Have you calculated how much interest this is going to save you?

It doesn’t appear to be very much savings. the $250 fee would probably wipe out the interest savings. You could just get more gazelle intense. Why not just get a personal loan from the credit union for both of the loans instead of a HELOC? Why put your house at risk for a car? I would put the extra money into the HELOC to give you room in case you need to sell the house. Are you underwater on the house?
I would not trade debt on a car for debt on a house. You have 3 years left to pay on a $10,000 car? Can you sell it and get a $5,000 car?