What causes the CX-5 heater core to get clogged and have issues? Only cold air comes out of vents. I noticed Mazda put out a TSB for the heater core what causes this to happen?

 

Never seen a Mazda CX-5 heater core get clogged. Coolant constantly runs thru the heater core( when the engine is running).

The heater box uses a blend flap to divert air past the heater core to warm the air.

In order to control the outlet air temperature, the blend flap is adjusted by a actuator to increase or decrease the % of air flowing past the heater core.

 

I'd be more inclined to think the flap is the problem as well.

 

After employing the dealership to perform a transmission flush (@35,000 mi), which requires the cooling system to be opened/refilled; the CX-5 had the symptom of some perceptible heat from the center of the dash tapering to almost nothing at the side vents (with all of the heat directed through the dash, maximum temp. setting and the engine at it's thermostat controlled temperature). The dealership inspected the symptom and introduced that a Technical Service Bulletin addressed this issue although they had never seen an example of it. To make a long story even longer, they covered the replacement of the heater core including the dashboard's R&R and the necessary cooling system flush and fill. This would have been a $1300.00 job otherwise. Problem solved.
*I know Mazda doesn't require transmission flushes and their transmission is included in the lifetime drive-train warranty but I'm old school and here in Florida, the heat kills automatic transmissions. Mazda's automatic's don't have a reputation for stellar reliability with age either so stop typing.
P.S. I ran into a Mazda mechanic from another dealership last weekend and told him the story. He admitted that he has seen it. It's uncommon but not not unknown. The cause is however...

 

I think I know what is clogging earlier model CX5 heater cores. I have two 2014 cx5'd, a his and hers. Recently, hers stopped blowing warm air on driver's side and check engine light illuminated. I used OBD scanner, and identified code P011A.

With aluminum block engine and low miles of 43k, I suspected bad cabin air filter. Replaced it, but no difference. Because the factory coolant, type FL23, is supposed to last 10 years, or 120k miles, I was puzzeled to cause. I decide to drain coolant and back flush heater core, in case it was somehow clogged.

We'll, what came out of heater core looked like several very time black pieces of rubber. I removed heater hoses to do this and back flushed with low pressure garden hose, for 45 minutes. I thin added new coolant to heater core to flush out water. I reatyached header hoses and filled radiator with new coolant. Heater is now blowing hot with no return of check engine light after one week.

I believe the small black rubbery pieces are from minor deterioration of cooling hoses. Don't know for sure though.

I became worried that my CX5 with 48k miles, would soon have this problem. I decided to proactively, drain factory coolant and add me coolant. I did this and during test drive afterward, my CX5 stopped blowing hot air. I then back flushed my heater core. It too had several tiny black rubbery looking pieces flush out of heater core. I filled it and radiator with 2nd batch ch of new coolant. I now have heat in it and no check engine light.

I suspect the coolant hoses are prematurely deteruorating. I may also be that the factory FL22 coolant is prematurely breaking down,.
​​​​
​​​

 

The heater core appears to become clogged with tiny pieces of black rubbers, presumably from coolant system hoses deteriorating, from inside out. I have had this happen on the two CX5's that I own. Bother are 2014, a his and hers. I detached the heater hoses and back flushed the heater core with water from garden hose. This expelled severak tiny black rubber looking pieces. I added new coolant to heater core, reattached heater hoses, and added new coolant to radiator. This resolved problem on both of my CX5's. One had 44k miles, other had 48k miles. In addition to lack of heat, each had check engine light, with associated OBD code P011a.

I think the FL22 coolant is breaking down before the Mazda's claim of 10 years, or 120k miles and is deteriorating coolant system rubbers hoses.

 

I've seen CX-5s from 2012 with over 90,000miles / 150,000kms on them , and never seen any heater issues. Maybe it's only a US spec issue??

 

Hi all,

My check engine light came on on my 2016 CX5. Mazda says it is due to a clogged heater core and is quoting me $1500 to fix (not covered by warranty due to it being a fluid clog, not a mechanical issue). My heater still works though oddly enough...

It sounds like you all have had similar problems and it may just need to be flushed? Any advice here would be appreciated. At 38k miles, I’m having a hard time with paying $1500.

 

I would get Mazda Corporate involved and argue that a fluid clog is a mechanical issue. If your engine blew up because oil wasn't circulating would they try to say it wasn't mechanical? I had a 1996 Outback that ended up having two heater cores replaced, no expense on my part. Taking the dashboard/instrument panel apart makes for a lot of labor expense.

 

Hi All, I read the information you've shared here and wonder if I have a similar problem at hand. My car has 90K miles on it and about a month or so ago, it started giving me an orange check engine light that would come and go. The code was P011A and I found a number of TSBs related to it. One of them says if both ECT sensors are working OK, the dealer could reprogram the PCM to correct the problem. Yesterday the car displayed red blinking thermometer icon and said 'coolant temp is too high' as my daughter was driving it, and I could smell some unpleasant odor (like rubber burning). So long story short, it is parked in the garage and no one is driving it in this condition. I started the engine today and ran it for a while to warm it up. The orange check engine light came up (no red blinking light this time). When I turned the heat on in the car, I saw that it was just blowing cold air. This got me wondering whether I have the "clogged heater core" issue mentioned here. Is there a way of telling whether it is to do with the PCM update or the heater core? My Mazda dealer wants to charge $125 for 1 hour of diagnostics in addition to labor and material based on whatever they will find out. Has anyone had any luck with Mazda Corp on this or similar issue? Thanking you in advance.