Running Engine too Cool?

[201er]

Running 55% power LOP (no rush, just wanted to prolong my time up there) on a cooler day I was getting CHTs as low as 280 on the front cylinders and no higher than 340 on the backs. My mech told me it's not good running engine too cool and 65-75% power is better. Another pilot once told me that it's better (without getting too hot) to run hot cause it reduces build up by melting everything out. The POH says the green arc (operating range) in terms of CHT is 300-475F. It's not even winter yet.

Is it bad to be running this cool or heck even cooler? Does it help to alternate flights at higher power and flights at lower power? Is there anything wrong with or bad for the engine from running low power and LOP all the time? What are the ramifications of running low CHTs?

Also if CHTs are pretty low at full power, is it ok to use that temp allowance to close cowl flaps (partly or full) or lean more in the climb? Or is it better to leave things and let the engine climb cooler (350F or less on max CHT)? If you may as well gain some efficiency by letting CHTs go higher (toward 380F or whatever is typical climb CHT in summer), is it better to close cowl flaps, make mixture leaner, or climb steeper (slow to Vy)?

[Ned Gravel]

I am not certain I agree with your mechanic.  Cooler is OK so long as it is warm enough to keep the oil flowing and the gas evaporating for the combustion event.  The idea of anything over 380 degrees would (and did) worry me. 

Mine are now like yours and they got this low once the overhaul was done and Clarence built me a new doghouse.  Well within my own comfort zone.

[jetdriven]

There are some articles but I think 250-275 or more is ok.  The barrels are bored with choke and need some heat to expand to a true straight cylinder.  

[Cruiser]

The lead scavaging compound Ethylene Dibromide needs 250°C (482°F) in the combustion chamber to do its job and capture the lead from the fuel and remove it out the exhaust. I don't think there is a problem during cruise operations but running too cold may contribute to lead buildup. If you start fouling spark plugs you may be running too cold.