August 1, 20232 yr On 7/25/2023 at 10:08 AM, Mace said: I had carb icing with an OAT of 61 degrees fahrenheit in this bird. Bob you and @sd_flyer can answer this. I was always taught that generally speaking above 60 you don't use carb heat. I know about the venturi effect BUT in your experience was I taught wrong? I always thought that even with venturi/pressure lowering temp that wasn't an issue until you got down to about 55degF or lower. There is no limit ambient temperature; it's dependent on too many factors, and will vary per engine. The Continental R-670 for instance is very cool running and famous for carb ice, and I've seen it in ambient temps well into the 70s in damp conditions. It's not uncommon to need it on immediately after start for taxi out on a humid NW morning... Not ideal because it's unfiltered induction air, but at least that engine is pretty high off the ground. Point is, you don't want to think of carb heat as something that's only applicable within certain conditions and then forget about it otherwise. Like so many things in aviation, the answer to "when do I need it?" is "when you need it." 😁 Andrew Crowley
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