Deja Vu - It's summer and #2 is HOT!

[MikeOH]

Sorry, time for my annual summer whine (5 years and counting) about high CHT on #2.  (IO-360A1A, 1970 M20F)

Yes, the silicone baffling has been replaced and all the metal baffles are in good shape and properly installed (first year attempt at a fix!)

Yes, I've swapped CHT probes...NOT the probe.

So, here's the bizarre part, #2 runs hot at full power (when OAT is > 95F I have to back off power to keep #2 under 400F), yet when I get to cruise and pull mixture to LOP, #2 is the LAST cylinder to peak!  That is, it seems lean at full power, but appears the richest cylinder when at cruise (22" and 2400 rpm).  I don't see how it can be an intake leak as at full power the 'leak' would not be noticeable, whereas at reduced power the leak would manifest as a lean condition, but the mixture pull to LOP refutes that!

And, in cruise, it runs about 40F hotter than the other three: 360F vs. 320F

Incantations, voodoo, wild theories, all welcome!

[Shadrach]

10 hours ago, MikeOH said:

Sorry, time for my annual summer whine (5 years and counting) about high CHT on #2.  (IO-360A1A, 1970 M20F)

Yes, the silicone baffling has been replaced and all the metal baffles are in good shape and properly installed (first year attempt at a fix!)

Yes, I've swapped CHT probes...NOT the probe.

So, here's the bizarre part, #2 runs hot at full power (when OAT is > 95F I have to back off power to keep #2 under 400F), yet when I get to cruise and pull mixture to LOP, #2 is the LAST cylinder to peak!  That is, it seems lean at full power, but appears the richest cylinder when at cruise (22" and 2400 rpm).  I don't see how it can be an intake leak as at full power the 'leak' would not be noticeable, whereas at reduced power the leak would manifest as a lean condition, but the mixture pull to LOP refutes that!

And, in cruise, it runs about 40F hotter than the other three: 360F vs. 320F

Incantations, voodoo, wild theories, all welcome!

#2 is my richest cylinder as well. #3 is my leanest and is also typically the hottest by 15 to 20°. During LOP cruise, #2 and #3 will trade back an forth as hottest, which is to say, not hot at all (<340).  Something is weird on your end. My #2 CHT rarely gets out of the 330s and I have my timing set to the dreaded and “highly aggressive” 25° BTDC. New baffle seals don”t necessarily mean well installed or well dressed.  Maybe put a shop light inside the lower cowl and look down through the cylinder fins from the top. I think this is likely an airflow issue.

[Guest]

3 hours ago, MikeOH said:

Sorry, time for my annual summer whine (5 years and counting) about high CHT on #2.  (IO-360A1A, 1970 M20F)

Yes, the silicone baffling has been replaced and all the metal baffles are in good shape and properly installed (first year attempt at a fix!)

Yes, I've swapped CHT probes...NOT the probe.

So, here's the bizarre part, #2 runs hot at full power (when OAT is > 95F I have to back off power to keep #2 under 400F), yet when I get to cruise and pull mixture to LOP, #2 is the LAST cylinder to peak!  That is, it seems lean at full power, but appears the richest cylinder when at cruise (22" and 2400 rpm).  I don't see how it can be an intake leak as at full power the 'leak' would not be noticeable, whereas at reduced power the leak would manifest as a lean condition, but the mixture pull to LOP refutes that!

And, in cruise, it runs about 40F hotter than the other three: 360F vs. 320F

Incantations, voodoo, wild theories, all welcome!

The number 2 cylinder on our new engine in our RV7 with an O-360 was running hot as well.  We slipped two washers between the cylinder head and the metal baffle, the temperature has come down about 20 degrees.

Clarence

[Ragsf15e]

I agree it’s a cooling/airflow issue and not a lean/hot cylinder issue. Anything weird right below your #2 with the oil cooler installation or guppy mouth? It’s got to be an airflow issue.

[MikeOH]

20 minutes ago, Ragsf15e said:

I agree it’s a cooling/airflow issue and not a lean/hot cylinder issue. Anything weird right below your #2 with the oil cooler installation or guppy mouth? It’s got to be an airflow issue.

