Heater question

[Robotazky]

I noticed my wife's 5 blowing cooler air when the car is idling.

It's well maintained and has the same coolant level it's always had, according to the overflow tank. The thermostat seems to work exactly like it did when new. No problems at all that I notice.

Are there any common electrical gremlins that anyone knows of that can cause this? Temp sensors or something?

 

[Vasy]

This is a very common symptom of the beginning of a failed(ing) head gasket. This is not related to Mazda specifically, lots cars can have it.
Her is how the pro would test it: https://www.youtube.com/watch?v=TDd0B7dSsTk
Here is DIY way: https://www.youtube.com/watch?v=CHp5E7XnbXo

Hope you don't have it this bad.

The idea behind the test is that you should not have any exhaust fumes in the cooling system, if you do, they are getting into the system through a bad head gasket.
This can happen totally independently of any oil mixing with coolant or any other signs of the failure.
For what ever reason the initial signs is no heat at idle, I'm not a mechanic, so can't explain how the two are related.

 

[Robotazky]

This is a very common symptom of the beginning of a failed(ing) head gasket. This is not related to Mazda specifically, lots cars can have it.
Her is how the pro would test it: https://www.youtube.com/watch?v=TDd0B7dSsTk
Here is DIY way: https://www.youtube.com/watch?v=CHp5E7XnbXo

Hope you don't have it this bad.

The idea behind the test is that you should not have any exhaust fumes in the cooling system, if you do, they are getting into the system through a bad head gasket.
This can happen totally independently of any oil mixing with coolant or any other signs of the failure.
For what ever reason the initial signs is no heat at idle, I'm not a mechanic, so can't explain how the two are related.

A failing head gasket, failing internally like that, would get coolant in the combustion chamber. You'd see white smoke or notice lower coolant levels. I can hear a failed gasket in most cases.

I'm leaning away from that and looking for other issues, but definitely thanks for the input. It's always something to consider.

 

[Vasy]

A failing head gasket, failing internally like that, would get coolant in the combustion chamber. You'd see white smoke or notice lower coolant levels. I can hear a failed gasket in most cases.

I'm leaning away from that and looking for other issues, but definitely thanks for the input. It's always something to consider.

Actually you would not see any signs at all, no smoke, no foam on the oil cap, nothing.
I really hope it is not but you can at least test.
Why I posted this, is I'm on another forum for my other car and the guy had this exact problem you are having and two shops diagnosed it to bad head gasket using this method.
He was posting on the forum thinking that it is total BS with out any other signs but two other mechanics on that forum confirmed that this is definitely a correct test and definitely the right Simptom and conclusion based on the test.

You can also have plugged heater core and at idle the water pressure is lower and can't deliver enough hot water to the heater core.

You can also have bad radiator cap, so at idle it does not build up enough pressure to deliver hot water through the system. I had that on my other car a few years back. But I actually had no heat at all, not just idle.

 

[chad99]

Geezz don't scare the guy, check the simple common stuff first. Has fuel economy dropped? any loss of power?

I like the clogged heater core idea, you should be able to feel the core hoses near the firewall and see how hot both hoses feel should give you an idea of which direction flow is through the core then you could disconnect the hoses and run water through it to flush it out, I have done that on a core with the same problems and gotten lots of crap out of it and it brought my heat back (on my audi).

Also could be an air bubble somehow got into the core and is preventing flow but I think the 5 is good at getting bubbles out on its own, judging from how the hoses are routed.

When was the last time you changed the coolant? Old coolant could have caused the scaly stuff to build up in the core.
Just a side note but using coolant color to judge life is no longer possible, nowadays engines don't change the coolant color.

 

[Robotazky]

Gents, I'm specifically asking about common electrical type items on these particular cars. Or even common trends with faulty thermostats on these cars. Whatever is going on will be very common, as it always is with Mazda.

I've been fixing cars for 25 years and understand all of the usual suspects. Things related to coolant are issues that I've dealt with and understand. It's the nitpicky little crap that Mazda does that worries me. My MX-3 would be a nightmare without a community behind me.

 

[Robotazky]

Geezz don't scare the guy, check the simple common stuff first. Has fuel economy dropped? any loss of power?

I like the clogged heater core idea, you should be able to feel the core hoses near the firewall and see how hot both hoses feel should give you an idea of which direction flow is through the core then you could disconnect the hoses and run water through it to flush it out, I have done that on a core with the same problems and gotten lots of crap out of it and it brought my heat back (on my audi).

Also could be an air bubble somehow got into the core and is preventing flow but I think the 5 is good at getting bubbles out on its own, judging from how the hoses are routed.

When was the last time you changed the coolant? Old coolant could have caused the scaly stuff to build up in the core.
Just a side note but using coolant color to judge life is no longer possible, nowadays engines don't change the coolant color.

It only has 50,000 easy miles on it. I'm not going down the coolant road unless I have to. Chances of idiot dealers screwing it up are too great, and I don't have time to work on this car myself. I'm not even in the same state as the car right now, if that says anything. That's why I'm asking for usual suspects from Mazda gearheads. Mechanics 101 is not what I'm trying to look at right now.

