Engine Break In

[brendon444]

Just got an 09 sierra denali 6.2 and it has about 600km on it and was wondering if my mileage will increase after more km's or if this engine is already broke in and this is all i will be getting. Is average since new 14.7 mpg or 16.0 l/100km

Looking to here from personal experience with your trucks.

[jwhjr]

On my 04 with the 5.3, I didn't start seeing my best mileage until about 8K or so on the engine.

[elcamino]

It might increase some but it might not. IMO what they tell you it will get and what you actually get will be lower. I have a 08 GMC with a 5.3L and in 18,000 miles my average (not one trip or cherry picked tankful) mpg is only 17.3. You have 2-1/2 tons of steel with a hi-perf engine. I would not expect great mileage.

[2COR517]

From the reading I have done, probably 95 percent of "break in" occurs in about the first 20 miles. The cylinders are almost completely smooth at construction now, and the rings are extremely consistent. To get the best break in, you need to drive the motor HARD for those first 20 miles. Not fast, but hard. 1/2 to 3/4 throttle accelaration, uphill/loaded is best. These conditions bring the cylinder pressure up, which pushes the rings tighter against the wall. This gives you the best ring seal, which means you have better compression for power and economy, and better oil film wipedown on the wall for reduced oil consumption and less ring sticking.

 

 

When I say break in, I mean rings to cylinder wall. There is virtually no more break in on bearings, cams, etc. due to very tight manufacturing tolerances, and the fact that bearing surfaces are separated by an oil film.

 

At 600km, your engine is basically broken in.

 

For those that report an increase in economy later in life, it is much more likely due to driving habit changes, or changes in fuel quality/composition.

[brims]

I've read all that break it in hard stuff. That sounds like a really bad idea to me.

[brendon444]

I don't think i agree with the break it in hard but its tough to say. My truck already had 100km when i bought it so i can only imagine what the people were doing who test drove it previous wanting to see what the 6.2 could do. Wish it would of had zero km.

Well im hoping for a mileage increase with more km's.

Also does anyone from Canada find our gasoline is a lot worse quality and maybe the ethanol in the gas is affecting the mileage. All the pumps in Saskatchewan say may contain up to 10% ethanol and i no ethanol blended gasoline you get a lot worse mileage. But thats just a thought.

[2COR517]

I'll see if I can find some of my reading. Also, ask any heavy diesel mechanic. They'll tell you the same thing.

 

In a nut shell, all you are breaking in is the rings/cylinders. The harder you push the rings against the cylinder, the better the seal will be. It is not the "spring" pressure of the rings, that pushes them against the wall, its the combustion pressure. So, the more combustion pressure, the better the seal. High combustion pressure comes from more fuel/air mix. Gotta open her up to do that. You don't need to max your RPMs, just the cylinder pressure.

[Zembonez]

Mileage isn't going to improve noticeably. These engines are built to very close tolerances and basically come to you broken in. Of course there is a few hundred mile actual breakin time frame but it's not anything like it used to be.

 

15-16 with a 6.2 is about all there is.

[brendon444]

Thanks for the input. Seems like the mileage you get leaving the dealership is all your going to expect. As to 6.2 mileage seems like some ppl on this forum are getting some pretty good numbers out of there 6.2 (18+ mpg highway)

 

Also did some talking to ppl with the new 5.3 owners and said there mileage drastically improved in the first few thousand miles.

[Ryan00TJ]

From the reading I have done, probably 95 percent of "break in" occurs in about the first 20 miles. The cylinders are almost completely smooth at construction now, and the rings are extremely consistent. To get the best break in, you need to drive the motor HARD for those first 20 miles. Not fast, but hard. 1/2 to 3/4 throttle accelaration, uphill/loaded is best. These conditions bring the cylinder pressure up, which pushes the rings tighter against the wall. This gives you the best ring seal, which means you have better compression for power and economy, and better oil film wipedown on the wall for reduced oil consumption and less ring sticking.

 

 

When I say break in, I mean rings to cylinder wall. There is virtually no more break in on bearings, cams, etc. due to very tight manufacturing tolerances, and the fact that bearing surfaces are separated by an oil film.

 

At 600km, your engine is basically broken in.

 

For those that report an increase in economy later in life, it is much more likely due to driving habit changes, or changes in fuel quality/composition.

 

This is spot on... I've done work with offshore Marine SBC's. Fired up to check for leaks and set timing. Then ran at varying rpms.. 2500-5000rpms to get oil temp up to 200*. Then WOT till redline all on the dyno. With modern manufacturing, all engine breakin is done before 50 miles.

[mattgob86]

My Truck did terrible during the break in and after a couple tanks it started getting better, right now im running 16 mpg's. I got the 6.2 also

[Daryl Z71]

I was told the Chevy Small Block usually takes at least 5,000 miles before it is fully broken in. You guys make me jealous though wish I had a 6.2, but the dealer didn't have any.

[Zembonez]

I was told the Chevy Small Block usually takes at least 5,000 miles before it is fully broken in. You guys make me jealous though wish I had a 6.2, but the dealer didn't have any.

4.8 / 5.3 / 6.0 / 6.2 are all the same architecture. They are all "small block" engines although they really don't use the term small block anymore. That term comes from the days when GM had a distinct small and big block offering. Yours is good to go.

[Black02Silverado]

I don't think i agree with the break it in hard but its tough to say. My truck already had 100km when i bought it so i can only imagine what the people were doing who test drove it previous wanting to see what the 6.2 could do. Wish it would of had zero km.

Well im hoping for a mileage increase with more km's.

Also does anyone from Canada find our gasoline is a lot worse quality and maybe the ethanol in the gas is affecting the mileage. All the pumps in Saskatchewan say may contain up to 10% ethanol and i no ethanol blended gasoline you get a lot worse mileage. But thats just a thought.

 

 

Ethanol will drop the mileage. It burns cleaner but your mpg will suffer.

[Badass69]

I was told the Chevy Small Block usually takes at least 5,000 miles before it is fully broken in. You guys make me jealous though wish I had a 6.2, but the dealer didn't have any.

 

 

As written above that is simply not true. After maybe 50 miles of use at worst your rings are seated. Properly machined walls and moly rings do not take long to wear into one another and make seal. Otherwise there is nothing else to break in. Bearings have never "broken in". If you have any amount of component to bearing contact your clearances are too tight and you are spinning that bearing. Roller cams have pretty well zero break in as well.

 

Ethanol has a higher octane rating but offers less energy per unit volume than gasoline. Hence why your mileage drops off on E-85 as it takes more fuel to achieve the same power output. Timing should advance more with the higher octane and offer some benefit to power. Whether it does or not I have no idea, no E-85 up here.

 

I have a custom tune in my SRT to run Husky's 94 octane premium. I was having too much knock retard with the fuel initially but setting the advance curve and richening up the fuel slightly solved it. Shooting for 30 degrees advance was crazy on my 6.1 anyhow, the chamber is most efficent at around 25 degrees at WOT. I was getting lots of knock on non ethanol fuel ( Esso and Shell Premium) so it was not the ethanol anyways. 10% ethanol is negligibe enough it should make little difference in mileage. You are more apt to getting a bad batch of fuel from the refinery, improper blend, or a bunch of contamination from the service stations tanks. Truck load outs do all the additive blending ( I should know, we have the maintenance on the local Shell and Petro Can truck load outs) and the systems are not overly precise. They are if everything works properly. All it takes is for a solenoid to stick, some crap in a meter and your fuel will not be properly blended. All fuel in this province has ethanol in it ( I am in Alberta) except for Shell and Esso Premium.