Although you did not provide the year or engine size of the vehicle, it is almost always at the bottom of the radiator on the left or right side.
If its the oil drain plug its under the engine on the back of the oil pan, but if your looking for a coolant drain plug afraid you wont find one about the only way i know to do it is to unhook the bottom of the coolant hose and bump the motor over without starting it.
2007 Chevy 2500 HD 6;0
To drain the coolant on a Mazda 626, locate the drain plug on the bottom of the radiator. Remove the plug and drain the coolant into a pan.
The radiator drain plug on a 1989 Chevy C1500 Silverado is on the bottom of the radiator.
The engine coolant drain plug, on a 1998 Ford expedition, is located on the bottom of the radiator. The drain plug will come out by turning to the left.
The coolant drain plug is located on bottom corner of radiator facing engine.
On either side of the engine block. It will require a 6 point 13mm socket to remove it.
Answering "Where is engine coolant drain plug for a 1.8 Nissan sentra engine?"
There is no drain plug, remove the lower radiator hose to drain coolant.
Remove the drain plug from the bottom of the radiator. Allow the coolant to completely drained out. Replace the drain plug to its original position. Fill the radiator with new coolant.
Drain at bottom of radiator so you can get antifreeze out.
Coolant drain plug is on the bottom of the radiator. You turn the knob and watch out. You need a wide drain pan not an oil change pan.