Car smokes when cold

Valve seals. Did you replace them when you had the valves out? Oil runs down the valve stems past the worn seals and into the intake and exhaust manifolds where it gets burned. This is not a catalytic converter problem.

On many engines the seals can be replaced without removing the head. Use a special hose and compressed air in the spark plug hole to hold the valves closed while you pull off the springs and seals. A lot of import cars are just about impossible to do that without removing the head because special valve spring compressors are needed to get the job done.

Caradiodoc

Boy, I suppose there could be worn piston rings that aren't sealing when they're cold but typically they will cause more smoking when the engine is warmed up and the oil is thinned out.

Is it possible there is a bunch of sludge blocking the return ports? That would cause oil to hang up and overload the seals. Also, if raw fuel got into the oil and diluted it, that would make it run past the seals very easily.

I think the secret is in your comment that there was no smoking when it was first started after reinstalling the head. There would have been no oil collected up there. The smoking started after the engine had been run. That's when there would have been oil around the seals.

What you might consider is removing the spark plugs to try to peek inside to see if there is oil dripping into a cylinder. We do similar things when the head is off to check for leaking valves. That would be hard to duplicate with the head off because you would have to remove the springs and lift up the seals which isn't real practical.

You might check the PCV valve and hoses too to see if oil vapors are condensing someplace where they can run into the intake manifold.

Caradiodoc

Probably not. Engines that burn oil that is getting past the rings will often have very good compression and engines with low compression might run just fine and not use any oil. That test really won't help in this situation. What you could try, if you can find the equipment, is a cylinder leakage test. With this test you are looking for the CAUSE of low compression that you have already measured but in some instances it will work for oil burning too. You can buy the equipment from the guys in the tool trucks like MAC, Matco, Cornwell, and Snapon, and you might be able to rent or borrow it from one of the auto parts stores. A lot of them are borrowing tools now for free with just a security deposit.

The test starts with removing the spark plugs and testing one cylinder at a time. You bring the piston to top dead center on the compression stroke. There is a hose you can screw in with a whistle on the end. When it stops whistling, the piston is near TDC. Then you use the timing mark to set it perfectly on TDC. The tester has a hose that is screwed into the spark plug hole and another one that is hooked to compressed air. The gauge on the tester will show the percentage of air leaking out of the cylinder. Less than 10 percent is good. The engine should be warm when doing this test. While the air is blowing into the cylinder, you listen in four places to see where it is coming out. That will identify the cause. Tail pipe means a leaking exhaust valve. Throttle body means intake valve. Radiator bubbles means head gasket or cracked head. And the oil fill cap or dipstick tube means piston rings.

It is very uncommon but a crack in the head could allow draining oil to seep into one of the runners for an intake or exhaust valve. If it is leaking into an intake valve, you might find a clue by starting the engine cold, then shut it off before the smoking stops and pull out the spark plugs to see if one is wet with oil. If they're all dry, that won't be conclusive, but if you find one that is covered with oil, that's where to look closer. You probably won't hear the leakage from a crack in the head because it will be much smaller than the leakage past the piston rings. Instead, remove the valve cover and look for signs of bubbling in the head casting.

I've also heard of people doing a full engine test but it's fairly involved and might not work as expected. This involves sealing the air intake, typically at the throttle body, sealing the tail pipe, and blocking the PCV hose, then you connect the hose from the tester to one of the vacuum ports on the intake manifold. This is supposed to allow you to look for bubbles or hissing at the valve guides and seals.

Another approach might be to use a "smoke machine" to inject non-toxic smoke into each spark plug hole, then watch for signs of it coming out someplace where there is normally oil. These smoke machines connect to the car battery for power and put out white smoke at 2 psi. They come with a lot of adapters but you might have to rig something up to fit a spark plug hole.

Caradiodoc

No. Too much clearance might just cause a little clatter until the parts warm up, but that won't cause smoking.

Caradiodoc

Probably. The only other way for oil to be burned is if it is getting past the piston rings, but then it should be smoking worse and all the time when the engine warms up.

Caradiodoc