Who has JPI 700 in Cessna 172

[JOhnH]

How many people actually have a JPI EDM- 700 engine analyzers in a Cessna 172? With an O360 engine?
I am sure you all are getting almost as tired of me asking about my high CHT readings as my mechanic is.

I have had several people tell me that most 172s run high CHTs but since they don't have the analyzer nobody knows or makes a big deal out of it.
I have spoken with a few people that had this combo and they also complained about high CHT readings. Are there people with this monitor in a 172 and showing "normal" temperatures? Especially in hot climates like Florida?

Could there be any truth to that? Should I just make like an ostrich and pull the damn thing out and relax?

 

[sba55]

Could there be any truth to that? Should I just make like an ostrich and pull the damn thing out and relax?

I wouldn't. It's not like the JPI is lying to you when it's showing you high engine temperatures and it's not like high temperatures are ok as long as the engine is in a 172 vs. other planes.

Most likely, you just don't get enough airflow over the cylinders or you're running too close to peak or some other factor or combination thereof. I'm sure it's very much possible to tweak some of these and achieve decent engine temps.

-Felix

 

[EdFred]

Which cylinders are hot? What are their temps? How much higher are they than the normal/cool cylinders?

 

[poadeleted20]

What type of CHT sensors do you have? CHT well bayonet probes? Spark plug gaskets? Something else?

 

[JOhnH]

Which cylinders are hot? What are their temps? How much higher are they than the normal/cool cylinders?

In level flight at 2,500 with OAT a toasty 87 degrees:
#1 about 400
#2 about 383
#3 about 413 (exceeds 450-460 during initial climb)
#4 about 420 (exceeds 450-460 during initial climb)
(remember, this is a new engine w 13 hours, and it is HOT around here).

Bayonet probes in all 4 cylinders.

But back to my question, and I know this doesn't make it right or "ok", but
does anyone know of an older (circa 1977) Cessna 172 with an O360 (180 hp) engine and an engine analyzer? If so what does it show? Perhaps if there were more of these and they all showed what mine shows, then more attention would be paid to this issue and these engines may go 3 or 4 thousand hours before major overhaul.

 

[sba55]

In level flight at 2,500 with OAT a toasty 87 degrees:
#1 about 400
#2 about 383
#3 about 413 (exceeds 450-460 during initial climb)
#4 about 420 (exceeds 450-460 during initial climb)
(remember, this is a new engine w 13 hours, and it is HOT around here).

Bayonet probes in all 4 cylinders.

Unless that JPI is extremely poorly calculated, 420 - not to mention 450 - is WAY above what's good for your engine.

But your other question - yes, if more people paid attention to good engine management, average engine lifespans would certainly increase. I know a few people who are at 2500+ for their O360 and IO540 - but that's because they make very sure not to exceed 380 degrees. Ever.

-Felix

 

[GMascelli]

I have the O360 and the JPI 700 in my Sundowner. I have the "Spark plug gaskets" and my number 1 CHT will run hot on climb out. I leave the fuel boost pump on until cruise. I find that a cruise climb will keep that temp in the 400 range. On really hot days I saw it peak at 450....never a warm and fuzzy feeling.

Have your mechanic shoot that cylinder with a Handheld Infrared Thermometer to confirm temps and back up what you are reading on the JPI. What do your EGT's look like, are they equal across the board or is the hot cylinder hotter?

 

[poadeleted20]

In level flight at 2,500 with OAT a toasty 87 degrees:
#1 about 400
#2 about 383
#3 about 413 (exceeds 450-460 during initial climb)
#4 about 420 (exceeds 450-460 during initial climb)
(remember, this is a new engine w 13 hours, and it is HOT around here).

Bayonet probes in all 4 cylinders.

But back to my question, and I know this doesn't make it right or "ok", but
does anyone know of an older (circa 1977) Cessna 172 with an O360 (180 hp) engine and an engine analyzer? If so what does it show? Perhaps if there were more of these and they all showed what mine shows, then more attention would be paid to this issue and these engines may go 3 or 4 thousand hours before major overhaul.

While those numbers are on the high side of good for cruise, if it goes over 460F in climb, that's downright bad for the engine. It won't kill the engine immediately, as going over 500F might, but over the long haul, your valve guides will suffer the consequences, and your engine won't "go 3 or 4 thousand hours before major overhaul." I'm not an expert on 172's, but I do know the 180 HP O-360 pretty well, and you need to find out why the engine is getting so hot in the climb, and fix it. Baffling and baffle seals are the usual culprits in this sitation, but sometimes a misadjusted carburetor can be running the engine too lean, and that can push up CHT's, too.

 

[poadeleted20]

I have the O360 and the JPI 700 in my Sundowner. I have the "Spark plug gaskets" and my number 1 CHT will run hot on climb out. I leave the fuel boost pump on until cruise. I find that a cruise climb will keep that temp in the 400 range. On really hot days I saw it peak at 450....never a warm and fuzzy feeling.

Keep in mind that those spark plug gasket thermocouples effectively operate on a different scale than the CHT well bayonet probes. Tanis ran some tests of the “actual” temperatures (i.e., those measured at the tip of the thermocouple in the CHT well – the “official” values used in certification) versus those measured other ways. They found that the spark plug gaskets read up to 80F high, with the largest difference at the top of the climb. Spark plug gaskets on the lower plugs read hotter than those on the top plugs.

 

[AirBaker]

Those are definitely hot, but still missing some other data:
EGT temps, Fuel Flow?

You also might want to get the plane in a dark hangar and use a flashlight to see if there are many gaps in the baffling. I sealed up every crack with GE Silicone II that I could find.