The Stovebolt Site Forums The Shop Area Engine Shop 55 1st ser. Blow by

How do you tell if excessive blow by? Thanks

Remove the oil cap. Accelerate the engine. If smoke comes out the opening that is blowby.
George

Excessive smoke and other vapor escaping through the engines upper vents. You didn't state the engine you have so the way it vents differs. Some have slots in the valve cover, a vented oil filler cap or the the vent pipe connected from the valve cover to the air cleaner.
Compression will also be so low as to easily turn the engine by hand.

235 c.i. Vents in valve cover. Breather pipe comes down rt. side eng. Between dist. and fuel pump. End is close to tie rod . Compression good last time checked. Runs great. Thanks,Dennis

What do you mean by blow-by?

And, does it happen after the engine completely warms up and is driven for 30 minutes?

Pale white smoke coming out valve cover vents and out breather pipe. Yes warmed up. Thanks Blow by i think is escaping air in block?

Do a search on 235 PCV and put an end to the smelly smoke.

yes

All engines have blowby. Whether it's excessive depends on your tolerance for smoke boiling out of your engine bay upon shutdown. As a rule of thumb, if you can see oil smoke coming out from around the hood and grill after shutting off a warm engine it's probably time for a rebuild. My '53 has less than 20K and I get a small amount of smoke out of the valve cover slits on shutdown. As a lad I had a '57 Ford 292 Yblock that would fog mosquitoes every time I shut if off.

Funny and thanks to everyone that had suggestions!

The vents in the valve covers serve 2 purposes in my estimation.
1) Allow intake of air caused by the vacuum caused by the road draft tube while under way. (Archaic crankcase ventilation.)
2) Allow water vapor to escape when not under way. Under normal conditions of a well broken in, but fully functional engine, you will see what appears to be steam wafting out of the vents. All engines, including modern engines produce this. You don't get to see this on modern engines since they have closed PCV systems.
If all you are seeing is some steam wafting out of the vents at idle or upon shutdown, you should be just fine.
Carl

Excellent post, Carl

One thing that people should check on trucks with significant “ blow by” out the vents in the valve cover: make sure the road draft tube is not clogged with “gunk”. It can be easily removed and then soaked in kerosene or diesel fuel. Other memembers can post advice on a more incendiary technique.

Also, if you do a lot of city driving, or driving under 15 mph, install a PCV valve - that is why Chevrolet put them on delivery vans and on large trucks (and eventually offered them as an option on all trucks). The road draft tube works very well above 15-20 mph, but is of no use at lower speeds.

Another method of cleaning out a road draft tube for the folks who don't like the "gasoline and a match" procedure is to invert the tube and fill it with a strong solution of Trisodium Phosphate and water (concrete cleaner) and let it soak overnight, then flush it out with a garden hose. It works even better if you warm up the vent/tube assembly with a Propane torch or a heat gun while the TSP is in there.
Jerry