Has anyone ever seen anything like this? Any ideas? Thanks in advance!Josh
Strange CHT anomoly C-180
Tue Mar 13, 2018 9:26 am
Strange CHT anomoly C-180
Alright guys, I've got a weird one here for you. I have a 53' C-180 with a O-470-K. I have single probe EGT/CHT. If i pull my cabin heat during any phase of flight I get a 50 degree drop in CHT temperature. Also my CHT's are running high with the cabin heat closed. (ie. around 400 degrees in cruise 100 degrees ROP) When i open the cabin heat i get normal CHT's. ( ie. 350 degrees in cruise 100 degrees ROP) I checked all of the scat hoses for air leaks. Inspected the CHT wiring from plug to gauge and all of it seems to be in its place and sufficiently tightened. I'm baffled... (no pun intended) Has anyone ever seen anything like this? Any ideas? Thanks in advance!
Josh
Has anyone ever seen anything like this? Any ideas? Thanks in advance!Josh
Last edited by MountainWave on Tue Mar 13, 2018 3:47 pm, edited 1 time in total.
- MountainWave offline
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- Aircraft: Cessna 180 / PA 22-20
Tue Mar 13, 2018 10:15 am
Re: Strange CHT anomoly C-180
I've seen that when pulling the Carb heat on, not cabin heat.
- MauleEnvy offline
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- Aircraft: 1985 Maule M5-180C
Tue Mar 13, 2018 10:26 am
Re: Strange CHT anomoly C-180
MountainWave wrote:Alright guys, I've got a weird one here for you. I have a 53' C-180 with a O-470-K. I have single probe EGT/CHT. If i pull my cabin heat during any phase of flight I get a 50 degree drop in CHT temperature. Also my CHT's are running high with the cabin heat closed. (ie. around 400 degrees in cruise 100 degrees LOP) When i open the cabin heat i get normal CHT's. ( ie. 350 degrees in cruise 100 degrees LOP) I checked all of the scat hoses for air leaks. Inspected the CHT wiring from plug to gauge and all of it seems to be in its place and sufficiently tightened. I'm baffled... (no pun intended)
Josh
What setting is the cabin air on? Have you looked at the cabin air/heat divider valve thing on the right side of your firewall? I think there is a certain setting at which the valve can allow cold high pressure air from the top of the cowling to bypass the cylinders and come around to the low pressure (bottom) side of the engine. This is hard to explain, but easy to see if you remove your cowling and look inside that valve assembly while playing with the controls to cabin air/heat.
Even with that, it seems that it would be hard to get so much airflow through there to change CHT's 50deg.
-Asa
Tue Mar 13, 2018 10:27 am
Re: Strange CHT anomoly C-180
First, I would never recommend running ANY engine lean of peak without a full multi probe engine monitor. That goes double for a carbureted engine.
Second: 100 lean of peak? Really? Who suggested that was a good idea? I’m not sure you could get there, assuming your one probe and instrument are accurate.
Or are you a troll?
MTV
Second: 100 lean of peak? Really? Who suggested that was a good idea? I’m not sure you could get there, assuming your one probe and instrument are accurate.
Or are you a troll?
MTV
Tue Mar 13, 2018 10:49 am
Re: Strange CHT anomoly C-180
mtv wrote:First, I would never recommend running ANY engine lean of peak without a full multi probe engine monitor. That goes double for a carbureted engine.
Second: 100 lean of peak? Really? Who suggested that was a good idea? I’m not sure you could get there, assuming your one probe and instrument are accurate.
Or are you a troll?
MTV
Sorry about that. That was a typo. I run 100 degrees RICH OF PEAK. That's what happens when you get on the computer and start your day before you break out the coffee. Good catch!
- MountainWave offline
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- Location: Wasilla / Pueblo
- Aircraft: Cessna 180 / PA 22-20
Tue Mar 13, 2018 10:52 am
Re: Strange CHT anomoly C-180
Do you still have the dual exhaust system,
or did you convert to single exhaust when you went to the K engine?
FWIW my 53 has a K, but still has the dual exhaust (converted to 4 bolt flanges).
Which cyl is your CHT probe on?
C180 TCDS #5A6 note 4 says it should be on cylinder #2 through s/n 18051445, which covers 1953 180 through 1964 180G.
That's on the LH side of the engine.
With the dual exhaust system the LH bank of cylinders ought to be supplying carb heat,
cabin heat is supplied by the RH bank.
Also, CHT's will read differently depending on whether you have a bayonet probe,
or a spark-plug-gasket type probe.
See engine TCDS #E-273, note 1.
Redline with a gasket type probe is 525,
with a bayonet type probe it's 460.
So calculate where in the operating range your in-flight CHT is accordingly.
or did you convert to single exhaust when you went to the K engine?
FWIW my 53 has a K, but still has the dual exhaust (converted to 4 bolt flanges).
Which cyl is your CHT probe on?
C180 TCDS #5A6 note 4 says it should be on cylinder #2 through s/n 18051445, which covers 1953 180 through 1964 180G.
That's on the LH side of the engine.
