Long Runups

----------------------Pet Peeve Alert----------------

We SEL GA airplane fliers are behind engines that are air cooled.

Guess how much air flows through when we're sitting on the ground?

Right -- not much.

This isn't new information. The Operating Handbook for my 1940 Lycoming O-145-B2 states:

Ground Running and Warm-Up -- The LYCOMING O-145-B2 engine is an air pressure cooled engine that depends on the forward speed of the airplane to maintain proper cooling. Therefore, particular care is necessary when operating this engine on the ground. To prevent overheating, it is recommended that the following precautions be followed:

Head airplane into the wind

Avoid prolonged idling at low R.P.M. as this practice may willr esult in fouled spark plugs.

Limit ground running to 4 minutes in cold weather and to 2 minutes at temperatures above 70 F.

Note-- Engine is warm enough for take-off when the throttle can be opened without backfiring or skipping of the engine.

Now, 4 minutes is mighty quick -- it takes me that long to taxi from my hangar to the end of the runway. I have a preheater but usually take off 7 to 9 minutes after startup. Oil pressure and temps are in the green but that's not much to go by.

With larger engines (IO-470/520/540) I will wait until oil temps are in the green, which might take a couple more minutes. I never idle below 800 RPM unless I'm stopping on the taxiway or doing an engine idle check (a new one for the checklist -- make sure the engine doesn't die when you pull the throttle all the way to idle).