around +3% in summer.

forgot to add that my car has a1200rpm closed loop cold start as well.

Checked tire pressure lately? Measure when cold, and set to the sidewall imprint max.

The cold weather certainly won't be helping. I'm just out of Waterloo and my mileage is dropping with the colder temperatures.

Strangely, winter gas is making my exhaust smell a lot nicer! As soon as I filled up with winter gas this time, the exhaust no longer smelled like someone was spraying gasoline straight into the air.

19 mpg, Subarus suck at mileage, always lower than sticker. It's that stupid way too over square boxer engine.

Wouldn't be so quick to blame the oversquareness. When they released the FB20 they said they had reduced friction 29% from the EJ20. 29 whopping percent. That is huge. Of course, having a more modern combustion chamber design helps, but we all know how much friction has to do with fuel economy. 29% is probably on the order of removing all pumping losses.

Not quick to blame, I had one a long time ago. You can reduce the friction all you want, but if the heat escapes through all that combustion chamber surface area, you loose.

tire pressure is good, my exhaust smell is actually worst off now. my whole driveway smells like a gas station when i start it up lol. i thought oversquare allows for lower friction losses?! one reason why maybe my BSFC sweetspot is wide from 1500-4000rpm at %80+ load? i think this has more due to do with the all-wheel drive and slightly large fuel pump and 500c injectors. also from what i have read the AVLS system is almost 90% of the time in high lift mode. and as for heat as i said i never see it go below 88'c wether at idle or highway cruising. i'm sure this engine just doesn't like gas asdditives, i mean i had no problems getting 33mpg in summer highway, now when i cruise it just doesn't go above 27mpg. reminds of running e85 vs pure gasoline in fuelflex cars. i think maybe my expectations are too high...

I have had this with a bad signal for intake air temp. Car going way to rich during start.

bad as in replace or clean? is that part of the MAF sensor? scangauge shows intake temp to be couple degrees higher than outside temp.

Wire had a brake in it. The computer showed -40 (according to Ultra gauge) MAF is separate but the temp probe samples the same air and the computer corrects the MAF for intake air temp(this was on a the Ford though most MAF systems are similar). If your scan gauge is showing a close number I would not suspect a problem there.

The smell of fuel is pretty indicative of a very rich mix.

Yea well, either way doesn't hurt to have double digit percentage increases in mechanical efficiency AND combustion efficiency :) (Mazda is undergoing a similar fuel efficiency leap lol)

But don't hate on short stroke engines, the BMW S65B40 for example is a beauty. Piston and head design matters more than dimensions anyways. Mazda Skyactiv engines may have good bore/stroke ratio, but the extremely high compression ratio usually gives the combustion chamber a bad shape, so they gave it that rather deep piston bowl. In fact the low compression ratio on the EJ engines probably helped the heat rejection (at a greater efficiency penalty of course).

Sometimes when fuel economy takes a dump in the winter it makes me want to drive much faster than normal just because I know its going to suck anyways...so if I pass you going 120km/hr compared to my usual 90 km/hr...that is why.

I keep all other items in place though..grill block, tires at 40 psi and block heater when below-15C...the entire year round..

I don't like over square engines. Fine for performance, but not fuel economy. combustion surface area increases buy the bore squared. 100 mm bore has 50% more area than a 80 mm bore.

• Prius:
1,497 cc 1.5 liters in-line 4 front engine with 75.0 mm bore, 84.7 mm stroke, 13.0 compression ratio.

Honda CRX HF: Engine Bore/Stroke 75.0x84.5mm

Saturn S series: 82 Bore× 90 mm stroke

Honda Insight: 72 bore × 81.5 mm stroke

Subaru EJ25

Displacement: 2457 cc
Bore: 99.5 mm
Stroke: 79.0 mm

And the most efficient mega diesels in giant ships have a 3 foot bore and a 9 foot stroke, with a scotch yoke to eliminate piston side loads. Longer stroke means a better lever. Not many short stroke engines are in the top percentages for best BSFC.

regards
Mech

Good point on airing up the tires. Adding a warm air intake helps my mpg in the cold weather.

i wouldn't worry about overheating your engine...if it doesn't over heat in the summer, you can block 95% of the grill opening and it will be cooler than in the middle of the summer....If it does, the fan will turn on and suck the cold air from under the car or anywhere else since it's much colder now...

What's your average speed on your trips? what's the average distance you travel at a time?

average speed is ~30mph because of dozen stops lights/traffic etc. the trip is about 15miles one way or 30minutes. summer mileage was 24.5mpg on the dot, now it's about 20mpg even though i do less rushhour time.

highway cruising at 70mph displays 26mpg when it used to be near 30mpg. car used to get real hot in summer here when temps were in 90s. coolant reached 103'c or 220'f. one reason why i got rid of the underhood insulation pad.

i will be reseting my ECU back to factory settings tomorrow and will see the difference.

That's what intuition tells us and it is a correct trend, but read the 1ZZ-FE development paper, where they compare different bore/stroke ratios. The difference is not as big as you'd think.

I see nothing outstanding here:

Gas Mileage of 2012 Vehicles by BMW

What about it? BMWs are big heavy cars overall.

i think 34mpg for a 3500lbs 328i with ~265 horses (read here why the power is underated) is pretty impressive. i just think that for a car that can haul 5 people comfortably, has a nice size trunk, 0-60 of 5s and handling of a sports car 34mpg is wow. plus BMW never inflates their numbers and if anything it always underrates its specs.

in canada the 320i model is available which is a 180hp version that gets 5.3l/100km or 44mpg. that's better than a hyundai elantra isn't it?
http://www.auto123.com/en/bmw/3-seri...rid=1120800110

In europe they have diesel models that have no problem getting even better mileage.

I believe modern engines are rated with all accessories attached and running, ie AC, electrical load, which just about accounts for the difference.