[HighFLyer]

Like Skid say's I wouldn't use just a small amount of carb heat. The gauge is just and indication, and will not really give you a good estimate. I would just check for ice by using full heat whenever you suspect a problem.
Another problem with carb heat, is that the air comes from a muff around the exhaust. I beleve that when you use carb heat, the air coming into the carb skips the air filter. That is why when you land on gravel or dusty runways you should always push the carb heat in right away. Then you lower the risk of ingesting dirt and particles in the engine.

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