while we are on the topic of lower friction, is it feasible to think that some percentage of mpg is lost as you near a car's need for an oil change? I run full synthetic and change it every 5,000 miles, and I always think I am getting slightly better numbers with nice fresh oil running through it. If it is possible, and not just a million other things that could be effecting mpg at that point in time, it kind of makes me wonder how much the oil is breaking down after 5000 miles. Just a thought...

You can test it and see exactly how much it's braking down. I always notice a 1-2MPG difference after a change. Also the engine seems to idle smoother. I can actually tell when it's really in need of a change by a slight increased rumbling or vibration at idle, it's very slight but you can tell it's lugging a bit more.

I would say the opposite is true. The longer your oil is used, the better MPG you'll get because oil shears to a lower viscosity. I've noticed this because the milage I get from my Yaris is worse at the start of new oil usage, and improves as the oil is "aged". I realize oil can thicken up too, with age, because of oxidation, but on balance, it often shears to a lowe viscosity, and thinner means less resistence for the crank to turn.

A quicker warm up will save fuel, so I agree on the grill block, tires aired up is a no-brainer, but octane is a bit trickier. Modern cars with knock sensors will adjust the max advance during cruise which highly affects mpg. I tend to run mid-grade 89-90 just to make sure my car is always at max timing. I find my mileage to be 7-10% better running the better gas.

If changing the oil at 5,000 miles is good.....
wouldn't it be better to change it every thousand miles?

I would think that the cost of the more frequent oil changes would out weigh the gains that you would get from it.

5x the oil changes gets expensive especially when you are talking about synthetic.

that is an oil change every month (or for some of us every 2 weeks)

colder weather reduces FE because it slows the atomization of fuel. egr valves recirculates part of the exhaust gas into the intake thus reducing emission(unburnt gas) and increasing FE..

it takes more time for water to evaporate during winter than it is during summer, same applies to gasoline

blocking the grills prevents the ram air from cooling the engine bay, creating hot environment for the engine and the air cleaner.. by then, the engine is sucking hot air.

i have my intake located right after the radiator. i use 93mon octane(lowest from where i am) its turbocharged and no ping even at full boost.

octane is over rated i think, most of the cars nowadays have better combustion design(except maybe overhead valves) withstanding compression ratios that were over the limits in the old days

i think you all get 89mon + 85ron /2 = 87

all else being equal(filter, your time, paying labor, etc), you WOULD save with synthetic. the $10 amsoil series 2000 is guaranteed for 35k miles or 1 year, so MUCH time and/or labor would be saved.

about cold temps...

amsoil has not only the highest flash point, it also has the lowest pour point IN EVERY GRADE. so you're covered hot or cold assuming severe enough cold would slow the flow of dino oil.

bowtie,

my response was for shatto that said why not change the oil every 1,000 miles vs every 5,000. which would mean you were changing your 5 times as much.

I was stating that the cost of the oil and filters (plus labor) would out weigh the gas mileage of the more frequent changes.

the big selling point in synthetic oils right now is the extended oil change intervals.

my response was intended for shatto and not really at the subject matter at hand.

Beef,

i understand. my thought was in regard to those that reach 3k miles rather quickly and use dino oil. and it just so happens that amsoil can be ~5 times the price of conventional oil.

i drive less than the average driver and still do not look forward to getting under my car twice per year(once for full change, once for filter only).