The International Cessna^® 170 Association

What is the EGT limit for a C-145? I have an EGT gauge but I don't have the appropriate red line on the gauge. I looked in the manual and couldn't find a limit. I did find that the CHT limit is 525.

Thanks, Mike

No limit that I'm aware of.

Use the EGT gauge to assist in leaning. Lean slowly to peak EGT and then richen by 50-75 degrees. I also note when the engine RPM rises during leaning and then move mixture to a richer position/slight decrease in RPM. There are bound to be more opinions on this but that is what the EGT is for.

no limits or required markings on an EGT gauge, and in fact for these engines it makes no difference what the markings mean, just guides. generally I have our gauges checked to verify scale accuracy, meaning that each mark is about 25 deg. so you know what the scale means. then just go to peak, richen (or lean if your fancier airplane has injectors that are set up for it) a specified amount for best power or whatever, and away you go. an O-300/C145 is not the Space Shuttle (or a U2, in your case!)

EGT's are extremely difficult to keep calibrated so folks with gauges marked with specific degrees (1200, 1300, 1400, etc) are usually fooling themselves, IMHO. But it's a good moneymaker for the shop to keep adjusting the cals.

EGT Instrumentation comes in two versions: Compensated and Non-compensated.
Non compensated gauges are the cheap ones and they are not "compensated" for ambient temperatures. I.E., their indications are "relative" not "absolute".

Compensated gauges are higher quality and read more accurately.

In either case, the C145/O300 is not likely to exceed any EGT limits for several reasons...the most obvious one being they never develop very high power with typical fixed-pitch props. (On takeoff with a standard prop you are only achieving about 120 H.P....not nearly 100% of rated power.)
Additionally, these very same cylinders/valves are used in the higher-output GO-300 series engines which are sometimes used with constant speed props and can develop 175 H.P.... and their EGTs are therefore higher (in the order of 1500+ degrees F). You do not have to worry about this in standard installations of C145/O300 engines, especially at typical cruising altitudes.

Having said that, I would set as my personal, arbitrary, goal not to exceed 1300-degrees in my O300. (PS> I don't even have an EGT gauge in my 170 because I don't think it's very useful at all. I lean according to RPM.)

EGT Myths Debunked
Alcor EGT Installation Instructions

One more thing too, attempting to operate a C145/O300 "lean of peak" is a ridiculous challenge with this engines silly carburetion. I suggest you do what the Operating manual for the engine recommends: Lean to max RPM...continue to lean to first indication of RPM drop, ...then enrichen back to max RPM.

Thanks for the replies. Now I will feel a little smarter the next time I am staring at that gauge wondering it's supposed to be reading.

I normally only lean on the ground and above 3k in cruise flight. When I lean I pull back until rpm decays and then push it back in a little. I never put much thought into doing anything else.

You really don't need an EGT gauge or tach to properly lean C-145/O-300 engines. When at cruise rpm, lean smoothly and steadily until you feel the power reduce and rpm fall (the engine may be smooth or it might just start to shake a little as the first (leanest) cylinder starts to drop offline). Then enrichen just a little until the engine gets power back and runs smooth, it doesn't take much! It will take a few times to get the feel but once you are used to it it will only take a second.

That procedure checked against a digital compensated 6-position EGT gives repeatable, consistent, correct results.

Note: The EGT spread between cylinders is awful so if you see they are not even, nothing you can do about it, it's the engine's design, not your EGT gauge.

I have the Electronics International UBG-16 engine instrumentation with 6 CHT and 6EGT's. I can use it to run "lean of peak" (hottest cylinder at 25 LOP) but the end result is exactly the same as following the book procedure of leaning to a slight roughness, then richening slightly for smoothness. My hottest EGT ends up around 1425 F, with about 50 - 75 or so spread. All my probes are 2 inches below the exhaust flange.

I haven't had carb ice since installing this instrument, but I'm confident I could use the across-the-board drop in EGTs to verify ice as the cause an RPM drop. Same effect as closing the throttle slightly. I would also think it would show a sticking valve or spark plug going bad. One interesting thing I've learned is that the standard baffling makes #5 and #6 CHT about 100F cooler than the other four. It REALLY makes me want to add some baffling to those front cylinders!

Is this instrumentation necessary? No, just a nice-to-have... just like the airplane itself.

cessna170bdriver wrote:I have the Electronics International UBG-16 engine instrumentation with 6 CHT and 6EGT's. I can use it to run "lean of peak" (hottest cylinder at 25 LOP) but the end result is exactly the same as following the book procedure of leaning to a slight roughness, then richening slightly for smoothness. My hottest EGT ends up around 1425 F, with about 50 - 75 or so spread. All my probes are 2 inches below the exhaust flange.

I haven't had carb ice since installing this instrument, but I'm confident I could use the across-the-board drop in EGTs to verify ice as the cause an RPM drop. Same effect as closing the throttle slightly. I would also think it would show a sticking valve or spark plug going bad. One interesting thing I've learned is that the standard baffling makes #5 and #6 CHT about 100F cooler than the other four. It REALLY makes me want to add some baffling to those front cylinders!

Is this instrumentation necessary? No, just a nice-to-have... just like the airplane itself.

You mean the end result is the same EGT, not the same fuel flow or power output, right?

My O-360 isn't good LOP. It gets rough before the richest cylinder has gone LOP. And with only four cylinders, that's rough in a way you O-300 guys have never experienced!

DaveF wrote:You mean the end result is the same EGT, not the same fuel flow or power output, right?

My O-360 isn't good LOP. It gets rough before the richest cylinder has gone LOP. And with only four cylinders, that's rough in a way you O-300 guys have never experienced!

The same EGT, and if the power and fuel flow are different, I can't tell. I don't track fuel flow precisely, just close enough to be able to use my watch to keep from running out of gas.

BTW, a C-145/O-300 running on 4 is pretty rough...

Apparently even the most advanced and technical instrumentation is unable to make a silk purse out of a sows ear.