Snowmobile Engine Rebuild Small Engine Repair - Snowmobile?

Small engine repair - Snowmobile? - snowmobile engine rebuild

Recently I had an engine rebuild the top half of the 3-cylinder liquid-cooled snowmobiles (1996 Polaris XCR 600 SP). I have a machine running and seemed to be very good if I have a small test on 2 occasions. at the third attempt I did a little more anti-gel deposition, if it is a little Liitle. If I pull the rope starter was a little difficult, but finally started. He seemed a bit murky, but not long term, when I noticed the coolant from the overflow tube. I turned away and a few minutes later, he opened the lid of the tank, knowing full well that it was still fresh, and came away from the freezing of bubbles. If you have any idea why it's so much pressure, and why the machine was difficult to stop? is the battle against the freezing of somewhere in the engine block that should not have. What is my next step is to check? Thank you.