Sometimes , Engine coolant loss may happen due to various reasons like loss due to minor splashing through radiator accessory tank aka no loss tank's vent hole, coolant loss while replacing the inlet or outlet radiator hose, coolant loss due to hose damage or evaporation of coolant (which is not common nowadays)
If you are caught in an emergency situation in the mid of the journey, you can topup with ordinary water to survive to the nearest mechanic shop. But first try to bring the mechanic to the breakdown point instead of moving your vehicle.
Now coming to the topup of coolant liquid, you can either fill the coolant manually through the radiator cap or no loss tank cap. Be very cautious while opening the radiator cap, since your coolant might be boiling inside with some pressure accumulated if your car is just stopped. Better wait for some time to cool the engine. Once the cap is removed, pour some coolant through the radiator cap until it fills, once it is filled start the engine and keep idling for 10 to 20 seconds, now you can pour some more through radiator cap. Repeat this until the radiator cap opening is filled.
Now, close the radiator cap and slighty press the accelerator pedal in 5 seconds frequency, and topup the coolant in no loss tank upto maximum level.
Keep the engine idling and some pressing of accelerator pedal in 5 seconds frequency. Now , you can see the level of coolant is reduced in no loss tank. Now, again topup the noloss tank.
The whole process will take approximately 15 minute . Do not rush, approach the process in a safe manner .
On the other hand,Luckily, if you reached the Garage for topup, if they have the pressurized vaccum coolant refilling machine, then the machine will pull out the existing coolant completely and fill out the new coolant through the raidator cap opening.