You still have air in the system.
This is the way I burp the system. When the car is cold start the car and let it idle. Turn the heater to full heat and the fan on to max heat. Remove the turbo reservoir cap and place a tight fitting funnel in the reservoir. Let the car run for like 30 minutes or until you start seeing the fans kick on and off. Watch the level of coolant in the reservoir now. You should start to see it move. As the fluid gets hotter it will want to expand into the reservoir. Just let it. It should not overflow. This is a little scary but just let it sit in the funnel. When the t-stat opens the fluid should drain back into the system. Now smack on the upper coolant hose and try to get any air out of it. You can do the same on the lower hose. Check the heat in your car it should be nice and hot. Do this procedure for like 15 minutes. When the fluid goes down one more time hurry and replace the cap. Then go for a test drive. Hopefully the temp gauge is steady. If it is you are done. If it is still unstable park the car and let it cool off. Then do it again. In that whole time don't rev the engine just let it idle.
Hope this helps.