Smoke from muffler

It may just be the cold, this can be condensation you will see it with the engine cold, go for a drive get the engine to normal temp and re check, let me know what you see, just changing oil and coolant will not cause this.

I did notice that after I used the engine flush, I opened the cap and I saw a little bit of white-ish mixture in there. Could it be that I flush both the coolant and the oil at the same time cause the contaminating anit-freeze in the oil cylinders?

This is just a bit of condensation in the top of the motor, nothing to worry about, there is no connection between doing both flushes and the condensation.

Okay thank you mhpautos, I will check when the temp is warm the next day and let you know how it went. I will be sure to get back to you with more information. Thanks

I've driven the car today and it seems that there is no smoke while it's warming up, but there is only a little bit when the car was driven for a while. I assume it is a normal thing right? I mean just a little bit doesn't mean anything right? can 'just' see it..

What colour is the smoke? black. blueish or white?

I can't really see it because it appears that only smoke come out during the night time. Not during the day. And it is not black I can tell you that. But in the day only slight, like barely can see it but it's there. And then I checked the engine oil and it isn't on the Full mark, just a little bit under not by much. I've used 10/30 engine oil, a person told me that for this old car no need to use 10/30 just use the 15/40 so it's not too loose, the oil might dry a little quicker on older cars if 10/30 oils are used. I don't know if that's true or not. And one more thing, the smoke at night smells sort of like petrol, but the fuel economy is so great I can hardly think it's burning excess fuel. What do you think?

I do not think you have anything to be concerned about,looking at the age of the car, a little Puff or smoke on startup that clears is nothing to worry about, just keep an eye on things and re post if you still feel concerned.