Two weeks ago I completed the conversion of my diesel Vanagon Westy turbo diesel over to the new style tank with new engine hoses. As I write this I am sitting in a Hardee's parking lot waiting for about the 15th time in the last two weeks for my engine temps to go down to the point I can drive the car. Before I left home for the short drive, I bled the cooling system according to the Bentley for the eighth or 10th time since making the conversion. I have only managed to have heat from the heater once or twice in the last two weeks. I am on my second blue coolant In that time. When I wake up in the morning I check it first thing. Always there is considerable pressure left in the system from the night before. I installed a new thermostat. I tested the old thermostat and the new thermostat on the stove, and they both operated exactly the same. I put the new one in anyway. Usually I can drive somewhere as to a store maybe 4 miles away. Going to a store or on an errand it's likely to run just fine with the needle steady in the center all the way there. Then on the way back I typically have to pull over just like I have done now. I can let it cool down maybe leasing the L some air out, and then be on my way with a slightly hi or sometimes normal temp gauge. I never know what to expect. But no longer can listen to audio because I have to keep my attention riveted on the temp gauge. It's not leaking. I'm not losing coolant. I just can't get rid of this air bubble. I don't think I have a leaking head gasket because yesterday I drove to a town 100 miles away and back without really having any problems. There are some steep hills along the way. The temperature stayed normal. I don't find any soot in the coolant or water in the oil. 

Any ideas? The temps were perfect before my "upgrade."

Jim