I had bad diesel in my VW the dealer said I need a new fuel system $16,000 instead I fixed it privately for $5000 is my warranty void?

Don't know where you live or what monetary standard you go by, but in the USA, you can buy a complete car for $16,000.

If you had a warranty to worry about, then the repairs would have been for free anyway. Since they were not free, then your warranty must have already expired. But private repairs not done by a dealer do NOT void a warranty. They only way you can void a warranty is by failing to do scheduled maintenance checks, regardless who does them. You can even do them yourself.
But even $5000 was more than a whole fuel system would cost. There really is no way the whole fuel system could go bad all at once.

Even if it was, you're better off this way than succumbing to what is clearly a scam.

Yes, it's void, and yes you do indeed have to learn to use punctuation when you write things.