Demonstrative Pronouns

I understand that a demonstrative pronoun is a word that replaces a noun as if pointing to it. For example, "I want to buy a car. This one is cheap. Those are expensive." This and those are demonstrative pronouns, they replace the noun car. But, if I say, "This car is expensive," what role does this play now? Is it still a demonstrative pronoun? Now the sentence has a noun and a pronoun? Or is ‘this’ now a different part of speech? Thanks for any clarification.