C7 Blow By

[GCecchetto]

For you folks with C7 powered trucks, I'm curious how much blow by you see out the breather. Thanks

 

[GeneralDisorder]

Lots unless you run them two quarts low. It will spit out what it doesn't want. CAT redesigned the breather to be more like the 3126 to avoid it but it doesn't fit under our cab.

The military guys all know about it and just run them halfway between the low and full which is 2 quarts. That's also what I preach and practice personally.

 

[GCecchetto]

Lots unless you run them two quarts low. It will spit out what it doesn't want. CAT redesigned the breather to be more like the 3126 to avoid it but it doesn't fit under our cab.

The military guys all know about it and just run them halfway between the low and full which is 2 quarts. That's also what I preach and practice personally.

Thanks, that's where my oil level is, but I was referring to gases coming out, not oil.

 

[AKPacker]

For you folks with C7 powered trucks, I'm curious how much blow by you see out the breather. Thanks

Mine smokes a good bit out of the breather on cold starts if it has been sitting for a while. Not nearly as noticeable during warmer weather and if it is driven more frequently.

 

[fuzzytoaster]

I've got 4 A1R trucks and had 11 over the years. They will all have some degree of blowby, it's a medium duty diesel so it's inherent that it will have some. If you can't visibly see the blowby that's a good sign. If it's blowing the cap/bung out that's a bad sign. Anywhere in-between is fine as long as fluids are good, performance is good, and you are satisfied with the engine as it is.

 

[Skyhawk13205]

If you want to big deal it you can have Cat do the blow by test with a special meter that is attached to the breather to get a specific CFM for acceptable blow by.

 

[GeneralDisorder]

I haven't noticed anything significant from mine unless it's over filled. Once it finds the level it likes (assuming over filled) nothing much is evident from the breather. Maybe a little vapor.....

I'll have to throw a go-pro down there and film it I guess to really compare since it's a pretty subjective thing to discuss without a frame of reference. It's a breather so I don't expect the inside of the hose to be dry for example.....

I do feel like the amount of breather activity has calmed down on mine - obviously in part from running the engine two quarts lower than full to avoid the chassis lube option.

I also feel like my engine has smoothed out significantly since I got my truck. 2,750 miles in 2021. About 28k miles today. The steering wheel vibrations are almost gone now.

 

[GCecchetto]

I have visible vapor coming from mine, most noticeable when the light is just right. My motor could still be wearing in, just coming up on 10k miles. For a medium duty diesel that’s not much. In the owners manuals for the Cummins powered rams it says not to use synthetic oils at less than 10K miles.

Anyway truck runs like a top, so not really worried about it. Next time I’m driving it, I’ll take a short video of the breather and post it.