I realize this thread is a couple of years old, but for anyone who comes across this who has the same question, here is at least one solution:
Let’s set up a car loan where you are borrowing money from an account called “Savings” and you want to pay it back over time from an account called “Checking”. You will create two new accounts – an asset account and liability account. You can name them whatever your want, but for this example we will call them “Car Loan Asset” and “Car Loan”, respectively.
From the main menu, choose “Tools” and select “Add Account”. In the dialog that appears, select the tab that says “Other Assets and Liabilities”, and choose “Assets”. Name the account “Car Loan Asset”. Do not worry about adding a starting date or a dollar amount – those tasks will be completed in the next step. Select “No” when prompted whether there is a loan associated with the asset. Quicken will create the new account, and will exit the dialog.
Choose the new account by clicking on “Car Loan Asset” in the list of accounts. At the top of the register on the right, click the settings icon (it looks like a gear), and select “Convert to a Lending Loan”. A new dialog will appear. Here you will enter the starting date of the loan, the dollar amount, and all of the other loan terms. Quicken will create an income reminder as part of the process. Select the next payment date and choose “Savings” as the deposit account.
From the main menu, again choose “Tools” and again select “Add Account”. This time, select the “Offline Account” tab, and choose “Loan” under the “Loan & Debt” heading. Name the account “Car Loan”, and enter all of the same terms you entered for Car Loan Asset account. Quicken will automatically create a bill reminder as part of this process. Choose the payment date and this time choose “Checking” as the account you will be paying from.
When you enter the transaction from the bill reminder, it will debit your checking account by the entire payment amount, it will credit “Car Loan” by the amount of the principal being paid back, and it will credit "Interest Expense" by the amount of the interest. When you enter the income reminder, it will debit "Interest Income" by the amount of the interest, it will debit “Car Loan Asset” by the amount of the principal, and will credit “Savings” by the amount of the entire payment.