Having better understood the purposes of recycling Engine Crankcase Vapors through the
Air Cleaner, I wanted to examine the transfer of Vapors from the Engine Crankcase to the Air Cleaner.
There is a Professional Gauge for the purpose. Not at my disposal, however.
David Brown adds to the discussion:
The experimentation on the Air Filter/Crankcase Breather question should provide some useful insights. I hope that you will keep me posted on it. The Air Filter should be pulling the air from the crankcase. I think that you will find some flutter at the outlet to the Breather Hose and you should perhaps be able to feel and maybe measure the vacuum at the Air Filter inlet. Really “loose”, worn engines may produce more crankcase pressure than the Air Filter produces vacuum. I suppose that it feeds into the engine in either case but the more crankcase pressure there is, the easier it will carry oil droplets all the way to the Air Filter. This is bad for the engine–oily crankcase oil getting into the combustion chamber reduces octane and promotes destructive detonation. This crankcase pressure comes mostly from poor Piston Ring sealing. I have a gauge that goes on the breather to measure this crankcase pressure. I used it on the Dyno when breaking in newly built engines and one can actually “see” the Piston Rings seating as the crankcase pressure drops. This is why a proper break-in procedure is so important. Worn Valve Guides can also add to the problem. Pressure up the Exhaust Valve Guides can add to the problem and pressure down the Intake Guides can deliver oil and air directly into the Combustion Chamber worsening the detonation problem. Try your testing both with a cold engine and a fully warmed up engine and you may see a big difference between them.
In order to test both the Oil Filler Outlet Tube and the Air Cleaner Inlet Tube, I chose a table napkin which I could separate into thin sheets. I cut a strip from one thin sheet in order to have something I could hold while testing.
Following David Brown’s advice, I started the engine and tested while it was not yet at operating temperature.
I removed the Breather Hose between the Tube at the Oil Filler and the Tube at the Air Cleaner.
I held the long strip of test paper to the Tube at the Oil Filler. The paper flapped vigorously. Actually, I could sense the output of Crankcase air pressure with my bare finger! It was a pretty good flow of putt-putt-putting air.
Next, I put the Test Strip to the Air Cleaner Inlet Tube. Nothing—or almost nothing. I then cut a small square from the test paper which would cover the Tube’s opening. The paper would stay on the Tube—just barely. I could not sense any vacuum at this Tube when placing my finger at (but not on) the Tube.
Holding the square of tissue just barely away from this Tube, vacuum would not pull the tissue onto the Tube. Very little vacuum!
From this primitive test, I deduce that the Crankcase output is sufficiently strong to propel the Vapors through the Hose and into the Air Cleaner. The vacuum at the Air Cleaner Inlet Tube is very weak but does not inhibit the intake of the Vapors.
David and I discussed the weak vacuum at the Air Cleaner Inlet Tube. We agree that the large volume of air being drawn into the Twin Air Delivery Tubes of the Air Cleaner precludes high vacuum at the Air Cleaner Inlet Tube.
I could not sense, with this crude test, a difference at Cold Engine and at Warmed Engine.
- David Brown continues to help us to test and discover.
- Our daughter, Janeva Sulman, made the video possible.
- Glory, the German Dappled Dachshund, belongs to our daughter
- Breather Hose Volkswagen Part #: N203741
- The Hose (on my Beetle) is approximately 17-3/8ths inches long/44 centimeters long.
I did a top-end over-haul on this original factory H0 engine about 16 years ago. I could find no evidence in the Breather Hose of any Crankcase oily residue, thankfully.