Just did the top end on my 800 E-Tec. 2016 XRS. I also had to weld my heat exchanger at the rear so I had to completely flush that out and dry it before welding. I had to disconnect those hoses under the gas tank that feed the heat exchanger. How do you know that you got everything out of the heat exchanger? Maybe if you pick the rear of the sled way up. I can't believe you have to pull the thermostat out to bleed the system. Do you have access to a manual. If not I can take a picture of mine with the procedure. I did prefill my heat exchanger before installing the hoses so I never did do a full system bleed. But I did measure what I put in and it was exactly what the manual said.