My Rental is operating at a loss for several years how many years allowed to claim deductions for rental?

As long as you have it. Your rental is, with little question, a business. What your thinking of is that a business that may actually be a hobby, can be looked at very skeptically after 4 or 5 years of losses...one would have to prove that it is an actual business with the prospect of making money, not just a hobby, which isn't deductible.

Understand that many things that cause a tax loss for a rental, depreciation for example, is recovered...that is on sale, the depreciation taken on the property is is returned and taxed at ordinary income rates (not capital gain), as ordinary income deductions were realized with it. The expense for tax is only a timing difference.