Westpac is marketing its first asset-backed bond in four years, with plans to refinance a pool of A$750 million in car loans that originated with its St George finance arm.The bank will sell the bonds in six tranches through the Crusade Series 2012-1 Trust. The Crusade series of trusts are entities that were used by St George to fund asset-backed bonds prior to its takeover by Westpac in 2008.St George last sold asset-backed securities in July 2008, and this week's move follows inquiries from investors. The average vehicle loan in the trust is $20,000 and the average seasoning on each loan is 19 months.A pre-sale report from Fitch Ratings put historical default rates on this type of loan from St George at between 1.1 per cent and 3.2 per cent. Fitch said loan arrears were below 3.0 per cent.Moody's has assigned provisional ratings to five of the tranches, ranging from Aaa to Ba1.Macquarie is the only regular issuer of asset-backed securities among local financiers, though Liberty Financial, Investec and NAB have all issued in the last two months.