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What cylinder head temperatures do you see with your O-360?
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Alan Williams



Joined: 04 Dec 2005
Posts: 444
Location: Chipley, FL

PostPosted: Wed Apr 28, 2010 6:07 pm    Post subject: Reply with quote

My CHT today ran at 360F. Sparkplug gasket thermocouple in cyl #3 on a carbureted O-360.
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Greg



Joined: 18 Dec 2005
Posts: 96
Location: Columbus MS

PostPosted: Thu May 27, 2010 6:13 pm    Post subject: Reply with quote

Flew today after several weeks of trying to get little maintenance stuff done. Noticed a couple of exhaust gaskets that seemed to be leaking after a run-up that didn't quite sound right. Broke one stud off during removal, but eventually got it off. Decided to replace all the rest of the studs and gaskets since we had already started. Ended up replacing 8 spark plugs too (ouch) but they were definitely showing their age. Tried trouble-shooting the CHT, and used a heat gun to see if the 300 deg F CHT I had at idle after warmup was also what the heat gun saw, which it was. So apparently I am getting a good reading at the gauge. Went flying, and during 90 kt climbout to 4000', the CHT climbed to 455 and stopped there. Back down to 400 again at cruise (2100 rpm). Glad I've got the other stuff done, but would love to figure out this CHT. Is it possible these cylinders are just tighter than normal? Also, one suggestion was that since the temp doesn't keep climbing, there may not necessarily be a problem. Am I risking damaging cylinders with these temps?? Any other considerations or ideas? Thanks!
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Alan Williams



Joined: 04 Dec 2005
Posts: 444
Location: Chipley, FL

PostPosted: Fri May 28, 2010 6:22 pm    Post subject: Reply with quote

Do you have a sparkplug gasket thermocouple or a bayonet probe?
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Greg



Joined: 18 Dec 2005
Posts: 96
Location: Columbus MS

PostPosted: Fri May 28, 2010 7:04 pm    Post subject: Reply with quote

Hi Alan,
Bayonet probe.
Greg
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AndrewK



Joined: 09 Jun 2009
Posts: 28
Location: Dallas, TX

PostPosted: Wed Jun 09, 2010 11:25 am    Post subject: Reply with quote

Greg,

This may not exactly be relevant in your case since you have a bayonet probe but who knows.
After the last annual I started seeing high CHTs (similar to yours for climb and cruise) from my O-ring probe gauge and couldn't figure out why. Plugs looked clean, oil filter was clean, carb responded favorably to mixture inputs, engine ran smooth and oil temps were normal. After scratching my head for a while I noticed that where the lead connects to the O-ring probe appeared closer to my exhaust manifold than what I remembered. I loosened the spark plug, turned the probe so that the connection to the lead was on the opposite side of the spark plug from the exhaust manifold and took it for a test flight. Sure enough, my temps were back to normal again. I guess the lead was picking up heat from my exhaust manifold which gave me an artificially high reading on the guage.
I am not sure how the bayonet type lead looks like or where it runs from on the cylinder but if it's close to the exhaust it might just be worth taking a look at.
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Greg



Joined: 18 Dec 2005
Posts: 96
Location: Columbus MS

PostPosted: Wed Jun 09, 2010 2:07 pm    Post subject: Reply with quote

Andrew,
I'll take a look - thanks!
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dusterdan



Joined: 11 Feb 2006
Posts: 80

PostPosted: Wed Jun 09, 2010 8:40 pm    Post subject: CHT Reply with quote

Each cyl has provisions for a probe. Is the lead long enough to switch to a different cyl? Dan
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John Singer



Joined: 03 Dec 2005
Posts: 131
Location: New London, NH

PostPosted: Thu Jun 10, 2010 7:45 am    Post subject: Cylinder head temperatures Reply with quote

There is a very nifty instrument available from Northern Tool (800-533-5545) for about $40 which can easily and quickly tell you if your CHT thermocouples are OK.

The one I bought or $25.00 is no longer listed in their latest catalog (CENTECH Item 93984) The substitute is Item # 715504-1006 at $39.99.

It is good for from -67 to 482 F. It is also very useful in the kitchen. Deep frying, oven temps etc.

You point it at the hot cylinder about 5 inches distant and push a button. The temperature reading where the laser pointer is aiming appears in the instrument's window . It converts IR radiation to a temp.

To use, immediately after shutdown aim the laser pointer at the spot to be measured. (Start at the front 2 cylinders thru the cowl openings.) Compare with the planes CHT instrument.

Open the Cowl for other cylinders.You can track the cool down rate and detect any difference between instruments easily. You can check accuracy by aiming at a pot of boiling water.

