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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 20396
Experience:  BEng hons Mech engineering, in auto industry 22 years
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heater blows cold for know reason

Customer Question

heater blows cold for know reason
Submitted: 2 years ago.
Category: Car
Expert:  Matt replied 2 years ago.


if you're sure that the engine is getting up to temperature then have a feel of the two coolant pipes that pass into the car through the engine bay bulkhead.

Both should be warm with a warm engine. If they're not then its likely the heater matrix is blocked and you should do a reverse flush on the cooling system to try and clean it out. This is done by removing the top hose from the radiator and placing a garden hose into the engine water outlet, and then run the hose until you get clean water coming out of the radiator.

If this doesn't help this only leaves checking out the motor / cable that move the air mixing flap that allows the hot air from the matrix to enter the car air system.

This flap is controlled by the temperature knob / dial etc and I think is controlled with a small motor for your car so the thing to do is first get access to the back of the control knob and measure the voltages is present there, then trace the wiring back into the dash from the control to locate the motor.

It’s worth first checking the fuses for the fan / control circuit

I'd recommend first removing the glovebox ( undo lower edge hinges from dash) to gain access to the dashboard inner and also allow you to shine a torch to the back of the central console so you can start tracing the wire back and see how things are put together

Customer: replied 2 years ago.

i get full heat for a short while then it goes cold the bottom pipes from the rad are cold


Expert:  Matt replied 2 years ago.
Hello Peter

if the rad pipe stays cold then either the water pump isn't working or the thermostat isn't opening

try bleeding the system 1st as I suggest as a big airlock can also have this effect

but I'd then be prepared to have the thermostat out and test it in boiling water to ensure it opens up

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