DODGE RAM FORUM banner

1 - 11 of 11 Posts

·
Registered
Joined
·
25 Posts
Discussion Starter · #1 ·
Had original intake manifold replaced with Dorman due to lots of blow-by oil. Dorman was a good price and has an accessible pcv tube. The original is all internal. Truck is making less power now. Does Dorman not flow as well or maybe the removal of the foam pad to fit the deeper Dorman is causing knock? This is very frustrating.
 

·
Registered
Joined
·
57 Posts
Forgive my ignorance, how do you get blowby thru an intake manifold? I always thought it was thru rings but I may be way off.
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #4 ·
Maybe it’s not the right term. The pcv valve is built into the factory manifold and vents from the back to the front. There is no way to stop it. Catch cans are marketed to go on the clean side breather tube which is useless as the clean side has never produced and oil residue. The Dorman manifold actually has a pcv tube you can split and put a catch can inline, which is a cool feature. Unfortunately the Dorman doesn’t seem to flow as much air.
 

·
Registered
Joined
·
57 Posts
I don't know what you mean by 'clean side'. Oil vapors travel from the engine block, thru the pcv valve (both sides), to the intake. A catch can would catch the oil vapor on either side of the pcv.



If you have excessive blowby oil entering the manifold, your rings are probably shot.
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #6 ·
So the clean side is the fresh air tube going from the intake tube to engine. That’s the direction of air. Clean. The pcv system is enclosed in the manifold and not accessible.
 

·
Premium Member
Joined
·
32,783 Posts
Air pressure builds up in the crankcase, below the pistons
This air pressure needs to be vented out of the lower part of the engine

Originally the pressure was relieved by a Road Draft Tube, it dumped the pressure from the back end of the engine block & hung down to the bottom of the engine compartment firewall

notice the black steel tube at the rear of this Chevy engine





Then smog emissions laws came into being
They made engine manufacturers plug up the road draft tube hole & design a hole that allowed the air pressure to come through the original vent & the new hole forced the air pressure to enter into the Valley Pan below the intake manifold

 

·
Registered
Joined
·
25 Posts
Discussion Starter · #8 ·
The original point was the dorman intake doesn’t flow as well. The secondary point was the original intake manifold pcv system is completely built in and enclosed. Poor design. I’ve had three mechanics say so
 

·
Registered
Joined
·
57 Posts
Sorry for misunderstanding. Just put your original manifold back on, it has nothing to do with excessive blowby regardless of the location of the pvc valve. Install catch can between pvc and intake. To fix the blowby you'll probably need rings. If your mechanic suggested replacing manifold to fix excessive blowby I recommend finding a new mechanic (or 3)
 

·
Super Moderator
Joined
·
34,750 Posts
Blowby is oil that blows past the rings; PCV residue comes from the crankcase up to the intake in the PCV tube and is not blowby
 

·
Registered
Joined
·
57 Posts
I believe the pressure in the crankcase comes from the blowby...oil is not blowing by the rings, combustion pressure is. that pressure (which contains oil vapor) is relieved by the pvc.
 
1 - 11 of 11 Posts
Top