2014 cx5, 2.5 engine. 190,xxx miles. We were just gifted this car from my partner's parents and generally love it. Only issue is that the heat rarely works, and is never as hot as it should be--often only warm in the middle vents, but never really hot anywhere. The coolant system has been flushed. I replaced the thermostat, and the heater core (the old heater core was definitely partially obstructed. When it's running at idle, coolant temp gauge #1 goes up to 200ish or so at idle as it should, but #2 gauge (at the heater) rarely climbs much above 70 at idle (it's cold outside). Based on some earlier leaks while swapping the heater core, I'm pretty sure that coolant isn't making it to the heater core most of the time when the heat is switched to on. The hoses going to the heater don't get hot to the touch. IF I take the car on the highway, the heat eventually comes on and starts working like normal....both coolant temperature gauges get very close to equal. What's involved in sending coolant that way when I have the heat on? Any suggestions?
Thanks!

 

It is likely you have air in the heater lines, your symptoms coincide with that problem. Bleed the air out of the system and see what happens.

 

Thanks for the suggestion! What's the process for that? I've never needed to bleed a coolant system before now...
Stephen

 

Yes I am waiting for that service procedure myself to read. haha!????

I would say it is a desperate DIY to resolving an unconfirmed problem area? cuzzz it isn't in any service procedure I have ever seen for a MAZDA ???? At least say manufactured form about 2013 to present?
Checked both my accounts on MAZDA service Data bank also ALLData service procedures.

I will say that CarpeDiem is a competent DIY and has posed some good information on this forum in the past.



Hers is why responses having to do with air in a cooling system generally do not apply. The thermostat in many cooling systems not just Mazda has a giggle valve. Very few except known head casting issues have casting flaws that create steam pockets. The cooling system has components that are higher than the engine.

Burping a cooling system stems more from vehicles manufactured pre 2000 and decades old. But is often suggested to do on many forums often members reporting it worked . But I am more incline to go back to how they really were cured as what I mentioned above.

 

I will only say and largely generally speaking the best way for OLD SCHOOL cooling system bleeding is to place the vehicle at an angle that the radiator cap or reservoir is higher than the engine. basically, drive up on ramps open the radiator cap and run the engine for a few minutes at normal operating temperatures. After the thermostat even partially opens the sir (if any) will be removed from the cooling system. Physic's 101 of a cooling system.

 

Update with more questions: After a few days of the heater core/thermostat replacement, everything started to work like normal--YAY HEAT! BUT a week later, it started to only give me heat under heavy engine load, and now it's occasionally flashing the red coolant overheat warning--what that happens, I immediately slow down or pull over until the light goes off. Showing the "non-matching coolant sensor readings" DTC again. Coolant level isn't dropping, and both the oil and coolant look like they should--no mixing, foam, or bubbles that I can see. No leaks around the heater core, thermostat, or anywhere I can see. I'm suspecting either a hose clog somewhere (but they all look fine from the outside), possibly bad water pump??? or maybe an air leak somewhere preventing it from reaching full pressure. How do you check for pressure leaks in this thing? With the vented/overflow pop-on cap on the coolant reservoir, air just flows right out the overflow hose if I try to pressurize the radiator--is that reservoir cap supposed to hold pressure???
THANKS!
Stephen

 

unfortunately update: after fiddling around for awhile, I took it to my mechanic today. Blown head gasket or cracked head. There's now obvious drops of oil in the coolant and coolant in the oil. Chugging vapor hard out of the oil fill cap when it's running with the cap off. Weighing options at the moment. Sad times. Fortunately we have another vehicle to use as we sort out what we want to do.
Stephen

 

Final update: after getting the head off, it was obviously cracked. Head replacement with all the stuff will likely add up to $3,500. Sad times.
Stephen

 

That's a bummer. At least the car was pushing 200k miles before the issue happened. Considering the market is still crazy as far as used cars go, getting the car repaired may be justifiable.