EGT sensors, CTLSi maintenance, failure rate?

[Roger Lee]

So what I'm saying is the instruments on a Lycoming or Continental are setup differently, the engines are different and the operation is different. You can't always apply only one thing when comparing very different engines, operating parameters, different instrument setup. He's talking about just normal running and not about the moment an engine fails or is starting to have a single cyliner issue.

Then you need to hear what Rotax says about him about several subjects and comments. He knows almost nothing about Rotax. EGT's are still a better and faster way to see if you have an engine issue. It's instantaneous.  Mike may know other aircraft engines, but him making statements about Rotax is apples and oranges different. You must compare apples to apples.

Here is what Eric Tucker says and it's a quote. He is the guru for Rotax and main instructor around the world.

"Hello all...

Just to be clear, Mike Busch knows zip about Rotax.  If you use his info then you will be supporting your local repair service soon.  Just fair warning.  Mike B is a great resource but not for Rotax.  

Cheers"

 

Another quote from another Rotax guru:

" Mike Busch is a strong advocate for some changes to how people maintain Lyconentals I have been to a few of his talks. However again he appears to know nothing about, or for some reason never mentions, Rotax engines.

I have come across a few people whom love his advice and seem unable to even contemplate that Rotax's are different and when they shift to a Rotax engine endlessly complain that it is not "right"."

 

When  a friend lost his exhaust lifter the CHT did nothing because it was the number #1 cylinder failure and the the CHT is on the bottom of the #3 cylinder and the change in cylinder head temp was almost non existent for a while because metal things take a while to either heat up or cool down, but the EGT was instantaneous and showed the #1 cyl. was very cold and failing vs the other 3 cylinders. 

[Anticept]

... Standard CHTs are on 2 and 3, EGTs on 3 and 4, at least for carb engines. Did they have a different aircraft or the injected model?

If he lost that lifter then he wouldn't need an EGT to tell him it's busted, that engine would have felt like a broken suspension on a Northern Michigan road.

Had a pipe fitting crack on an engine and it lost its coolant. Guess what didn't show on EGT?

I think the point is going over your head. Pilots don't need to be freaking out about EGTs. Without other symptoms, its a red herring. We have many topics about EGTsplits, obsessions about them being 50 degrees apart... etc and we keep telling them its probably a bad probe or nothing to even think about because that's the only issue they have and there will be SOME installation variance.

Unless there are other symptoms, there's nothing to worry about unless they're above the redline, and that would be impressive to ever actually have temps that high, something would have to be VERY wrong. They're going to land anyways and won't need an EGT to tell them that.

For maintenance, they're helpful. When the engine isn't smooth, they're helpful. When you're chasing issues, they're helpful.

But if there's nothing going on and the engine's smooth, there is nothing an EGT is going to warn you of that a CHT won't, while CHTs will tell you of issues that wont show on EGT.

If anything, rotax could benefit from a 4 place CHT and EGT system, but if I had to choose only one, CHT.

[Roger Lee]

"Standard CHTs are on 2 and 3, EGTs on 3 and 4, at least for carb engines."

That's on some planes others have all 4.

"If he lost that lifter then he wouldn't need an EGT to tell him it's busted, that engine would have felt like a broken suspension"

Correct and the EGT would tell you which cylinder if it was a firing cylinder issue. It would still shake if the prop weight inside the prop comes lose or a mount breaks or any other item like that.

"Had a pipe fitting crack on an engine and it lost its coolant."

The CHT is slow to read and at a reduced throttle you can get the CHT back in an operating range. Plus when the coolant goes away then the CHT doesn't read correctly anyway especially if it was in the coolant and not just the head metal temp.  It may be an oil issue.

"I think the point is going over your head. Pilots don't need to be freaking out about EGTs. Without other symptoms, its a red herring."

Now we're getting some where. Since the digital age for our instrumentation and a lot more information that we are exposed to people have not educated themselves to what all these readings mean or when one is out of spec where to look and what to look for. People aren't used to all the information from their instruments nor have many ever learned what they all mean or how one may affect the other.

"there is nothing an EGT is going to warn you of that a CHT won't"

This one isn't true because of the limited CHT info we have. Only two cylinders and slow reading and a CHT won't tel you which cylinder if it's a cylinder issue. The CHT isn't going to tell me if I'm running lean like if I change the needle clip position. Many times for that the CHT doesn't show hardly any difference.

BINGO

"For maintenance, they're helpful. When the engine isn't smooth, they're helpful. When you're chasing issues, they're helpful."

EDUCATION IS THE KEY FACTOR FOR THIS ENTIRE DISCUSSION AND DEBATE.

 

[Jim Meade]

So you're saying EGT and CHT on Rotax are different than on other engines?

[Roger Lee]

Probe placement is different and the way they are mounted are different and the Rotax engine is different.

[Jim Meade]

Roger, you did not answer the question. 

