High CHT and one High EGT

[Pilotja5]

MooneySpacer's, My partner and I just installed a JPI 900, and the highest CHT was 468 with most of the others around 450 on climb out.  This is a Mooney 1968 M20C with the fixed cowl flaps.  It has the box around the cylinders for baffling.  Any ideas on how to lower the CHT's.  Also Cylinder number 3 EGT's are approximately 200 degrees warmer than the others at cruise settings.  Is this normal or cause for concern?  It was 55 degrees last night during the flight.  Thank you for the help.  Here is the pic of the JPI on the flight back from the shop.

[Andy95W]

450-468°  is way too high.  The conventional wisdom is to keep CHTs below 400° at all times, although I will admit to seeing 410° during climb on very hot summer days.

#3 EGT 200° higher than your other cylinders is not abnormal for a carbureted Lycoming engine.

To get your CHTs lower, first step is airspeed- you should be climbing out at about 120 mph after clearing any obstacles.  Next step is to address the "box" around the engine (you'll see it referred to around here if you do a search as "the doghouse").  To have CHTs as high as yours, you probably have some significant issues with air leaks that need to be addressed.  When your mechanic looks at your doghouse, have him ensure your cowl flaps are adjusted per the maintenance manual.

The next thing to try is to look at different throttle settings.  At full throttle, extra fuel is added through the carburetor. Try leaving the throttle all the way in, but pull the prop back to 2500-2600 rpm.  And of course not leaning in the climb until you reach an altitude where it is necessary.

[Hank]

Good Lord! 14 gph in a C! Mine runs 9 . . . But I also don't fly at 25"/2500. If you ignore units and just look at the numbers on the MP and Tach dials [that you used to have], these would be 25 / 25. Using the Key Number approach, this gives 25 + 25 = 50, which puts you at pretty high power. For the O-360 engine in our Cs, we should fly at Key Number of 47 or less.

When going short distances down low [~3000 msl], I generally run 23/2300.

At mid-level altitudes [~3000-7000/7500-ish], I general run 22/2400.

When cruising high, where the Owners Manual says I'm below 75%, I run WOT-/2500.

High power makes for high temps. What was your altitude on this trip? What does your Owner's Manual say that your % Power was [from the Performance Charts at the back]?

When I say "WOT-" that means level off at full throttle/2700 [just like I climbed], let it accelerate then ease the throttle back to close off the fuel enrichment circuit--this will make the MP needle just begin to move. Stop and leave it there. Then pull the prop back to 2500 and lean.

[Igor_U]

I am sure you'll get more detail responses but yes, those CHTs look very high to me. I would look at the baffling firs and maybe Fuel flow at 100%  power. What is it?

EGT value doesn't matter that much as temps would change if your probes are not installed at the same distance from the flange. By a box around cylinders, I suspect you thing about "doghouse".... I am more familiar with regular baffling I have on M20F but there's a lost of discussion on MS regarding it and how to improve it.

good luck.

 

 

[Pilotja5]

5 minutes ago, Hank said:

Good Lord! 14 gph in a C! Mine runs 9 . . . But I also don't fly at 25"/2500. If you ignore units and just look at the numbers on the MP and Tach dials [that you used to have], these would be 25 / 25. Using the Key Number approach, this gives 25 + 25 = 50, which puts you at pretty high power. For the O-360 engine in our Cs, we should fly at Key Number of 47 or less.

When going short distances down low [~3000 msl], I generally run 23/2300.

At mid-level altitudes [~3000-7000/7500-ish], I general run 22/2400.

When cruising high, where the Owners Manual says I'm below 75%, I run WOT-/2500.

High power makes for high temps. What was your altitude on this trip? What does your Owner's Manual say that your % Power was [from the Performance Charts at the back]?

When I say "WOT-" that means level off at full throttle/2700 [just like I climbed], let it accelerate then ease the throttle back to close off the fuel enrichment circuit--this will make the MP needle just begin to move. Stop and leave it there. Then pull the prop back to 2500 and lean.

Hey Hank, I was between 3000 and 4000 last night.  I will definitely take a look at what you are talking about.  The temps come down in cruise to normal levels.  It is only in climb out.  

 

[Pilotja5]

10 minutes ago, Andy95W said:

450-468°  is way too high.  The conventional wisdom is to keep CHTs below 400° at all times, although I will admit to seeing 410° during climb on very hot summer days.

#3 EGT 200° higher than your other cylinders is not abnormal for a carbureted Lycoming engine.

