D was employed by Weeks Brothers, Inc., which was a customer of P. D and Weeks Brothers agreed that D would purchase, for $16,000.00, the tractor/trailer then owned by Weeks Brothers. P agreed to finance the purchase, provided that Weeks Brothers would cosign the note. D and Weeks Brothers executed a promissory note and security agreement for $16,000.00. The note was to be paid by D in six months. P paid the $16,000.00 proceeds to Weeks Brothers but did not transfer the title to D. Title to the tractor/trailer was held at P in the name of Weeks Brothers, subject to all security interests of P. D had possession from June 17, 1981, until trial. D maintained and repaired the truck, spending $4,658.98 for parts and claiming $2,000.00 for his labor. D moved from Idaho to South Dakota bringing the truck with him. D did not make any payment on principal or interest. P sued for repossession. D counterclaimed for the repairs on the theory of a possessory mechanic's lien, detrimental reliance and promissory estoppel, and negligence seeking recovery of the $6,658.98 spent on maintenance and repairs. The trial court ruling that Bank P entitled to possession and D was entitled to his repair costs based upon detrimental reliance and promissory estoppel. Both parties appealed.