Does your coolant temp drop when you turn the heater on max?

[SparkYellow]

One thing that I have learned after a cooling disaster on my MINI is that by turning on the heater, the coolant in the heater core gets to mix with the rest of the fluid and helps bring down the temperature slightly.

Now that I am watching the temperature of the CX-3 more closely, I tried this and nothing happened. By turning the heater on max (max temp and fan, nothing sophisticated on my Touring). After five minutes of running like this at 65-75 mph, the coolant temp continued to fluctuate as if the heater was off. The heater was blowing hot though. Is this normal?

I am 80% positive that I tried this once last year and the temp went from 212 to 190 in stop and go traffic. There is a 20% chance that my memory failed me and that it was in the MINI.

Any insights are appreciated.

 

[Buzzman12]

A lot of this has to do with the size of the engine.
In my experience (60 years driving), a larger displacement engine will maintain the engine temperature regardless of the heater settings. Lately however, this trend towards small displacement engines, and smaller coolant capacities, puts a little more strain on the cooling system, having to keep the engine at a steady level, while also delivering enough warm coolant to the heater core to warm the interior.
I know for a fact that the Honda 1.5L turbo CR-V has issues in cold weather. The engine takes forever to heat up, and the cabin heater and defroster drain any heat that might have built up from the engine. My brother in law had one of these, and it was brutal in our Canadian winters. You could let this thing idle for 20 minutes, and it would still be stone cold.
I don't know the particulars with some Mazda models (my 2017 Mazda 6 was fine), but I imagine any small capacity engine will have similar issues.

 

[SparkYellow]

Thank you! I thought small displacement with small cooling system capacity would be faster to warm up. All my street cars are small displacement (2.0, 1.6, 1.1) so I always worry about overheating.

I feel that the cooling system is behaving differently from what I remembered. There are parts that I should replace before they fail, starting with the easy one, radiator cap. I am prepared for more though, car has 8.5 years and 166K miles.

The first car that I picked and owned independently was a 2009 Mazda5. After three years of care-free ownership, I moved onto a MINI and had many lessons to learn. The CX-3 has been drama-free until this May.

 

[Jmaz]

One thing that I have learned after a cooling disaster on my MINI is that by turning on the heater, the coolant in the heater core gets to mix with the rest of the fluid and helps bring down the temperature slightly.

Now that I am watching the temperature of the CX-3 more closely, I tried this and nothing happened. By turning the heater on max (max temp and fan, nothing sophisticated on my Touring). After five minutes of running like this at 65-75 mph, the coolant temp continued to fluctuate as if the heater was off. The heater was blowing hot though. Is this normal?

I am 80% positive that I tried this once last year and the temp went from 212 to 190 in stop and go traffic. There is a 20% chance that my memory failed me and that it was in the MINI.

Any insights are appreciated.

Your MINI no doubt had a heater valve the opened to allow hot coolant into the heater core. The displaced colder coolant then caused the temperature to temporarily drop as you have stated.
Our Mazda's (and probably all newer cars) lack a heater valve and coolant is continually flowing through the heater core at all times. The temperature is now controlled by the position of the blend doors.

 

[Jmaz]

Thank you! I thought small displacement with small cooling system capacity would be faster to warm up. All my street cars are small displacement (2.0, 1.6, 1.1) so I always worry about overheating.

I feel that the cooling system is behaving differently from what I remembered. There are parts that I should replace before they fail, starting with the easy one, radiator cap. I am prepared for more though, car has 8.5 years and 166K miles.

The first car that I picked and owned independently was a 2009 Mazda5. After three years of care-free ownership, I moved onto a MINI and had many lessons to learn. The CX-3 has been drama-free until this May.