To get your CHTs lower, first step is airspeed- you should be climbing out at about 120 mph after clearing any obstacles.  Next step is to address the "box" around the engine (you'll see it referred to around here if you do a search as "the doghouse").  To have CHTs as high as yours, you probably have some significant issues with air leaks that need to be addressed.  When your mechanic looks at your doghouse, have him ensure your cowl flaps are adjusted per the maintenance manual.

The next thing to try is to look at different throttle settings.  At full throttle, extra fuel is added through the carburetor. Try leaving the throttle all the way in, but pull the prop back to 2500-2600 rpm.  And of course not leaning in the climb until you reach an altitude where it is necessary.

 

10 minutes ago, Andy95W said:

450-468°  is way too high.  The conventional wisdom is to keep CHTs below 400° at all times, although I will admit to seeing 410° during climb on very hot summer days.

#3 EGT 200° higher than your other cylinders is not abnormal for a carbureted Lycoming engine.

To get your CHTs lower, first step is airspeed- you should be climbing out at about 120 mph after clearing any obstacles.  Next step is to address the "box" around the engine (you'll see it referred to around here if you do a search as "the doghouse").  To have CHTs as high as yours, you probably have some significant issues with air leaks that need to be addressed.  When your mechanic looks at your doghouse, have him ensure your cowl flaps are adjusted per the maintenance manual.

The next thing to try is to look at different throttle settings.  At full throttle, extra fuel is added through the carburetor. Try leaving the throttle all the way in, but pull the prop back to 2500-2600 rpm.  And of course not leaning in the climb until you reach an altitude where it is necessary.

I agree with the dog house.  I do need the mechanic to look at it.  I am going to take the cowling off this weekend and shine a light through to see what I get.  I would love for it to be around high 300's to low 400's on climb out.  I appreciate everyone's help.  Any ideas please send them my way.

[skydvrboy]

With CHT's that high and brand new installation of the JPI, I'd first check the accuracy and calibration of the sensors.  If nothing else has changed other than the replacement of your old gauges with the JPI, then the CHT's shouldn't have changed either.

[Hank]

3 hours ago, skydvrboy said:

With CHT's that high and brand new installation of the JPI, I'd first check the accuracy and calibration of the sensors.  If nothing else has changed other than the replacement of your old gauges with the JPI, then the CHT's shouldn't have changed either.

But he might now be getting accurate readings, for the first time.

[Oscar Avalle]

Well, I share your pain! I own a M20C 1970. I had it since 2003 and my high CHTs, I particular #3 has always been a headache. I had readings similar to yours. I did everything! So let me walk through some of the things I did:

a) doghouse: I replaced my old doghouse and baffling with a new one. Results: marginal (slightly lower CHTs but still above 450)

baffling: I replaced all the baffles in particular around the cowling entrance. results: marginal

c) cowling mod: I changed the air inlet form (droopy nose was replaced with a newer looking model). Results: marginal

d) carburetor: you have to get a high fuel flow on take off (16.5 gal at least) to ensure cooling. I overhauled the carburetor and had it checked to make sure it was up to standards. Results: significant. First time CHT really changed for better. I still got 430 on number 3 but much better than 470.

e) technique: I applied a take off and climb procedure similar to the one described above, ensuring higher speed before climbing and playing with the throttle and RPM. Results: good, on average a 15 degree lower CHT

d) clean up inside cowling: you have to avoid having hoses interfering with the airflow inside the cowling. Results: marginal

e) cowlflaps: make sure that the cowlflaps aperture is large enough. Results: marginal

So my experience has been that (besides the carburetor and technique) there is no silver bullet but that all these measures help keeping the CHTs low.

I hope this helps you and does not get you even more confused.

Oscar





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[Hank]

Fuel flow needs to be higher than 16.5--the chart in my Owners Manual shows 18.2gph at sea level.

[MIm20c]

To keep the cylinders cool during the climb I have to use 25/2500. With this setting everything stays below 380. I also cruise at 22/2400 @ 9gph and everything is smooth and happy. Increasing to 24/2400 only picks up a few kts. 

[Oscar Avalle]

Fuel flow needs to be higher than 16.5--the chart in my Owners Manual shows 18.2gph at sea level.

Yes, that was my main problem with my old carb. I checked with the guys from savvyanalisys and they told me that the acceptable fuel flow was between 16 and 18.5. With my old carb I hardly got 15 on take off!!! Then overhauled carb got me 16.5 and often even 17.5. So big improvement.


