Recommend EGT/CHT Guage for O-300D

[Rob Schaffer]

Looked today at our engine while it was being worked on in the shop. We currently don't have an EGT guage, and it was recommended we consider one or a combination with CHT guage to better monitor our engine and leaning process.

I saw different ones on Aircraft Spruce and Chief Aircraft, but I'm new to all this, and need some assistance in the research. Anyone have good experience with a particular model that is affordable,.. LOL,.. aviation affordable ,... I think just a standard guage with dial would do, nothing with downloads and fancy LED's is necessary.

Engine is a Continental O-300D, 6 Cylinder

To late now to get installed, but pending what is out there maybe something in the near future oil change or annual in June.

 

[wsuffa]

I sure like the EI stuff, but it's not a "cheap" gauge.

 

[slowjoe]

I've got an O-300-C and I put in the Westach K31X CGT/EGT single cylinder gauge. It's only a couple of hundred bucks. It's handy, but I tell you what, it's not really needed. Sure, I can lean down a bit farther but how the manual says to do it is pretty damn good: lean to peak RPM for best power then 50RPM lean of peak for best economy. That 50RPM lean of peak puts the EGT at 40-75F lean of peak. (peak on my engine is right around 1,400F)
If I had the money I'd put in a JPI or EI engine monitor w/ fuel flow. But again, it's not really necessary. It's really difficult to hurt an O-300.

 

[Ted]

The single cylinder CHTs/EGTs are probably marginally better than nothing, but only marginally. For the effort that goes into installing one, I would suggest you're best off getting an engine monitor or nothing at all. I recently installed an Insight Gemini 1200 in the Aztec. The unit itself works fine, but customer support is, at best, garbage. Additionally, the one feature that the GEM doesn't have that I wish it did was automatically scrolling through the CHTs and EGTs like the JPI will. The JPI is a better unit, and there are some other good options out there for single engine aircraft worth considering. If you do anything, do something like that.

However, I'd question whether or not it's really a necessity in that airplane. If your baffles are in good shape (which they very well may not be), the lean until rough and then richen until smooth method of leaning for carbureted engines has been pretty effective. Do make sure your baffles are in good shape, though. They're there for a reason, and putting new baffle material on isn't hard to do at all. The ones on my right engine were in such bad shape that when I fixed them I gained a solid 5 mph in cruise (no joke). My oil temps went down a lot, too. I don't want to think about how high my CHTs were prior to the fix (prior to my engine monitor).

 

[Rob Schaffer]

However, I'd question whether or not it's really a necessity in that airplane. If your baffles are in good shape (which they very well may not be), the lean until rough and then richen until smooth method of leaning for carbureted engines has been pretty effective. Do make sure your baffles are in good shape, though. They're there for a reason, and putting new baffle material on isn't hard to do at all. The ones on my right engine were in such bad shape that when I fixed them I gained a solid 5 mph in cruise (no joke). My oil temps went down a lot, too. I don't want to think about how high my CHTs were prior to the fix (prior to my engine monitor).

That was the method of leaning we were using, but apparently we were still sitting near peak when the engine was running smooth. Mechanic is recommending 80* ROP for operation, but we don't have a EGT guage to judge that, so he said probably about 1/4" richer will put us in that range of 80*-100* ROP. See my blog link below for yesterday's post with photos after I spoke with him in the morning.

I don't think we have typical baffles around our engine to direct air over the cylinders themselves. The air comes in the front cowling and is blocked by a separation piece from the back of the engine on the top, which fits tight to the cowl IIRC,... I'll have to look closer next time I am at the plane. Here's a photo from yesterday morning.

 

[charlie]

If you want to run 80 ROP the no egt method is to lean to the edge of rough on one mag then go back to both mags and you'll be at about 75 ROP. This is much better than guessing how much control travel it take to get there. As long as the mag timing is set right this works well. Charlie Melot Zephyr Engines

 

[slowjoe]

Why is your mechanic recommending 80 ROP? That's the worst place to run an engine. Follow Cessna's recommendation: peak RPM for most power and 50RPM LOP for best economy. You'll be much happier with performance and fuel consumption. 7:1 compression engines will NOT be damaged by running LOP, especially at the levels recommended by Cessna.

