I have an 09 Mazda CX-9 Grand Touring and I'm at a loss on my heating issue. I have owned the vehicle for about six months now and in that time have replaced the heater core, thermostat, flushed and burped the system and I still cant get any heat in the winter. I can rev the engine to get some heat for a few seconds but ill will go straight back to cold air. The water pump is going bad but I'm not sure that's contributing to not having heat. It is stated in the Carfax that the radiator was replaced at some point. If the temperature is blow 50 (give or take a few degrees) I will not get heat whatsoever. if its above 50 degrees, I get some heat. then above 60 degrees, everything acts as normal. My gauge reads correct in the cab and does not show the coolant overheating. My theory is its a sensor at this point, or that a tube/part wasn't connected properly and I have outside air rushing in somewhere.
Is your blend door operating properly?
How would I go about checking that? When its warm enough to get hot air in the vehicle, I have switched between the heat/ac and it will switch seamlessly and go from hot to cold.
If your blend door is buried in the dashboard where you can't see it you'd need to use a bidirectional scan tool for diagnosis. If your engine is reaching normal operating temperature and both heater hoses going to your heater core are nice and hot the blend door is a prime suspect if not getting enough heat.
My dad has shot them with a temp gun on at least 5 different occasions now and they are both operating properly. He is 61 and has been working on cars his entire life and it even has him stumped. That's when we tried to manually burp the system and it didn't help in the long run. We bought a kit online and did it the right way but it still didn't help. We have a diagnostics tool but its nothing that's in depth and hasn't given me any codes. Should I take it to a shop at this point to get see if their computer might find something different?
If the heater core itself is getting hot the problem pretty much has to be that the blend door isn't letting the hot air through. If you have a trustworthy local mechanic with a suitable scan tool it might not be a bad idea to take it in. I'm not familiar with your particular vehicle but on many you need to take the dash apart to get at the blend door and actuator, and you don't want to go there unless you have to.
I don't know if this helps but it was found with a quick online search:
They had to take it apart to replace the heater core, cost me $650 (I bought the part from RockAuto for $60) I wish I'd have had them do the doors and sensors then. My uncle owns a company that I work for. We have a mechanic we take all our vehicles to so I might take it up to him to see if he can tell me anything more. Thank You very much for al your help
There no chance it could be due to the failing water pump, could it?
Only if the impeller blades have deteriorated to the point where coolant no longer flows sufficiently through the heater core. I'd think if the flow was that weak the engine would overheat. From what you're saying though both heater core hoses are getting hot.
I was told by the mechanic who replaced the heater core that the water pump would need to be replaced soon and I had seen in Scotts videos where he said that they are great vehicles, the water pumps are just prone to going out if the system isn't maintained. I purchased an used car warranty with the vehicle and the water pump and timing chain are covered under it. I might try to get it covered and fixed to see if that solves the problem. If not the blend door will be my next move.
It depends on what the problem with the water pump is. Typically they either leak and/or the bearing goes bad. For coolant flow to be affected the impeller would need to have come loose or rotted away, which is possible but less common.