Lycoming CHT's

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Glasair

Filing Flight Plan
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ermed5
Howdy all. Glasair driver here... Lycoming IO-360 B1A. 800 since O/H. Bendix mag on the left, Lightspeed EI (Hall module) on the right. I have an interesting dilemma that is confusing numerous mechanics. For many years, my engine ran fine... EGT's around the 1370/1380's, and CHT's in the 380's in all 4 cylinders. All consistent. I run about 40 degrees ROP, for smoothness and engine longevity. But over the last 4-5 years, both EGT's and CHT's have started to climb. EGT 1400's/high 1300's, and now all CHT's in the low 400's. Recently had a scare, where #4 (then #1) CHT's suddenly climbed to 500! Yikes. Reduce power, then back to airport. JPI EDM700 went bonkers. Turns out, it was a "MUGS board" that needed to be replaced. But with 15 years of uninterrupted service out of it, who's complaining! However, my CHT's are still high... 405-420's all across. EGT's are higher (1390/low 1400's). My main concern is toasting pistons with these high CHT's. Everyone seems baffled. We put in an O/H Precision fuel servo (previous Bendix was last checked in 2002!). Babyfood jar test showed same fuel levels in all. Overhauled the divider. Cleaned all injectors. Timing is spot on (25 BTDC). Intake testing showed no leaks, but we replaced all 4 hoses and gaskets, as the originals were getting pretty dry and cracked. Exhaust had some leaks in #1 and 2 (flanges), so repairing those now. No evidence of baffling issues.

My mechanic is suggesting we check the valves/possibly ream them/check for wobble. Then if that doesnt work, retard the timing to maybe +/- 23 degrees BTDC or so (power loss should be minimal to not noticeable, based on my limited mechanical skills).

Suggestions? Thoughts? Comments? I don't feel comfortable with these CHT's.

Many thanks!!!
 
Glasair said:
I don't feel comfortable with these CHT's.
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Have you verfied your current temp readings are accurate? Given your history of stable readings then to have all readings increase collectively, then have an indication failure.... Usually an engine will start to fail by cylinder vs a collective effort in most cases. Perhaps rule out that part first.
 
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Dumb question, but have you checked and cleaned the plugs for lead clinkers? I know when I get one CHT's go up considerably.
 
Given that EGTs and CHTs are both up? I’d think EGTs drive the increase of CHT, and that’s mixture related. Something’s changing in the fuel delivery.
 
Stewartb said:
Given that EGTs and CHTs are both up? I’d think EGTs drive the increase of CHT, and that’s mixture related. Something’s changing in the fuel delivery.
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Thanks, folks, for the comments.

Mixture related.... as far as I know, this was checked. Fuel flow was checked. New fuel servo installed.

Plugs all in good shape. Odd, tho, that all cylinders would increase over time, rather than 1 or 2 fouled plugs AND plug changes over time.

Temp readings. JPI was emailed, asking again about longevity of wiring harnesses and probes. From what I read, they last a long time. They also suggest no maintainance to the probes themselves (like cleaning off any soot). I hesitate to spend $850 on new probes and wiring, at least for now. Again, odd that all 4 cylinder temps are slowly going up.
 
Could your leaking exhaust flanges have been blowing exhaust on the temp sensors? Also, 40 degrees ROP seems a bit close to a bad spot, detonation?
 
Generally 40 ROP is about the worst spot you can run for engine longevity. If you are also running high power settings (above 65% in cruise) I would suspect that what you are witnessing is light to medium detonation in your cylinders. Depending on how much power you run, it is advisable to run either LOP (or at least at peak EGT in a Lycoming) or considerably richer, like 100-125 ROP. The reason why it progressively getting worse might be the simple fact that the engine is wearing out.
 
My IO-320 in my Glasair used to have one high EGT. I usually lean to 100 degrees rich or about 8.5 gal / hr. It got to the point where I couldn’t lean to anything under 10 gal / hr or the EGT would go over 1450 degrees.

This will sound silly but I tried MMO in the fuel and the first flight after, the temp went down to normal. I know, there’s no data that supports MMO doing anything for cleaning fuel injectors, valves, spark plugs etc., but it worked for me. Either that or it just happen to clear itself on that flight.
 
Velocity173 said:
My IO-320 in my Glasair used to have one high EGT. I usually lean to 100 degrees rich or about 8.5 gal / hr. It got to the point where I couldn’t lean to anything under 10 gal / hr or the EGT would go over 1450 degrees.

