IO-540 CHT's

Stephen Shore

Stephen Shore

Pre-takeoff checklist
Joined
Sep 30, 2017
Messages
422
Location
Longview, TX
Display Name
Display name:
sshore
My 1995 Commander 114B has 1946 TTH including the engine. I have been very careful with this engine, but now I am faced with some high CHT's. I am running the Electroaire ignition and just had a newly rebuilt magneto installed. The EIS has been installed since last August. However, since the magneto was re-built, I have seen CHT's increase:

MARCH 6

EM%2003-06-19_zps06krgfsq.jpg


NOTE: fuel flow was not installed with the Engine Monitor. I am using the one that came in the plane.

I run by the book - 22MP / 27 RPM @ 8,000 MSL at 14.0 gph

Adjustments made:

Plugs removed and cleaned / re-gapped.
Injectors removed and cleaned.
Magneto timing checked (checked OK)
Compressions checked - between 77-79 on every cylinder - there was some blowby.

On the flight today:

March 22
EM%2003-22-19_zps57fbq2jr.jpg


Again - no issues until the magneto was rebuilt. Now this.

Or maybe the fuel flow meter that dates back to 1995 is not accurate?

Any ideas?
 
I would have the timing checked ASAP. I'm not saying it's wrong, just want it verified. It's possible it was wrong before cause lower CHT. How long have you been flying this airplane?
 
Does cylinder 5 have a different CHT probe? Is that where the factory probe is/was?

That 453* on 4 at the top is alarming.

Weird that it's the even bank that's hotter. Isn't the cooler in front of the odd bank? Maybe a baffling problem? Nevermind, it's a Lycoming. Saw a big bore six and assumed Conti.
 
Engine grounding might have been disturbed during the magneto work. If that engine is not properly grounded to the airframe, through very clean, tight ground connections, you can get silly instrument readings.

Normal electron flow for the instruments is from the engine case, into the sensor, out of the sensor and through the lead, into the gauge or readout, out of the gauge and to the bus, then to the battery and out of the battery into airframe ground, and back to the engine through engine ground straps.

The alternator feeds the bus and battery by drawing electrons from the bus and pumping them into ground. The alternator is grounded to the engine case, and often also has a ground cable of its own. If there is any resistance in either grounding path, electrons start looking for an easier path. They often find such paths in engine control cables and instrument sensors. More electrons than usual are forced into the sensors and out into the instrument or readout, boosting the readings.

Cessna had a problem with high oil temp readings with their legacy airplanes that had the electric temp gauges. They recommended the installation of a dedicated ground wire between the engine crankcase and instrument case to eliminate small voltage differentials that cause the erroneous readings. 18 or 20 gauge wire, it was. Not hard to do. But the engine and alternator grounds should be checked first.
 
That may be explained also by the fact that I just got a complete new panel.

Any chance this grounding issue is related to that?
 
I run a TIO540 and I'd shat myself if I saw those temps in cruise. You have a problem. A serious problem. you need MX help, not internet conjecture.
 
AP has been working on it. He made some improvement as shown by the two photos.

No issues before new avionics and rebuilt mag installation.
 
Also need to check eis leads and see if they have the proper spacing from gt and cht wires. That could cause the eis to fire wrong.
 
I am also starting to think about fuel issues. Cleaning the injectors helped quite a bit. Compare the second picture to the first.

I am wondering if I need to continue on to the fuel distribution block ("spider") and have that cleaned? It looks like some cylinders are being run in a too lean condition.
 
don't mess with your fuel distribution block ("spider")....it either works...or you'll screw it up.
 
JCranford said:
Yikes! And I get antsy if one CHT goes to 410 in a climb!
Click to expand...

I get two or three regularly sub-420 in climbs. When the first one pops the JPI, I push over a bit. #2 gets a modified step climb. #3 gets a level off and pull back on the throttle 3-4".
 
fuel flow....at the engine driven "fuel pump". That could be increased...but, that one is doubtful since you had the mag worked on.
 
Checkout_my_Six said:
what about the internal mag timing?
Click to expand...
Internal mag timing has to do with the strength of the spark, not its timing to the engine.

One could spend a lot of time and money chasing fuel and ignition and a whole lot of other stuff, only to find in the end that it was some stupid, simple little thing that made the instrumentation read wrongly. Engines have been rebuilt to address low oil pressure indications, then they find that the gauge was pooched. Oil coolers replaced to try to fix an erroneous oil temp reading. Stuff like that can happen when you don't make sure you're getting the truth first.

