Ever Notice You Get Less MPG Just After an Oil Change?

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Over the years it has been my observation that oil changes (of the same exact type) result in less MPG early on. Then as the oil milage increases, the MPG gets back up to normal for each car. Then it stabilizes for the remainder of the oil run. Have you noticed the same? Sure, fuel dilution can do this but many cars do not have this problem. And rapid "shearing" can do the same. But many oils are very shear stable.

Engine manufacturers certainly know this and specify viscosity grades accordingly. In Ferraris the spec'ed oils routinely drop a grade or two within a few hundred miles. The specified 60 grade Shell oil in the Enzo dropped to a 40 grade oil almost immediately. Every 40 grade oil for the other cars drop rapidly to 30 grade oils then stabilize there.

Thoughts?

Ali
 
Over the years it has been my observation that oil changes (of the same exact type) result in less MPG early on. Then as the oil milage increases, the MPG gets back up to normal for each car. Then it stabilizes for the remainder of the oil run. Have you noticed the same? Sure, fuel dilution can do this but many cars do not have this problem. And rapid "shearing" can do the same. But many oils are very shear stable.

Engine manufacturers certainly know this and specify viscosity grades accordingly. In Ferraris the spec'ed oils routinely drop a grade or two within a few hundred miles. The specified 60 grade Shell oil in the Enzo dropped to a 40 grade oil almost immediately. Every 40 grade oil for the other cars drop rapidly to 30 grade oils then stabilize there.

Thoughts?

Ali
Maybe you need to be looking at a better quality of of oil or possibly fuel is the issue.
 
The oils I used don't shear down two grades thinner, resulting in any noticeable drop in fuel efficiency. If I use a 5w-30, it's still in grade when I drop the fluid.
 
The oils I used don't shear down two grades thinner, resulting in any noticeable drop in fuel efficiency. If I use a 5w-30, it's still in grade when I drop the fluid.
Yes but did you get less MPG just after the oil change that later came back up to your "normal" MPG for that oil in that car?

Ali
 
The smaller the engine, the more effect in my experience. Back in the 1970's I noted every tankful and mileage of every car/truck I've ever owned. A Toyota Tercel was one of those. It ALMOST always got slightly less mpg the first few tanks after an oil change. At first I thought I might be idling the engine long enough to be wasting fuel, as I'm checking for leaks, etc. But after a few years I began to graph the mpg values, and I noted there was an immediate curve downward with a reversion to the mean. Of course, graphs like this aren't smooth, as many variables affect mpg from tank-to-tank. But on graphs, yes, it's apparent that this slight decrease in mpg following an oil change was common in my cars/trucks.
 
I'd like to hear the dynamic which occurs.
Q: How much reduction in mpg, expressed as a percentage (approximate)?
GUESS: Does the thicker (new) oil resist pumping so there's loss of engine efficiency?
 
I have never noticed this at all with any of my cars and I have always kept a close eye on my fuel economy. With my Civic it has a screen that gives me the fuel economy for every drive that I make and I’m always looking at that screen. With my previous Civic I had a Scangauge 2 in it that also showed me the MPG for each drive I did.
 
I have noticed an INCREASE in fuel mileage by the tank when I get closer to an oil change interval. As if the oil has thinned out allowing my car to get better MPG.

I have a Turbo Veloster and use Valvoline 5w40 Euro with 3,500 mile OCI's. I am thinking the small engine and turbo shears the oil out of grade starting around the 2500 mile mile mark.

After an oil change I do notice the mileage is a bit lower like the OP stated.
 
Yes but did you get less MPG just after the oil change that later came back up to your "normal" MPG for that oil in that car?

Ali
None that was measurable. I could see a possible noticeable increase or decrease of fuel efficiency if I dropped a grade or two, but starting at a 30 grade and ending at a 30 grade, even when the grade is within the outer limits of the grade is not necessarily recordable not only due to such small differences in grade, but allowable drive habits, weather, etc.
 
Some people notice the exact opposite.

https://bobistheoilguy.com/forums/threads/better-fuel-economy-after-an-oil-change.314947/page-2

This past summer after changing to Kirkland 5w30 in the RAV4, the first 1200 miles or so of the interval I was seeing never seen before top scores on the mpg calculator. Thereafter never saw those top scores or anything close no matter how much I tried to hyper mile or how easy the route was. By no means a scientific study and the next oil change was with a different brand/grade and in a different climate. It's hard to nail these things down in the real world, but the guys who drive the same longer routes every day can keep a closer eye on things, and I tend to believe them. Some people are just able to notice smaller differences in things without getting scientific measurement tools out.
 
Holy moly, shearing two grades?!

As far as mileage increase, I’ve never noticed and I keep written logs calculated at each fillup. My numbers are usually really close to the onboard counter as well.
 
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