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Furthermore, can you top up the coolant with water?
If your coolant level is too low (below or near the lower mark), top it up using a 50/50 mixture of water and antifreeze (for normal driving conditions), or pour pre-mixed antifreeze straight into the reservoir. You can use clean tap water in an emergency, but antifreeze should be added as soon as possible.
Herein, can you just top off coolant?
Topping off coolant ignores the root cause of the problem. Fluid will continue to leak, meaning you'll have to continue to top off the coolant to stay ahead of the leak. Leaking coolant leaves you at a higher risk for an overheating engine.
Driving with low engine coolant is never a good thing to do. It can create air bubbles in the system, which in the worst case can damage your engine seriously.