2013 Hyundai Elantra temperature gauge lights up when it’s not cold out

the temperature gauge lights up even when it is not cold outside.
at different times… sometimes after stopping at a stop light or just comes on. Then goes off

It seems that your engine is over heating and I am not sure why you think the outside temperature is relevant . I think you need to have a shop look at this but first check your coolant level . If you don’t know how find a friend that does before you destroy your engine.

the heater didn’t seem to work either when the temperature gauge would light up… gauge would come on after stopping at a stop light and starting up or would just come on even when it is cold outside

Explain what you mean by “temperature gauge would light up”.

Have you checked the coolant level—when cold?

The little symbol that looks like a littler red flag in water

@cdaquila Apparently this person has 2 threads with slightly different user names.

I would guess that is your overheating warning to shut it down immediately.
Have you checked the coolant yet?

Uh oh. Heater not working due to low coolant due to: leak, neglect, head gasket. Sorry had to say it. Classic sign. Been there.

Get this to your dealer immediately, preferably with a tow, or at leas t a refilled radiator (properly done). You may need an engine replacement (under warranty).

It’s 7 years old though. Is there an extended engine warranty?

Hyundai vehicles have a 10 year/100,000 mile powertrain warranty for the first owner. Repairing a coolant leak on the engine might be covered, a damaged engine caused by driving with insufficient coolant will likely be rejected.