EGT and CHT are in general similar concepts across engine types.

You said that because Mike Bush was not familiar with Rotax engines he was not competent to comment on CHT and EGT.  I contest that.  Mike Bush is highly experienced and highly regarded.  I have heard him say he is not familiar with Rotax engines, but that does not mean my offering of his comments on EGT and CHT are not germane to engines in general and aircraft engines in particular and Rotax engines specifically.  

Citing Eric Tucker in a general sense is not credible.  We need exact quotes in context.

Back to the bottom line - I offered Mike Bush's comments on EGT and CHT as informative to the discussion.  I stand by my offering and Bush's expertise in the subject, regardless of engine type.  End of discussion.  

[Tom Baker]

11 hours ago, Roger Lee said:

Probe placement is different and the way they are mounted are different and the Rotax engine is different.

Probe placement is different, that means temperature ranges will be different. CHT is still a measure of the metal around the combustion chamber, or in the case of the newer Rotax it is an actual measure of the coolant temperature. EGT is a measure of the exhaust temperature to tell what's going on with the combustion inside the cylinder. This is the same for all engines. While operating and maintenance procedures are different for the Rotax engine, it is still just a four stroke internal combustion engine. In principal it is no different than any other four stroke internal combustion engine. Physics don't change because of the manufacture of the engine.

 

[Anticept]

"The CHT is slow to read and at a reduced throttle you can get the CHT back in an operating range. Plus when the coolant goes away then the CHT doesn't read correctly anyway especially if it was in the coolant and not just the head metal temp."

It will still read very abnormally and EGT isn't going to change noticeably.

"This one isn't true because of the limited CHT info we have. Only two cylinders and slow reading and a CHT won't tel you which cylinder if it's a cylinder issue. The CHT isn't going to tell me if I'm running lean like if I change the needle clip position. Many times for that the CHT doesn't show hardly any difference.'

I get where you are coming from but I did specify all things equal.

if you only have 2 cht and 2 EGT, I would honestly prefer them to be on separate cylinders, but we don't get that privelage since EGTs go in the back and CHTs cross, with cyl 1 unmonitored and 4 double monitored.

As for running lean: I haven't commented on this on the forum here yet but this seems a good a topic as any. I am not sure why it matters for position 2 vs 3.

When I first became a mechanic and got trained up, I found the needle position on my carb on 2 on both sides at around a thousand hours. Never had a warning, and after swapping to 3, the engine ran for another thousand hours before taking it out of service for TBO. Engine looked absolutely fine internally.

So not sure if this qualifies as an issue to get twisted up about,.and even if it did become an issue, the engine wouldn't generate power correctly and cylinders would get HOT if it ran on peak as a result.

[Tom Baker]

1 hour ago, Anticept said:

As for running lean: I haven't commented on this on the forum here yet but this seems a good a topic as any. I am not sure why it matters for position 2 vs 3.

When I first became a mechanic and got trained up, I found the needle position on my carb on 2 on both sides at around a thousand hours. Never had a warning, and after swapping to 3, the engine ran for another thousand hours before taking it out of service for TBO. Engine looked absolutely fine internally.

I had one several years back that I did a hose change on, and did the carbs. At that point I hadn't given much thought to the needle position, and would just put it back as I had found it. It was about 20°F when I went to do a test flight, and I wasn't happy with the ignition check. While it was technically with in limits it had about a 250 RPM drop, and was rougher than normal. I found the culprit to be the clips in the #2 slot instead of #3. Once switched running was back to normal, and the customer said it was the smoothest he had ever felt it since he owned it.

[Anticept]

I suspect fuel quality plays a big role. I also only had one data point so I didn't want to really say if it is a good thing or not and make it an argument here, just merely that the needle clip position doesn't seem to carry a risk of the engine exploding or setting valves on fire.

Anyways, all that said, I do want to be clear to Roger and everyone else: I said earlier I would prefer 4 place everything. To get back to the base of what I argue, it's this:

• EGT indications alone don't make an operational difference. If you're really, really good at being familiar with what is normal and what isn't with THIS EXACT AIRCRAFT (I would put roger as one of the few people who could take generalizations across the fleet and be correct because there's an enormous number of factors), or are chasing down issues, THEN EGTs can be useful to you. Everyone else: unless you are crosschecking and seeing indications or symptoms elsewhere too, don't freak out about a weird EGT reading. If it's running smooth, making power, and not overheating, what the fuel is doing inside the cylinder doesn't really matter but keep an eye on things.
• CHT indications should always be taken seriously. These tell you the health of the cylinder itself. Even if the engine is running smooth and making power, unresolvable, abnormal CHT readings should be considered an emergency and you should get to safety ASAP (if they're showing a little warm, pull power back, level out, etc and let em chill out some). Coolant loss is one example where engine damage occurs but the engine can still be running well for quite some time... until it doesn't.