I have seen several posts from people saying they bled there cooling system and have had cooling system issues after. these issues include 1. lack of heat 2. temp gauge never reaching normal temp 3. pinging while driving 4. overheating. All of these issues are caused by not bleeding the cooling system after you drain the coolant. Anytime the system is drained when you fill it trapped air will remain in the coolant. If this trapped air is not removed then you will have poor cooling system performance and severe engine damage may result. The best way I found to bleed the system is using a compressed air operated bleeding tool that pulls a vacuum on the system and then you fill into the vacuum. This is a 150 dollar kit and unless you work on a lot of cars I don't suggest you buy this kit. The way I do it without a bleed kit is to fill the system and then run the car with the cap off the expansion tank and the heater on full blast out the dash vents. while bringing the engine rpm's run the engine at 1500 rpm's or so and let it burp the air out and add coolant as needed, then when you feel strong steady heat out the vents top it off and put the cap back on.