Last year I pre-emptively replaced some cooling system parts on my 2014 at the 10 year mark. I used Mazda radiator hoses and thermostat. Thermostat was a chore and chose Mazda part because I don't trust aftermarket for such a critical item. Not worth risking overheat/engine damage. The original worked fine (and still did) for 10 years. Lot more parts to remove to change it compared to prior cars owned. The price for Mazda radiator cap was obscene (~$30) so I purchased a quality, made in Japan, "Sankei 555" brand cap for ~$12. Coincidentally, it was time to do 2X drain and fill of the coolant using ZEREX ASIAN formula coolant. The serpentine and water pump belts also got replaced with Mazda parts. At 10 years of service they needed replaced.
The valve cover gasket also got replaced because of a small amount of oil around the base of #1 spark plug before replacing the plugs also.

 

[SparkYellow]

Your MINI no doubt had a heater valve the opened to allow hot coolant into the heater core. The displaced colder coolant then caused the temperature to temporarily drop as you have stated.
Our Mazda's (and probably all newer cars) lack a heater valve and coolant is continually flowing through the heater core at all times. The temperature is now controlled by the position of the blend doors.

Thank you for confirming this! I believe the 1993 NA that I briefly owned was also like this, but I thought that was old tech.

 

[SparkYellow]

Last year I pre-emptively replaced some cooling system parts on my 2014 at the 10 year mark. I used Mazda radiator hoses and thermostat. Thermostat was a chore and chose Mazda part because I don't trust aftermarket for such a critical item. Not worth risking overheat/engine damage. The original worked fine (and still did) for 10 years. Lot more parts to remove to change it compared to prior cars owned. The price for Mazda radiator cap was obscene (~$30) so I purchased a quality, made in Japan, "Sankei 555" brand cap for ~$12. Coincidentally, it was time to do 2X drain and fill of the coolant using ZEREX ASIAN formula coolant. The serpentine and water pump belts also got replaced with Mazda parts. At 10 years of service they needed replaced.
The valve cover gasket also got replaced because of a small amount of oil around the base of #1 spark plug before replacing the plugs also.

Thank you! I am adding more parts to my list. For items that are easy to access and replace, I'd buy whatever I can get quickly on Amazon that has decent reviews. Otherwise OEM due to limited access to shop/help. The radiator cap (16 psi) that I ordered has a built-in temp sensor.

I searched for videos on thermostat replacement and watched a clip about coolant control valve which is in the vicinity. It made me anxious because I have never gone that deep.

What is your coolant temp with Zerex Asian? I didn't use FL22 either.

 

[N7turbo]

The FL22 (according to these forums) Mazda later modified with a higher concentration to prevent corrosion. I don't have a way of knowing if non-Mazda fluids have accounted for that.

 

[Jmaz]

Thank you! I am adding more parts to my list. For items that are easy to access and replace, I'd buy whatever I can get quickly on Amazon that has decent reviews. Otherwise OEM due to limited access to shop/help. The radiator cap (16 psi) that I ordered has a built-in temp sensor.

I searched for videos on thermostat replacement and watched a clip about coolant control valve which is in the vicinity. It made me anxious because I have never gone that deep.

What is your coolant temp with Zerex Asian? I didn't use FL22 either.

Can't see the coolant making any sort of difference in operating temperature since that's the thermostats job and have no idea what the coolant temperature is at any time unless I plug in my scanner, which isn't very often. Don't have any gauge readouts of any sort other than what came stock on the instrument panel. The coolant is clean and topped off and the car doesn't overheat. I don't give it much thought really.

 

[Jmaz]

The FL22 (according to these forums) Mazda later modified with a higher concentration to prevent corrosion. I don't have a way of knowing if non-Mazda fluids have accounted for that.

I don't know either and I'm not particularly concerned for the following reasoning. Last summer when changing the thermostat and radiator hoses, the 4 year old Zerex from the previous service was clean and no buildup/deposits inside the hoses either. Prior to that ,the original factory fill was clean when drained at the 6 year mark. Recently checked heater core in and out temperatures and they agreed and the heater works well (well as good as it's gonna get but that's Mazda's design, same with the A/C which seems a bit weak sometimes). This discussion reminds me to get some pH test strips that I forgot about, so I can periodically monitor for changes. I guess we do what we can do.