With the dual exhaust system the LH bank of cylinders ought to be supplying carb heat,
cabin heat is supplied by the RH bank.
Also, CHT's will read differently depending on whether you have a bayonet probe,
or a spark-plug-gasket type probe.
See engine TCDS #E-273, note 1.
Redline with a gasket type probe is 525,
with a bayonet type probe it's 460.
So calculate where in the operating range your in-flight CHT is accordingly.
Cessna Skywagon -- accept no substitute!
Tue Mar 13, 2018 11:03 am
Re: Strange CHT anomoly C-180
Maybe messy cable routing and older probe is picking up heat transferring from the exhaust or muff and the exhaust is cooling with cabin heat open in cooler temps, bit of a stretch though?
Haven't had any luck at all with accurate readings on those older needle gauges here for CHT/EGT's. A half decent multi-channel with ungrounded probes for accurate EGT's you can lean to and CHT's you can monitor closely on each cylinder is a great investment and piece of mind in my opinion.
Haven't had any luck at all with accurate readings on those older needle gauges here for CHT/EGT's. A half decent multi-channel with ungrounded probes for accurate EGT's you can lean to and CHT's you can monitor closely on each cylinder is a great investment and piece of mind in my opinion.
Tue Mar 13, 2018 3:31 pm
Re: Strange CHT anomoly C-180
hotrod180 wrote:Do you still have the dual exhaust system,
or did you convert to single exhaust when you went to the K engine?
FWIW my 53 has a K, but still has the dual exhaust (converted to 4 bolt flanges).
Which cyl is your CHT probe on?
C180 TCDS #5A6 note 4 says it should be on cylinder #2 through s/n 18051445, which covers 1953 180 through 1964 180G.
That's on the LH side of the engine.
With the dual exhaust system the LH bank of cylinders ought to be supplying carb heat,
cabin heat is supplied by the RH bank.
Also, CHT's will read differently depending on whether you have a bayonet probe,
or a spark-plug-gasket type probe.
See engine TCDS #E-273, note 1.
Redline with a gasket type probe is 525,
with a bayonet type probe it's 460.,
So calculate where in the operating range your in-flight CHT is accordingly.
hotrod180,
I have the same setup that you do. When we converted from the J to the K we went with a new knisley dual exhaust with the 4 bolt flange. The left and right banks are supplying air as you have stated above. Because of that it seems even more strange the cabin heat is causing any fluctuation in the CHT.
As far as the CHT I have the gasket type probe on cylinder #2. But i did not realize about the note on the TCDS about the difference in CHT redlines. Looks like I will have to do some research on that. I guess the temps may not be quite as high as i think they are. Thanks for pointing me in the right direction on that.
Josh
- MountainWave offline
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- Joined: Thu Jun 12, 2014 3:15 pm
- Location: Wasilla / Pueblo
- Aircraft: Cessna 180 / PA 22-20
Tue Mar 13, 2018 3:34 pm
Re: Strange CHT anomoly C-180
asa wrote:MountainWave wrote:Alright guys, I've got a weird one here for you. I have a 53' C-180 with a O-470-K. I have single probe EGT/CHT. If i pull my cabin heat during any phase of flight I get a 50 degree drop in CHT temperature. Also my CHT's are running high with the cabin heat closed. (ie. around 400 degrees in cruise 100 degrees LOP) When i open the cabin heat i get normal CHT's. ( ie. 350 degrees in cruise 100 degrees LOP) I checked all of the scat hoses for air leaks. Inspected the CHT wiring from plug to gauge and all of it seems to be in its place and sufficiently tightened. I'm baffled... (no pun intended)
Josh
What setting is the cabin air on? Have you looked at the cabin air/heat divider valve thing on the right side of your firewall? I think there is a certain setting at which the valve can allow cold high pressure air from the top of the cowling to bypass the cylinders and come around to the low pressure (bottom) side of the engine. This is hard to explain, but easy to see if you remove your cowling and look inside that valve assembly while playing with the controls to cabin air/heat.
Even with that, it seems that it would be hard to get so much airflow through there to change CHT's 50deg.
-Asa
I will most certainly take a look at this. Thanks!
Josh
- MountainWave offline
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- Joined: Thu Jun 12, 2014 3:15 pm
- Location: Wasilla / Pueblo
- Aircraft: Cessna 180 / PA 22-20
Wed Mar 14, 2018 8:08 pm
Re: Strange CHT anomoly C-180
Sounds like someone has plumbed your cabin heat controller into the carb heat... Stranger things have happened.
Otherwise a cowl leak sounds plausible, but I can't imagine how that would happen? Then again, I don't know the 180 cabin heat setup.
Otherwise a cowl leak sounds plausible, but I can't imagine how that would happen? Then again, I don't know the 180 cabin heat setup.
Thu Mar 15, 2018 4:29 am
Re: Strange CHT anomoly C-180
I would say you should think about stopping using the phrase CHTs. What you have is a single probe and in reality have no idea what the other 5 cylinders are doing. My opinion is even that one probe is highly suspect. You are chasing a shadow.
My two cents,
gunny
My two cents,
gunny
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