delvic

Twice now had idled my Journey at -30 C and -12 C while loading vehicle' maybe 15 mins. Each time. Headed down highway, temp. gauge showed zero on needle. Checked screen it said running at less than 40 C. This indicated a thermostat stuck open. First time, I drove to work and after work everything was normal. Second time, I pulled over on the side of highway, shut off the engine and waited ten seconds. In affect, rebooting the gauge. Everything went back to normal. What's happening?