Synthetic or Conventional??
 

K, I'm a brand new Honda owner
Car is 2005 Honda Accord 4 cylinder
204000 KM or 121000 mi
It looks like the previous owner took pretty good careof the car, the maintenance schedule in the owners manual is filled in with great detail

I'm guessing that he used a conventional oil as the oil changes were approximately every 6000 km - (3600 mi)

I'm anticipating (expecting) this engine to last at least another 200000 km

Is it safe to switch now to a synthetic?
Will that damage the engine?

I live in a Northern climate where winter temperatures are about 5 months duration and can consistently be -30 to - 40 c (-22 to -40f)

I believe from the service records that the previous owner took the car to the dealership for all of the oil changes.
I noticed a little sticker in the windshield of a quickie lube place... suggesting the next oil change in 3000 km (1800 mi) which has me very concerned actually.

Should I stick with a high mileage conventional engine oil?

no it won't hurt the engine thats an old wives tale about synthetic additives dissolving engine deposits around the oil seals and making it burn oil its all bull****. you could switch back from conventional to synthetic every oil change and it wouldn't make any difference whatsoever. modern conventionals have just as much detergent's and additives as synthetic. the major upside to synthetic is its superior metal protection and long life. mobile1 can go 10,000 miles and Amsoil can go 15,000 miles but the oil filter needs to be replaced accordingly to the manufacturers recommendations which is usually before the oil breaks down. bottem line is if you replace everything by the oil manufacturers recommendation you won't have anything to worry about. side note honda switched to all synthetic fluids years ago.

Stick with what Honda recommends and you will be fine.