Is it safe to run my motor without the thermostat ? I was having problems putting a new one back in, it just wont go back into the hole it is supposed to with the o ring or seal on .
You don't absolutely have to have it, but 90% of wear takes place while the motor is warming up. The hole probably needs cleaning and scraping to get rid of the buildup thats keeping it from going back in. You are much better off with the thermo installed.
The purpose of the thermostat is to keep the powerhead at a constant temperature. Without it, you will have hot and cold spots (water rushing through too quickly) and that will cause problems.