Smoke coming out oil filler hole on old Ford straight 6. What's normal?

[ArtDecoWorld]

I went to look at a Falcon retrofitted with a 250 inline 6. Seems to drive decently.
The oil cap is one of those old vented ones, and it was smoking a fair amount at idle (both on start-up and after driving for 15 minutes). How much smoke is 'acceptable'?

What potential issues can smoke from the oil filler hole indicate?

 

[bullwinkle]

Does it have a PCV system? I've seen some oldies puff smoke pretty hard, but a compression test would be the way to know how bad.

 

[Graham Piccinini]

It's quite normal and harmless for these old mills. They will puff, smoke, and still roll on reliably. If too bothersome - a piston soak with Berryman B12 will clean things up pretty good. Plus some B12 in the carb and "feed it the onions", aka proper italian tune-up.

 

[PimTac]

Check for a plugged crankcase vent. The other possibility is worn rings.

 

[Snagglefoot]

This is exactly why you could cut the smog in LA with a knife back then.

 

[measureman]

That's normal for old cars.
They just vented it out into the air.
No PCV systems.

 

[Wrenchturner44]

If the engine does not have a PCV system, then it might have a road draft tube (see illustration attached). That tube could be plugged forcing more than normal gases out of the oil filler cap.

 

[samven]

Yea those old motors were suppose to have a crankcase vent, if its all sludged up then the oil fill becomes the crankcase vent. Could also be rings but a compression test will help diagnose that.

 

[andyd]

I can remember taking off the draft tubes on Chevy 6es, dunking it in the gas bucket, then setting it alight on the gravel driveway to clean them out. Easiest way to deal with a terrible job. Still took an hour or so to burn out.

 

[Lubener]

It's blowby past the rings. The smoke will increase out the filler if you pull out the PCV valve. If there's so much smoke resembling a tea kettle, the engine likely is worn out.

 

[Malo83]

It's still breaking in.