1979 GMC C3500 Blowby

CSE2_27

MEMBER
1979 GMC C3500
7.4L
V8
4WD
AUTOMATIC
100,000 MILES

What are the causes of blowby on a 1979 454 GMC and how can it be fixed?

Wednesday, March 5th, 2014 AT 1:28 PM

1 Reply

HMAC300

MECHANIC
48,601 POSTS

Blowby can be caused by many things but biggest culprit is a clogged pcv system and valve replace the vale and check hose and where it connects for good vacuum. The hose may be soft and sucking together. The engine could have detonated then went into preigniton blowing a hole in piston as well.