The Stovebolt Site Forums The Shop Area Engine Shop crankcase ventilation tube blowing oil

This may have been covered before. What would cause my 1954 235 chevy engine to blow oil out the crankcase tube?
Ben

having oil in the crankcase
do you mean there's an actual spray out the tube, or a visible cloud of smoke, or that you find oil on the ground where it's been parked?

Bill

After answering Bill's question, here are a few other 54-specific questions:

1. Do you have a PCV system (probably not)?

2. Do you have a valve cover with vent-slits in the top (54 had slits)?

3. Do you have a vented or non-vented oil-fill cap in the valve cover (no need for vented cap, if you have the 54 valve cover)?

4. How often do you drive your truck?

5. What is the length of your driving when you get the drips? And, what was your average speed?

Bill,
All of the above.

Tim,
1. No
2. No
3. Non vented
4. Daily-- sometimes
5. Just a few miles--under 20 miles

I have oil dripping off the spark plug wires and the engine only on that side.

Ben

bad valve cover seal and incorrect oil cap, should be vented, what you're seeing as being from the crankcase vent is both leaks running down the engine and pressure build up in the crankcase

Bill

Bill, has your answers covered.

In case you are interested: the 1954 non-PCV engine would had a vented valve cover and an unvented oil cap. They designed upper-engine ventilation at the valve cover and lower engine ventilation at the road draft tube.

If you are traveling under 20 miles, you are not getting the engine warm enough to vaporize moisture that has gotten into the engine.

Another consequence of driving short trips is that you get more rust developing in the exhaust system.

I solved all this with a PCV system for these trucks. Its here:

http://speedprint.com/deves50/pcvinstall.php

But it uses the vac from the intake, so if you have vac wipers, it may not work for you.

Deve, I have a question about your PCV setup. You are utilizing intake manifold vacuum. Vacuum at this location is highest at idle, and significantly lower once the throttle plate opens up. I am concerned with the potential of excess crankcase smog entering the combustion chamber at idle, affecting the smoothness of the idle. With a fresh rebuild, there wouldn't be much of an issue, but with significant blow-by of a more seasoned engine, it could be problematic. Most PCV setups which came later have the hose attached to the air cleaner. This only pulls significant amounts of crankcase fumes once throttle is open where the venturi draws it in, thereby diluting the fumes in the larger volume of air/fuel mixture as compared to your setup which pulls most of it in at idle where the volume is significantly less. BTW, I watch a lot of Sunday car and truck shows while I stay at the Holiday Inn Express. So I may be all wet on this one.
Carl

I have a 261 engine,which is S.C.O.,(no oil filter). The draft tube is plumbed exactly the same way,(from the factory),as Deve plumbed his. I have no problems with blow-by,so I'm not leaking any oil. It doesn't even smoke,when warmed-up.The hydrovac,and 2-speed lines,are connected to the same port,also. Have no problems with either one. Electric wipers,so no problem there,either. What intrigues me is "This set-up is much better for your engine,and will extend the life of it." Anything that will benefit my engine,I'm game for! Installation looks easy,and fairly inexpensive. any more info.,on the benefits,over the stock configuration? Is 52 Carl's theory,(sounds like it),even more efficient? THANKS, DEVE,and CARL!!

Thanks for the tips guys. I don't have wipers yet so I think electric and a pcv system is what I need.
Ben

I have a 261 that uses a vented oil breather cap with a hole for a pcv valve in it. I then ran a piece of hose to the intake manifold and have been running it this way for years with no problems. the original hole in the block for the vent tube has been plugged with a freeze plug.

Carl,

You refer to "Most PCV setups which came later have the hose attached to the air cleaner.".

Later than what PCV system? Later than Deve's system, or later than the original GMC-style 48-59 (at least) PCV system (which had a hose to the air cleaner)?

Since the 60's most PCV systems have a vacuum line to the PCV valve, and a fresh air line to the air cleaner. It all acts like a loop to purge the crankcase. An important part of the design is the baffle that is under the PCV valve, which is normally in the valve cover or valley cover. Without a baffle, oil will be drawn through the system.

I would think that plugging a PCV valve right into the freeze plug would suck up a lot of oil, hence the suggestion in the article to use a little hole, which I still don't like.

[b]The PCV valve is connected to full vacuum, not ported vacuum. The valve itself will control the flow during various vacuum levels.[/b] There are also generally two levels of PCV calibration, one higher than the other, so all PCV valves are not the same.

The crankcase needs to breath, or you will end up with every gasket in the engine seeping oil.

I did Deve's PCV mod on my 216. It worked great with the exception of manifold vacuum sucking up too much oil into the intake. The high mile engine has noticeable blowby which pushed more oil out to the PCV valve, even tho it does have the deflector plate installed.
So I cutoff the down tube on the road draft vent pipe and mounted the PCV in the cutoff stub pipe. All that internal baffleing of the road draft vent is keeping the oil in the engine and not sucked out to the intake.
It works so well that I'll be swapping the setup over to the 235 I'm building.
I haven't noticed any adverse problems and I feel that the engine breathes much better w/the PCV setup.
Dave

Yeah, reports back to me say that some people 10% or so say there is oil being sucked up. Mine doesn't do that, and I believe Dave's assessment. You don't have to put the valve directly in the hole if it makes you nervous, put it further up the line. In any case, it works great and you don't have a drip of oil on your concrete due to a dirty oil draft tube.

Tim, I was referring to later than 59 (I am not familiar with the GMC-style 48-59 system).
From what you describe (hose in the air cleaner), it uses venturi action for purging the crankcase once the throttle plate opens, but not while throttle plate is closed (at idle).
The venturi driven setup would make more sense to me due to the fact that there would be more blow-by occurring when the engine is running at RPMs above the idle level. With Deve's setup, maximum purging takes place at idle and is likely much reduced (in theory, I will admit) once the throttle is opened.
Carl

Carl,

I agree with your theory, but I know little about PCVs.

The PVC on the 54/55 GMC COE I am restoring was gone and in its place was a jury-rigged hose routed from the front top of the non-vented valve cover to the lower rear of the engine (serving as a road draft tube, I guess).