How do you record a new vehicle purchase (part down payment, part loan) in Quickbooks Online?

I don't use Quickbooks online, however, the entry should be the same unless there is something unique about online vs desktop:

You will need to make two entries to record the purchase:

1.  Create a check for the downpayment,  to record it in the fixed asset account (debit Fixed Assets, credit checking).

2.  Record the loan via journal entry (debit Fixed Asset, Credit Loan Payable)

Note:  Loan amount + downpayment = fixed asset value of vehicle

OK.  How do I account for loan payments and the interest on them?

It's my pleasure to share tips on how to handle your loan concern, @a-mitchell.

You'll first have to set up a liability account to record your loan and its payments. That should include the interest you've paid. Then, record your loan repayment by creating a check or expense. From there, you'll have to select the expense account from the Category drop-down to record the interest accordingly. Let me guide you how.

1. Click the Gear icon, then select Chart of Accounts.
2. Hit New.
3. From the Account Type ▼ dropdown, select Non-current liabilities. Note: If you plan to pay off the loan by the end of the current financial year, select Current liabilities instead.
4. From the Detail Type ▼ dropdown, Loan Payable.
5. Give the account name.
6. Choose when you want to start tracking your finances. In the Balance field, enter the amount in the account, and determine the as of date. Enter today's date if you want to start tracking immediately.
7. Hit Save and close.

Once done, you can now use the account when creating a check or expense transaction for the interest payment.

1. Click the + New button, then select Check or Expense.
2. Choose a Payee, a Payment date, and a Payment method.
3. From the Payment account drop-down menu, select the bank account.
4. Choose the account from the Category column.
5. Enter the amount of the interest charge.
6. Click Save and close.

You might want to check out this article for more details: Set up a loan in QuickBooks Online.

Additionally, you can also pull up the Transaction Detail by Account report. This way, you're able to monitor your expenses and manage them accordingly. Just go to the For my accountant section from the Reports menu's Standard tab. I've recommend visiting the following article to learn how to personalize reports in QuickBooks: Customize reports in QuickBooks Online.

I'm just around the corner if you have any other QuickBooks concerns. I'm always willing to lend you a hand so you can achieve your goals. Thanks for dropping by and have a good one, @a-mitchell.