Is too much carb heat a bad thing?

[Simonta]

I know that carb heat results in a less dense charge and therefore less power and that adding carb heat in some scenarios can actually precipitate carb icing but, assuming that engine temperature is OK and you don't need the power, is flying with the carb heat on deletirious for other reasons?

Cheers

[Von Klinkerhoffen]

Yes , it can cause pre-ignition/detonation if you have a lean cylinder and if RW is the same as FW , carb heat is unfiltered.....not so good for engine life !

[Agaricus bisporus]

As you've said carb heat results in a wee bit less power.
Air is unfiltered so hovering may ingest dust or debris, but you'd have to do a lot of that to make much differece to your engine unless you were very unlucky.
Pre-ignition? Well, maybe, but I think you'd be running unwisely lean for that to happen at all, and that's gonna harm your engine more than a few seconds of pre-ignition that I hope you'd notice. Anyway, who ever flies high enough in a helo to lean it? (OK, in mountainous countries maybe, but not a general scenario.)

I think the idea that it can make icing worse in certain conditions is a bit like saying that drinking water can be dangerous - ie it is so vanishingly unlikely that you really don't need to know about it. If you did operate in the arctic or in the Himalayas you'd find it specialist local knowledge that applied to the territory, but for normal worldwide ops, it just ain't gonna happen. (incoming!!)

You have to use carb heat at the times specified by the flight manual, and don't use it at any other time (unless you suspect conditions are right for icing, which is very unlikely as the flight manual covers all realistic eventualities). Why worry what it does if used outside those times, cos you ain't gona do it, are you? You don't worry what happens if you always drive your car with the choke out - you never do it, so what's the worry?

[the beater]

All the air is filtered - heated or not - if it's in a Robinson. Don't know about other types (the only piston types I fly are Robinsons).
In very cold conditions the carb-heat can result in the very cold air being raised in temperature into the yellow band in which case you could elect to run below the yellow band.

[Von Klinkerhoffen]

Re pre-ignition : Inlet manifold gaskets do become hard and brittle with age/heat cycles and it is not unknown for small sections to break away and be sucked through leaving a small gap to lean the cylinder out . The same goes for induction manifold rubbers , they become hardened and crack , often becoming loose it the process and again leaning the cylinder out . Tell tale signs are blue stains from the fuel dye on the induction tube . Have also seen fuel leaking out when the primer is used......can result in a fire if it comes into contact with a hot exhaust !!!