I used Preston Extended Life Coolant in my 2007 BMW328i & now serv. engine lig

Putting in the wrong coolant is not good, but it also won't immediately cause an engine to shake. You have another issue and the fact that you are losing coolant with not leaks may indicate it's burning in the cylinder. This can cause a misfire so i would check for a blown head gasket.Use this link to find a good shop near you. https://repairpal.com/repair-shops Alex

These are know to have a lot of problems with Electric Water Pump and Engine Coolant Thermostat, as well as there are Cooling System Bleeding Procedure that if not followed can also cause problems regardless of the coolant used. I recommend using coolant that meets BMW minimum specifications, following bleed procedures, having vehicle properly diagnosed. If you are adding coolant every 3 days that should not be too hard to find by a competent technician at a quality repair facility. If you need it diagnosed we have BMW dealer trained TECH and master/world class certified technicians on our staff. 757-456-0722