Oil cooler is stock mounting and location.  I do have an after market cowl, not guppy mouth, but not sure what brand.

[Ragsf15e]

11 hours ago, MikeOH said:

Oil cooler is stock mounting and location.  I do have an after market cowl, not guppy mouth, but not sure what brand.

Is it pretty well sealed between the front of the cowling and the cylinder?  I thought there were some places in the front air could get below before actually getting to the cylinder?

[MikeOH]

54 minutes ago, Ragsf15e said:

Is it pretty well sealed between the front of the cowling and the cylinder?  I thought there were some places in the front air could get below before actually getting to the cylinder?

I don’t know! I will check that.

Also, there is a sheet metal “half” baffle directly in front of #2 that blocks air. It has always seemed weird to me. I just looked at the parts manual and I’m not sure it’s there! Maybe part of the after market cowl? I’ll get a picture and post.

[Ragsf15e]

3 hours ago, MikeOH said:

I don’t know! I will check that.

Also, there is a sheet metal “half” baffle directly in front of #2 that blocks air. It has always seemed weird to me. I just looked at the parts manual and I’m not sure it’s there! Maybe part of the after market cowl? I’ll get a picture and post.

I have the Lasar closure and I don’t remember having anything blocking #2. Do you know which one you have?  I’ll get a picture, but might be Monday.

[MikeOH]

37 minutes ago, Ragsf15e said:

I have the Lasar closure and I don’t remember having anything blocking #2. Do you know which one you have?  I’ll get a picture, but might be Monday.

Thanks.  I'll dig thru the logs to see if I can find out what I've got.  I'll get a picture today or tomorrow in hopes someone knows if it's by design...can't imagine why it would be installed, if not!

 

EDIT: Laser cowl closure STC SA4535NM installed back in 1995

[MikeOH]

Ok here are pictures of the cowl and baffle:

[Guest]

From the IPC. It doesn’t show the additional piece in front of cylinder 2.  You could loosen the lower baffle tie rods and slip a few AN960-10 washers between the baffle and the cylinder head at item 46, to increase the airflow.

Clarence

[Shadrach]

2 hours ago, MikeOH said:

Ok here are pictures of the cowl and baffle:

Mine does not have that piece nor is are the baffles “glued” to the engine.. Use of blind rivets only on the extra piece suggests it was added after the baffle was installed.

[MikeOH]

There are two extra baffles on the number 1 side, as well.  But, I don't have an overheat problem with #1 or #3, or #4 for that matter.  I haven't been able to find any entries in the log books for these extra baffles, either.  Wonder why they were added??  And, the bigger question, do I remove them?

[Ragsf15e]

12 hours ago, MikeOH said:

There are two extra baffles on the number 1 side, as well.  But, I don't have an overheat problem with #1 or #3, or #4 for that matter.  I haven't been able to find any entries in the log books for these extra baffles, either.  Wonder why they were added??  And, the bigger question, do I remove them?

Mine doesn’t have any of those extra pieces either.  My #1 is consistently cooler than the others, so maybe a little one would help balance?  Anyway, my 2 has nothing in front of it.

[Shadrach]

Also worth noting is that #1 and #4 are my coolest (often <300°) cylinders and track within 5° to 10° of another

[MikeOH]

11 hours ago, GEE-BEE AEROPRODUCTS said:

We’re the seals die cut ?

correct thickness 

the two on the rear back are .062 thickness

 

You can’t make these correct with a roll of material.

 

 

You tell me; I bought them from YOU.

[MikeOH]

2 hours ago, Ragsf15e said:

Mine doesn’t have any of those extra pieces either.  My #1 is consistently cooler than the others, so maybe a little one would help balance?  Anyway, my 2 has nothing in front of it.

Thanks. That’s pretty good confirmation that they’re not part of the Lasar cowl STC.

[MikeOH]

1 hour ago, Shadrach said:

Also worth noting is that #1 and #4 are my coolest (often <300°) cylinders and track within 5° to 10° of another

Same here; #1 and #4 track within 10, but mine are usually around 320. Can fall to a little under 300 in colder weather if at 65% power. 
Two owners back, when the cowl was installed, the plane was based in Wisconsin. I’m wondering if the extra baffles were installed because the temps ran too low!?

