Air in coolant when warmed up 2015 pro rnk 800 turbo

[PrestigeMind]

This is my first post hello everyone. I appreciate any help I can receive here.

Here is the issue.
2015 My Polaris pro 800 163 turbo

Air is bubbling in coolant tank only when sled is heated up to 120 the point on the thermostat opening.
If you go to open the coolant with the sled cold air rushes out and the coolant bubbles.

Now I have checked all the hoses and clamps could this be a bad radiator cap ? I don't think it's a bad gasket or o ring as it only bubbles when thermostat opens and high rev. Not all the time.

What can cause air to lock into the reservoir?

I have ordered a new cap but I'm super confused on this one.

 

[PSI 800]

sounds to me like a cylinder head o-ring is shot.

 

[diamonddave]

Maybe but have you tried cracking the bleeder screw on top of the Thermostat housing?

Start sled cold, Crack the bleeder screw (5/16"/8mm (6) point socket on a long 1/4" drive extension) with the front of the sled elevated some. Close when you get no air/full coolant to come out. Probably get some air.

Wait for engine to warm while maintaining roughly a 1/2 coolant reservoir. Leave cap off during this.

Wait for engine to warm up and thermostat to open (usually 128 degrees), then crack bleeder again. You want to see no air and steady stream of coolant. Once you have no air/full coolant, close bleeder, top off coolant and reinstall cap.