When to lean mixture?
 

At what altitude do you guys lean out the mixture when flying cross countries? I don't know if it matters from aircraft to aircraft, but I fly a Cessna 172, and I only lean it out if I'm over 3000' AGL. Thanks.

My instructor told me to lean the mixture between 4,000 - 5,000 feet or when it gets a big rough. In a Tomahawk, so not quite as zippy as a 172 :)

3000 is the standard thats what i was taught but you can do it any time in cruise flight.

Engines differ and some can be leaned all the time, even on takeoff so there is no hard and fast rule you just have to know an engine and its peculiarities. 3,000' msl would be a good time to do it if it hasn't been done by then. Make sure you have setting the mixture back to full rich before getting into the traffic pattern on your checklist, especially when there is any doubt about how your engine will run leaned out. Back when I did my very first solo cross country I descended to the pattern at the destination without going back to rich and the darned if the engine didn't cut out. I knew what was wrong and managed to airstart it right away, and that airplane was more sensitive than most, but you could get in trouble if you didn't richen the mixture coming back down from altitude.

I think you mean 3000' MSL. Just turn the mixture knob lean until you hear the engine begin to run rough, then turn back to the right 3 full turns. then you are at the correct mixture.

BINGO! There are many airports (mine included) that are way above 3,000' MSL, so we always lean...we even lean for taxi here and it makes a noticeable difference in how the engine runs just idling around. Not to mention the fact it keeps from fouling plugs as often.

Yep... MSL.
-Cub

Unless the POH says otherwise you should lean for taxi at all altitudes...this will keep the plugs from fouling in those engines that are prone to that. A long hold idling at full rich can foul them badly enough that a mechanic will have to remove and clean them.

Too true. We lean everything except the DA20s. For some strange reason, they don't foul up. All the other planes will fail a mag check if you don't lean the mixture for taxi. As far as leaning for cruise goes, the POH should give you some advice on that. Check there. 3000 MSL is just a Rule of Thumb.

i fly Cherokee's and ever since ive started leaning on taxi, ive been having rougher run-ups when i check the magnetos......i end up smoothing it out with the mixture, but wasn't this the reason i leaned for taxi in the first place?