Heavy smoke at start up

Hello,

White smoke out of the tailpipe can be due to a number of reasons.
It could be for a blown head gasket, cracked cylinder head, intake manifold gasket leak.
Keep in mind that it is possible to have a small leak in the head gasket which is allowing coolant into the engine, but it is small enough that is not easily noticeable on the oil.

Here is helpful guide:

https://www.2carpros.com/articles/white-smoke-or-steam-coming-from-the-exhaust-pipe

It might be a good idea to do a chemical head gasket leak test. On that test it measures any combustion gases in the coolant. Which is a sign of head gasket leak.

Here is a video showing how to do that:

https://youtu.be/5zpNjYmmiYY

Please let me know of any questions.
Thank you.

Okay, but why does the smoke stop after about 30 seconds and gas mileage drop during this time? I've had blown head gaskets and I've never seen the smoke stop. I'm not arguing, I'm just wondering.

Sometimes with a small amount of leak the coolant can just accumulate overnight. So, on the first startup it burns through the combustion chamber, and you see the smoke till it clears off.
In some I have seen excessive condensation build up and creating the white smoke.

Is this something just started to happen or has been going on for some time? And any drivability issues?

It started a week ago. Been driving the car for over a year with no issues like this. No problems on Saturday, but smoke and gas mileage reading dropping on Sunday morning. Coolant level has not dropped at all and no overheating.

From what you are describing it does not sound like a blown headgasket, especially since you are not loosing coolant. But then again if the leak really minor it might not be noticeable for several weeks. Let me know if you are able to do the test, this way you can either confirm or check it off the list.

Try as I might, I could not get the test to change color. It stayed blue, and I tried for 10 minutes.
I'm with you, the head gasket does not sound like the issue. I'm back at square one and have no idea what the problem is.

Does it only happen in cold start in morning?
Does the engine idle differently while you have the smoke?
What about check engine light, is it illuminated?

Another possibility is that you could have faulty injectors that gets stuck in the open position and on cold startup it creates the white smoke.

It only happens when the car has been turned off for a while. I started it the other day in 60-degree weather, and it smoked.
Idle does not change. It idles smoothly no matter what.
No check engine codes. The computer has no idea anything is wrong.
I thought of injectors and replaced them.
One thing I noticed today is that the overflow container is the same level cold or hot engine. I also noticed that there was no flow in the overflow when the engine is running and warm. It's a sealed cooling system. No radiator cap. The only access is the overflow.
This car has been a headache since I got it. No free car is actually free!!!

If there was a coolant flow issue, it would likely cause the engine to overheat. Keep in mind that some of these cooling systems it might be obvious of the coolant flow, just by looking at the overflow reservoir.

We had someone with this type of excessive white smoke issues that ended being a cracked intake manifold, which was causing to have excess condensation.

You can check to leak in the intake manifold by spraying carb cleaner into the base. If there is a leak the engine will react to the chemical and idle high, until the chemical is burnt off.