All Mazda-made Wankel rotaries, including the Renesis found in the RX-8, burn a small quantity of oil by design, metered into the combustion chamber to preserve the apex seals. Owners must periodically add small amounts of oil, thereby increasing running costs. Some sources, such as rotaryeng.net, claim that better results come with the use of an oil-in-fuel mixture rather than an oil metering pump. Liquid-cooled engines require a mineral multigrade oil for cold starts, and Wankel engines need a warm-up time before full load operation as reciprocating engines do. All engines exhibit oil loss, but the rotary engine is engineered with a sealed motor, unlike a piston engine that has a film of oil that splashes on the walls of the cylinder to lubricate them, hence an oil "control" ring. No-oil-loss engines have been developed, eliminating much of the oil lubrication problem.