Hello - I have a Volvo D13 2012. It has a heating problem.

Heat only works sometimes - usually it works best when the coolant level is very low. It barely works when driving - however from time to time it will work for a few hours while driving and then blow completely cold air. Today it worked while I was driving, then when I slowed down to make a turn it stopped working completely for as long as I continued driving. As soon as I stopped heat came back. Then after 30 minutes of idling it got cold again, blowing cold air.

Heat usually works when I'm stopped but as soon as I start driving it blowns cold air again. Then as I'm driving it may or may not blow warm air (usually cold). Last week it worked for 6 hours straight while I was driving and I thought it fixed itself miraculously, however then it randomly decided to blow icey cold air.

It's very random - but heat works best when the truck is stopped and the coolant level is low.
I'd drive it with low coolant level - but it loses power as soon as the "low coolant level" warning sign comes on the dashboard.

Any thoughts or ideas on what the problem might be?