Suzuki X-90. (engine newly replaced). Check Engine light came on and the code referred to cooling system failure. (levels were low, so filled to capacity). Coolant levels monitored and found to be low when engine reaches normal operation temp. Stop leak added buy mechanic. Problem persisted. As engine warms to normal operating temperature, a ‘gurgling’ can be heard from under the hood. Engine does not overheat - but radiator is low (approx 1 quart) and anti-freeze / coolant is NOT drawn from reservoir. Cooling system inspected by radiator shop and no leaks or obvious signs of malfunction. Thermostat removed and condition greatly improved (but not entirely. Also no heat - yikes). A “pressure test” revealed too much pressure.(?) Thermostat replaced and condition returned. Lines between radiator and reservoir are clear. The mechanic has no idea on what to do next. If I had any hair, I would pull it out.