I agree Ken, if anything, having an oil filter in front of the carb would give off more heat from the hot oil.
I've experienced carb icing while flying a carbureted Lycoming, scary minuet or so till the carb heat kicked in. I was low and slow a few miles out from the pattern waiting for the traffic to clear when the power just started to drop off. It generally only happens when the engine is throttled back like on landing where the butterfly is only partially open. It's standard operating procedure with any carbureted air-cooled engine to add carb heat as soon as you throttle back on your approach or if you experience a gradual power loss. AOPA has a real good Safety Advisory out on Aircraft Icing. Page 11 & 12 discusses induction system ice. Keep in mind that the engines they are discussing are air cooled engines taking air in directly from the out side, not water cooled engines with the intake inside the engine compartment and behind a radiator as in our ADs. Carburetor icing in and automobile engine is quite rare.
I might add that in my biplane I have a Lycoming IO360 with Bendix fuel injection and no carb heat is necessary.
I don't understand why in a water-cooled stock Stovebolt, if the throttle is open and you’re running along at highway speeds, why your carburetor would ice up. I might be able to see it if you were stuck in heavy traffic and idling for a long period.
A few years ago, using a laboratory digital thermometer I did some temperature studies on my stock 1950, 216. Measurements were taken all around the intake manifold flange and at points all around the Rochester carburetor. I was trying to isolate the percolation problems we have with them at shut down. It's surprising how much heat is transferred up to the carb float bowl by conduction after the engine is shut down. When the engine is running the cast iron base runs cold as would be expected because of evaporative cooling but not enough to form ice.
Denny Graham
Sandwich, IL
