Gasoline Mileage improvement after break in.

My wife's car improved about 10% after 15K or so. I have bought a few vans new over the years and I thought they got a little better mileage after about 10K on the clock.

When I had the rear end rebuilt and new gears in my Excursion, it lost 3-4% until they got broke in after about 1000 miles. Back to normal after that.

I do think there are things to break in, but not just the engine. Everything in the drivetrain is tight when new and just gets looser from there.

Of course..... YMMV!

Only ecoboosts that are getting mid twenties @ 70mph are 2wd and 3.31 rear end.

3:55's and 3:73's will give you about 17-18 @ 70mph. If you want low 20's drive 60 mph.

Higher mileage after break in is probably more of a myth carried over from the old days when we set up race engines on the loose side of tolerances to make them rev higher and easier. With modern manufacturing techniques, they probably get it pretty close to right before it leaves the factory. Like others have often mentioned, if we want mileage, get a Prius.

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It might be possible to temporarily run rich fuel in heavy duty non-EPA regulated engines during break-in, but I don't know why.

Running a richer mix during break-in is reminiscent of old gas/oil mix 2-stroke engines used in dirt-bikes. I can't see how that could affect a modern 4-stroke unless straight gasoline had lubricating qualities. I would think a greater fear would exist that excess "dry" fuel would wash down cylinders thereby depriving them of adequate oil film. That was a reality with the old carburator "ball-park" systems and one of the reasons modern FI (fuel injection) engines last longer. Remember how backyard mechanics used to whine about EPA and FI? Now it's diesel owners turn.

What would break-in for better 4-stroke fuel economy on modern engines? Maybe it's a leftover tale from the past.

Consider an older flat tappet camshaft, for instance. Apparently the newer roller cams help with friction, particularily regarding the use of more aggressive lobe profiles to stretch the powerband at both ends and the middle, idle to rated hp. But that shouldn't affect newer roller cammed engines during break-in. Old engine designs, yeah.

The piston rings used to have more static tension and now have less to reduce friction. That again wouldn't affect newer engines break-in as much as older designs.

I was considering adding 10W30 motoroil to changeout an old (1978 IT) dirt bike transmission this weekend and couldn't remember what oilgrade OEM called for. My son mentioned that he had read that newer oils have added friction modifiers and standard motoroil now affects the wet clutch. A web check said 10W30 OEM, so that is what it got. Unfortunately I discovered the ancient air-cleaner foam had turned to dust, so no trial. But the point is, ordinary oil may be slipperier than in the past. Again, that would not affect breakin.

Bearing inserts haven't changed much.

So what breaks in now... as someone else asked earlier?

Wes
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Fordlover wrote:

These guys (link) managed 32 MPG, hypermiling an Eco F-150 that was loaded up to it's GVWR.

Or are they a bunch of liars involved in a conspiracy just to mislead Tom?

I have no idea who they are, what their agenda is, or if there was any monitoring of the test. I do see one interesting word in the write up. I think we have all "observed" fantastic (or terrible) mileage while driving. Had a big old diesel Suburban back in the eighties that got 30 mpg on occasion. Think what they could have done with it using today's mileage tricks and technology. 40 mpg?

"Here's a look at CleanMPG's observed Interstate highway steady state fuel economy at different speeds:"

goducks10 wrote:
I get my best mpg's when the price of fuel rises:)

LOL! Me too.

Fordlover wrote:

TomG2 wrote:
I think most of the ecoboosts are getting upwards of 26 mpg. At least that is what the salesman said.

These guys (link) managed 32 MPG, hypermiling an Eco F-150 that was loaded up to it's GVWR.

Or are they a bunch of liars involved in a conspiracy just to mislead Tom?

It's funny they got a MPG stat @ 40 mph in 6th gear with 3.15 gear. That little Eco boost must have been running about 500 RPM. It also must have about 10 miles of vapor line to get 10 gallons over it's tank size.:h

I get my best mpg's when the price of fuel rises:)

Sport45 wrote:

bob_nestor wrote:

Interesting. My previous RV was on an E350 chassis with the V-10 so I did a lot of searching for information on the V-10. One article I remember reading indicated the on-board computer is factory programmed to run a rich mixture for the first 10,000 miles to help with the break-in period. If really true, I'd assume that this technique may be used by other manufacturers as well. Sorry I don't have a reference to that original article.

Did you notice any better mpg's after 10,000 miles?

My 2002 Winnebago Signseer 30B on the Workhorse Chassis was getting about 7 mpg. I'm now averaging about 9. My best ever was 11 on a road trip. My tires are inflated to 85lb and I replaced the oil with full synthetic and I drive for economy, so some or all of that contributes to my improvement. My 1998 Lincoln is getting 27mpg on the road. It has 150k miles and has been on synth oil since about 20k miles. I do believe synth oil after initial break-in does improve mileage, at least for me.

bob_nestor wrote:

Sport45 wrote:
In 13 years and a whole bunch of miles I haven't noticed any mpg gains at all with my Triton V-10.

Haven't noticed any losses either...

Interesting. My previous RV was on an E350 chassis with the V-10 so I did a lot of searching for information on the V-10. One article I remember reading indicated the on-board computer is factory programmed to run a rich mixture for the first 10,000 miles to help with the break-in period. If really true, I'd assume that this technique may be used by other manufacturers as well. Sorry I don't have a reference to that original article.

Why would an engine need an over rich mixture during break-in? :h What exactly needs more fuel during break-in to break it in?

And what is really breaking in anyway that causes this huge increase in mileage?