New engine Cylinder Temp Question

I have a factory new IO-390 and have completed 3 short (5 min) ground runs one of which was a full power run (snip below). On all 3 runs #4 EGT & CHT are noticeably the coolest but nothing too crazy. My question revolves around the how fast the EGT dropped around the 3:45 mark as compared to the other cylinders. Is this indicative of a something that should be investigated further at this point, monitored closely, nothing to worry about, etc...

*The airplane was fully cowled during the test run below facing into ~15kt breeze.

Interested in getting a take on the variation in #4 EGT also, considering the other cylinders shared a very similar pattern

Fly

I understand concern $$$ , time, effort, order delays etc. I’d say fly your plane before trying to learn with it on the ground. Lots of air flow, pressures, baffling etc can play a role. Honestly, I’ve been informed by those I respect , that EGT is good for trending, leaning and diagnosticsnin the air/flying. WOT to me on the ground for 5 minutes does not sound like something I would do. Breaking in likely completed at the factory, if not, be careful with short wot runs of short duration. I watched a guy chase a oil leak on the ground after a overhaul..... glazed two cylinders, had to pull jugs and bore YMMV , I’m no A&P.

CHT low across the board. EGT erratic, low at part power, higher than the rest at high power.

I'll venture one bad plug, plug wire, connector etc, or simply fouled. The high EGT under power indicates late peak pressure.

Is the mag check normal?

BH1166 said:

WOT to me on the ground for 5 minutes does not sound like something I would do. Breaking in likely completed at the factory, if not, be careful with short wot runs of short duration. .

Click to expand...

WOT throttle was for a duration of probably less than 5 seconds and was part of the requirements of testing the stops on the prop prior to first flight.

DanH said:

CHT low across the board. EGT erratic, low at part power, higher than the rest at high power.

I'll venture one bad plug, plug wire, connector etc, or simply fouled. The high EGT under power indicates late peak pressure.

Is the mag check normal?

Click to expand...

Dan - I've limited the ground runs mentioned to <250 CHT or five minutes which ever is first. Mag checks were fine, #4 plug was pretty oily, differential was 76/80.

If the granularity of the data capture was not available I would not have noticed.

The other short runs showed a similar lag pattern on #4 as well, but the engine runs & idles smooth and exhibits nothing that be noticed if the detailed data were not available.