My oil overflow tube puffs smoke
 

What does that mean?

That's compression loss past the rings.

you mean the crank case breather tube




?

The truck only has 256k miles and runs great and seems to have been maintained well. Is this bad?

I think so? It dumps underneath the truck towards the middle-front

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"1st test. Remove the vacuum hose from the vacuum pump and cap it off. It must not be able to pass air. Road test for long enough to determine if fixed.
If the vacuum pump cannot hold a vacuum in the A/C system and 4WD controls, it will become a AIR pump and pump this air into crankcase in high volume. It is much worse at high RPM as the vacuum pump is a positive displacement unit.
If this fixed the oil fog, repair the leak"

Taken from cumminsforum... does this sound accurate? There is nothing hooked up to my air pump so maybe this is the issue.. (even though I thought I put a cap on it)

After 220k they all start this.

Oh they do? Phew!! Is this an o.k. thing or is this major? Its not a ton of smoke, just gently puffing, but it still has me worried!

when you say it puffs smoke, does it puff or is it a steady stream of smoke. puffing not good steady stream is ok. puffing is a hole or gauld piston

yup its just some blow by never too bad unless its puffing

Good question. I'll take note of it tomorrow and report back! The truck runs fantastic though, so I'm doubting a hole or gauld piston

I'll take a peak tomorrow. Thanks guys

if it makes you feel better mine does the same thing, you have to look closely but I can see a slight haze when its cold.