Gas Mileage Drop w/synthetic

Joined
May 10, 2005
Messages
168
Location
Alamo, TN
I have used Schaeffer's 9000 5W30 in my Avalon(just posted a UOA Analysis) the last three changes. Each time I have noticed a drop in gas mileage as indicated on the dash monitor. I know this is not absolutely accurate but it should be relatively accurate. Has anyone else noticed such a drop? Overall, when I used dino in the car, I got higher reading by about 2-3 mpg. I would have thought the opposite. So far the mileage increases a bit after 1-2K mi. Thoughts? John W.TN
 

Bill in Utah

Staff member
Joined
Nov 11, 2002
Messages
12,849
Location
UT
Don't go by any computer / MPG display. The ONLY thing that works is miles driven and gallons used over MANY tanks. (on paper) EVERY MPG on the dash units have been off more than they should be. MY Subaru is off 2-3mpg most of the time. My Moms truck is off that much or more. You will not see a decrease or increase within the noise level using any oil in the same weight. Going from a 5w-30 to 15-40 will affect it a little. Take care, bill PS: On your UOA, SI is a *little* high but other than that, doing well!
 
Joined
Dec 4, 2008
Messages
134
Location
Wi
Most likely not the syn oil. Could be a fuel filter needing replacement and/or need to clean the throttle plate.
 
Joined
Feb 20, 2007
Messages
5,281
Location
Southeast
1. what kind of oil were you using before? It could be the same posted viscosity; though in reality the previous oil could have been thinner. 2. try a different oil. 3. hard to believe 2-3 mpg is all oil. I've seen at most, 0.5 mpg difference between different oils (same or neighboring VI). 4. My MPG computer is dead-on in my jeep, I've run the #s a few times. M
 
Joined
Jan 30, 2008
Messages
334
Location
Mojave Desert, CA
 Originally Posted By: Corvette Owner
I change my new cars to Mobil 1 after 3,000 miles. I usually see a gain of almost 10% with synthetic.
I was expecting to see a winking smiley face but I didn't so I'm going to assume you aren't pulling our leg, right? 10%? That's not the oil thats making a difference like that.
 
Joined
Jan 20, 2003
Messages
18,449
Location
East of IGO
 Originally Posted By: Corvette Owner
I change my new cars to Mobil 1 after 3,000 miles. I usually see a gain of almost 10% with synthetic.
Most likley and in all reality it would be break in that causes the increased MPGs.
 
Joined
Feb 29, 2008
Messages
11
Location
Kentucky
My 08' Nissan Frontier gets 2-3 mpg better mileage when the air temp is above 60 deg. F. I was getting 22-23 mpg last summer and it dropped off as it got cooler to around 19-20 mpg. I thought something was wrong with the truck and took it in to the dealer. They could find nothing wrong. Now that the temps are getting back up my mieage is getting better again. Must have something to do with the air density. Could this be what you are seeing?
 
Joined
Jun 17, 2005
Messages
4,942
Location
Billings, MT
Colder air is more dense, and thus has more oxygen for its volume. Your engine is still moving the same volume of air, but the increased oxygen level requires more fuel to burn. Engine, transmission, gear and power steering oil also don't flow as freely at cold temperatures, and will rob more power from the engine. Even rubber belts and greases cause more mechanical loss when cold. It also takes an engine longer to warm up when it is cold, which lengthens the time it takes before it starts running in closed loop. Open loop will use more fuel, since it is not using the oxygen sensors to tune the AFR. Winter blended fuel also has an impact on fuel economy. It's really a whole bunch of things that compound to make cold weather driving far less efficient.
 
Joined
Sep 5, 2006
Messages
19,479
Location
Chicago Area
chevrofreak - Your theory about cold air is incorrect. An engine will only use more fuel with colder air when we use full throttle - and that is only a maybe - a possibility. At any other condition, the fuel is metered and controlled to provide the same mixture.
 
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