What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

High EGT on takeoff

Ed_Wischmeyer

Ed_Wischmeyer

Well Known Member
So the RV-9A is just out of the shop after condition inspection. First flight was fine.

On the second flight, I goofed on the mag check and momentarily turned off both mags. No backfire.

The engine momentarily ran rough on takeoff, then smoothed out after a second or two. If I'd been thinking more clearly, I would have aborted, but since it cleared up, I kept going. Recorded data showed a momentary decrease in cylinder 2 EGT, so maybe that was a stuck valve. (O-320, carbureted).

Then the EGTs got high, 1480° on the highest, 100° more than on previous flights. I told tower I needed to stay in the pattern, and landed no problem. Recorded data showed that cylinders 3 and 4 had the highest EGTs with power up for a minute before I pulled power back for pattern speed. When the power came back, they swapped temperatures, as did cylinders 1 and 2.

However, the EGTs stayed elevated another minute, then dropped quickly. I'm wondering if the vernier mixture was pushed in all the way, but the vernier kept it from being full rich. But that doesn't explain the the EGTs stayed high after power reduction before dropping quickly.

Running low on ideas here. Maybe the engine instrument interface was having a bad day?
 
EGT

Ed_Wischmeyer said:
So the RV-9A is just out of the shop after condition inspection. First flight was fine.

On the second flight, I goofed on the mag check and momentarily turned off both mags. No backfire.

The engine momentarily ran rough on takeoff, then smoothed out after a second or two. If I'd been thinking more clearly, I would have aborted, but since it cleared up, I kept going. Recorded data showed a momentary decrease in cylinder 2 EGT, so maybe that was a stuck valve. (O-320, carbureted).

Then the EGTs got high, 1480° on the highest, 100° more than on previous flights. I told tower I needed to stay in the pattern, and landed no problem. Recorded data showed that cylinders 3 and 4 had the highest EGTs with power up for a minute before I pulled power back for pattern speed. When the power came back, they swapped temperatures, as did cylinders 1 and 2.

However, the EGTs stayed elevated another minute, then dropped quickly. I'm wondering if the vernier mixture was pushed in all the way, but the vernier kept it from being full rich. But that doesn't explain the the EGTs stayed high after power reduction before dropping quickly.

Running low on ideas here. Maybe the engine instrument interface was having a bad day?
Click to expand...

If only one mag was firing, the EGTs would have been high. Are you sure you got the mag switch back to BOTH mags?
Ed
 
edclee said:
If only one mag was firing, the EGTs would have been high. Are you sure you got the mag switch back to BOTH mags?
Ed
Click to expand...

Possible, but I probably would have noticed it when I did the after landing mag check. And there's still the question of why the EGTs stayed high after power reduction.

Thanks, though. I might try that on the next flight, when things are working as expected.
 
EGT’s will stay higher than expected anytime you run on one mag. In cruise flight one EGT jumping up 100 to 150 degrees is a classic sign you dropped a plug in that cylinder. Everything you posted sounds like running on one mag.
 
The two most typical causes of elevated EGT is running near peak EGT (i.e. lean of best power) or retarded ignition timing . In my experience, dropping one mag will cause all 4 EGTs to rise about 150-200* above that with both mags. That can vary a bit based upon where your mixture was. Given the temp swap from 3/4 to 1/2, I am inclined to speculate that mixture was the culprit. When running above 2000 RPM, it is pretty hard to miss the change in engine noise when one of the mags either starts or stops working. Why I do an inflight mag check in cruise, it is very difficult not to notice the change in engine noise. No indication of carb vs FI, but water and air in the lines can cause short term issues like this also, as they act to lean the mixture. The roughness on TO makes me think water, especially if you had recently topped off.
 
Last edited:
You must log in or register to reply here.
Back
Top