 

[chad99]

If it were common thing it would pop up in a search I am ass.u.me ing you did that and found nothing

What your asking for is some electrical problem that comes up when the engine speed is decreased or engine load decreased that is related to the HVAC SYSTEM that causes loss of heat and is repeatable.
There is none....thats why I listed the core.

If you have auto climate control sensors are:
Ambient sensor
Passenger sensor
Evap temp sensor
R134 press sensor
solar sensor

None of which would change just with engine speed

What I don't understand is why do you think its electrical?
The most obvious place to look would be the core

 

[Robotazky]

If it were common thing it would pop up in a search I am ass.u.me ing you did that and found nothing

What your asking for is some electrical problem that comes up when the engine speed is decreased or engine load decreased that is related to the HVAC SYSTEM that causes loss of heat and is repeatable.
There is none....thats why I listed the core.

If you have auto climate control sensors are:
Ambient sensor
Passenger sensor
Evap temp sensor
R134 press sensor
solar sensor

None of which would change just with engine speed

What I don't understand is why do you think its electrical?
The most obvious place to look would be the core

Correct, you don't understand because I didn't elaborate on why I need to know about sensors. I'm out of state and can have a next door neighbor use my DMM on the car. I inspected the coolant system multiple times and there is no issue there. Nevermind. I'll figure it out.

 

[Silentnoise713]

If you have auto climate control sensors are:
Ambient sensor
Passenger sensor
Evap temp sensor
R134 press sensor
solar sensor

Do you know where each of these sensors are located?

Ambient sensor - in front of the radiator.
Passenger sensor - is this referring to the F. passenger seat/weight sensor?
Evap temp sensor - where exactly?
R134 press sensor - where exactly?
solar sensor - typically on the dash, toward windshield is that correct for this car?

Nevermind. I'll figure it out.

Robo - Make sure you update us. Ironically, both my previous and current car gets hot as hell!. It seems the heater core is always hot and blow warm or hot air, even when outside ambient temp is cool. Drives me nuts in the spring/summer/fall -great in winter !...

 

[chad99]

Robotaz sorry meant that to be sarcastic funny but I just came off as rude. It really does just sound like a clogged core though.

Silentnoise713:
Ambient sensor - in front of the radiator. Yes
Passenger sensor - reads the inside car temp its on passenger side between HVAC controls and glove box, it has vents cut in the plastic.
Evap temp sensor - right on the evap core fins, evap core is right where you change the cabin air filter.
R134 press sensor - passenger side engine compartment, follow the line that goes to the receiver/drier/condenser (condenser is in front of radiator)
solar sensor - typically on the dash, toward windshield is that correct for this car? Yes

 

[Robotazky]

Robo - Make sure you update us. Ironically, both my previous and current car gets hot as hell!. It seems the heater core is always hot and blow warm or hot air, even when outside ambient temp is cool. Drives me nuts in the spring/summer/fall -great in winter !...

I think we have similar situations where I have some readings making it go one direction and you have them making yours go the other.

The one point of interest here is that the car was doing this when it was about 0F outside. Is it possible that it is just not noticeable under normal conditions? Absolutely. But, and this is a big but )), based on my experience with all cars, and especially my Mazdas, I'm inclined to believe I either have sensors or relays that are out of spec, or it's considered normal for this vehicle. I don't believe a car that's been driven and maintained like ours would have a heater core issue already. That doesn't mean it doesn't though.

Robotaz sorry meant that to be sarcastic funny but I just came off as rude. It really does just sound like a clogged core though.

Silentnoise713:
Ambient sensor - in front of the radiator. Yes
Passenger sensor - reads the inside car temp its on passenger side between HVAC controls and glove box, it has vents cut in the plastic.
Evap temp sensor - right on the evap core fins, evap core is right where you change the cabin air filter.
R134 press sensor - passenger side engine compartment, follow the line that goes to the receiver/drier/condenser (condenser is in front of radiator)
solar sensor - typically on the dash, toward windshield is that correct for this car? Yes

Thanks this is exactly the type of info I'm looking for if nobody has had this exact issue and tracked it down. It looks like I need to get into the manual and send the DMM values to my neighbor and ask him to check it out, which he is capable of. I have to come home and deal with a busted Koni shock on that car, but won't have time to deal with the heater, especially now that it's warm out. It will be interesting to see if there are any cooling issues this summer.

Thanks chad99.

*EDIT* I just read through the sensor list and had a lightbulb go off. My car has auto climate control. I bet that driving around in 0F temps, then sitting at a light, is messing with the outside temp sensor. Or some combination of events. Time to ponder.

 

[loosenut]

Robotaz, you say this was happening in 0deg weather. Has the thermostat been replaced?. They are notorious for sticking open. If it is stuck it will be very hard for the engine to reach operating temp. This would present itself as lack of heat especially at idle. The engine will make enough heat to make warm air while driving down the road because of the load on the engine.