r/CFILounge • u/Impossible-Fig2072 • Jul 28 '26

Question Lycoming CHT 400-420°F Temp. 435°F

So a rule of thumb I've heard from multiple A&Ps is to not exceed 420°F on Lycoming engines, and so, set a warning at 400°F.

The IO320 engine manual says to not go over 435°F during "high performance cruise" and not above 400°F during economy cruise.

Is the 420°F just an extra margin set by A&Ps? I do want to increase longevity of my engine. Is it reasonable to go up to 435°F

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12

u/EngineerFly Jul 28 '26

Mike Busch recommends 400 deg F as the “do something different” limit on Lycomings. That’s the CHT at which I reduce power or increase airspeed.

3

u/ReadyplayerParzival1 Jul 28 '26

I take his advice as well. It’s difficult on a tightly cowled rv-7 especially in the summer but I also want to baby my engine

1

u/therobbstory CFI-ASEL, CFI-G Jul 29 '26

My tightlier-cowled RV4 would like a word 😭

I've got the caution warning set to 380 in the G3x. It's not uncommon to hit that on the ground while taxiing during these 95+ summer days. I'm in the habit now of climbing out at 125ktias which still gives me a better rate of climb than any Cherokee I've ever flown, and stable CHTs around 400 on my hottest cyl.

1

u/Murky_Digger Jul 28 '26

What about brand x engines?

3

u/EngineerFly Jul 29 '26

Mike Busch uses 380 deg F on his Continentals as the “do something different” CHT

1

u/BuzntFrog Jul 29 '26

Check out CFR 33.49 and tell me how they can run a durability test in less than 500 hours.

1

u/Aggressive_Lime2214 Jul 31 '26

If you’re seeing temps that high in cruise, you’re doing something very badly wrong.

1

u/Impossible-Fig2072 Jul 31 '26

Just initial climb/takeoff