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[Tetleysmooth]

I know there's not much use for a full blooded heater at the moment, but the heater in my 2000 2.5 cdx gets barely tepid.
As far as I can make out, the problem started when the previous owner had the cam cover gaskets and thermostat replaced, so I'm assuming there's some sort of airlock somewhere.
The car does not get hot while running. Since I've had it, the auxiallary fans have not come on. The temperature guage sits at the 80 - 90 mark and only raises slightly in heavy traffic, as demonstrated on the M6 last Monday while driving back from the Wirral to Essex.
The car uses no water.
Any suggestions and courses of action chaps?

[Kevin Wood]

What state is the coolant in?

Might be worth a flush of the cooling system, blasting out the heater matrix with a hose while you're at it by removing the two hoses by the bulkhead that feed it.

Does the car warm up to normal temperature quickly? I.E. within a couple of miles from cold? It is sitting just below mid point on the gauge when on the move and perhaps slightly above in traffic (temperature markings vary, so best to go by position of the pointer).

[Tetleysmooth]

Does the car warm up to normal temperature quickly? I.E. within a couple of miles from cold? It is sitting just below mid point on the gauge when on the move and perhaps slightly above in traffic (temperature markings vary, so best to go by position of the pointer).

Yes to all those.
From what I've seen so far, the cooling system looks to be in pretty good order
I really don't like these newer push button heater controls though, much prefer the twist knobs - ooo-er.

[Kevin Wood]

OK. Other possibilities... Could be the HBV, I suppose, if there's inadequate flow through it...

Also, once you've got coolant flow through the heater matrix, the temperature is controlled by blending flaps. These are independent for driver and passenger side, so didn't ring alarm bells initially, but worth checking the situation is the same for both sides of the car. Sometimes they can get confused and need a reset of the climate control, and sometimes they can be disconnected from their servo motors. Usually this only affects one side.

Try resetting the climate control (hold down Auto and Off buttons for about 5 seconds until you hear the servos whirring).

Now warm up the engine fully and turn up both sides of the climate to Hi and check if it is achieving the same temperature through the vents on both sides of the car.

Check the flow and return temperatures at the heater matrix (the metal pipes that run through the left hand side of the driver's footwell are a good spot to check this. Both pipes should be piping hot. If one is a little cool it indicates poor coolant flow through the matrix.

[Tetleysmooth]

Do you hold Auto and Off buttons together, or one at a time?
Sorry if that question is stupid, but this is a learning curve for me, I've only ever had the more conventinal heater controls, i.e. sliders or knobs.
Thanks for the help.

[martin42]

together 

[Tetleysmooth]

Ta 

[jimac]

I had the same problem with mine. It was cured completely by flushing the heater matrix.

Oh, and having both inlet and outlet pipes very hot isn't really an indication that all is OK. The pipes will be hot if coolant is flowing through them both, but isn't circulating round the matrix. That's what happens when the matrix is blocked or restricted.

[Kevin Wood]

I had the same problem with mine. It was cured completely by flushing the heater matrix.

Oh, and having both inlet and outlet pipes very hot isn't really an indication that all is OK. The pipes will be hot if coolant is flowing through them both, but isn't circulating round the matrix. That's what happens when the matrix is blocked or restricted.

Yep, was thinking to try that in case the HBV is restricting flow. Granted, it'll just bypass the core of the heater matrix if it's blocked. Probably one of the reasons why it's prone to blocking in the first place.

[jonnyboyws6]

I had same on my MV6, again cured by flushing out the matrix: hoses off and connect a hosepipe to it, and try flushing in both directions. Loads of crud came out of mine and it was spot on after that.

[Tetleysmooth]

Thanks for the advice. I'll give that a go.