1994 Cadillac Seville Owner's Manual - Page 257

NOTICE: If you try to do yourown service work without knowing enough about it, your vehicle could be damaged. FUEL Use premiumunleaded gasoline rated at 91 octane or higher. It should in meet specifications ASTM D4814 the U.S. and CGSB 3.5-92 in Canada. These fuels should have proper additives, so you should not the have to add anything to thefuel. In the U.S. and Canada, it's easyto be sure get the right kind of you gasoline (unleaded). You'll see "UNLEADED" right on the pump. And only unleaded nozzles will fit your vehicle's filler neck. into Be sure theposted octane is at least 91. If the octane is lessthan 91, you may get a heavy knocking noise when you drive. an emergency, you (In may be able to use loweroctane -- as low as 87 -- if heavy knocking does not occur.)If you're using 91 higher octane unleaded gas and you still or get heavy knocking, your engine needs service. 244