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Mileage - How much is too much to buy?

BainMan

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What condition & prior service history? I think there are members on this forum with over 500,000 miles. These old pushrod motors can go a long way when treated well.
 
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EXT4ME

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I bought my 2003 Z-66 a year ago with 242K miles on it.

So far, so good with 252K miles.
 

bpdutton

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Like BainMan said - depends on condition and how it's been maintained. Mine has 141k and runs like a top. It's had regular routine maintenance done to it and things that break/wearout get fixed/replaced. I expect it to last at least another 100k miles.
 

ygmn

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Where is it from?
Rust Belt where they salt roads?
California?
South?

Rust I think is biggest issue for these older trucks.... most expensive thing to repair.
 

Andrew1

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I bought an 08 with 166000 and it runs and drives fine luv this truck
 

WrenchIt

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Wikipedia lists the engines in all the Av’s.

this is a rundown of common problems:


If you want power, I’d stay away from high-mileage L76 engines with AFM that were fleet or rental vehicles early in life. The L76 is the 6.0 gas engine. I ended up w/ the 2500 with the L18 engine. That engine is unstoppable if it’s maintained.

I’d Carfax any L76 truck, or check service records (haha! I made a funny) to see if they had a reputable place disable the AFM and replace the camshaft early in the engine’s life. Some of them you can tell they disabled AFM cause there’s an AFM disabler module plugged into the obd port that has to be there-blegh.

AFM tries to save mileage by only firing 4 cylinders instead of 8 when lower power is called for. The first engine that had AFM on the Av was in ‘07, I think? Maybe somebody can confirm or correct that.

There are lots of prob’s with AFM. The mileage gain is only about 10% because you still have to lug around the weight, and push a boxy truck through the air.

also Uneven combustion makes the engine heat up unevenly, over and over again. This sometimes make gaskets fail early, screw with the truck’s timing and wear down the camshaft prematurely. Check the service record for a camshaft replacement (not an upgrade) under 75k miles. That’s a huge clue that AFM altered that vehicle’s timing and caused engine components to bang in that camshaft until it was pitted and unusable, or even bent. You just spent all the gas money you saved on an engine rebuild.
I test-drove like 3 of the 2nd gen trucks with the 6.0 in them, thinking I’d get maybe the gas alternative to the duramax Silverado. They’d be better ‘cause they’re newer than first-gen, right? Newer is better... Well, not in those two trucks. Both of them had replaced camshafts before 70k. First one had a pretty big vacuum leak around the intake, and the rear seal had popped on the second one.

Of course, many people might have a great experience with the 6.0. That said, being around these trucks for a lot of years, plus experiencing those test drives, made me think the risk isn’t worth it. More experienced Chevy guys than me tell me “walk away” from the old L76’s. FWIW
 

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My 2004 EXT has the LQ9 6.0 HO engine.

At 232K, it is currently sidelined with a cracked driver's side (Non-Castech) head.

Come to find out, the Castechs are not the only heads on these engines that are prone to cracks.

Coolant coming from the head crack and draining into the crankcase over the past year and a half before the truck was taken out of service, makes this engine unreliable for me.

Due to the truck's age and mileage and the fact that the rest of the truck is in remarkably good shape, a reman engine is in the plans.

I could not replace this truck with one in similar shape for the cost of the engine swap.

My current daily driver, a 2003 Avalanche Z-66, has the LM7 5.3 engine.

Knock on wood, at 255K this engine is still performing well.

There is always tomorrow.
 

Raekal

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(I wrote this a couple hours ago but forgot to hit send, lol)

To be fair, any engine containing an AFM can have these problems. The 5.3L had it in the 2nd generation while by comparison a 1st gen Ext with the 6.0L did not AFAIK.

Fact of the matter is that the more that you put in an engine, the more of a chance it has to fail. This is why Toyota is well regarded for reliability, not because they have the best engineers on the planet (not saying they're bad either, lol) but Toyota got away with re-using the same tech for decades. Hell, most of their vehicles today use very similar versions of their older four cylinders. If it aint broken dont fix it.

Then EPA restrictions came along and the big 3 had to make their motors more fuel efficient. GM and Chrysler went with AFM and Ford went with ecoboost. Frankly, im not sure there's a single engine from any of their lineups that id trust to get me as far as a pre 2006 model.

