1950s Help! Smoking coming from oil fill

[Daffer]

I just started my 1950 cadillac after a gasket rebuild on the engine i had to fix a small gas leak but after when I went to start it again white smoke started coming from the oil fill whats wrong! is it just the timing??? This is its first start since the rebuild. **Update** started the car again, ran it and excessive smoke came out, left it running smoke slowed down. So I timed it, there was some knocking, but I got that to go away, after timing it. it seems as though the smoke is less but theres still some. I'm wondering, could it be moisture that's burning off?

[Lexi]

It is normal to see smoke coming out of the oil filler neck. Just how much is "normal", is hard to say without seeing it. Unlike modern cars which have emission control and crankcase ventillation systems, Cadillac engines from this era are vented directly to the atmosphere. So seeing some smoke is normal. It appears that your vent cap is also missing its filter screen material. That may perhaps, very slightly increase the presence of smoke. Further, that if you had spilled any oil in that area, some may be burning off of the hot engine after warm up. Smoke may very well be apparent where the spill occured, even a lot of it. If no further spills take place, the amount of smoke there will dissipate. Clay/Lexi

[TJ Hopland]

Gasket rebuild?  Including head gaskets?  But no new rings or bearings or other hard parts?

Is it possible you never really looked that close at it before?  My guess is its normal just the way engines are before PVC systems.   Have you checked the oil to make sure it doesn't smell like gas?  Was your leak external or a carb issue?  If it was in the carb maybe it leaked into the engine.   

[Bob Hoffmann CLC#96]

 

excessive smoke usually indicates blow by.

[Daffer]

Gasket rebuild?  Including head gaskets?  But no new rings or bearings or other hard parts?

Is it possible you never really looked that close at it before?  My guess is its normal just the way engines are before PVC systems.   Have you checked the oil to make sure it doesn't smell like gas?  Was your leak external or a carb issue?  If it was in the carb maybe it leaked into the engine.   

Yea new cylinder head gaskets aswell, I didn't call it a normal rebuild because at the time I didn't know how to replace rings now I do but I never did that sadly. That is probably the only thing that I didn't do during the rebuild

[Daffer]

excessive smoke usually indicates blow by.

Thing is it never did it before. And after the first time starting it was fine, until the second start when it was warmer. So I wonder could it just be moisture burning off?

[TJ Hopland]

Ya moisture could be part of it.  Did you have the pistons out? 

[Daffer]

Ya moisture could be part of it.  Did you have the pistons out? 

No never. I will say they looked very good, mius some carbon build up but I cleaned that up

[James Landi]

You might consider assembling a simple pcv arrangement.  A "passive" way to capture blow-by smoke has piping running from the top of both valve covers into the outside of the air cleaner...so that the smoke, noxious fumes, and moisture have a place to go rather than surrounding the underside of the car.  As pistons wear increased blow by can become embarrassingly evident and stinky. 

[Daffer]

You might consider assembling a simple pcv arrangement.  A "passive" way to capture blow-by smoke has piping running from the top of both valve covers into the outside of the air cleaner...so that the smoke, noxious fumes, and moisture have a place to go rather than surrounding the underside of the car.  As pistons wear increased blow by can become embarrassingly evident and stinky. 

Ahhh yea I do notice the car running smells like a lawn mower. Idk if thats normal in old cars? But like I said earlier if I knew how easy it was to replace rings I would've.  As for the smoke it does seem considerably less after I had ran it for less than 5 min (3rd start). I just have no idea as to why it would smoke so much on the second start.

[TJ Hopland]

Just keep a close eye on fluids and not only check the oil level but give it a sniff to make sure there isn't gas in it.

I don't know this car specifically but the way the crankcase ventilation typically worked on these is there is what is called a draft tube that connects somewhere near the back of the engine and then hangs down below the car pointing back, this is the outlet.  The inlet is that oil fill cap.  When going down the road the air rushing past that tube creates a suction that draws fresh air in through that filler cap/filter thing through the engine picking up blowby gasses along the way and then exhausts them under the car. 

One of the 'features' of this system is if the car isn't moving at a decent speed down the road there is no suction force so the gasses just build up and escape where they can, the tube is kinda long and bendy so its not the easiest path so the oil fill tends to be where it goes.  Another feature is that the fumes also have some oil in em that ends up flowing with the vapors so you get a slime build up around the filler especially if you idle or move slow a lot and you also get drips of oil from that draft tube under the car. 

PCV I think started coming in in the early 60's.  Initially just replaced the draft tube with a PCV valve which was then routed into the intake below the carb so fumes and vapors get burned in the engine and in later years treated by the cat.  Initially they kept the same inlet setup but eventually started routing that to the air cleaner housing to catch any vapors that go the wrong way.  Some engines didn't have a PCV system they just routed a crankcase vent to the air cleaner. No inlet outlet setup just one pipe.  On these if its outside the air filter the filter tends to get gummed up pretty quick.  If its inside the carb gets gummed up. 

Engines that don't have PCV are way dirtier inside and out plus as noted 'smell like a lawnmower' when running.  I was recently driving a 57 and while stopped at a long light saw and smelled smoke from under the hood.  First thought was 'crap what now' but then remembered no PCV and it was just the way the wind was blowing or maybe lack of wind. This car has done a lot of sitting and got better after I got about half a tank of gas through it.  Still smokes a bit and stinks but more of the old lawnmower, not something is wrong.   

