KATOOM

The only thing I'll add to all your comments is along the same as totalloser said which is that all engines have blowby, not just diesels. The reason our trucks do what they do is because the ISB Cummins is the last open loop emissions 5.9 Cummins that does not have a PCV or EGR valve. Which means that all the positive engine crank gases which are normally recirculated back into the intake on other engines is allowed to escape into the atmosphere on the ISB. The mechanic obviously knew this so I'm not sure why it was noted as excessive. As Tate mentioned, a vacuum leak will cause more than normal blowby but if there is a vacuum leak then depending on the size of the leak, there will be other vacuum controlled functions which wont work properly.