This is not the first time I've posted this issue on here but I'm still scratching my head. I have a 2007 with 140000 on it. At 135000 I had the timing chain, radiator, thermostat, temp sensor, and radiator cap replaced. Before the work was done it ran fine (other then the noise from the works timing chain). Water temp was good and steady and plenty of heat came out of the vents. Since the service has been done, the vehicle still runs fine but my temperature gauge fluctuates. I can run the vehicle for about 20 minutes or so and then gauge rises to normal operating temp and holds pretty steady, then it starts to climb up to about 1/2 way, then to the hot side of things and back down again. It does this non stop as long as I'm driving it. I've bled the system numerous times and have gone through 2 thermostats. I actually tested the first one I put in and it tested fine. I get loads of heat out of the vents at idle and while driving. This problem did not exist before the timing chain was replaced so I don't believe head gaskets or water pump are the issue. It this point I'm scratching my head. I have no idea what it could be. Unless my bleeding procedure is incorrect. Also I've noticed that no matter how long I drive it, my bottom radiator hose is always cold. This tells me that the coolint isn't getting circulated the way it should. I don't know. I'm stumped on this one. Any help would be greatly appreciated.