High CHT at cruise.

[will1874]

Cruising yesterday at 7,000'  I don't have an engine monitor. But I'm running ROP. WOT and 2300 RPM. OAT is 15°-18°C. Cowl flaps are closed when this picture was taken.

 

Nope...don't like that. I went the rest of the way with the cowl flaps open halfway. 
 

This is my first summer of ownership so I'm not sure what normal is during these warm months. 
 

What's everyone else doing with their cowl flaps in the heat of August?

(I do have plans to install an engine monitor soon)

[ArtVandelay]

Altitude?

I fly higher in summer if possible (>8000’) to get to cooler and smoother air.

What’s the 50° placard mean?

[Will.iam]

47 minutes ago, will1874 said:

Cruising yesterday at 7,000'  I don't have an engine monitor. But I'm running ROP. WOT and 2300 RPM. OAT is 15°-18°C. Cowl flaps are closed when this picture was taken.

 

Nope...don't like that. I went the rest of the way with the cowl flaps open halfway. 
 

This is my first summer of ownership so I'm not sure what normal is during these warm months. 
 

What's everyone else doing with their cowl flaps in the heat of August?

(I do have plans to install an engine monitor soon)

A little more data would help. You say ROP but are you 50 degrees ROP 100 degrees ROP or full rich? 7000ft I’m guessing 23” or 24” MP but would be better to post what your gauges indicated. 
 

My initial guess would be to double check your baffling to make sure there is not a gap somewhere. If there is not an issue there then either run more rich - cool with fuel or run LOP but I wouldn’t do LOP until you have an engine monitor that you can verify all cylinders are not too hot. Even right now you have no idea what temperature the other 3 cylinders are at. Maybe one of the other ones are at redline already? 
and yes in summer if I’m pushing the motor hard I’ll open the cowl flaps in trail to keep my cht’s below 385 (my personal limit)

[will1874]

2 hours ago, ArtVandelay said:

Altitude?

I fly higher in summer if possible (>8000’) to get to cooler and smoother air.

What’s the 50° placard mean?

I was at 7000 feet.

I don't have any idea. One of the previous owners had an affinity for label makers… My panel is covered in homemade placards. 
 

 

[mooniac15u]

2 hours ago, ArtVandelay said:

What’s the 50° placard mean?

Looks like a caution against shock cooling.  The arrow seems to indicate a movement to the left on the gauge. The full text of the placard isn't visible but it looks like it might read "50°/Min"

[Ragsf15e]

I have an engine monitor, so I can see all 4 chts exactly, but here’s a general observation that might apply… especially when flying in warmer air at higher power (but can also help up higher when thin air doesn’t cool as well too), slight changes in mixture can make a big difference in cht.  Say I’m cruising at 9500’ in warm air like last weekend. I set up ~90 ROP based off my leanest cylinder.  Im just above 65% power. I notice #3 cht is about 385.  I turn mixture slightly richer and bring down EGTs maybe 10 degrees.  The cht slowly cools to 370.  LOP it’s even more sensitive.  So maybe just try a smidge richer (or leaner if LOP) since it’s impossible to tell where you are running without a monitor.

How do you know you’re ROP and how far?  Just based off the single egt?

[Marauder]

Looks like a caution against shock cooling.  The arrow seems to indicate a movement to the left on the gauge. The full text of the placard isn't visible but it looks like it might read "50°/Min"

The infamous shock cooling. Wonder how you would go about determining 50° per minute with a non graduated marked gauge?


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[will1874]

1 hour ago, Will.iam said:

A little more data would help. You say ROP but are you 50 degrees ROP 100 degrees ROP or full rich? 7000ft I’m guessing 23” or 24” MP but would be better to post what your gauges indicated. 
 

My initial guess would be to double check your baffling to make sure there is not a gap somewhere. If there is not an issue there then either run more rich - cool with fuel or run LOP but I wouldn’t do LOP until you have an engine monitor that you can verify all cylinders are not too hot. Even right now you have no idea what temperature the other 3 cylinders are at. Maybe one of the other ones are at redline already? 
and yes in summer if I’m pushing the motor hard I’ll open the cowl flaps in trail to keep my cht’s below 385 (my personal limit)

Yes, the manifold pressure was around 23" 

I agree about the engine monitor. It was supposed to be installed at the last annual...but there were some communication issues (to put it mildly) so that didn't happen. 

[Fly Boomer]

3 hours ago, will1874 said:

Cruising yesterday at 7,000'  I don't have an engine monitor. But I'm running ROP. WOT and 2300 RPM. OAT is 15°-18°C. Cowl flaps are closed when this picture was taken.

If your CHT gauge is accurate and linear (huge if) then mid scale is 365.  For engine longevity, you should plan on no higher than about mid scale or a little higher.  No clue what the other cylinders are doing.  Do whatever it takes to cool it down.  And get an engine monitor.

