Unless you have a very short credit history, paying off a loan early is not supposed to make your credit score lower...I've done it several times.
A word of advice about these 0% financing rates: There is always a catch. 99% of the time manufacturers offer 0% or cash back, not both.
Do the math, and you will find that in many cases, over a 4 year period, you really are not getting any benefit from the 0% offer.
One dealer near me said that he can sell me a brand-new 2012 Wee still in the crate for $7699 plus t/t/t. I asked him about the 0%, to which he said "Well, the price will be $8299 if you want the 0%...the $7699 price is for cash".
Same thing applies with new car advertising.
I did some research and found that my credit union offers 1.89% financing on new motorcycles for 4 years.
$7699 at 1.89% is still a better deal than $8299 at 0%.
Note: in some very rare cases, when manufacturers are desperate, they will offer both a 0% and big cash back to get rid of stock, but, there is always a catch to these deals.
1995 Honda CB750 - sold
2005 Honda Rebel -sold
1990 Honda PC800 -sold
2007 DL650 - sold
2011 DL650A - current