Long story shot the wife kept on driving her 2010 IS250 with low coolant until it was too late
I had no luck finding a post or member in CL who had done an engine replacement (4GR-FSE with another 4GR-FSE). Post found were only engine upgrades.
Will it be possible to change an engine without ECU re-programming or any other complications?

 

Depending on how severe....you may have lost only the head and not the entire engine

 

Yeah, how badly is the engine "blown"? Are we talking windows in the block or just a blown headgasket(s) from overheating?

 

Its a direct swap. No ecu programming.

 

I would get it taken apart by an indy mechanic to diagnose if you need a whole new engine

 

That's the thing I'm trying to figure out but it's difficult without the car not even starting. Checked dipstick and There is no sign of coolant mixture with engine oil, no sign of oil in the coolant cap either or any leakage under the car. Checked spark plugs after cranking it for a while and they come out dry.
What I did find and kind of intrigues me was some coolant in the gas tank precisely inside the fuel pump assembly now how that coolant got in there it's a mystery.
Now she's telling me that she tried to add coolant with the engine running about 3-4 minutes after she started it in the morning and that the engine shut off right after!? Goshh

 

No offense and please don't take this the wrong way...but is it possible your wife put coolant into your gas tank and flooded the engine as a result ?

 

go to the garage with her and have her show you what she did. direct engine swap simple, old engine out, new engine in. make sure it's from a close year or else there may be some electrical complications.

 

I asked and she pointed at the coolant cap so no she did not put it in the gas tank lol. I'll be checking the injectors probably replace them with new ones and next would be checking the compression in the cylinders, keeping my fingers crossed!

 

There's NO other way coolant would enter the fuel system! If you truly have anything but petro in the tank, flush it out, along with all 6 injectors, and pray it all still works. Oh, the fuel pump might have gone out too with it having to work harder attempting to pump that "heavy" coolant.