Hi all, replaced the oil, oil filter, air filter and coolant today, when i restarted the engine to check it over, the idle speed starting bouncing up and down between 1500 and 2000 almost like i was revving the engine and at the same time the engine started to warm up and overheat with the gauge going well beyond the half way mark before i kill the engine.cant understand?i have done this before and never had this problem.Thermostat is working as coolant starts to flow in top radiator once correct temp is reached..hmmm i feel doh doh!

 

YOu might have an air bubbles in the cooloing system,

 

As Kevin says, air is a possibility. We assume you did not have an overheating problem before you changed the coolant. If so, it is not likely you have a serious problem. Do a search on coolant air or something like that.