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-   -   Egt and Cht, what should they be? (http://www.piperforum.com/f8/egt-cht-what-should-they-3177/)

cathead 02-03-2013 08:47 PM

Egt and Cht, what should they be?
What should my egt and cht be on a Cherokee 140 with an 0-320 160hp? I am seeing on takeoff 1350f on #1, 1100f on #2, and 1250f on #3 and 4. During cruise I'm seeing 1450, 1250, and 1350 on 3 and 4.

Orest @ CYFD 02-03-2013 10:31 PM

Getting, understanding, and using an engine monitor is probably the single most important thing you can do as a pilot, not just for $$ reasons (engine longevity and streamlined diagnostics), but for safety as well.

Absolute EGT values are relatively meaningless. But, EGTs are useful for finding "peak", as well as for diagnostics.

You need to primarily manage and limit CHTs to protect your engine. Never let the CHT climb to above 400F. If it does, enrich mixture (if running ROP), level out or even descend, drop back the throttle, whatever it takes. At 400F aluminum has lost half of its tensile strength.

This is a very large subject. Mike Busch has some outstanding (free) webinars available through the EAA website, you don't have to be a member. A great place to start.

* Orest

GM. 02-03-2013 10:49 PM

Cherokee operations just weren't designed to be complicated.

As I remember (but it's been a while) the Max.CHT is 500 with Max.425 forcontinuous operations. Normal is about 350.

EGT around 1400 in leaned cruise with all reasonably close as yours are is satisfactory.

The numbers will never match up and soon looking at them will become as routine as glancing at the steam gauges since replaced.

Orest @ CYFD 02-03-2013 11:18 PM

GM - That is what Lycoming indicates, but using 500F for a "maximum" is way over the top, that is a temp that you might see during detonation runaway. 425F for "continuous" operations is too high as well. Keeping it cool, makes it last.

It really doesn't matter the plane, a small trainer or a big reciprocating twin, an engine is an engine. The more information you have, and the more you understand it (I'm no expert, but make an effort), the better things are going to run, and the longer it will last. Effort invested in this will have payback.

* Orest

bartmc 02-03-2013 11:21 PM

425 for continuious operation is not good, an O-320 is fairly bullet proof and tolerant of bad technique but that doesn't mean flying around at 425 is a good idea.
If I hit 380, the cowl flaps are coming out, if that doesn't work, richen up or even descend. My "issue" with CHT is mainly during the climb out in summer, I just drop the nose and climb slower to keep the CHT reasonable.

EGT, the actual numbers are fairly meaningless,i.e. they're dependent on where the probe is located etc..
What you're looking for is where the EGT peaks on each cylinder. i.e. watch a cylinder lean lean lean it will go up up up, then down when it drops, that cylinder is Lean of Peak. The actual numbers can be wildy different between cylinders, but if you're lucky, they all peak around the same mixture setting (This is where fuel injection and GAMI comes to the table).

What you chose to do with that "Where it peaks" information is more religion than anything else.

Next thing you know, you'll be running red box software and saying how it's pure luck people who run 50ROP have gotten dozens of engines past TBO. :)

My motto is, if you're running the engine at 75% power or less, it doesn't matter. When I'm down low, I run 23/2300 and 100ROP.

And, lean till rough then richen it up a little is fine for O-320s. I've seen many O-320s past TBO without CHT or EGT gauges.

Orest @ CYFD 02-04-2013 12:19 AM


The moto is good, but I might want to modify it just a bit -- at 65% you can certainly do what you want with the mixture control, at 75% indicated or calculated, I'd still be a bit cautious but then I'm pretty conservative.

Whenever I drop to LOP, which is where I normally cruise, even if "powered down" by thin air I still do a quick mixture pull (by memory) and then adjust by fuel flow. Prefer not to do the classic slow mixture pull/monitor EGT, to find peak and below.

* Orest

GM. 02-04-2013 12:54 AM

As I said CHT numbers are maximum numbers as with any other red line determined by the mfgr. With this engine you will have to try real hard to exceed them. In my IO-360 I've not seen over 375 in the dead heat of summer in the north or the south. I have little concern and even more so about EGT. Lycoming leaning technique to roughness of the leanest cylinder with richening 50 degrees works equally well.

For an normally aspirated engine under 180 HP I put the purchase and installation of an analyzer equal to my neighbor spending $75,000 for rooftop solar panels.

Orest @ CYFD 02-04-2013 01:05 AM


Sure, leaning to rough, and then enriching to just smooth will generally put into safe operation territory, typically a little lean of peak.

But, is a rumble trouble, or not? Is one cylinder overheating? Which plug is fouled? Truly assess the ignition system at runup. Catch an exhaust valve before it fails. With only four cylinders, if you lose one, you have much less margin than if you have 12 in a twin,. My opinion -- an engine monitor in a low powered hp 4 cyl has even more of a critical role, not less.

And, I'm definitely not into solar power. ;)

* Orest

GM. 02-04-2013 02:00 AM


Originally Posted by Orest @ CYFD (Post 36961)
My opinion -- an engine monitor in a low powered hp 4 cyl has even more of a critical role, not less.

* Orest

I'll agree when JimC puts one in the Cub.

Orest @ CYFD 02-04-2013 02:03 AM

Well, he'd need an electrical system first, but then he would be well served!

Once you fly with one, you won't want to fly without one again. And, the cost of the system will be quickly offset by maintenance savings.

* Orest

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