Both the radiator & heater matrix in my 2001 Vogue have been replaced by @Gilbertd & the hater has been working fine. However during our journey to France a couple of days ago the heater was working fine when we left home & when we got of the ferry in Cherbourg but after a 3 hour drive to our cottage I noticed that the hot air being blown into the car was barely above ambient.
I investigated yesterday. There was no book symbol on the HEVAC so it didn't look like a blend motor problem. I suspected an so lifted the bonnet took the cap off the header tank then started the engine. I put about a pint of coolant in as I brought the engine up to working temperature then put the header tank cap back on.
I felt the hoses that go to the heater matrix. Looking towards the rear of the engine the hose on the right was hot as though full of near boiling coolant whereas the hose on the left (presumably the return hose) was cool in comparison. I loosened the clip & pulled the left hand hose off. It was full of air then a tiny trickle of cool water came out. I had the engine running all this time. I squeezed the other hose a few times & eventually very hot water came dribbling out. I checked inside the car & hot air was coming out of the vents. Thinking that it had been an airlock that I cleared I reconnected the hose & put the clip back on. Then went back inside the car to find the air from the vents was cooling down & in a couple of minutes was barely above ambient again. I went under the bonnet & pulled the hose again & there was just a tiny trickle of water coming out. I squeezed the hot input hose a few more times but there was still only a dribble of hot water coming out of the return hose.
Thinking the problem must lie elsewhere I took the car out as we needed to collect a piece of furniture my wife had bought on Facebook. After a few miles the heater started working properly with very hot air coming out when switched to HI. It also pushes out very cold air when switched to LO.
The root cause of the problem must have been an air lock in the heater matrix that I somehow managed to clear by squeezing the hoses. We got back in the dark so I haven't checked the coolant level with the engine cold but will do that this morning & report back.
How do people reliably remove airlocks from the system? I had no problem when I replaced the water pump a couple of months ago. I just followed the directions in RAVE ie run the engine with the cap off the header tank & top up as necessary as you run the engine up to working temperature.
Manningtree, UK & 22320 Saint-Martin-des-Près, France
2001 Range Rover Vogue 4.6L