Burning oil will either make blue or white smoke, I've seen both. Pt cruisers have known cylinder head issues with either valves burning or valve stems wearing out. This issue sounds like it could be either a coolant leak or oil leak. Some simple engine diag is needed. What I would do is get a cooling system pressure tester and pressurize the cooling system with the engine warm and leave it for 20 to 30 minutes. Then remove a couple spark plugs and peak inside the cylinder for coolant. If you can't see crank the motor for few seconds and see what comes out. If you get nothing then you most likely need to have your cylinder head rebuilt which isn't too bad, most machine shops will rebuild it for under $200 once removed. Its not a huge concern but be aware that dumping oil into the exhaust will eventually cause the catalytic converter to be destroyed which is usually around 600 for a new one.

Before you said the mechanic diagnosed it as valve stem seals. Those usually leak oil after sitting for a long time and a cold start. I mentioned it sounded more like worn valve guides.

But now that you've filled in the details, it sounds more like a head gasket leak. Oil leaks produce blue smoke on startup. And they usually do it on cold starts. The catalytic converter burns off excess oil once it warms up so you can be burning oil but not see it once the cat is warm.

But once an engine is warm and the cooling system is fully pressurized, it can leak small amounts of coolant into the cylinders when you shut it down. That would produce WHITE smoke on startup.

Are you losing any coolant? That would be a sign of a leak.

your mechanic is telling you the truth. as long as it is not a continues cloud of smoke then it just means it is a slow leak. eventually it will get worst, but as long as you keep an eye on the oil level, it will be fine for a while. i will still need to get fix, but no rush.

You didn't mention if it is a Turbo or not? This will make all the difference in the world when diagnosing this type of concern!

Hello.. I asked a question earlier about this and I just wanted to add more details.. I own a 07 pt cruiser with 110k miles on it and it is in amazing shape other than a valve seal issue.. I have to add a quart of oil in every other week or so.. When I start the car cold I don't see any smoke come out of the exhaust.. The only time I see white smoke is when i start the car when the engine is hot after it has been parked for a bit.. For example.. I run to Walmart and I'm in the store for a half hour.. When I come out and start the car I get a cloud of white smoke.. I get a cloud of white smoke that only lasts for a few seconds and then it is fine.. If I let the car get cold I get no smoke when I start it.. My mechanic says it is OK as long as I keep an eye on the oil and I can get it fixed down the road when I can or if it gets worse.. He says if I see consistent smoke it's obviously a problem.. I just want a second opinion or advice from anyone that has delt with this.. I don't drive many miles a day.. My job is only a few miles down the road and on my days off I run around a bit but nothing excessive.. Thank you for reading :-)