heater only blowing cold air...

Post Sat Dec 29, 2012 12:08 am

Hi

OK big problem heater only blows cold air, not hot. I have checked all the fuses and they all seem fine.

Any help please would be great ???? the car is a M3

thanks

Post Sat Dec 29, 2012 12:17 am

are your top and bottom rad hoses getting warm ? is the cooling fan kicking in ? where does the temp gauge sit ?

Post Sat Dec 29, 2012 12:21 am

virdi325i wrote:Hi

OK big problem heater only blows cold air, not hot. I have checked all the fuses and they all seem fine.

Any help please would be great ???? the car is a M3

thanks

It won't have anything to do with the fuses.
Have you refilled the system recently?

Post Sat Dec 29, 2012 2:22 pm

Hi,

Both the Radiator hoses are getting warm, the temp gauge is spot on sitting in the middle.

No i have not recently refilled the system. However i did top it up yesterday to see if it makes any difference, but nothing.

Post Sat Dec 29, 2012 3:47 pm

you need to check the hose's (for heat) that go into the cabin thru the firewall, not the radiator hose's.

Post Sat Dec 29, 2012 4:26 pm

Hi there

How can i get access to these hoses that are in the cabin
thanks

Post Sat Dec 29, 2012 5:42 pm

you can access them in the engine bay....

Post Sat Dec 29, 2012 5:56 pm

ok cool, i'll have a look tomorrow during the day.

thanks

Post Sat Dec 29, 2012 6:20 pm

the heater pipes are on the left side of the brake servo (looking from the front of the car)

Post Sat Dec 29, 2012 8:45 pm

Sounds like the heater control valve has failed and stuck shut. It's an electronically operated valve which sits on the inlet to the heater matrix.

On your m3 it will be behind the centre console next to the accelerator pedal.

Post Sat Dec 29, 2012 11:06 pm

Ok cool, I'll also take off the centre console off tomorrow and have a look...

How will i know if its working or not? is there anything i need to look out for?

many thanks

Post Sat Dec 29, 2012 11:11 pm

kam-325i wrote:you need to check the hose's (for heat) that go into the cabin thru the firewall, not the radiator hose's.

Answer the questions and find the problem logically. Don't go following "it might be this", "it might be that" random suggestions, or you'll waste time, money, and possibly end up with new problems that you didn't originally have.

Post Sat Dec 29, 2012 11:48 pm

you tried bleeding you coolant system...wak the heater and blower on full..then crack the bleed nipple ..when my m50s thermostat housing seal was drawing air it gathered in the matrix did the air bubble and made her blow cold.

Post Sun Dec 30, 2012 10:29 am

Morning..... ok i have bleed the system allowing all little bubbles out and still no heat.

next...... I going to take off the centre console and have a look at the heater control valve...

Post Sun Dec 30, 2012 11:08 am

ok .... the pipes coming into the car, bottem one is warm and the top one is cold.
from the engine bay the 2 pipes going through the firewall the top one is cold and the bottem one is warm. ... is this normal?

So what next ?

how do i check the if the heater control valve is the prob?

Post Sun Dec 30, 2012 3:36 pm

virdi325i wrote: how do i check the if the heater control valve is the prob?

Brian is your man for this......

I know how to check it off the car, but this involves losing all your coolant......

I think the test involves appling 12v to the valve to see if you can hear it "clicking", but dont quote me on that !!!

Post Sun Dec 30, 2012 4:17 pm

A cold heater is normally the result of an airlock but it could be other things. Disconnect the cold heater hose at the bulkhead. Anything there? If not, start adding coolant into the rad/expansion tank until it starts to flow. It may be a blocked matrix so it's worth disconnecting both hoses and running a garden hose through one of the heater stubs. The heater valve may be stuck but without 12v they default into the hot setting. Try these first though.
If the heater valve is knackered, you can remove it and drill a 5/6mm hole down into the short stub where it bolts to the matrix. This bypasses the valve so you at least have heat whilst you get a new valve.

Post Sun Dec 30, 2012 5:19 pm

hi there,

cold heater hose at the bulkhead - is this the one on top?

'disconnecting both hoses and running a garden hose through one of the heater stubs'
- doing this will i have to drain the system (raditor)

is it running a garden hose through the pipes removed or plug the hose from where the pipes have been removed (in to heater valve)

sorry just wana makesure, don't want to screw it up even more.

thanks in advance

Post Sun Dec 30, 2012 5:47 pm

virdi325i wrote:hi there,

cold heater hose at the bulkhead - is this the one on top?

- It 's the one that's cold.......

'disconnecting both hoses and running a garden hose through one of the heater stubs'
- doing this will i have to drain the system (raditor)

- No.

is it running a garden hose through the pipes removed or plug the hose from where the pipes have been removed (in to heater valve.

- Both hoses off.

sorry just wana makesure, don't want to screw it up even more.

thanks in advance

Post Sun Dec 30, 2012 8:47 pm

If you connect a garden hose to the heater stub pipes, it MUST be connected to the bottom stub, or the valve is likely to be damaged, even if it isn't already.

Post Sun Dec 30, 2012 9:49 pm

Very unlikely to be an airlock. M3s self bleed, and I've never heard of anyone getting an airlock in one.

The one hot and one cold pipe to the heater is a clear indication there's no flow, the input will get warm through heat transfer and turbulence in the water system.

Imho if the rest of the cooling system is in decent condition then it's very unlikely the matrix will suddenly clog, I'd put money on it being the control valve at fault.

I had one go randomly on my e36, but it failed open so was constantly hot, others have had them fail shut.