I believe you are having problems getting the thermostat housing into the stainless steel mounting coupler that goes in the engine and then when you insert the thermostat housing into the coupler it is actually not going in all the way.
We have had a couple of other customers call us with this and we have found that the spec is out on the stainless coupler. We checked the couple hundred we had in stock and found a few more that we out of spec and threw them in the trash.
If anyone else is having issues and the thermostat does not go all the way in easily please contact use so we can send you a new one ASAP.
info@c3powersports.com