Had a P0128 code come up. Check the fluid, overflow bottle is empty. Filled with G05 Zerex, ran it until nice and hot, double checked level - good to go. Have a little over 100k on this GC Mainstreet that we bought new. Never had to add fluid before. A couple weeks go by, same thing happens. I don't see fluid leaking anywhere. Dipstick looks fine, so I don't think its getting in the oil. Not seeing it out the exhaust. Wondering if anyone else has had problems with coolant loss.

 

the p0128 sets when the coolant does not reach a set temperature in a predetermined amount of time. the montor knows the temp at start up and knows after a certain run time it should be at X temperature. if it isn;t at this temp a rationality dtc sets ie p0128.

pressure test the coooling system to find and fix your leak...if the p0128 resets, replace the thermostat.