Unusually High CHT Continental IO-360
Thread Starter
Unusually High CHT Continental IO-360
G'day All,
Sorry about a pretty tech-simple question (probably a broken gauge) but a little C172XP I've been flying seems to have unusually high CHT indications. It will pretty much get to 400 degrees and stay there (lowest it will get is 380), just wondering if this is a known issue on 172XP airframes, or if it is just a faulty gauge.
Cheers,
Steve
Sorry about a pretty tech-simple question (probably a broken gauge) but a little C172XP I've been flying seems to have unusually high CHT indications. It will pretty much get to 400 degrees and stay there (lowest it will get is 380), just wondering if this is a known issue on 172XP airframes, or if it is just a faulty gauge.
Cheers,
Steve
Many factors; and you don't mention when you first notice this; and you don't mention if this is pre-leaning or after leaning the fuel flow..
There is mixed thought on what is normal; but treating 400 as a maximum and 380 as normal would be OK.
The most important item to check on a Continetal IO-360 is the Fuel Flow at takeoff power. Check the cockpit placards and/or POH for the MINIMUM fuel flow required at takeoff power. This is very important as correct the fuel flow at the 'top' end setting determines the fuel flow before leaning in the mid range.
If the fuel flow at takeoff power is not correctly adjusted then your LAME can make minor adjustments, but checking the 'unmetered' flow/pressure requires gauges to be attached for ground checks.
The same applies to all the Continental injected engines.
There is mixed thought on what is normal; but treating 400 as a maximum and 380 as normal would be OK.
The most important item to check on a Continetal IO-360 is the Fuel Flow at takeoff power. Check the cockpit placards and/or POH for the MINIMUM fuel flow required at takeoff power. This is very important as correct the fuel flow at the 'top' end setting determines the fuel flow before leaning in the mid range.
If the fuel flow at takeoff power is not correctly adjusted then your LAME can make minor adjustments, but checking the 'unmetered' flow/pressure requires gauges to be attached for ground checks.
The same applies to all the Continental injected engines.
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Thread Starter
Cheers Petro!
Might be worth saying it is at all mixture settings, I've flown a few 172XPs, and this seems to be the only one doing it, seems to have a semi-standard takeoff fuel flow aswell
Might be worth saying it is at all mixture settings, I've flown a few 172XPs, and this seems to be the only one doing it, seems to have a semi-standard takeoff fuel flow aswell
M1M,
Dont take this the wrong way ..
There is no such thing as semi standard fuel flow; its either set correctly or incorrectly. Very important for Continental engines.
Dont take this the wrong way ..
There is no such thing as semi standard fuel flow; its either set correctly or incorrectly. Very important for Continental engines.
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Thread Starter
Nah, will never take valid info in the wrong way, I think what I meant to say is they were quite similar between each aircraft (de-rated 172xp)
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I do not know the answer, but it would be worth your while sending your contact details to David Brown of Advanced Pilot Seminars. I have done their course, it was brilliant. And if anyone in Australia can help you it is Andrew and David.
Probably takeoff fuel flow, but if it is still high when LOP, then magneto timing. From what I learned this is a very common cause for this kind of description.
Email him at davidbrown 'at' advancedpilot.com and I did that so he does not get so much spam attraction.
Probably takeoff fuel flow, but if it is still high when LOP, then magneto timing. From what I learned this is a very common cause for this kind of description.
Email him at davidbrown 'at' advancedpilot.com and I did that so he does not get so much spam attraction.
CHT anomalies can be anything from simple timing issues to baffling, to expensive crankshaft issues. I remember the PA-31 crankshaft issues could be detected by increasing CHTs when everything else seemed normal before they let go. Anything non normal and you should get help from an engineer as abnormally high CHT can indicate some bad things, if its just a gauge, replace it, you don't want faulty indications to start with.
Check whether the correct CHT pick up is installed, there are bayonet and a spark plug type fitting for CHT, had a spark plug fitting on an RV-6 I was test flying and CHT was very high, should have had a bayonet, that fixed the problem.
The top end of CHT green band in c172a (o300c) is 215degC, which is 420degF.
The red line is 500degF (260degC).
The aluminium melts at 660degC, meaning it loses half of its strength at 300degC. However it substantially gets weaker with the temperature and it is too late when it reaches the red line (500F). I suggest don't go above end of green (420F).
Your 380F-400F sounds right to me.
The red line is 500degF (260degC).
The aluminium melts at 660degC, meaning it loses half of its strength at 300degC. However it substantially gets weaker with the temperature and it is too late when it reaches the red line (500F). I suggest don't go above end of green (420F).
Your 380F-400F sounds right to me.
It sounds like it’s time to take the cowl off and take a good look at your baffles and baffle seals. I’m not sure if a wiring issue like a corroded ground can cause this but it’s worth checking when the cowl comes off.
