Heater goes cold on idle. Hot when revs rise. Water pump on the way out?
Guys, really strange issue I noticed for the first time tonight on my AUM 20vt
Parked up in a carpark, waiting for my GF to pick her up from town, engine on to get the heater going, and the heater wouldn't blow hot.
Checked coolant temp on climate 49, and it was up to 107 degrees, despite 0 degrees outside.
Held the revs up to 2k for a few minutes whilst static, and the heater came through hot, and temp dropped back to 94 (remained at 90 on the dash the whole time)
Let it drop back down to idle again, and within 30 seconds the heater cooled all the hot water in the matrix, the air went cooler again, and the temp on climate 49 rose back to over 100.
Anyone else had this happen before? Seems to be like perhaps the waterpump has issues and is no longer circulating enough water on idle. Once moving, the car seems fine.
Car has done 111k currently, and last had a cambelt done at 55k. Unsure if teh water pump was done at the same time. So it's due a cambelt and waterpump in 4k anyway.