datorres88
Daniel Torres
- Joined
- Feb 15, 2015
- Messages
- 1,296
- Reaction score
- 696
OK, so I have had a few posts here and there searching for the cause of high #3 CHT on climb out. Well, a few months ago I did a flight where I climbed to 7000 and did a level flight full throttle test with a mixture sweep. This can be seen between 00:26 and 00:28 here: https://www.savvyanalysis.com/flight/1191951/dc8f2972-9f86-48e7-a1c7-b29d6e198ebc.
What was revealing about this test is that the problem was not related to climb, rather it was related to full throttle operation. It appears that #3 (and to a lessor extent #4) are running too lean at FT and when mixture is leaned, these EGT stay higher until the other EGT climb to that level and then they all move together. OK, fine, but I was still stumped.
As some of you may recall, I've tried just about everything to solve a high CHT problem including baffles, induction issues, etc. I even disconnected my #3 primer line to isolate that. Still no solution.
Then, after reading an older article by Walter Atkinson where he recommends running at FT but then slightly pulling the throttle off the stop to slightly cock the butterfly valve to generate turbulence in the induction system, I decided to give that a try on climb. So today I did a flight and at 300 AGL, I pulled the throttle off the stop as far as I could before seeing any drop in MAP. Eureka!!! All EGT's came in line and #3 CHT stopped climbing. Throughout the flight all numbers seemed to be in line. The flight can be seen here:
https://www.savvyanalysis.com/flight/1272803/37b52c69-a6f9-4673-9f4f-6644a310890e
You will see how #3 EGT is higher than the others for a short period, then you see it come right back down to join the others. This is where I pulled the throttle back. And interestingly enough, %HP actually went up when I did this.
So I am now on the theory that the induction system as a fundamental design flaw and that prolonged operation with the throttle at the full stop should be avoided. There appears to be no power loss penalty by slightly pulling back the throttle.
I recall others on this forum indicating that they have similar traces to the ones I have shown, so I hope that this might be helpful to others who are having the same high #3 CHT issues.
What was revealing about this test is that the problem was not related to climb, rather it was related to full throttle operation. It appears that #3 (and to a lessor extent #4) are running too lean at FT and when mixture is leaned, these EGT stay higher until the other EGT climb to that level and then they all move together. OK, fine, but I was still stumped.
As some of you may recall, I've tried just about everything to solve a high CHT problem including baffles, induction issues, etc. I even disconnected my #3 primer line to isolate that. Still no solution.
Then, after reading an older article by Walter Atkinson where he recommends running at FT but then slightly pulling the throttle off the stop to slightly cock the butterfly valve to generate turbulence in the induction system, I decided to give that a try on climb. So today I did a flight and at 300 AGL, I pulled the throttle off the stop as far as I could before seeing any drop in MAP. Eureka!!! All EGT's came in line and #3 CHT stopped climbing. Throughout the flight all numbers seemed to be in line. The flight can be seen here:
https://www.savvyanalysis.com/flight/1272803/37b52c69-a6f9-4673-9f4f-6644a310890e
You will see how #3 EGT is higher than the others for a short period, then you see it come right back down to join the others. This is where I pulled the throttle back. And interestingly enough, %HP actually went up when I did this.
So I am now on the theory that the induction system as a fundamental design flaw and that prolonged operation with the throttle at the full stop should be avoided. There appears to be no power loss penalty by slightly pulling back the throttle.
I recall others on this forum indicating that they have similar traces to the ones I have shown, so I hope that this might be helpful to others who are having the same high #3 CHT issues.