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[Hector]

I get over 18 on takeoff at sea level (67C). During the worst of the summer here in Florida I have to watch it because it will climb to 420-430 if I climb at Vy for too long. Typically, I climb at Vy to 1000 AGL then quickly transition to 120 mph. With this method everything stays below 400 and below 380 if the temps are 65 or less at sea level. My typical cruise power setting is 22/2400 above 5000 and temps will stay 340-360 in all cylinders running 80 ROP. CHECK THE FUEL FLOW AT FULL POWER. CLIMB AT 120 MPH. PLUG ANY HOLES IN THE DOGHOUSE. COWL FLAPS OPEN.


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[Shadrach]

14 hours ago, Oscar Avalle said:

d) carburetor: you have to get a high fuel flow on take off (16.5 gal at least) to ensure cooling. I overhauled the carburetor and had it checked to make sure it was up to standards. Results: significant. First time CHT really changed for better. I still got 430 on number 3 but much better than 470.

I’ve always thought that the O360 was borderline on take off fuel flow. Why does an engine with same capacity (albeit slightly lower compression) consume 1-3gph less fuel  on full rich take off than it injected sibling of the same capacity. I have never seen a CHT above 420 and that incident was of my own doing as a green Mooney pilot.

[Shadrach]

9 hours ago, Hector said:

I get over 18 on takeoff at sea level (67C). During the worst of the summer here in Florida I have to watch it because it will climb to 420-430 if I climb at Vy for too long. Typically, I climb at Vy to 1000 AGL then quickly transition to 120 mph. With this method everything stays below 400 and below 380 if the temps are 65 or less at sea level. My typical cruise power setting is 22/2400 above 5000 and temps will stay 340-360 in all cylinders running 80 ROP. CHECK THE FUEL FLOW AT FULL POWER. CLIMB AT 120 MPH. PLUG ANY HOLES IN THE DOGHOUSE. COWL FLAPS OPEN.


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That’s the richest take off FF I’ve ever seen quoted for a C and I mean that In a good way. Did you sort the carb out yourself?

[Shadrach]

14 hours ago, Hank said:

Fuel flow needs to be higher than 16.5--the chart in my Owners Manual shows 18.2gph at sea level.

Most people complaining about CHTs aren’t getting that. That’s on a standard day too. It been in the low 20s here with DAs in the negative 1500-2000 range.

[Hank]

2 hours ago, Shadrach said:

I’ve always thought that the O360 was borderline on take off fuel flow. Why does an engine with same capacity (albeit slightly lower compression) consume 1-3gph less fuel  on full rich take off than it injected sibling of the same capacity. I have never seen a CHT above 420 and that incident was of my own doing as a green Mooney pilot.

There are two different carbs for the O-360, the difference seems to be mostly in the jets. If your carb has the smaller jets, it won't have high enough fuel flow.

That's all I remember right now. Searching may reveal the details, but it may not. If you don't match book fuel flow, have your A&P adjust it. If he can't adjust it high enough, do some carb research. 

[cliffy]

Here's a very good manual on how our carbs work and how to trouble shoot them.

It also gives a very good explanation of how the "economizer" works .

http://www.insightavionics.com/pdf files/MA-4 Carb Manual.pdf

Suffice it to say that an air bleed from the lower pressure in the venturi is imposed on the top of the fuel bowl to lower the "pushing" pressure pushing the fuel through the main metering jet into the discharge nozzle and from there into the engine intake. The faster the air goes through the venturi the lower the pressure in the venturi and lower still will be the "push" pressure in the float bowl. More RPM  means leaner fuel flow to engine by way of the very precise air jet in the economizer system. When NOT at WOT position. 

This is for CRUISING conditions only. FULL throttle climbing (WOT) is a different story. We need more fuel for cooling than the main metering system (with the economizer working) can deliver. For this reason they put a spring loaded shutoff needle in the air delivery channel for the economizer that shuts off the venturi bleed air to the float bowl at full throttle. When the throttle is pulled back for cruise, the spring loaded pin opens the passage and venturi bleed air is allowed to flow to the float bowl lowering the fuel flow  (by the amount predetermined by the air bleed jet) as so much fuel is now not needed for cooling purposes. 

Now, here's the kicker- This venturi bleed air reduction in fuel flow only works until you begin to use the mixture control to lean out the engine for cruise above 5,000 feet. You will be leaning to a lot lower fuel flow than the economizer system can do. You can leave the throttle wide open all the way up AND during cruise (above 5,000') and use your mixture control to lean the engine. You DON"T have to pull back the throttle to get the venturi bleed to open before you lean with the mixture control knob. The total fuel flow to the engine, through the carb will be governed by the mixture control and not affected by the economizer.  You can stay at WOT  for cruise as long as you are leaning with the mixture. It makes no difference. Low altitude cruise, without using the mixture control, is a different story. In that case you do need to pull the throttle back a little to open the bleed air needle and get rid of the extra climb cooling fuel flow. 