This will sound silly but I tried MMO in the fuel and the first flight after, the temp went down to normal. I know, there’s no data that supports MMO doing anything for cleaning fuel injectors, valves, spark plugs etc., but it worked for me. Either that or it just happen to clear itself on that flight.
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I would run 40-50 degrees ROP over the years, and FF would be about 10.1-10.3 GPH. At one point, I was "chastised" because 10gph in cruise in an IO-360 was possibly
using too much fuel. Engine smoothness was found at that spot... otherwise, anything less caused rough running/vibration. A borescope 10 days ago showed no unusual changes.

Maybe I HAVE been running this engine too lean over the years? An additional 0.5gph wouldn't hurt at the fuel pump, but then that would consume about 10.8-11gph, which I thought would be unusual for an IO-360 180hp Lycoming.

Never tried MMO, but always thought it wasnt recommended.
 
Bell206 said:
Have you verfied your current temp readings are accurate? Given your history of stable readings then to have all readings increase collectively, then have an indication failure.... Usually an engine will start to fail by cylinder vs a collective effort in most cases. Perhaps rule out that part first.
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Bell's comment above and the bad JPI board makes me think there is still something amiss with the JPI system--probes or receiving unit. Since all probes are affected look at areas of commonality.

Would muffler blockage raise or lower CHTs/EGTs?
 
Are you using GAMIjectors? If not, it might be a worthwhile investment. It would definitely allow for smoothness at leaner mixtures and a balanced mixture distribution is a plus no matter at what mixture setting you decide to use.
 
@Domenick muffler blockage would increase both EGTs and CHTs, since the exhaust gases get trapped and the engine has to work harder to push them out.
 
Waiting to hear back from JPI. I think it's odd that all 8 probes would be affected (4 CHT's and 4 EGT's). Yes, I have GAMIjectors, and recently cleaned them the proper way. I remember after install years ago, engine ran smoother. No muffler.... so no exhaust departure concerns.
 
Glasair said:
Waiting to hear back from JPI. I think it's odd that all 8 probes would be affected (4 CHT's and 4 EGT's).
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Depending on how their circuit is designed and what might be wrong, it wouldn’t be at all odd to see all the thermocouples affected. The engine monitor is something I’d consider suspect at this point. Maybe consider checking temps with another measuring device utilizing the same thermocouples and see how close they are. Or, you could check the calibration of the engine monitor.
 
Glasair said:
I think it's odd that all 8 probes would be affected (4 CHT's and 4 EGT's).
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Not really. As I recall all 8 probes share the connector on the back of display and by extension they all share the same internal circuits that you have stated failed previously. Until you can verify the accuracy of the temps being displayed through a separate source the JPI could still be the common problem.
 
All CHT and EGT temps rising imply a leaning mixture. First thing I would look at is the mixture control rigging. I lost count of the number of control cables I found loose and slipping, particularly the cable housing clamps. Push your mixture control in all the way (don't screw the vernier in, just push it) and see if there's any "bounce" between the knob and the panel. If the knob bottoms out, you have a problem. The housing clamp may have let the housing slip and you might not be getting full rich. Or the clamp bracket has shifted. Several possibilities here.

All this stuff is annual-inspection stuff, which means that a lot of airplanes get it checked about once every fifteen annuals. That's what it looks like to me, anyway.
 
The monitor just came back from JPI 2-3 months ago, as again, it had a motherboard that went bonkers. Repaired and updated. Y'all are correct, tho... wiring and connectors remain the same. Thinking about the possible endless enjoyment of getting under the panel (Glasair panels = the need for circus contortionists, then trips to the chiropractor!) to replace wiring and probes.
 
Why not just push the mixture knob in a little to cool off the temps? Or use the monitor to go LOP and cool it off that way?
 
Old dogs dont change very fast (me, that is). But I'm thrilled to have input from so many experienced flyers.... that's the reason i joined and posted here. Ideas and thoughts from knowledegable folks is THE best. Thanks.
 
Glasair said:
turns out, it was a "MUGS board" that needed to be replaced
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A mux board, perhaps? Temperature multiplexer... there's only one A/D converter (analog thermocouple voltage to digital signal), and the multiplexer connects the temperature inputs to that converter one at a time, several per second, to convert those voltages to temperatures.

I'd start with a GAMI lean test, to see if something fundamental had shifted in the engine... like an induction leak? That could explain higher EGTs and CHTs... You don't have to have GAMIjectors, or even injectors at all, to perform and benefit from a lean test. The form and directions are at www.gami.com

Paul
 
Glasair said:
...No muffler.... so no exhaust departure concerns.
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I know nothing about Glasairs, but no muffler? Really? Just an open pipe from exhaust valve to the world at large?
 
