I agree. They don't seize while just sitting there. I guess it'* possible the head gasket was blown and a cylinder filled with coolant. Not likely but possible.

Is your friend experienced with this sort of thing? (not attempting to diminish their diagnosis, I just don't know if they do this for a living, or learned about a wrench and a crankshaft from Youtube yesterday, or are somewhere in-between).

I am curious what the voltage shows when you try to turn it over.

What voltage does it show when testing?

What voltage does it show while attempting to start it?

Hi,
My friend has worked on cars for several years. He used to race and seems to know lots about cars as he used to work on his own race car.
The voltage with jumper cable hooked up to another car it gives 14.3V . Without jumper hooked up about 11.5V . I think with jumpers connected and trying to start the engine, about 13V .

If head gasket is blown, but temperature is now around 5-10 degrees celcius, I would think any ice formed in engine should have melted.

he believes that the starter is engaging but engine doesn't want turn over.

BAD BATTERY.
Until you put a good battery in it I'm done here.
When you do finally put one in and it fixes it you will likely drive off and never return to tell us.

Or drive the Malibu instead.

Okay cool. Hard to tell from the other side of the Internet. Now we have some perspective.

Okay good, so the other car is charging . . . a lot.

This tells me bad battery.

Ice doesn't really matter for our purposes here. Coolant in a cylinder will prevent the cylinder from compressing as coolant (primarily water) is not compressible. If it did have a cylinder and the coolant turned to ice, then the engine is toast because water expands as it turns to ice. That having been said, properly mixed coolant won't freeze until much colder than most Buicks have ever seen. Like I said before: This is not likely but possible.

If the current battery is original to your car then it is toast and it needs to be replaced. I've hinted at it but not asked directly: How old is the current battery?

Battery is original (5.5 years old). I will try and take to shop to have tested then replace once confirmed it is bad.

Wow! Over five years old. It is bad. Amazing that it lasted this long. You can save yourself some trouble and just replace it. Take the old battery with you when you go to buy the new one to save messing around with the core charge.

That battery is beyond weak you would need to resurrect it from the dead.
A battery with a bad cell will not be solved with a jump. It pulls the jumper down as well.
It MUST be replaced.

Hi Jungloverano!

Just curious: Did you get the car going yet?