Might even just be engine baffling disturbed during the mag work.
 
Speaking of oil temp, what's that read? If the cht's are really that high, and not an erroneous reading, I would expect that to be elevated as well.
 
Dan Thomas said:
Internal mag timing has to do with the strength of the spark, not its timing to the engine.

One could spend a lot of time and money chasing fuel and ignition and a whole lot of other stuff, only to find in the end that it was some stupid, simple little thing that made the instrumentation read wrongly. Engines have been rebuilt to address low oil pressure indications, then they find that the gauge was pooched. Oil coolers replaced to try to fix an erroneous oil temp reading. Stuff like that can happen when you don't make sure you're getting the truth first.

Might even just be engine baffling disturbed during the mag work.
Click to expand...
Yup...it very well could be anything. o_O
 
Chip Sylverne said:
Speaking of oil temp, what's that read? If the cht's are really that high, and not an erroneous reading, I would expect that to be elevated as well.
Click to expand...

Oil temp is well within limits - at the most 200-210 degrees.

Also - no CHT problems in climb. All the way to 10,000' at Vy stays well below 400 degrees with cowl flaps open.

In cruise, I have to leave the cowl flap open in order to keep CHT's below 400 degrees.
 
So if not in climb, when are you seeing these elevated CHT’s? In cruise with the cowl flaps closed and leaned to the gills? Or what.
 
You had a leak down test yet?
 
JCranford said:
So if not in climb, when are you seeing these elevated CHT’s? In cruise with the cowl flaps closed and leaned to the gills? Or what.
Click to expand...

In cruise with cowl flaps closed. Opening them gets the temperatures down below 400. This is a new development, post mag replacement and new panel.

The more I look into this on Lycoming literature, the more I am suspecting fuel flow issues. Will check that next.
 
I am rarely able to fully close my cowl flaps if I don’t want to go over 400 and run properly leaned, but I don’t see those numbers. I would also look at the fuel flows
 
Stephen Shore said:
Oil temp is well within limits - at the most 200-210 degrees.

Also - no CHT problems in climb. All the way to 10,000' at Vy stays well below 400 degrees with cowl flaps open.

In cruise, I have to leave the cowl flap open in order to keep CHT's below 400 degrees.
Click to expand...

How about relative to temps before replacing the mag? Since you are also running the Electro Air, in cruise your timing is way advanced, and the fixed timing of the newly serviced mag is really not a factor. How lean of peak are you cruising? Maybe not lean enough (or rich enough, depending on how you fly your engine) for the amount the EA is advance to get the temps you want. Have you GAMI balanced your injectors? Might be worth going through the exercise.
Kinda odd being 1,2 and 6. 6 would make me think baffles. The other two are right up front.
 
Success....

After many hours, found the main problem - the alternate air flap was rigged so that the "flap" was slightly open all the time. We fixed the rigging and got a good seal. In addition, we went ahead and replaced all six of the rubber hoses on the air intake tubes. They were probably original to the airplane (1949 TTH) and were hard as a rock. We suspected air leakage on some of them as well.

Bottom line - air leakage on the intake side of it.

Test flew today. The airplane has never run better and the engine monitor has never looked this good. 13.8 gph @ 6,000'. 24 MP and 2700 RPM.

Final%2004-01-19_zpsap8lzjz7.jpg
 
What'd this evolution run you in AMUs to solve?
 
Unit74 said:
What'd this evolution run you in AMUs to solve?
Click to expand...

Not as many as you might expect...

My next door neighbor (hanger) is an A&P and we worked on my airplane together for the past two weekends and several evenings during the week. He probably charged me a total of 10 hours total during all this time. He is a great young A&P and he was wanting to get some experience working on Commanders. He works full time for a well known Mooney shop in Longview TX. He has lots of experience, but almost all on Mooneys.

We were really going down a rabbit trail until his DAD advised us that in his opinion the cause of my high temperatures was an air leak somewhere in the system. We ran with that and in the end, that is exactly what was the cause of most of the high CHT's. Cleaning the injectors and plugs did help, but not until we sealed up the intake system did we really solve the problem.
 
You must log in or register to reply here.
Back
Top