[Will.iam]

4 hours ago, Ragsf15e said:

I have an engine monitor, so I can see all 4 chts exactly, but here’s a general observation that might apply… especially when flying in warmer air at higher power (but can also help up higher when thin air doesn’t cool as well too), slight changes in mixture can make a big difference in cht.  Say I’m cruising at 9500’ in warm air like last weekend. I set up ~90 ROP based off my leanest cylinder.  Im just above 65% power. I notice #3 cht is about 385.  I turn mixture slightly richer and bring down EGTs maybe 10 degrees.  The cht slowly cools to 370.  LOP it’s even more sensitive.  So maybe just try a smidge richer (or leaner if LOP) since it’s impossible to tell where you are running without a monitor.

How do you know you’re ROP and how far?  Just based off the single egt?

He could do it old school and do a big mixture pull until the engine runs rough then richen only enough until the engine stops running rough and not a bit more and he should be LOP. If while doing the slight enriching of the mixture he looks at the egt at the time it should be rising in temp if it’s level or is decreasing then he is not LOP on that particular cylinder and being a proxy only for the other three cylinders to be safe i would not run the engine more than 65% power so if another cylinder is already rich of peak at least you will not be abusing it. 

[LANCECASPER]

18 hours ago, will1874 said:

Cruising yesterday at 7,000'  I don't have an engine monitor. But I'm running ROP. WOT and 2300 RPM. OAT is 15°-18°C. Cowl flaps are closed when this picture was taken.

 

Nope...don't like that. I went the rest of the way with the cowl flaps open halfway. 
 

This is my first summer of ownership so I'm not sure what normal is during these warm months. 
 

What's everyone else doing with their cowl flaps in the heat of August?

(I do have plans to install an engine monitor soon)

Post a picture of your engine baffles

[buddy]

Try adjusting your cowl flaps so that they are about 3/8” open when you fully close them in the cockpit.  Cowl flaps are easy to adjust and should help with cooling.

[GeeBee]

Verify CHT is accurate

Then check baffles and seals

Then check magneto timing

[Nippernaper]

Try adjusting your cowl flaps so that they are about 3/8” open when you fully close them in the cockpit.  Cowl flaps are easy to adjust and should help with cooling.

This. I spent a lot of time working through baffle issues, oil cooler flushing, etc. and the ultimate solution was to adjust closed flap position in the summer months.


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[mooneyflyfast]

Here’s my ship CHT showing a similar needle position with a reading of 363 on the no. 3 cylinder on the JPI.  I believe the ship CHT probe is on number 3.  This was at 7,000 wide open throttle and 2,500 rpms OAT abour 15 C.  Cowl flaps closed.

 

I dont think you have any problem and I wouldn’t worry about it.

[Shadrach]

27 minutes ago, mooneyflyfast said:

Here’s my ship CHT showing a similar needle position with a reading of 363 on the no. 3 cylinder on the JPI.  I believe the ship CHT probe is on number 3.  This was at 7,000 wide open throttle and 2,500 rpms OAT abour 15 C.  Cowl flaps closed.

 

I dont think you have any problem and I wouldn’t worry about it.

His CHT gauge spans about 225°. Assuming it is linear, he is indicating ~420°. That’s well above normal for angle valve in cruise. I would definitely investigate before next flight. Baffle, seals and exhaust riser would be areas to focus on. Make sure the “pocket” in the baffle on the backside of #3 is oriented in such a way that air is flowing behind the cylinder.

[carusoam]

Kind of shows why the engine monitor is so popular…

The green arc of the CHT gauge is comforting until better data can be collected…

+1 for the recommendations above on how to lower or check for things that can lower the CHTs….

Getting a decent engine monitor is pretty easy… getting it installed is a bit expensive…

Best regards,

-a-

[mooneyflyfast]

3 hours ago, Shadrach said:

His CHT gauge spans about 225°. Assuming it is linear, he is indicating ~420°. That’s well above normal for angle valve in cruise. I would definitely investigate before next flight. Baffle, seals and exhaust riser would be areas to focus on. Make sure the “pocket” in the baffle on the backside of #3 is oriented in such a way that air is flowing behind the cylinder.

I think I demonstrated that it is not linear.  2 needlewidths warm of middle is not a big deal. Green means normal.  Ask your mechanic.  You are going to waste a lot of time and money trying to get that Model A gauge to read exact mid range.

 

[PT20J]

4 hours ago, mooneyflyfast said:

Here’s my ship CHT showing a similar needle position with a reading of 363 on the no. 3 cylinder on the JPI.  I believe the ship CHT probe is on number 3.  This was at 7,000 wide open throttle and 2,500 rpms OAT abour 15 C.  Cowl flaps closed.