John Singer
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Greg



Joined: 18 Dec 2005
Posts: 96
Location: Columbus MS

PostPosted: Fri Jun 11, 2010 7:48 pm    Post subject: Reply with quote

My mechanic had a heat gun, so we took a couple of readings for comparison with the gauge. The engine will typically reach about 300 deg F while idling for takeoff, so I let it warm up to this temp, and then we checked it with the heat gun. Unfortunately, it was reading very close to the same 300 deg F indicated on the CHT gauge Sad As the temperature rises to around 450, I suppose the gauge and/or thermocouple/line error may increase more rapidly (perhaps exponentially vs straight-line?) but the fact that it is pretty close at 300 leads me to believe the gauge indication may be fairly accurate. I still have one or two more ideas to try...thanks for the suggestions everyone!
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Greg



Joined: 18 Dec 2005
Posts: 96
Location: Columbus MS

PostPosted: Tue Jan 04, 2011 9:05 pm    Post subject: Reply with quote

I just finished installing a Elec Intl SR-8A, which allows me to check 4 CHTs and 4 EGTs - love it! What I found out, however, is that the #3 CHT (which was the single CHT I was monitoring before), is the one that is running hot, and is still showing numbers similar to before. Cylinder #4 also runs hotter than #1 and #2 (which I would assume is to be expected with less airflow in the back), but #4 does run a fair amount cooler than #3. If #3 peaks at 450 dF in the climb, #4 seems to be around 400 dF, and #1 and #2 around 350 dF. So I would guess that would eliminate timing, or fuel issues, as I would think problems in those areas would show up as problems on all 4 cylinders. (And I've double checked the timing, and made sure I'm hitting the full carburetor stop with the mixture full in). So next I'm going to try to get another opinion on the baffling (although it certainly seems just about perfect), and making sure that all the inter-cylinder fins are installed and positioned correctly. Not sure what would be next if that all looks OK. There is a good engine shop nearby, and I was thinking a boroscope would be a good thing to do, although I'm really not sure what they may actually be able to tell from that concerning the CHT. I guess as a minimum, it would be a good check on the valves/guides. I also need to get smarter on EGT readings (since I can now read all four), and how to use them to possibly help troubleshoot (e.g., lean of peak mag checks, etc.) Any other ideas out there? Thanks!
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jsh



Joined: 19 Dec 2005
Posts: 354
Location: Burnet, TX

PostPosted: Tue Jan 04, 2011 9:36 pm    Post subject: Reply with quote

see Dec 2010 issue of Sport Aviation article about how to read EGT's. Look at this recorded webinarhttp://www.savvymx.com/index.php/all-about-egtcht
and while there....view the webinar on Cylinders, it will tell you what to look for when you borescope that cylinder.
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Alan Williams



Joined: 04 Dec 2005
Posts: 444
Location: Chipley, FL

PostPosted: Wed Jan 05, 2011 6:22 pm    Post subject: Reply with quote

Is that carburated or injected? What are the EGT readings when #3 is running that hot, how much spread?
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Greg



Joined: 18 Dec 2005
Posts: 96
Location: Columbus MS

PostPosted: Wed Jan 05, 2011 8:13 pm    Post subject: Reply with quote

Here are the CHT and EGT readings from last week:
Position 1-8: CHT 1-4, then EGT 1-4:



Before takeoff, leaned 240 241 258 256 1042 1068 1066 1012

1500 MSL, full power climb 321 327 409 395 1282 1250 1414 1313

2000 MSL, full power climb 325 325 429 406 1275 1286 1398 1362



2500 MSL, 2100 rpm, full rich 313 334 388 370 1352 1325 1329 1257

2500 MSL, 2100 rpm, leaned 310 335 397 386 1465 1465 1475 1414



As I leaned, one cylinder EGT peaked at 1545.
I had to stop the climb at 2500 due to clouds. If I had continued to climb full power like the week earlier, I would have expected number 3 CHT to rise to 450, with 1 and 2 around 350, and 4 around 400.

Alan, I'm using a carburetor. Do I remember correctly, seeing that you rebuilt this carb. for Gary a while back?
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Alan Williams



Joined: 04 Dec 2005
Posts: 444
Location: Chipley, FL

PostPosted: Thu Jan 06, 2011 8:22 pm    Post subject: Reply with quote

Yes I did o/h that carb for Gary. Notice the high # three cht coincides with a high #3 EGT. Check real close for a leak in the intake for #3 at the intake port gasket, or for loose intake tube clamps, damaged hose, etc. How long has it been running hot? Was there any maintenance that preceded it starting to run hot?
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Greg



Joined: 18 Dec 2005
Posts: 96
Location: Columbus MS

PostPosted: Sat Jan 08, 2011 8:22 am    Post subject: Reply with quote

Hi Alan,
It has actually been running hot since I got the airplane from Gary about 5 years ago. But I don't usually climb much higher than 1000' anyway so I never had the power up for too long, and kinda babied the CHT that way, knowing that I was going to have to figure out what was going on at some point.
Gary had just done a top end, and thought that the CHT would maybe go down by itself as the cylinders got some time on them (Not to put words in Gary's mouth, I think that was the jist of it). The fact that it had been running cooler prior to the top end made me think it may not be a baffling problem. I saw the carb had been rebuilt around the same time, so I thought maybe a too lean fuel adjustment could be one cause. With the ability to now see all 4 cylinders, I don't think the fuel mixture is the cause, or the timing either. Is there something else done during the top end that could cause this?
I'll also take a close look at all the intake components. FWIW, I also have new spark plugs, REM 38E I think, although I'm not home to look at the logbook right now. I'm not sure if there is a 'cooler' spark plug for the O360, but I think that's the one I should be using.
jsh, thanks for the EGT info - I've been reading a lot of Mike Busch's articles and he has a lot of good engine information.
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