I never gave much credence to carb icing on my Lycoming O-320 knowing that the carb is mounted on the bottom of the oil pan. I always figured there would be enough heat from the oil to keep everything nice and warm. I have to admit I very seldom pull the carb heat control (maybe a dozen times in 560 hours) so today was no different. I also did not put much stock in the little heat muff from Vans thinking it was marginal at best.
On my Continental C-85 in the Cessna 140A, I have actually seen the outside of the carb completely encased in blue ice on a humid 70 deg day. There was not a hint of icing inside the carb though since the engine ran fine. However I always use carb heat on that engine.
So the weather today was 1200' with 10 miles visibility and the OAT was 43 deg. These conditions gave me my first real life, certified run in with carb ice! I had been easing forward on the throttle to maintain cruise RPM until I figured out RPMs were dropping without a reduction in throttle position. Another dead giveaway was the engine was starting to run rough. I pulled on the carb heat and instantly the RPMs started to rise by almost 200 revs and the roughness disappeared. The little heat muff actually works. I am in the "it can happen" camp now.
On my Continental C-85 in the Cessna 140A, I have actually seen the outside of the carb completely encased in blue ice on a humid 70 deg day. There was not a hint of icing inside the carb though since the engine ran fine. However I always use carb heat on that engine.
So the weather today was 1200' with 10 miles visibility and the OAT was 43 deg. These conditions gave me my first real life, certified run in with carb ice! I had been easing forward on the throttle to maintain cruise RPM until I figured out RPMs were dropping without a reduction in throttle position. Another dead giveaway was the engine was starting to run rough. I pulled on the carb heat and instantly the RPMs started to rise by almost 200 revs and the roughness disappeared. The little heat muff actually works. I am in the "it can happen" camp now.