As for your baffles you should have a nice seal between the bulkhead and cowling, all the way up around the top and along the sides. You should also have baffles between the cylinders. There is also baffling across the front of the engine. The side and front baffles (soft baffles) are in the lower cowling.

 

[Ted]

There's nothing wrong with running your engine at peak EGT. That's where my engines spend most of their time, and they're quite happy there. If I ran them at 80 ROP the CHTs would be most unhappy. I would disagree with your mechanic's suggestion.

 

[el con]

I like my E.I. EGT/CHT
If i had to go cheap I would look at a westach single gauge with the 4 0r 6 position switch set up with probes to check all cylinders manually.
To me a single gauge checking what would normally be just the hotest cylinder is better than nothing ,but not by much. Knowing all cylinders are running within range gives me some piece of mind.

 

[Trapper John]

To me a single gauge checking what would normally be just the hotest cylinder is better than nothing ,but not by much. Knowing all cylinders are running within range gives me some piece of mind.

For a single point gauge, I'd want EGT for the cylinder that peaks last. For CHT, I'd want the one that runs the hottest.


Trapper John

 

[Dr. O]

For a single point gauge, I'd want EGT for the cylinder that peaks last. For CHT, I'd want the one that runs the hottest.
**********************************
And the point that Trapper is making is that they are not the same cylinder - and how do you know they are even on the the 'right' cylinder? You don't...
And the right cylinder at 2400 rpm may not be the right cylinder at 2500 rpm...

So, what to do?
I can't argue against single cylinder EGT and CHT, I have them on the Apache and the engines make TBO... However, I use them as a guide, not the last word... For running down low at cruise power, I simply raise the EGT by 50 degrees from full rich, knowing that will reduce my fuel flow by 7-10% - close enough for government work...
Up higher, or with power at 65% or less, I lean to peak... Sometimes I have to sweeten em up slightly from peak because they get rough on one cylinder - depending on humidity, temperature, etc...
These engines have been run this way for decades and do just fine...

denny-o

 

[Rob Schaffer]

As the mix goes from way rich to way lean it will rise to a point where it starts dropping, that is known as peak, if you continue to lean the temps will start to drop unil the engine starts to studder/stumble/vibrate. that is the point we stop and push the mixture toward the rich, until we are rich enough to run smooth.

that is a point near 50 degree lean of peak.

This was posted by Tom D, in another discussion thread, and it is the way we typically have leaned the engine during flight. So, I guess my understanding is, that our mechanic is recommending to enrichen the mixture about 1/4" further than smooth, as he states we are still to hot by running the engine the way we lean. So, if we are still lean of peak or at peak, richening the mixure will burn slightly more fuel, but keep the cylinder temp down, correct?

We are currently replacing cylinders 1 & 4 on the engine, and both show signs of high temperatures/burned valves and some cylinder wall scoring on the one cylinder. The number 4 cylinder had a siezed valve in the open position, and has some pitting of the cylinder near the top too.

 

[poadeleted20]

While you may not want a "fancy" engine analyzer, you should want a probe on each cylinder. A single cylinder gauge is too likely to deceive you into thinking everything's OK when it's not. The low-cost solution to that is six probes, a rotary switch, and one gauge for each function (CHT and EGT).

 

[el con]

For a single point gauge, I'd want EGT for the cylinder that peaks last. For CHT, I'd want the one that runs the hottest.


Trapper John

I agree totally

That's why I have an E.I. US-8A,as I said IF I had to go cheap I would get the Westach single(1 needle for EGT,1 needle for CHT) put probes on all cylinders and manually scan .
I personally decided to spend more money on these types of things than fancy radio's ,transponders, etc.
I'm VFR only, if mechanically my planes flying and I know it, that gives me more confidence than a nifty flip flop radio or digital transponder.
But that's me,I don't pipe in music either , I like to listen to what's going on with the plane.
Probably get that from my old farm day's listening for bearings going out or other noises that usually happen just before things fly apart or break

 

[Ted]

This was posted by Tom D, in another discussion thread, and it is the way we typically have leaned the engine during flight. So, I guess my understanding is, that our mechanic is recommending to enrichen the mixture about 1/4" further than smooth, as he states we are still to hot by running the engine the way we lean. So, if we are still lean of peak or at peak, richening the mixure will burn slightly more fuel, but keep the cylinder temp down, correct?

