Hi my 2001 patrol wagon is doing lots of weird things in regards to cooling/heating the first thing I noticed was that the temp gauge would sit under half way as always but the heater would only blow out cold air then suddenly hot air, but no other issues? But now it's using some water, and the temp gauge will randomly go all the way to near the red then drop under half as normal then 5 minutes time do it again but the engine seems to run like a dream, so I'm not sure what to think, but normally if using water and no visible leak I'm thinking maybe a cracked head?