[Shadrach]

2 hours ago, MikeOH said:

Same here; #1 and #4 track within 10, but mine are usually around 320. Can fall to a little under 300 in colder weather if at 65% power. 
Two owners back, when the cowl was installed, the plane was based in Wisconsin. I’m wondering if the extra baffles were installed because the temps ran too low!?

Could be. I fly in the mid Atlantic and frequently fly in the teens.  In cold OATs, #1 and #4 CHTs sometimes sometimes run in the 270s.

[PT20J]

So, here's an interesting thing. I had a EDM 700. When I replaced the engine, I replaced the CHT probes with new from JPI on Cyl #1, 2, 4. Cyl #3 had the factory probe and a sparkplug ring probe which I replaced with a ring probe on the factory bayonet. Afterwards, Cyl #2 generally read about 20 deg higher than 1 and 4 and Cyl #3 read about 20 deg lower. I expected the lower reading on 3 because of the ring probe, but I could never figure out why #2 was higher. All the probes (CHT, EGT, Oil temp) always read ambient temperature before start up. At the time of engine replacement, I sent the EDM to JPI to have it calibrated and fuel flow added.

Last year, the EDM was removed and a Garmin G3X with EIS installed. The EGT probes and CHT probes (except Cyl #3) were retained and a new JPI bayonet CHT probe replaced the factory probe in Cyl #3. Now, most of the time all four cylinder CHTs are within a few degrees of each other.

I kind of wonder how accurate some of this instrumentation really is.

Skip

[MikeOH]

18 minutes ago, PT20J said:

So, here's an interesting thing. I had a EDM 700. When I replaced the engine, I replaced the CHT probes with new from JPI on Cyl #1, 2, 4. Cyl #3 had the factory probe and a sparkplug ring probe which I replaced with a ring probe on the factory bayonet. Afterwards, Cyl #2 generally read about 20 deg higher than 1 and 4 and Cyl #3 read about 20 deg lower. I expected the lower reading on 3 because of the ring probe, but I could never figure out why #2 was higher. All the probes (CHT, EGT, Oil temp) always read ambient temperature before start up. At the time of engine replacement, I sent the EDM to JPI to have it calibrated and fuel flow added.

Last year, the EDM was removed and a Garmin G3X with EIS installed. The EGT probes and CHT probes (except Cyl #3) were retained and a new JPI bayonet CHT probe replaced the factory probe in Cyl #3. Now, most of the time all four cylinder CHTs are within a few degrees of each other.

I kind of wonder how accurate some of this instrumentation really is.

Skip

Yes, I've always wondered about accuracy on these monitors, as well.  As you say, they all read within 1 degree at ambient.

However, I swapped the probes on #2 and #4...and, then "#4", really number 2, ran hot.  So, I concluded it wasn't the probe but cylinder #2 was hot.

[Ragsf15e]

13 hours ago, MikeOH said:

Yes, I've always wondered about accuracy on these monitors, as well.  As you say, they all read within 1 degree at ambient.

However, I swapped the probes on #2 and #4...and, then "#4", really number 2, ran hot.  So, I concluded it wasn't the probe but cylinder #2 was hot.

No air blocking pieces on mine.  PRC sealing a few gaps along the edge.

 

[Shadrach]

Box stock 67F front baffles.  I don’t think the goofy caulk  that I’m seeing in other other applications serves much purpose.  This engine runs very cool without it…in spite of the 25° ignition timing.

[Bunti]

It looks to me that the SB-182 had been installed in this Mooney. 

https://mooney.com/wp-content/uploads/2020/12/SBM20-182.pdf

That includes the pieces of metal in front of cylinder 1 and 2.

[Ragsf15e]

5 minutes ago, Bunti said:

It looks to me that the SB-182 had been installed in this Mooney. 

https://mooney.com/wp-content/uploads/2020/12/SBM20-182.pdf

That includes the pieces of metal in front of cylinder 1 and 2.

Nice find! Yes it does look like that!  I wonder if he has the fixed air scoop it mentions?