Low CHT with "high" EGT, is this a problem?

Flying yesterday in the DC area my CHTs ranged 300-315 while my EGTs at times topped 1400 at 75% power. And for the first time ever, one cylinder's EGT slightly topped 1400 (i.e., 1407) during takeoff with full rich and WOT. [In the summer months temps usually run around 350 and 1350, respectively.] All CHTs are close to same. EGTs usually spreads within 30 degrees. Are these numbers within "normal" for an IO-360?

Check ignition timing— may be retarded.
What is WOT fuel flow?

If the OAT is colder than your previous observations, that keeps CHT?s low and cold air is dense so your mixture will be leaner this higher EGT?s.

If the OAT is the same as your previous observations then yes something else has changed.

I think WOT at takeoff is about 13.7. I'll confirm this when I fly tomorrow or Wednesday. Is anyone alarmed about EGTs in the low 1400s? Also, fuel flow below about 10.5 at 72-75% power and ROP is where the EGTs start to climb into the low 1400s. Don't know if this is important info so just putting it out there. Thanks for your replies.

If constant speed prop? 13.7 is quite low for WOT takeoff.

schaplerrh said:

Is anyone alarmed about EGTs in the low 1400s?

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In my experience, EGTs are one of the most misunderstood pieces of engine monitor data. Absolute EGT values have almost no meaning, particularly because they are HIGHLY dependent on where the probes are located... a few millimeters can make a huge difference in reading. If any individual EGT reads dramatically higher or lower than it normally does for a particular power setting I would investigate. Otherwise, use EGT's for leaning and ignition system checks but don't chase them. Mike Busch has written about this extensively, so you might start reading there.
Hope this helps.

EGTs can rise due to mixture or timing. As most know, EGTs peak around stochiometric mixture and fall on either side (ROP or LOP) of it. Also, as timing is advanced toward optimum (well above the 25* typical setting), the EGTs will fall and CHTs will rise. Timing that is retarded from your normal setting/baseline, will show rising EGTs and lowering CHTs, relative to what you are used to seeing.

This all varies a bit with ambient. Low compression can reduce both (CHTs more so), but quite unlikely to happen equally across all cylinders.

There are far too many factors involved to compare "normal" across different planes. Some RV's can't keep CHTs below 400 and others routinely run in the low 300's.

Larry

Stuck exhaust valve?

I would also check (wobble test) on your exhaust valve for that cylinder. Before my valve completely stuck I had those symptoms. It's easier to fix now before it bends a pushrod.

Good luck!

It sounds like your timing has become more retarded (less advanced).

As the fiber/plastic cam follower block on the points inside a magneto wear, the timing slowly retards. If it has been a while since you checked mag timing, start there.

13.7 gph is way too lean for WOT take off power on a 360. Should be more like 16.5 -- 17+ depending on parallel valve or angle valve, other factors.