Had a CEL indicating car was not reaching operating temps, and gauge was indeed reading low. Replaced thermostat, during which about 1/2 gallon of coolant lost, and put that much back in, overflow bottle to full mark. Upon running, the temp gauge moved nowhere, very hot air out the vents, smelled like engine getting hot. So... being a long time since I've replaced any vehicles fluid, realized I forgot to burp system, so maybe had air trapped. Still, AFAIK the temp sender is low enough where coolant ought to be even with an air pocket somewhere, so that's a question mark. The car is at a nearby parking lot where I left it. Just checking for ideas, like why temp gauge didn't show any warmup. Should I disconnect the high line to the overflow tank and use it as a filling point to make sure the radiator is properly filled? Thanks.