Possible problem with heater matrix?

[Randy]

Hi folks.
I noticed today when driving to work that the vents were only blowing out cold air, no matter how warm the car was. Temp levels were reading normal, and when I was pulling into work I noticed some loose, rotating noise coming from under the dash. This only happens when going over a bump or something like that.
Any idea on what this could be?

[leamyj]

Hmm, coolant levels ok?? Sometimes a non working heater can be a sign of low coolant..

[Randy]

Hmm, coolant levels ok?? Sometimes a non working heater can be a sign of low coolant..

Coolant's good man, but I would need to give it a check in the morning maybe. temp readings are good on the cluster too.

[pjmazda]

Thermostat stuck, coolant not circulating thru heater hence no internal heat.

[Randy]

Investigated this further on the drive home. It stopped making any noises, but still wasn't warm inside. When I popped the bonnet, the fluid in the overflow tank was boiling.. Any ideas?

[Fergus]

Fluid overflowing in the tank usually is a sign of either water pump/thermo failure OR the crank belt driving it is slipping badly.
If fluid is being pumped into the tank then your engine IS overheating, no matter what the dial shows.
When did you last get the timing belt replaced and did they put in a new water pump as per Mazda Mx5 instructions ?

[Randy]

Fluid overflowing in the tank usually is a sign of either water pump/thermo failure OR the crank belt driving it is slipping badly.
If fluid is being pumped into the tank then your engine IS overheating, no matter what the dial shows.
When did you last get the timing belt replaced and did they put in a new water pump as per Mazda Mx5 instructions ?

Water pump and timing belt kit both done at the same time, over a month ago. Been driving fine since.
I topped up the coolant this morning and drove it for approx. 15 mins, without any issues. Checked under the hood when I stopped and all looked good.

[Fergus]

Are you 'sure' the water pump was replaced ? There should be no need to top up the coolant if it's not over heating (unless you have a leaking gasket but you don't as the tank is being filled with boiling coolant).

It will take more than 15 minutes of driving for the coolant to boil up into the tank.
Leave the car get up to temp and then drive it hard to the red line for 5 minutes, if the tank fills up then....water pump or thermo or crank belt slipping.

[Steve]

I'd start with replacing your radiator cap and thermostat.

[Merlot man]

I'd start with replacing your radiator cap and thermostat.

That sounds like a good and easy first step to me .

[Yolo]

I had a lack of heat problem when I got mine but it turned out to be the thermostat. A cheap and easy fix. Definitely go there first.