New Tuxing compressor

Is this a new compressor startup or a new problem that wasn't previously happening? Only way the cap comes off is with a rapid increase in pressure inside the tank. IF the compressor head has a leak high pressure air to coolant passage this could happen. If something upon startup pushes on the plastic tank side it can have a squeeze effect. Can you see air bubbles inside your tank?
I’ve used the compressor four time with no issue then yesterday it popped the top four times. I kept turning it off and on the last time left the top off and let it fill my bottle and it just stopped on its own.
 
Ok. So 4 uses and the cap keeps popping off. Cap is just a push on style plastic cap. Make sure you did Not go above the fill line on the tank. If that is so then you have a leak HP air side to coolant...assuming nothing is touching the plastic reservoir trying to squeeze it. Observe the oil condition/color and/or coolant condition/color for any changes. Since it sounds like you caught it early it may no be obvious yet. Keep an eye on it every time and put cap on. Do Not drill any vent hole to mask the symptoms. Good luck and keep us posted.
 
Ok. So 4 uses and the cap keeps popping off. Cap is just a push on style plastic cap. Make sure you did Not go above the fill line on the tank. If that is so then you have a leak HP air side to coolant...assuming nothing is touching the plastic reservoir trying to squeeze it. Observe the oil condition/color and/or coolant condition/color for any changes. Since it sounds like you caught it early it may no be obvious yet. Keep an eye on it every time and put cap on. Do Not drill any vent hole to mask the symptoms. Good luck and keep us posted.
So yes, High pressure air is somehow feeding into the cooling lines, tank or gun will not fill up any more. The air pushes the all the coolant into the reservoir. The reservoir is only half full at this time. Trying to contact Tuxing or AliExpress now for a refund. Hate to have to tear a brand new unit open after less than 2 hours of operation.
 
So yes, High pressure air is somehow feeding into the cooling lines, tank or gun will not fill up any more. The air pushes the all the coolant into the reservoir. The reservoir is only half full at this time. Trying to contact Tuxing or AliExpress now for a refund. Hate to have to tear a brand new unit open after less than 2 hours of operation.
Ouch...mine has done well no for 6 months. Gun fills only but I had many leaks at first. My coolant reservoir was shipped defective and leaking..Tuxing sent replacement and it works well. My connection tube from filter top to filter top leaked bad...bend radius of tube was not proper causing leak..again Tuxing sent replacement and it works well. I hope you get it worked out...they may want you to tear into it and send parts to you. Keep us posted how it goes. 🤞