I also have the mishimoto racing thermostat. It definitely improved hot temperature operation, but if I ever take my Veloster out in colder temperatures it does struggle to stay up to temp. I have actually blocked a significant amount of airflow to my radiator and oil cooler for winter to keep the engine and oil temps sitting within a few degrees of 200°f.
the mishimoto thermostat compared to the OEM thermostat:
| mishimoto | OEM |
Opening temp: | ~150°f | ~190°f |
Distance open at 208°f (boiling point for the barometric pressure and 5000ft I was at when measuring) | 9.6mm | 6.9mm |
my assumption is that flow will be increased for the racing thermostat at higher temperatures too since the it will impose less restriction on the water loop. This should increase thermal efficiency.
As to Shark racing’s thermostat, I couldn’t say, but I enjoy mine.