Is there any way my boyfriend can keep the car he technically helped pay for?

Never, ever, ever, ever go in with someone else no matter what it is or what you want! If you can't afford an apartment without a roommate don't move in to it. If you can't afford a car don't get one. Don't live beyond your personal means. Example: drinking champagne on a beer budget it will never work out to your advantage. Relying on other will cost you more in the long run. Be self supporting....

Was the money he gave to his grandfather a gift or a loan

If its a gift then that's the end of it and the grandfather can do what he wants with his car

If the money was a loan and they both signed an agreement for the loan to be paid back, then that document can be shown as proof that your b/f lent him the money, and he is owed the money

The money he paid out covered his use of the vehicle. It didn't grant him an ownership interest. So no, he can't keep the car if his name is not on the title.

Whoever has the car's title owns the car wherever the money came from.

Nope. Assuming there wasn't any sort of contract or agreement that he owns part of the car because of the money he put towards it, the money he have your grandfather is essentially a gift, and doesn't constitute any sort of ownership

Whoever owns the title owns the car. It's really very simple.

If your boyfriend wants to dun his dying grandfather for $3,000, find a better boyfriend.

Not if his name is not on the ownership paperwork.