Borrowing for property investment by self-managed superannuation funds is on the radar of the Reserve Bank of Australia as being a source of future financial instability.In the minutes of its September monetary policy meeting, released yesterday, the RBA said that "property gearing in self-managed superannuation funds was one area identified where households could be starting to take some risks with their finances." It said RBA staff would "closely monitor" the trend.Data on this segment is patchy. Westpac recently estimated that the self-managed superannuation loan market is worth A$6 billion to $7 billion, with about 30,000 funds currently borrowing to buy property.Speaking in July, the head of the SMSF trustee division at Westpac, Sinclair Taylor, said Westpac and St George had a combined SMSF loan book of around $2 billion, giving it a big market share.The group's average loan size is around $300,000 and the maximum loan-to-valuation ratio is 80 per cent.The Australian Securities and Investments Commission has also highlighted borrowing as a concern in a review of advice to trustees of self-managed funds published in April. One of its main concerns was the increase in geared investment strategies in SMSFs.ASIC has said it has seen evidence of several inappropriate arrangements involving loans, such as long-term loans being arranged for older investors, and borrowing being used to acquire a single asset for the fund. It also found that trustees were not always advised of the high upfront costs of a geared property investment.In a speech this week, Greg Tanzer, an ASIC commissioner, reiterated these themes, noting there were "pockets of poor advice… including an increase in geared investment strategies."