Fan is on high speed

I have a Dell Inspiron 13-7378 2-1. the LT has always been a great machine. A few months ago I turned it on and the fan ramped up to high speed and nevered slowed down. now it's on high speed all the time. this is what I did. cleaned the fan, replaced the fan with a new one. cleaned CPU and GPU applied new thermopaste, new CMOS battery, Replaced LT battery, reinstalled Win 10, downloaded all drivers and BIOS. I don't know what to do next. ANY HELP would be greatly appreciated. THANK YOU.