Short answer. You, the bailee, must pay for ordinary upkeep of the borrowed boat. Under Civil Code Article 1941, the bailee is obliged to pay for the ordinary expenses for the use and preservation of the thing loaned — the lender bears no share of these day-to-day costs.
What the law says
The bailee is obliged to pay for the ordinary expenses for the use and preservation of the thing loaned.
Civil Code, Article 1941 — Ordinary Expenses. Read the full provision →
The rule: ordinary upkeep is the bailee's burden
A commodatum is a gratuitous loan for use — the lender hands over the thing for free and expects to get it back. Because the bailee is already getting the benefit of the loan at no charge, the law places the cost of keeping the thing in working order on the bailee's shoulders. Ordinary expenses are those that arise in the normal course of using and caring for the thing: engine oil changes, minor repairs, routine cleaning, storage costs during the loan period, and similar upkeep. These are the bailee's problem, not the lender's.
What counts as 'ordinary'
The line between ordinary and extraordinary is not always obvious. A general guide: if the expense is the predictable cost of keeping the thing functional for the purpose it was lent, it is ordinary — and it falls on you. Fuel, minor tune-ups, and cleaning a borrowed boat after use are ordinary. An unexpected overhaul needed because a storm damaged the hull is a different matter; that kind of significant, unforeseen preservation cost may shift the analysis toward the extraordinary expenses rule under a separate provision. When in doubt, document what you spend and the circumstances that made it necessary.
Why the rule is placed on the bailee
The logic is straightforward: the bailee uses and benefits from the thing, so the bailee absorbs the wear-and-tear costs that flow from that use. The lender receives nothing in return for the loan — commodatum is by definition gratuitous — so imposing ordinary upkeep costs on the lender would mean the lender effectively pays for the privilege of lending. Philippine law treats this as unreasonable. The bailee who cannot or will not shoulder ordinary maintenance probably should not be borrowing the item at all.
Practical steps if you are the bailee
Keep receipts for every maintenance expense during the loan period. This protects you in two ways: it proves you discharged your duty to preserve the thing, and it documents that an expense was ordinary (not extraordinary) should any dispute arise later. If you anticipate a large, unexpected repair that goes beyond routine upkeep, notify the lender before you spend the money — the rules governing that kind of extraordinary preservation cost require prior notice to the lender in most situations. Treating all costs as your own problem without checking with the lender can create confusion; treating all costs as the lender's obligation without legal basis is inaccurate.