Heater taking longer to provide heat

Technical Area Engine, Transmission, Exhaust etc
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  1. My model of MX-5 is: NC 3.75__
  2. I’m based near: Glasgow__
  3. I’m looking for technical help or recommendations on: Why is my heater taking longer to provide heat?

2013 car. Changed the thermostat about 2 years ago as a precaution with water pump as coolant was due to be changed. I used to start feeling nice warm heat about 2 miles into my journey. Now it’s taking about 7 miles/15 minutes. The heat does eventually come through though and can be controlled. Is this a thermostat issue?

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Yep - sounds like thermostat.

Get an ELM327 OBD dongle and download the “torque” app on to your phone.
Then you can see live data on coolant temp.

I was surprized how low the temp can be when the gauge reads normal if the thermostat has gone.

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3

It would be my first guess. It sounds like it is sticking in the open position.

:heart:

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Thanks. I’ll get one ordered.

5

OK, so I used the Torque pro app as suggested and for the first few drives to work in the morning, everything worked as it should. Coolant temp sensor indicating coolant goes gradually up to 100C and nice toasty heat from heater within 2-3 miles.

Yesterday however, coolant temp went gradually up to 100C as before, but, air from heater remained lukewarm at most until several miles down the road. Only then did the heater provide proper heat.

So, it looks like coolant temp is behaving predictably, but heat from cabin heater is a bit hit and miss at the beginning of journeys.

Do you think this is still likely to be the thermostat issue?

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For the heater problem, your system probably needs “burping" to get excess air out. Here is the official Mazda procedure but I found parking on a slope with the front raised and the filler cap off and running at various revs, also carefully squeezing the hoses, topping up where necessary does the trick. Very satisfying when you get a good burp! Also a bit of spirited driving helps (filter cap on.)

When it’s working, air from the vents should be hand-burning hot.

Mazda procedure

  1. Refill the coolant into the coolant reserve tank up to the F mark on the tank.
  2. Install the cooling system cap.
    CAUTION:
    If the water temperature gauge rises too high, stop the engine and decrease the water temperature to prevent overheating. Then, verify the malfunctioning part and repair or replace it.
    If the engine coolant level in the coolant reserve tank is below the L mark during engine coolant air bleeding operation, stop the engine, and after the engine coolant temperature decreases, add engine coolant. Then, resume the engine coolant air bleeding operation.
  3. Start the engine and warm up the engine by idling.
    NOTE:
    If the accelerator pedal is depressed continuously for a specified time, the engine speed may decrease to the idle speed. This is due to the fuel cut control operation, which prevents overheating, and it does not indicate a malfunction.
  4. After the engine warms up, perform the following steps. At this time, be careful of the coolant temperature to prevent overheating.
    a. Run the engine at approx. 2,500 rpm for 5 min.
    b. Run the engine at approx. 3,000 rpm for 5 s, then idle.
    c. Repeat step (b) 4—5 times.
  5. Stop the engine, and inspect the coolant level after the coolant temperature decreases. If it is low, repeat steps 7—10.
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7

Thanks Andy. I’ll try all that and see if it works. :+1:

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Just to add to Andy’s post - I find it works better if you can park the car facing up hill.

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Well, it turned out coolant level was about 600ml too low. Kinda proves I should have looked for the obvious first. I’ve topped it up and things seem to be working OK. I guess I’ll now need to watch out for more coolant loss incase there’s a leak somewhere.

Thanks for all the advice.