Hello everyone- I did a search and didn't find anything on this topic so I hope it's not super uncommon. My wife has a 2016 GT model. Since we're just now getting cold weather we've noticed that the heater has stopped working. At first it was just blowing cold on the driver's side (heat still worked on passenger) but now it's both sides blowing cold. I visually saw the driver's side blend door actuator moving and I assume the passenger side works as well. During the past weekend the heater would periodically start working fine

In the engine compartment I looked for the heater hoses. I found two that appear to be the heater but I also see two others. The online diagrams only show two connectors (one in, one out?). I can feel the top hose is warm, but the bottom is cool.

When I quickly rev the engine the heater will start working, which leads me to think the water isn't circulating. Do Mazda's have water valves that control the heat coming in? I can't find anything definite online. I assume with one heater core there must be some sort of blocking of the heat to moderate the different temperature.

The car isn't overheating, and the coolant level is right where it should be.

Oh, and I should note that we've had issues with the rear controller not working on heat, however since we don't have small kids anymore and rarely does anyone sit in the back so we never had it checked out (about two years ago the dealer wanted something like $250 just to run a diagnositic so we told them no thanks)
Any thoughts? Would a flush help? If this was an old car I would suspect a clogged heater core but it's only 8 years old.

Thanks!
Steve

 

I've heard that Mazda's coolant change recommendation time was too long. The additives in the coolant became depleted allowing particles to form that clogged the heater core. You might try a heavy duty cooling system cleaner, not a simple flush, and see if that helps. The alternative is to remove the heater core which is buried in the dash.

If your heater is still working fine do change the coolant now! Drain the radiator and refill with Mazda FL22 coolant and do future drains & refills on a shorter schedule than what's in the manual. Or use any top brand Asian-engine green coolant and drain & refill that even sooner.

 

I've been reading that about the coolant issue. Not a safety problem so no recall... on my older cars I do a reverse flush periodically. The idea being to push whatever might be blocking backwards. I hope they can do it with the CX-9. There isn't a lot of room in the engine bay to get to the heaters so I'll let a professional handle it.

Interestly I could find several videos on removing the heater core from a CX-5, but nothing for a CX-9. I wonder if they're similar design? in this video the guy removes the core WITHOUT taking the dash out (which would be fantastic!).
So far the heater is "working" albiet at intermittent times. I'll keep my fingers crossed the flush works.

 

Just to be sure I watched (sped through ) that video... this guy is an *above average experienced DIY(Do-It-Yourself) (or more? ) so keep that in mind when anyone is considering this service and following his rather good video.

* This like so few services how to are done with good intention but bad procedures. This one while it does have a couple of questionable things for the most part can be done with some that have worked in confined spaces and know how things are attached where they go and how to reconnect them without causing damage.

 

Well I wanted to give a follow up to the problem. Turns out the radiator had a hole in the top. Not sure why I didn’t smell the sweetness of the antifreeze but bottom line it wasn’t building enough pressure. New radiator installed and we now have heat!