[Jeff Rosansky CLC #28373]

I'd bet it's blow by.
When we first started our 55 (which we bought 7 years ago today by the way), so much smoke was coming out of the middle of the car I thought i had an exhaust leak. It was blowby. A few hundred miles of driving with Marvel's in it seems to have fixed it.
But as others have said, no pcv and that's what they did back then.
You more than likely had oil in the cylinders from when things were apart. I wouldn't worry about it. Check the fluids, and just drive it.

[Jon S]

Blow by should be handled by the blow by pipe on the passenger side of the engine. The oil fill breather lets fresh air into the engine when it is running and blow by exits from the lower blow by pipe previously mentioned. When the engine is turned off (hot) faint vapors are expelled from the filler cap if the cap screen is clean. Check the blow by pipe on the passenger rear of engine to ensure it is not clogged up.

[Daffer]

Just keep a close eye on fluids and not only check the oil level but give it a sniff to make sure there isn't gas in it.

I don't know this car specifically but the way the crankcase ventilation typically worked on these is there is what is called a draft tube that connects somewhere near the back of the engine and then hangs down below the car pointing back, this is the outlet.  The inlet is that oil fill cap.  When going down the road the air rushing past that tube creates a suction that draws fresh air in through that filler cap/filter thing through the engine picking up blowby gasses along the way and then exhausts them under the car. 

One of the 'features' of this system is if the car isn't moving at a decent speed down the road there is no suction force so the gasses just build up and escape where they can, the tube is kinda long and bendy so its not the easiest path so the oil fill tends to be where it goes.  Another feature is that the fumes also have some oil in em that ends up flowing with the vapors so you get a slime build up around the filler especially if you idle or move slow a lot and you also get drips of oil from that draft tube under the car. 

PCV I think started coming in in the early 60's.  Initially just replaced the draft tube with a PCV valve which was then routed into the intake below the carb so fumes and vapors get burned in the engine and in later years treated by the cat.  Initially they kept the same inlet setup but eventually started routing that to the air cleaner housing to catch any vapors that go the wrong way.  Some engines didn't have a PCV system they just routed a crankcase vent to the air cleaner. No inlet outlet setup just one pipe.  On these if its outside the air filter the filter tends to get gummed up pretty quick.  If its inside the carb gets gummed up. 

Engines that don't have PCV are way dirtier inside and out plus as noted 'smell like a lawnmower' when running.  I was recently driving a 57 and while stopped at a long light saw and smelled smoke from under the hood.  First thought was 'crap what now' but then remembered no PCV and it was just the way the wind was blowing or maybe lack of wind. This car has done a lot of sitting and got better after I got about half a tank of gas through it.  Still smokes a bit and stinks but more of the old lawnmower, not something is wrong.   

I'd bet it's blow by.
When we first started our 55 (which we bought 7 years ago today by the way), so much smoke was coming out of the middle of the car I thought i had an exhaust leak. It was blowby. A few hundred miles of driving with Marvel's in it seems to have fixed it.
But as others have said, no pcv and that's what they did back then.
You more than likely had oil in the cylinders from when things were apart. I wouldn't worry about it. Check the fluids, and just drive it.

Thank you both for explaining what is more than likely happening. Its especially nice hearing other have run into thus issue aswell. I ran the car again today and the smoke did seem less but more like my 3rd start from yesterday. Will be doing some small tweaking on the engine tomorrow. But I will update on the amount of smoke if any.

[TJ Hopland]

Have you been able to get a good test drive in yet?  Or are these other issues preventing that from happening so far?

[Daffer]

Have you been able to get a good test drive in yet?  Or are these other issues preventing that from happening so far?

I have a small leak on a fuel fitting which I'll be fixing today, then I'll be able to do a test drive

[dn010]

Probably already covered above but rebuilt or not, you'll get smoke regardless from the oil cap vent while you're stopped - that's what it is there for. When you're underway, the road draft tube takes over and pulls the "smoke" out of the engine. The only way to stop it is to get a cap that will seal the oil fill tube, remove the draft tube and install a makeshift PCV valve. This will pull the byproducts out of the engine whether you're stopped or not and you'll never see anything because it's getting mixed with the intake air and getting burned off. Get the engine tuned to spec, close the hood and enjoy the driving.

[TJ Hopland]

Getting it out on the road and good and warmed up should help.  Keeping a fire extinguisher in the car is never a bad idea.  In a box in the trunk is only very slightly better than not having one at all.  On the floor behind the driver is a great place because you can grab it quickly. 

[Daffer]

Probably already covered above but rebuilt or not, you'll get smoke regardless from the oil cap vent while you're stopped - that's what it is there for. When you're underway, the road draft tube takes over and pulls the "smoke" out of the engine. The only way to stop it is to get a cap that will seal the oil fill tube, remove the draft tube and install a makeshift PCV valve. This will pull the byproducts out of the engine whether you're stopped or not and you'll never see anything because it's getting mixed with the intake air and getting burned off. Get the engine tuned to spec, close the hood and enjoy the driving.

Yea I'll probably just leave it original knowing its normal, it just worried me before.

[Jeff Rosansky CLC #28373]

Yea I'll probably just leave it original knowing its normal, it just worried me before.

It was a different time back then. Things we worry about now, and wouldn't think acceptable, were perfectly normal back then.
Just drive it. She will smoke, ooz, and drip. That's part of their charm.