Is it necessary to clean when replacing antifreeze (coolant)?

If the antifreeze (coolant) is the same brand and model, there is no need to clean it. It is better to clean it, because the old antifreeze will remain in the car and has lost its efficacy because of its long use. Replacement method of antifreeze (coolant): There is a drain valve on the back of the bottom of the car water tank, which is usually black. You can unscrew the water tank and drain the water. Never remove the drain valve when the engine is at high temperature. The antifreeze of high-pressure engine will be sprayed from the valve port, which may cause serious burns. However, it is necessary to open the antifreeze cover or replace the water tank cover. Wrap the water tank cover with a thick cloth, slowly turn the water tank cover for a quarter turn to release the accumulated pressure, and then unscrew it completely. Never remove the water tank cover when the engine is in a high temperature state. Drain the old antifreeze, and then clean the liquid channel with clean water. Add clear water to the antifreeze replenishment tank, then inject clear water into the tank to make the clear water continuously flow through the engine cooling system, and then idle for 3 to 5 minutes for water circulation. At first, the water in the tank was a little pink. Continue to inject clean water until the flowing water becomes clean. If there is a washer, it is best to replace the screw washer of the drain valve and check whether all hose clamps are tightened. Then, add another bucket of antifreeze into the antifreeze tank until the antifreeze tank is almost full, and drive for about 10 minutes. At this time, the liquid level of the cooling system drops, because some air is pumped away. Then, add antifreeze and fill it at the highest mark "MAX" of the liquid storage tank until now.