I keep losing the coolant after aproximately 600 or so miles. I had my shop put it on a test and they put it under a pressure test and could not find a leak. They told me to replace the coolant cap and that did nothing.
Start the engine from cold and watch for drips underneath for 10 minutes while it warms up. I have seen a water pump leak intermittently while the engine warms up.
I can confirm the possibility that circuitsmith suggested. If this is the case, the water pump is ready to blow.
However, I’d want to check for a headgasket breech also. That can be done in s number of ways, including a check of the coolant for evidence of hydrocarbons and a pressure leakdown test of the cylinders. Coolant could be getting drawn in through a breech and burned with the fuel (pushed out the exhaust as vapor).