Cylinder Head Temps

[pabrouss]

I'm a relatively new pilot and DA40 owner and this is my first post to this forum.

I've noticed recently that my #1 cyliner head temp is difficult to keep below 390 at low altitudes. I have to richen the mixture to 11 or 12 gph to bring the temp below 380. The other 3 cylinder head temps are all 375 or below at 10 gph. I usually fly at 10 gph to get max true airspeed of 145. I've had a mechanic look at it and the timing was adjusted from 25 tap dead center to 23. This has done nothing to alleviate the issue.

Any ideas? ALL are welcome.

[Gnomad]

Welcome to the forum!

Not an expert by any means, others might have more opinions, but my first thought is that your #1 sensor is off. I have been seeing something similar for the entire time I've owned my 40. #2 ALWAYS reads about 15 degrees cooler than the others. Also, my oil temp ALWAYS reads a bit cooler than what would be expected.

Or maybe it's something mechanical, but I'd suspect the sensor first.

[pabrouss]

Welcome to the forum!

Not an expert by any means, others might have more opinions, but my first thought is that your #1 sensor is off. I have been seeing something similar for the entire time I've owned my 40. #2 ALWAYS reads about 15 degrees cooler than the others. Also, my oil temp ALWAYS reads a bit cooler than what would be expected.

Or maybe it's something mechanical, but I'd suspect the sensor first.

Thanks for the welcome and the idea! I hadn't thought about the sensor. By the way, it's a 2007 DA40 XL. The G1000 is great and shows the individual temps. Otherwise I wouldn't know anything about it. Maybe that would be better................

[Tim H]

My oil temp always ran about 30 deg cooler than I thought it should. When the engine is cold (sat over night without running) turn the master on and turn the G1000 to the ENGINE page. Check the oil temp, EGTs and CHTs. You will be amazed at how close they are. After I changed my oil temp sensor, the oil temp fell in line and all the temps were within 1 deg of each other.

[Rich]

This probably isn't the issue for you, but my 2002 DA40 had exactly this symptom when I first got it. The fix was the updated right side baffle inlet, which not only brought it more in line with the other cylinders, but cooled them all down.

Another possibility would be a problem with the cooling baffle seals, allowing air leaks from the upper cooling plenum area. This can result in all cylinders running hotter than necessary and affect the balance among them.

Keep in mind that the cylinders will have some variation in temperature. 20 degF wouldn't be any big deal in itself.

[pabrouss]

My oil temp always ran about 30 deg cooler than I thought it should. When the engine is cold (sat over night without running) turn the master on and turn the G1000 to the ENGINE page. Check the oil temp, EGTs and CHTs. You will be amazed at how close they are. After I changed my oil temp sensor, the oil temp fell in line and all the temps were within 1 deg of each other.

Thanks, I'll try this.

[pabrouss]

This probably isn't the issue for you, but my 2002 DA40 had exactly this symptom when I first got it. The fix was the updated right side baffle inlet, which not only brought it more in line with the other cylinders, but cooled them all down.

Another possibility would be a problem with the cooling baffle seals, allowing air leaks from the upper cooling plenum area. This can result in all cylinders running hotter than necessary and affect the balance among them.

Keep in mind that the cylinders will have some variation in temperature. 20 degF wouldn't be any big deal in itself.

What is your opinion of a normal range for CHTs? I've always been told to keep them under 380 and never to hit 400.

[Rick]

What is your opinion of a normal range for CHTs? I've always been told to keep them under 380 and never to hit 400.

Pat, those are the same parameters I use - under 380, and 400 as a "never exceed" for me.

You could swap the #1 & #3 CHT sensors and see if the increased temperature moves with the sensor or stays with the #1 cyl. If it stays, I would next suspect the cooling baffles. Also, as Tim mentioned, check the exact values of all 4 CHTs, EGTs, plus the oil temp and OAT sensor after the plane has been sitting a long time and the outside air temperature has been stable for a few hours - they should all read within a degree or two of each other. You can check this in your log files if you have data from several trips to look at.

If the temperature difference is real, it is also possible that GAMI injectors would help balance the fuel flow and hence the cooling, but I wouldn't go there until you have checked the other things first, and then performed a "GAMI test".

Good luck!

[Rich]

Another thing - fuel injectors can get partially clogged. There's a "bottle test" one can do to see if there's an imbalance caused by this effect.

[pabrouss]

What is your opinion of a normal range for CHTs? I've always been told to keep them under 380 and never to hit 400.

Pat, those are the same parameters I use - under 380, and 400 as a "never exceed" for me.

You could swap the #1 & #3 CHT sensors and see if the increased temperature moves with the sensor or stays with the #1 cyl. If it stays, I would next suspect the cooling baffles. Also, as Tim mentioned, check the exact values of all 4 CHTs, EGTs, plus the oil temp and OAT sensor after the plane has been sitting a long time and the outside air temperature has been stable for a few hours - they should all read within a degree or two of each other. You can check this in your log files if you have data from several trips to look at.

If the temperature difference is real, it is also possible that GAMI injectors would help balance the fuel flow and hence the cooling, but I wouldn't go there until you have checked the other things first, and then performed a "GAMI test".

Good luck!

Most helpful! This sounds like a plan.