Domenick said:
I know nothing about Glasairs, but no muffler? Really? Just an open pipe from exhaust valve to the world at large?
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It is quite common to find piston twins and experimentals that have no “muffler” like what people expect to see on type certified single engine airplanes.

My friend’s Glasair doesn’t have one either.
 
mondtster said:
It is quite common to find piston twins and experimentals that have no “muffler” like what people expect to see on type certified single engine airplanes.

My friend’s Glasair doesn’t have one either.
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No heat?
 
Bill said:
No heat?
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Just because it has heat doesn’t mean it has a “muffler”. A common sight on experimental aircraft is a heat shroud that passes air around an open exhaust pipe to pick up a little heat for the cabin as it passes by. They generally have marginal results. The “mufflers” commonly found on single engine airplanes generally are more of an exhaust restriction intended to slow the flow of exhaust so there is more opportunity for heat transfer for use as cabin heat.
 
Mufflers also create some back-pressure in the exhaust system. I always thought this somewhat slowed the exhaust gas velocity through the exhaust port, allowing more heat transfer from valve and seat to the exhaust gases.

But now, on second thought, it seems most heat transfer would occur metal-to-metal when the valve was closed, and I suspect the exhaust gases may be hotter than the valve seat and valve.

School me.
 
First 40 degrees ROP is the worst possible place to run your engine. There is lots of information on that.
As far as the symptoms you are experiencing I would focus on timing. How long has it been since the mag was serviced? Timing can slip internally in a mag. If the mag is good look carefully at the light speed. Are you running a advance schedule or fixed? You can check the actual timing and I would have a mechanic make that check. The light speed also uses Manifold pressure if I recall to advance the timing. I would make sure that connection is good. I bet money one of your mags is to far advanced.
 
Domenick said:
Mufflers also create some back-pressure in the exhaust system. I always thought this somewhat slowed the exhaust gas velocity through the exhaust port, allowing more heat transfer from valve and seat to the exhaust gases.

But now, on second thought, it seems most heat transfer would occur metal-to-metal when the valve was closed, and I suspect the exhaust gases may be hotter than the valve seat and valve.

School me.
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Reduction in back pressure results in cooler CHTs, slightly higher static RPM, and slightly improved rate of climb. Guys have been gutting mufflers for those reasons for a long time. These days there are some approved, too.
 
Domenick said:
But now, on second thought, it seems most heat transfer would occur metal-to-metal when the valve was closed, and I suspect the exhaust gases may be hotter than the valve seat and valve.
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Mine is experimental but the exhaust is three into one on each side. No back pressure and it has a wonderful note to the exhaust. I do plug the exhaust tips shortly after landing to prevent cold air from entering the engine through the exhaust. So far, so good.
 
maybe the CHT's were wrong for all those years and are correct now ? I have read articles about JPI and EI and spark plug Cht probes varying from 30-80 degrees. If you want to see lower CHT's switch from JPI probes to EI probes.
 
40 ROP is not necessarily a bad place to run your engine depending on power settings. If you are running 40 ROP at high power settings, then yes, I would agree, you are running your engine too hard.

Also, do you lean to a degrees rich of peak, regardless of fuel flow? Or do you lean to the same fuel flow every time? Since you're talking in GPH above, it seems like you're leaning to a specific fuel flow. In which case, I think you could run into problems just due to changes in outside temp - I know that for my plane, all else being equal, everything runs hotter in the summer and cooler in the winter, and I have to adjust the way I operate and lean my engine accordingly. If I just ran the same power settings and leaned to a specific fuel flow regarding of the situation, I'd be way too hot in the summer, and a bit too cool in the winter. Given that we're just coming out of the summer months, maybe you're running hot because simply because it has been hot?
 
Why would you run CHTs > 380 in cruise on purpose? I don’t get it. I could care less how many degrees lean or rich of peak I am, if the cylinders are that hot I’m not going to run it there. Personally, for longevity, I just richen until my CHTs are below 370. If they go below 360 I’ll lean some. Don’t care where it is relative to peak.
 
If you can keep CHT’s on the 3 and 4 cylinders below 370 you are doing way better that me. My Tiger would probably be drinking 13 gallons per hour to see temps that low. I have 50 hours on an overhauled engine with new cylinders. I have good baffling too. I wonder what CHT probes you are using. I have alcor bayonet type. There is a deference.
 
first things first, have you checked the EI timing with a timing light as klaus spells out? not just the led on the hall effect. a degree or two advance on the EI will cause CHT's to climb very high.
 
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