You can not effectively fill the coolant system at the overflow bottle. The engine head, heater, and most of the rest of the system will not fill from the bottle after draining the coolant system. However, you can add make-up fluid to the overflow bottle after the system has been filled.

The fill point must be at a greater elevation than the top of the engine, else techniques other than plain gravity fill must be used.

To refill a drained system, start at the fill cap. Add as much fluid as it will take, lightly close the cap, set the heater controls to full heat, and start the engine. Run about 1 minute, shut off and top off the fluid at the fill cap. Continue this process until no more can be added, then fully close the fill cap. Make sure there is fluid in the overflow bottle.

Next, begin the thermal cycling to complete the fill. Start the engine and partly warm up. Don't over do this warm up part at this juncture because there may not be enough fluid in the heads. Let the engine cool. It should suck fluid from the bottle as it cools. You don't have to wait until the engien is completely at room temperature. Add fluid to the overflow bottle as necessary and repeat the thermal cycle. The thermal cycling can be stopped after the "hot" level in the overflow bottle stablizes to its proper fill.

Next, take the car for a short drive, just enough to warm it up; Check the fluid level in the bottle. If it is low, more fluid is needed. Let the engine cool and top off the bottle. The coolant system should be fairly full at this point. Watch the fluid level in the bottle for at least the next two thermal cycles of the engine.

I recommend getting a service manual for your car and read through the section about draining and refilling the coolant system. There are enough variants in today's automobiles that one precedure does not fit all makes and models.

If you intend to use water pump lubricant on refilling, add this this first before the other fluid. This ensures there will be enough room for it.

Tip 2:

When refilling the coolant system, premix the antifreeze mixture in another container and label it. for example, antifreze, 50% ethylene glycol - 50% water. This is the easiest way to fill with a proper mix. Don't assume that you know how much it will take to refill and try to fill by adding antifreeze, then water. You don't know how much fluid remained in the system after draining.

Store the left over fluid on a high shelf away from kids and pets. This become a supply of makeup fluid for future use.