The Stovebolt Site Forums The Shop Area Engine Shop valve cover smoking

I have a 1942 GMC with either a 228 or 270 GMC engine. I noticed small wisps of white smoke coming out of the vent on the top of the valve cover during and after it have been running.

Is this normal?
What is the reason for this?
How worried should I be?

Thank you,
Akguy34

That's normal as far as I know. It's just vapors escaping from the crankcase. My 56 Chevy half-ton does it and so does my 49 Plymouth sedan.

Does it smoke after driving 20-30 miles at highway speeds? Or, after 20-30 minutes of steady driving (not start-stop) after the engine warms up?

I've seen it smoke after just idling for 5 minutes but it smokes the same amount as it did when I drove it home about 10 miles, I was going slow about 20-25 MPH

look at the flat pad located behind the dist. the first three numbers will tell you what the engine size is.

there is no pcv valve on your truck so any gasses that are being formed (blow by) are not being sucked into the carb and burned. the road draft tube which is that pipe in front of the dist. pointing to the ground is where the smoke, fumes or what ever is sucked out of the engine when the truck is moving at a moderate speed. as its being sucked out fresh air is being drawn into the slits along with whatever is in the air (dirt, moisture) on the valve cover, that is a simple ventilation system but works as long as your moving. when you stop the vapors come out the valve cover. you can always pull your valve cover and run the engine and see whats going on under there. once i understood how the system worked i stopped worrying about it. find a 350 or larger gmc and swap over the pcv system it has over to yours. no more smoke and the air entering is now filtered.

I agree with everything 51ashton posted.

Nonetheless, water (water-vapors) in the engine will most likely not be "burned-off" after 10 miles of relatively low-speed driving. That type of driving is why Chevrolet put a standard PCV system on delivery vans after 1947.

Drive your truck 20-30 miles at as high a speed as you can handle (about 30 minutes of driving at 30-50 mph) and see if it then still smoking.

I don't think I've ever seen white smoke out of the rocker breathers that had anything to do with coolant in the oil. Coolant usually settles under the rocker cover in the form of white slime because the rocker cover is still cold and it condenses and emulsifies there. Once it is warmed up, it is probably invisible vapor. I think all he has is blowby which really doesn't hurt anything. Our preferred way to get rid of these fumes was to plug the breather and run a line from the breather to the top of the air cleaner. This way we didn't have to worry about a PVC sticking and causing a vacuum leak and it kept the fumes out of the cab.

Thank you all, removing the valve cover is on my list of things to do, since I have a hard time leaving things alone

I'll have to look into the PVC But right know I need to get the brakes working.

Thank you again,
Akguy34

my 235 smokes also
...click...

less on the longer drives

I'd say that DADS50's wispy white smoke/vapor has as much probability being water vapor as it does being other volatile substances.

Dads50,is that a 1954 235 ?
I believe it's the only year that had the vents like yours.


Tim

That is right, Tim: 1954/55-1st valve cover.

Yes. 54 235 (car)

I realize the thread is regarding a GMC,

Just posting I have a somewhat similar issue.

DADS50

Thanks for posting the video.

I find light wisps of vapor to be normal and will continue for a little while after shutdown.
I have seen moisture in the oil increase the amount for a while as would some low boiling contamination like gasoline,diesel,solvents, etc. but would lessen after running a while at good temperatures as these boil away.
Where you get concerned is when the amount increases greatly as the engine load/cylinder pressure/throttle opening increases.
I would expect my good engine, breathing lightly at idle, when the throttle is suddenly opened a increase in vapor would be not much, but noticible.It should be smoothly issuing not puffing which would indicate one cylinder leaking more at the rings than it's neighbors.If it's an automatic you can hold the brake while in gear and really load it for an observed test.
When a lot of blow-by is present, it can fog smoke out the draft tube and vented cap and become noticible behind the car and even in the cab---this will lessen with light load and increase with throttle opening/heaver load.RPM doesn't make as much difference as the load which is greater momentarily when throttle is opened.
The draft tube system is designed(?) to create a draft by air flowing over the bevel cut tube--so the valve cover slots are to let air in--when the draft is established.If no air across the tube--no draft so the engine breathes whatever it needs to at the vent providing the least restriction.The fan can provide an air flow over the draft tube, but not at idle.
Many older industrial engines used draft tubes and under load the issuance was a pretty good indicator of cylinder sealing efficiency.

Thanks for the info guys


@Akguy34, hope I didnt cloud the issue for you.

thank you

No problem it was very helpfull, as regards to the video it looks like the same exact thing in my 228 GMC

Do you have an oil filler hole in the cover? stick your finger into the hole and slide it on the underside of the cover. Does white creamy colors goop come off on your finger? That is condensation.

My valve cover smokes also. When I pulled the cover off, here is what I found .

Dale

No oil hole in the top just two vents I'll pull it off later I have some stuff going on this weekend and my knee is finally healed enough I should be going back to work so no more hours playing on my truck

di1953gmc I hate when those things get in the engine they are a pain to get out once they get rooted. Check your transmission they breed like bunnies an infest everything

A dedicated tomcat can help that problem.

[quote=akguy34]No oil hole in the top just two vents /quote]

then where do you add the oil. or is it on the draft tube?

I beleive its on the draft tube I'm not sure still trying to figure everything out on the engine.

tell me i am crazy but i took the draft tube out and replaced it with a oil fill tube off a 60's v8 intake. was going to put a pcv valve in the end and cover it with a breather but an old timer told me the draft tubes really didnt work as engineered. so just to put the breather on and leave it alone. havent run it yet but he swears it will be fine. if it doesnt i will put the pcv in as originally planned. got the idea of the pcv off here just put my own twist on it with the 60's intake pipe.