1962 C182E Continental O-470R Elevated CHT Cylinder #1
JPI EDM 930 Engine Data
Inter-cylinder baffle engine case gap cylinders 1,3 (large gap)
Inter-cylinder baffle engine case gap cylinders 2,4 (small gap)
Hello All. First post. I look forward to learning from the collective forum brain trust. I've tried to be as complete as possible. Please forgive me if you believe I've omitted important detail. Let me know and I will add anything missing.
The attached graph displays EGT(left axis) in upper half and CHT(right axis 1) in lower half. Blue data is fuel flow(right axis 2). Data is collected with JPI EDM 930. Altitude was 7000 feet. Cylinder #1 typically runs 40-50 degrees hotter in cruise than the others (shown in red in approximate middle of graph) and the odd cylinders in general run hotter than the even cylinders. Graphic display indicates the usual wide range of CHT's, however CHT 1 is starkly separated from the group. EGT 1 is well grouped with others. We have replaced baffle seals, have tweaked fuel flow and mixture, and A&P I/A has checked for induction leaks using a block off plate and air pressure all to no avail. This was done while carb was out for overhaul. I adjust mixture to keep cylinder 1 below 380 degrees in cruise as well as in warmer weather lower nose in climb out as required for cooling. As you can see CHT 1 requires I maintain about 12.7-13.2 gph in cruise to keep temperature at 380 or less. Savvy Aviation suggested GAMI lean test and induction leak test and suggested we check for induction leak based on results. A follow up from them stated the CHT temperature profile is normal.
In going further down the rabbit hole, I was recently inspecting the inter-cylinder baffles and noticed there is an approximate 1/2-3/4 inch gap between the inter-cylinder baffle between cylinders 1 and 3 and the engine case(first pic). It seems like a fairly large gap through which quite a bit of cooling air could be escaping and thus not forced through cylinder head cooling fins. The remainder of inter-cylinder baffles have an engine case gap no greater than approximately 3/16 inch(or less, second pic)
Thoughts and questions:
1) Is this CHT profile normal? If not:
2) Could the gap between the inter-cylinder baffle at cylinders 1 and 3 and the engine case be responsible for the above
cylinder head temperature profile?
3) What is the proper gap between the inter-cylinder baffle at cylinders 1 and 3 and the engine case for this particular
aircraft and engine?
4) Have we overlooked something?
5) The plan is to inspect the inter-cylinder baffle at 1,3 and if possible close the gap at next oil change.
Finally, my persistence in this pursuit stems from the belief if CHT 1 were to be reined in closer in temperature to the
others, mixture could safely be further leaned. Thoughts?
Brian
Comments
Hi Brian
The 0470 series is notorious for lousy fuel distribution. Before you get too carried away on a rabbit hole if you're really interested in playing with it would be to swap the probe with another cylinder and make sure you don't have a probe that's a little bit skewed. Your temperatures are certainly not outside normal operating parameters so I wouldn't get too concerned about it. You don't mention the hours on the engine but noting that you got different cylinders on it I suspect it's a high time engine?
Make sure the cylinder baffles are in the correct locations that seems a little odd to have that gap. It's possible the inter cylinder baffles might be in the wrong spot.
Can certainly fabricate a little extra baffle plate and try that.
CHT is a functional indicator of mechanical efficiency. Which means good compression no blow by excellent valve dynamics and of course good baffling. As well as perfect lifters. Unless you're pushing in the 450 range I would say you're pretty normal. Too . actually all your other cylinders seem awful low. But you're running some pretty big fuel flow.
Not to mention that unless somebody has changed it your cabin heat supply is taken right above cylinder number one , so in essence number one is kind of an orphan for air supply. So making sure your top cowling baffling is top notch will help to.
Carl
IA 47yr A&P DAL A/C Inspector 172n
Hi Carl, Thanks for your insight. FYI, Engine time is 880 tach hours presently. You are correct, cylinder #1 was replaced at around the 500 hour mark if I recall correctly. I purchased the aircraft with 850 tach hours and I'm presently trying trying to iron out some of the details. I further thought given Cyl #1 is a replacement, the baffle could be out of place and/or the temp probe could have been affected in some way. As you suggest, we plan to ensure baffle is properly placed and/or fabricate a little extra baffle.
As you mention, I'm "running some pretty big fuel flow" and the other "cylinders seem awful low" (in temperature). I wholeheartedly agree and that is what's driving the deep dive here. Having to keep the fuel flow relatively high for one cylinder is a little frustrating. If additional baffle closing the air gap doesn't solve the problem, we'll try swapping the probes to see if there is a probe issue. I did speak with a very informative JPI rep over the phone who informed me the probes generally register lower temp or no temp when failing however, I'm willing to try whatever it takes to ensure there is nothing else to be done.
The cabin heat supply is in the factory location above cylinder 1. The baffle seals were recently replaced and appear to be sealing well all around. I haven't considered it until you mentioned, but perhaps we could try a test flight with heat supply blocked off to determine effect on CHT profile. The heat is certainly not needed in Louisiana now!
I will report back if any of our efforts appear to be fruitful.
Brian
Sounded good Brian see what you come up with. And keep in mind being a carbureted engine you're limited by your first cylinder that either hits the EgT limit or maxes out on CHT which doesn't seem to be a problem this is kind of an issue we have when we started getting highly accurate instruments. For 60 years nobody knew any of the stuff was going on and I was constantly fielding questions from customers who said I've got a mag drop of 10 RPM is that okay? Before you couldn't even tell. It's conceivable your carburetor could be running a little bit on the Rich side. A good indicator would be how far back we have to pull the red knob in order to get a good peak. 380 on CHT is nothing to worry about my 172n with the H2AD regularly runs between 350 and 380 Cht.
If you want to play rabbit hole do a hot compression on cylinder number one and also chk the compression at the low end. See how much blow by you got.
Carl
IA 47yr A&P DAL A/C Inspector 172n