Q: How do you know when the thermostat is stuck when the meter is broken?

Hello. If the engine is leaking coolant then the reservoir is always the first part to read low. I usually start by checking for any visual leaks on the ground or on the engine. The most common cause of a coolant leak on this engine is the intake manifold gasket, the radiator, or the water pump. If no visual leaks can be found then I would do a pressure test of the engine as the pressure would help to produce the leak. If nothing is found at that time, then a dye test could be done to find the leak. If you want to have this looked at, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose the leak and move forward with the proper repairs.