Driving home tonight and the heater was on maximum heat. Car got a bit hot so turned the dial back to 3/4 and I noticed cold air was coming out. After some experimenting, it turns out that if I have the heater dial on full, it puts out hot air. Anything else, even just one notch back from full heat, it puts out cold to warm air.

Any ideas what this could be?

 

Any leaks on the heater matix also checked for air in the system

 

Just checked the system for air locks and yes a fair amount of air bubbles came out. I kept testing until no more bubbles appeared but sadly the heater is still doing the same.

Would a stuck thermostat cause this issue?

 

I don't think the thermostat interrupts the flow of water to the heater matrix. Might be best to drain and refill the coolant system and fill it via the turbo coolant pipe. Seems to be the best way to fill them up. I did it and had no problems at all.

 

Mine has the same issue. The heat doesnt work untill the second To last click and then perfect temp for me then last click is really hot. Hasn't really bothered me much but it does make a kind of whistling noise that changes pitch with fan speed. Not sure if it could be a dry bearing or something?

 

And get a sniff test done for head-gasket failure, soonest.

 

Would these really be symptoms of head gasket failure? It has been like this since I got the car almost 2 years ago but not really bothered me so I haven't got it sorted. Surely if it was head gasket it would have blown big time by now. No mayonnaise in the oil cap etc.

 

I would agree don't suspect head gasket problems sounds more like an air lock, the fact you have already got air out of the system doesn't mean its all out yet. Keep bleeding the system till your sure its free of air.

 

But ask yourself how the air got in? And where's the water gone?

 

Thanks for the advice everyone. Might try and drain the system. If not, the car is going in for service, MOT at the end of the month and I have spoken to the garage who are going to do a sniff test so I may just get them to do the drain as well.

 

There was no mention of coolant loss just air in the system and poor heating. If I saw coolant loss and air in the system I would have suspected head gasket.

 

I'm changing the rad on mine this week so hopefully that will fix my heater issue if there is air in the system and maybe if I change the fan it will take the whistling away? Thanks

 

But how's air got into the system if it was correctly filled?

 

Just to update this. Heater working fine now. Seemed as though it was an air lock. Whilst getting all the air out of the system, I also discovered the header tank cap was leaking so I have now replaced this as well.

Thanks for the help everyone.

 

glad its all sorted