Will already means want in English. That's the deontic sense of will; its epistemic sense of 'expected future' is what's often called "the future tense". But like all modal auxiliary verbs, will has several senses. The deontic sense of will as 'want to, be willing to' can be found in if-clauses, where the epistemic sense of will is not allowed, but the deontic is OK:
- *If he will come today, it's OK (ungrammatical epistemic: should use comes)
- If he'll sign the documents, it's OK (grammatical deontic = 'if he is willing to sign')
In German, where modal auxiliaries are inflected and have infinitives and participles, they are not used to represent the future like will is. German uses the verb werden 'become' for its future construction. The German modal auxiliary that's cognate to English will (both come from the same prehistoric root) is wollen, which simply means 'want'. So Ich will gehen doesn't mean 'I will go' but rather 'I wanna go'; the way you'd say 'I will go' is Ich werde gehen.
There is also a verb will which refers to magical, theological, political, or mystical results achieved by mental (or magical, theological, political, or mystical) means. You see this in the reports of the First Crusade in 1096 CE, with the slogan Deus le veult, or 'God wills it'. The present participle of this inflected verb will, willing, is often used in constructions like be willing to
VP referring to potential agreement.
So, to answer the question, there are some occasions where will and want can both occur in the same place without much difference in meaning. But not usually, because they're different types of verbs and follow different grammar rules -- the modal will hasta be followed by an infinitive, for instance, but the verb want doesn't; and want has tensed and participial verb forms, whereas will doesn't.