REFLECTOR: Blow by

Grover McNair grover at mcnairperformance.com
Sat Mar 10 13:18:00 CST 2012


Higher oil consumption can be the result of a higher oil level. When the oil level is high the rod journals are closer to the oil. As the crank turns, the windage can actually airate the oil. That air and oil mix is vented through the crankcase vent. The result is higher consumption than when the oil level is lower. 
Blow by also increases oil consumption by creating higher crankcase pressure which causes the air/oil mix to exit again through vent. The pressure from blow by can also push oil by oil seals as well.
If you have a lot of blow by, it is likely the rings and cylinders are worn. This can cause oil to get by the oil control rings which allows it to get into the combustion chamber and be burned.
I would not be overly concerned if your engine uses oil when full and little when  only a quart low.
Grover McNair 

Sent from my iPhone

On Mar 10, 2012, at 12:01 PM, "Lou Stedman" <stedmanlou at roadrunner.com> wrote:

> Last week we were discussing the amount of oil different engines burn in a given time. I mentioned that I do not fill up my crankcase because the first quart will blow out within an hour if I do that . However if I fill to six quarts I don’t go through another quart for about four to five hours. After that  I got a note from someone that I should not do as I described as it is a indication that there is a blow by problem with my engine (Lyc IO-360). If this is true, what is the cause of blow by?
>  
> Lou Stedman
> Velocity SEFG
> N7044Q
> Olean, NY
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