Hell, GM still uses the same engines today that they did back then with alterations. But these alterations in the name of fuel efficiency have had a greater effect on reliability. All i ever hear is bitching about the ecotec line, but the ecotec 5.3L at it's core is still more or less the same engine with a new name. To this day, i'm not sure that anyone has figured out how to perfect AFM amd at this point it's here to stay. It's that or a turbocharged (Smaller than an engine should legally be in a truck) engine it seems. AFM has limited impact, which is why we've seen GM and Ford go in together on the 10 speed.


That said, in regards to the original post. Body condition + Service History > Mileage.
 
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To be fair, any engine containing an AFM can have these problems. The 5.3L had it in the 2nd generation while by comparison a 1st gen Ext with the 6.0L did not AFAIK.


The 2002-2006 EXT's all came with the LQ9 6.0, AWD and no AFM.

The 2007-2008 EXT, as I understand it, came with the 6.2, AWD and even though the engine contained the AFM hardware, the AFM was not activated in the computer.

The 2009-2013 EXT's came with an AFM activated 6.2 and AWD.

If this is true, then for me, the 2007 and 2008 would be the preferable EXT's to have.

I'm sure someone will correct me if I am wrong.
 

Raekal

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The 2002-2006 EXT's all came with the LQ9 6.0, AWD and no AFM.

The 2007-2008 EXT, as I understand it, came with the 6.2, AWD and even though the engine contained the AFM hardware, the AFM was not activated in the computer.

The 2009-2013 EXT's came with an AFM activated 6.2 and AWD.

If this is true, then for me, the 2007 and 2008 would be the preferable EXT's to have.

I'm sure someone will correct me if I am wrong.
at least according to the wiki for the L92, engines built before april 1st 2006 had the afm components but no computer, whereas models after that had the extra components removed as well until later modified as the L94 where the AFM was enabled. Just goes to show how far ahead the engineering world is of changes to a product line. Interestingly, I guess 2009 was a transition year where there would be some L92 flex fuel models running about before the change to L94 the next year.

Either way, I would agree with your assessment. To think, i turned down a pretty nice 2007 to avoid AFM when I hadn't known any better. lol
 

WrenchIt

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(I wrote this a couple hours ago but forgot to hit send, lol)

To be fair, any engine containing an AFM can have these problems. The 5.3L had it in the 2nd generation while by comparison a 1st gen Ext with the 6.0L did not AFAIK.

Fact of the matter is that the more that you put in an engine, the more of a chance it has to fail. This is why Toyota is well regarded for reliability, not because they have the best engineers on the planet (not saying they're bad either, lol) but Toyota got away with re-using the same tech for decades. Hell, most of their vehicles today use very similar versions of their older four cylinders. If it aint broken dont fix it.

Then EPA restrictions came along and the big 3 had to make their motors more fuel efficient. GM and Chrysler went with AFM and Ford went with ecoboost. Frankly, im not sure there's a single engine from any of their lineups that id trust to get me as far as a pre 2006 model.

Hell, GM still uses the same engines today that they did back then with alterations. But these alterations in the name of fuel efficiency have had a greater effect on reliability. All i ever hear is bitching about the ecotec line, but the ecotec 5.3L at it's core is still more or less the same engine with a new name. To this day, i'm not sure that anyone has figured out how to perfect AFM amd at this point it's here to stay. It's that or a turbocharged (Smaller than an engine should legally be in a truck) engine it seems. AFM has limited impact, which is why we've seen GM and Ford go in together on the 10 speed.


That said, in regards to the original post. Body condition + Service History > Mileage.
Raekal, very true. Thanks for the extra info
 

Avalanche Krazy

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As everyone above has said, condition is more important than miles. Of the 8 avalanches that I have had 3 of them I purchased with over a 100000 miles but 4 of them I drove to just below 200000 and sold them in excellent condition with no mechanical issues. One of the two 08's that I had was taken in under warranty and the top half of the engine replaced due to excessive oil use. It was giving me no problems except the high volume of oil it used. The dealership tried a TSB fix that didn't seem to work so the offered to change out rings and pistons and valves I think. But every other one I have had has served me well with good maintenance habits.
 

Dandy

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Jul 28, 2021
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I have over 225000 on my 04. It has been with me since 06 though. I fully intend of driving it for many years to come.
 
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