Invoicing for loaner vehicle repairs

There would not be an Invoice of any kind.  No more than you'd invoice yourself for any other repair work done in the offices.  It's an internal business expense.

They could set up a Loaner Car Maintenance Acct similar to other Expense Accts for running the business if they want to break it out.  But pending how much activity and dollars involved, it might take more hours than it's worth the track it. 

@S of PSI 

Actually, I agree that an invoice is the best way to track this.  Since, the shop is most likely creating POs/entering bills that contain a combination of parts for loaner vehicle repairs as well as customer vehicle repairs, putting them into inventory and then expensing them on an in-house invoice sounds most efficient.  As long as the parts on the invoice are inventory products and they are entered at $0.00, the cost of those parts will get booked to COGS and there will be no income, which is what you want.

This is what I was trying to achieve but when I check my client's books and remove the amount on the invoice doesn't change the COGS total. I guess I'll have to work with them to figure out the steps they are using to enter parts and then figure out what is missing.

Any other thoughts of suggestions would be appreciated.

@S of PSI 

If you're running the report on accrual basis, and the parts are not getting booked to COGS, then either the parts are non-inventory items or there's no cost associated with them.

If you're running the report on cash basis, the invoice will not change COGS.  If your client is on cash basis, then they should not be tracking inventory because cash basis taxpayers do not carry inventory on their balance sheet.