We are currently replacing cylinders 1 & 4 on the engine, and both show signs of high temperatures/burned valves and some cylinder wall scoring on the one cylinder. The number 4 cylinder had a siezed valve in the open position, and has some pitting of the cylinder near the top too.

Well, running the engine as your mechanic suggests will result in higher CHTs than at peak. Remember that peak CHT is about 50 deg ROP EGT. So if the things are too hot, I would first look to your baffling (or lack thereof) as a potential issue rather than your leaning technique.

 

[flyersfan31]

2 things:
1) I would go with JPI
2) I would listen very carefully to Ted. He runs fully-instrumented aircraft engines for a living, torturing them in unimaginable ways. If the person who told you to run at 80ROp is who I think it is, well, I trust Ted.

 

[poadeleted20]

For a single point gauge, I'd want EGT for the cylinder that peaks last. For CHT, I'd want the one that runs the hottest.

While that might be a nice thing to have, the cylinder with the hottest/coldest CHT/EGT can change with throttle setting, altitude, OAT, and other factors -- even how much any one plug or valve is crudded up. That's why I said that not having instrumentation on all cylinders is potentially deceptive. If another cylinder was having a problem, the indications on the one instrumented cylinder could lull you into thinking everything was fine, and you'd never know about the problem until it developed into something you couldn't miss -- and that could be really, really bad.

 

[Trapper John]

While that might be a nice thing to have, the hottest/coldest CHT/EGT changes with throttle setting, altitude, OAT, and other factors -- even how much any one plug or valve is crudded up. That's why I said that not having instrumentation on all cylinders is potentially deceptive.

Absolutely. I was just looking at it from the, "If I only could have 1" perspective. There's no question having EGT & CHT probes for every cylinder connected to a deluxe analyzer is a much better solution, but when the plane is an older 172 worth maybe $30k, putting $2k into a deluxe analyzer might be a little hard to justify.


Trapper John

 

[poadeleted20]

As I said above, you don't need a deluxe analyzer -- six probes, a rotary switch, and one gauge will do for that O-300 for a fraction of the cost. I've seen quite a few such installations. Moreover, if you put the right sort of probes in all cylinders, an upgrade to a "deluxe analyzer" is a lot cheaper later on when you have the extra bucks.

 

[Tom-D]

A single point gauge is all you need in the C-145/0-300 place the CHT in the right rear cylinder, and the EGT in the same cylinder 2" below the exhaust port gasket.

In a -172/170 with the 0-300/C145 that is the cylinder that runs the hottest and the cylinder that will peak last.

 

[Rob Schaffer]

That's also the one we just replaced along with #4. It's been run now by the mechanic and parked pack in our spot for us to put 3 hrs
on it before they check some things again. Bob and I may
meet soon to go over things. Thanks for the input and feedback.

 

[poadeleted20]

A single point gauge is all you need in the C-145/0-300 place the CHT in the right rear cylinder, and the EGT in the same cylinder 2" below the exhaust port gasket.

In a -172/170 with the 0-300/C145 that is the cylinder that runs the hottest and the cylinder that will peak last.

That's true only if everything is running by the book. Hence, my caution about the potential for being deceived by a single-cylinder system.

 

[bbchien]

A six probe engine analyzer is about $2,300 installed. You might want to consider that that's two cylinder kits and some mechanic time, right there.

If you run 65% power only, it's hard to do any damage even if you are in Walt's red box. There just isn't enough thermal power to do it. 75% is a whole 'nother kettle of fish.

 

[Ted]

2) I would listen very carefully to Ted. He runs fully-instrumented aircraft engines for a living, torturing them in unimaginable ways. If the person who told you to run at 80ROp is who I think it is, well, I trust Ted.

Thank you, Andrew.

 

[weirdjim]

A single point gauge is all you need in the C-145/0-300 place the CHT in the right rear cylinder, and the EGT in the same cylinder 2" below the exhaust port gasket.

In a -172/170 with the 0-300/C145 that is the cylinder that runs the hottest and the cylinder that will peak last.

When you say "right" I'm presuming you mean starboard? Passenger side?

How about an elderly 182A O-470L, which cylinder do you say runs the hottest? Is it a function of baffling or airflow coming over two hot cylinders before it gets to the rearmost cylinder? And less space between cylinder and baffle on starboard than port?

Jim