BTW, fuel flow in a carb'd engine is governed by the main metering jet and the mixture controls. Once the designer sets the size of the main metering jet, (for maximum delivered fuel flow) the total maximum delivered fuel flow going through the carb can not be adjusted in any way by a mechanic UNLESS the main metering jet is changed out. This is why we have different part number carbs (different jet and air bleed sizes for different engine models). Changing the jet would invalidate the model number call out sheet for parts on that model carb. Fuel injected engines are a different story.

Hope the manual helps.

[Shadrach]

8 minutes ago, cliffy said:

Here's a very good manual on how our carbs work and how to trouble shoot them.

It also gives a very good explanation of how the "economizer" works .

http://www.insightavionics.com/pdf files/MA-4 Carb Manual.pdf

Suffice it to say that an air bleed from the lower pressure in the venturi is imposed on the top of the fuel bowl to lower the "pushing" pressure pushing the fuel through the main metering jet into the discharge nozzle and from there into the engine intake. The faster the air goes through the venturi the lower the pressure in the venturi and lower still will be the "push" pressure in the float bowl. More RPM  means leaner fuel flow to engine by way of the very precise air jet in the economizer system. When NOT at WOT position. 

This is for CRUISING conditions only. FULL throttle climbing (WOT) is a different story. We need more fuel for cooling than the main metering system (with the economizer working) can deliver. For this reason they put a spring loaded shutoff needle in the air delivery channel for the economizer that shuts off the venturi bleed air to the float bowl at full throttle. When the throttle is pulled back for cruise, the spring loaded pin opens the passage and venturi bleed air is allowed to flow to the float bowl lowering the fuel flow  (by the amount predetermined by the air bleed jet) as so much fuel is now not needed for cooling purposes. 

Now, here's the kicker- This venturi bleed air reduction in fuel flow only works until you begin to use the mixture control to lean out the engine for cruise above 5,000 feet. You will be leaning to a lot lower fuel flow than the economizer system can do. You can leave the throttle wide open all the way up AND during cruise (above 5,000') and use your mixture control to lean the engine. You DON"T have to pull back the throttle to get the venturi bleed to open before you lean with the mixture control knob. The total fuel flow to the engine, through the carb will be governed by the mixture control and not affected by the economizer.  You can stay at WOT  for cruise as long as you are leaning with the mixture. It makes no difference. Low altitude cruise, without using the mixture control, is a different story. In that case you do need to pull the throttle back a little to open the bleed air needle and get rid of the extra climb cooling fuel flow. 

BTW, fuel flow in a carb'd engine is governed by the main metering jet and the mixture controls. Once the designer sets the size of the main metering jet, (for maximum delivered fuel flow) the total maximum delivered fuel flow going through the carb can not be adjusted in any way by a mechanic UNLESS the main metering jet is changed out. This is why we have different part number carbs (different jet and air bleed sizes for different engine models). Changing the jet would invalidate the model number call out sheet for parts on that model carb. Fuel injected engines are a different story.

Hope the manual helps.

If this is indeed the case (and I have been told this numerous times about various carbureted engines), why do so many folks claim to see a reduction in CHTs when backing the throttle off after take off.  I have read numerous times that that leans the F/A ratio and should indeed cause an increase in CHTs.

[cliffy]

Maybe they are going further in power reduction than the increase in temp would be with just opening the pin valve? It doesn't take much movement to open the pin valve. Maybe seeing even a slight reduction in MP is enough to cause the temps to go down? 

[DXB]

4 minutes ago, Hector said:

I get over 18 on takeoff at sea level (67C). During the worst of the summer here in Florida I have to watch it because it will climb to 420-430 if I climb at Vy for too long. Typically, I climb at Vy to 1000 AGL then quickly transition to 120 mph. With this method everything stays below 400 and below 380 if the temps are 65 or less at sea level. My typical cruise power setting is 22/2400 above 5000 and temps will stay 340-360 in all cylinders running 80 ROP. CHECK THE FUEL FLOW AT FULL POWER. CLIMB AT 120 MPH. PLUG ANY HOLES IN THE DOGHOUSE. COWL FLAPS OPEN.