 

I dont think you have any problem and I wouldn’t worry about it.

The factory probe is indeed installed on cyl 3 in an M20J. THE #3 CHT thermocouple for an EDM 700 must either go under a spark plug or under the factory probe. When I had my EDM 700, the spark plug probe read about 40 deg F high compared to the factory gauge. When I switched to the ring probe under the factory probe, it read about 25 deg F low compared to the factory gauge. My 1994 J had the Sigma-Tek factory gauges which seem to be more accurate than the earlier gauges,

Skip 

[Shadrach]

1 hour ago, mooneyflyfast said:

I think I demonstrated that it is not linear.  2 needlewidths warm of middle is not a big deal. Green means normal.  Ask your mechanic.  You are going to waste a lot of time and money trying to get that Model A gauge to read exact mid range.

 

The truth is none of us have any idea what the actual number is. The OP won’t know until he gets a proper engine monitor with a bayonet thermocouple.  There is parallax affecting the view of the gauge in your pic. Looking at the E and M in “TEMP”, it’s obvious his is almost a needle width higher than yours.  #3 is the cylinder most prone to over heating in this application. It can be tamed by ensuring the baffle and seals are in good shape and properly oriented. Baffle and seal issues are compound problems. The sum of many small problems can manifest as a large issue.  If I were him, I would investigate to ensure everything is as it should be. 

[A64Pilot]

Is it just me, or do you guys think 23 squared cruise in the middle of Summer cowl flaps fully closed is normal?

I open my cowl flaps as necessary to keep CHT in the middle of the green, sometimes that’s fully open, only time I cruise with them fully closed is if that gives me middle of the green.

I doubt he has a problem either, just isn’t using his cowl flaps when he should

23 squared is close to 70% power?

[hammdo]

I do that all the time  here in Texas. 23 sq 3000- 6000', cowl flaps closed, in the summer. 395° is the highest CHT temp I go. Below 3000' I go 2300 rpm and 20" cowl flaps closed. I have a G2 InSight.

No issues this far...

-Don

[PT20J]

3 hours ago, A64Pilot said:

Is it just me, or do you guys think 23 squared cruise in the middle of Summer cowl flaps fully closed is normal?

I open my cowl flaps as necessary to keep CHT in the middle of the green, sometimes that’s fully open, only time I cruise with them fully closed is if that gives me middle of the green.

I doubt he has a problem either, just isn’t using his cowl flaps when he should

23 squared is close to 70% power?

In my experience with M20Js, the CHT is dependent on a lot of variables (in no particular order):

1. OAT

2. Mixture

3. Airspeed

4. Power 

5. Cowl flaps.

If it’s running hot, I just vary mixture, airspeed and/or cowl flaps as needed depending on the operational requirements.

the later Js have the a left cowl flap that looks like the right one to allow increased airflow when closed. The older ones with the flat left cowl flap can be rigged so that the left cowl flap is slightly open when closed.

According to the power table in the POH, 23/2300 is closer to 60% power.

Skip

 

[Shadrach]

13 hours ago, A64Pilot said:

Is it just me, or do you guys think 23 squared cruise in the middle of Summer cowl flaps fully closed is normal?

I open my cowl flaps as necessary to keep CHT in the middle of the green, sometimes that’s fully open, only time I cruise with them fully closed is if that gives me middle of the green.

I doubt he has a problem either, just isn’t using his cowl flaps when he should

23 squared is close to 70% power?

My cowl flaps are almost never open in cruise. I close them in climb about 100’ shy of cruise altitude and open them when I drop the gear for landing. Keeping temps under 350 in cruise is not really a challenge. I almost always cruise at 2500rpm, max throttle and mixture setting varying from LOP to peak to best power depending on altitude and goal. My cowl flaps are placarded “Do not open above 150mph”, so they’re not even technically usable under a lot of cruise scenarios. If I’m flying high enough to be indicating less than 150MIAS the engine is not making a lot of heat.

[A64Pilot]

13 minutes ago, PT20J said:

 

According to the power table in the POH, 23/2300 is closer to 60% power.

Skip

 

I use this app, because it’s easy, and conservative, but of course it’s just engine, no airframe losses which there are always.

But it makes one wonder how or why it could be so different, my take is my J’s airframe losses are minimal, about ad good as it gets, very good induction as evidenced by the ram air being mostly ineffectual, and while I can’t validate the exhaust, based on my experience from other aircraft, in my opinion it’s a very good exhaust, good as in free flowing.

Still my point is, if the Cyl head temp is above the middle of the green, open the flaps until it’s not.

I know my baffling is in very good condition, it’s 300 hours old, and I can’t cruise 23 squared ROP in Summer with the cowl flaps closed without getting above the middle of the green, and mine are rigged so that closed isn’t fully closed