Toyota Repair: 2001 or 2002 Toyota MR2 heater, mr2 spider, toyota mr2

Question
My son's MR2 spider gets very little heat from the heater.
He was told by the dealer that sold it to him that the MR2's get air trapped in the heater core which causes loss of heat.(Not a Toyota dealer) One of the hoses coming from the heater core has what appears to be a bleed valve on it. We opened it with the engine running and indeed engine coolant and air came out. The heat got better (not great) for about a day, and then went back to just warm. The dealer also said that MR2's are known for this. The temperature gauge runs at about midpoint, which is the same as in warm weather.Coolant is very clean. It has a manual transmission and A/C. Any ideas? Thanx!

Answer
Getting all the air out of the system can take some time, try starting the engine then turn the heater on with the fan setting on HIGH, remove the coolant filler cap and add coolant slowly as it goes down, if it starts overheating and forcing coolant back out turn the engine off and let it cool down and repeat the process, eventually it will stop bubbling and the coolant will circulate.