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This is way outside my experience, and I have a '68C and a JPI900 like the OP.  I would love to figure out the difference one day.  There are no movable cowl flaps in the '68, but that alone doesn't seem like that makes such a difference. I've done everything reasonable to address the issue in my plane.  The doghouse is tight now.  Fuel flow is always >17gph, sometimes touches 18. Timing is fine.   I have the richer carb model (see prev. threads here - there are 3 model numbers).  I don't think there's more to do there.  I transition from Vy to 120mph IAS even well before 1000 AGL if there's no obstacles.  

On a cold winter day, I can keep hottest CHT in climb below 400, but not 380.  On a hot summer day, a carefully managed climb will keep the hottest cylinder under 420. CHT in a  bad climb on the hottest may touch 440 or even higher.  The biggest predictor of a scary hot climb in the summer is a long ground run and high CHT when starting your takeoff roll. Really limiting rpm and then leaning way back to prevent fouling does help if you must run on the ground for a while in the summer.

Fixing the doghouse may partly address the OP's problem  - bad baffling exacerbates the innate problem with the Cs, and he definitely has something going on.  But it will not fix the issue- the Cs run hot because the cowl is a crap design.  

[M20F]

18 hours ago, Hank said:

But he might now be getting accurate readings, for the first time.

Or he might not.  I would concur that validating the accuracy of the probes and the set up is cheap and easy.  Start with the easy cheap things. 

Case in point awhile ago I was having intermittent issues with an EGT probe so ordered a new one.  It sat around for a couple of weeks and finally got annoyed with the intermittent readings just pulled the old probe on my oil change.  Pulled it out of the exhaust, cut the zip ties, all the way back to find the loose connection.  We tend to be the worst practitioners of our own advice....

[Hank]

27 minutes ago, cliffy said:

Maybe they are going further in power reduction than the increase in temp would be with just opening the pin valve? It doesn't take much movement to open the pin valve. Maybe seeing even a slight reduction in MP is enough to cause the temps to go down? 

The higher I cruise, the further I have to pull the throttle back to make the MP needle move. 3000 msl, ~1/4 travel or less; 10,000 msl, about half. Then set RPM, then lean. It works for me.

I tried WOT once on a 400nm trip outbound, my way coming home. Seems the return used less fuel. YMMV.

[DXB]

Just to clarify the carb issue, there are 3 flavors of the Marvel Schleber MA-4-5 carb that are approved for the O-360-A1D in the C model:

P/Ns are:  

10-4164-1  - higher fuel flow

10-3878 - lower fuel flow

10-3878-M -  10-3878 modified to have the same fuel flow as 10-4164-1

It's worth making sure you don't have 10-3878.  Unfortunately there is no max fuel flow adjustment that can be done without removing the carb.  Changing the idle mixture has essentially no effect on fuel flow at takeoff.   I've considered removing my carb for overhaul to help maximize fuel flow (last done in 2000), but decided it doesn't make sense because its performance seems very stable now w/ >17gph at takeoff, which hasn't changed in my 5 years of ownership.  It will get overhauled with the engine when the fateful day comes.  

[Hector]

This is way outside my experience, and I have a '68C and a JPI900 like the OP.  I would love to figure out the difference one day.  There are no movable cowl flaps in the '68, but that alone doesn't seem like that makes such a difference. I've done everything reasonable to address the issue in my plane.  The doghouse is tight now.  Fuel flow is always >17gph, sometimes touches 18. Timing is fine.   I have the richer carb model (see prev. threads here - there are 3 model numbers).  I don't think there's more to do there.  I transition from Vy to 120mph IAS even well before 1000 AGL if there's no obstacles.  
On a cold winter day, I can keep hottest CHT in climb below 400, but not 380.  On a hot summer day, a carefully managed climb will keep the hottest cylinder under 420. CHT in a  bad climb on the hottest may touch 440 or even higher.  The biggest predictor of a scary hot climb in the summer is a long ground run and high CHT when starting your takeoff roll. Really limiting rpm and then leaning way back to prevent fouling does help if you must run on the ground for a while in the summer.
Fixing the doghouse may partly address the OP's problem  - bad baffling exacerbates the innate problem with the Cs, and he definitely has something going on.  But it will not fix the issue- the Cs run hot because the cowl is a crap design.  

There does appear to be quite a bit of variability between C’s. I have the Lasar cowl enclosure and adjustable cowl flaps. Cowl flaps remain wide open until I reach cruise altitude and cowl flaps closed is in reality about 1.5-2 inch open. Don’t know exactly the measurement now but they never complete close. Took of from KSSI just about one hour ago and it had to be close to 80. Temps all stayed below 400 but made sure I transitioned to 120 ASAP. Guppy mouth C’s May have more trouble keeping temps in check.


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