M20J Cylinder Head Temps

[bruce.m]

Does anyone know why this baffle plate is installed in front of the #1 cylinder?  My #1 and #3 temps run around 40 degrees higher than #2 and #4.  So much so that with cowl flaps closed, they will get to 400+ so I run them in the trailing position to keep them well below 400.  I’ve tried adjusting the flaps and it makes no difference.  I was thinking about removing this plate to see if it changes but wanted to ask before doing so.  Thanks!

[alextstone]

18 minutes ago, bruce.m said:

Does anyone know why this baffle plate is installed in front of the #1 cylinder?  My #1 and #3 temps run around 40 degrees higher than #2 and #4.  So much so that with cowl flaps closed, they will get to 400+ so I run them in the trailing position to keep them well below 400.  I’ve tried adjusting the flaps and it makes no difference.  I was thinking about removing this plate to see if it changes but wanted to ask before doing so.  Thanks!

 

[N201MKTurbo]

That plate is there so the air flows around more of the fins. You have to remember that these are pressure cowls. The idea is to build up pressure in the top plenum which causes the air to flow around the cylinders and down to the lower pressure area in the lower plenum. 

I know it looks like the air would blow on the cylinders more if it wasn't there, but I think it may stagnate there and you would get a hot spot.

That being said, When I replaced my baffling a couple of years ago, I got that plate, but the STC for the turbo indicates a replacement plate that covers the barrel all the way to the top of the cylinder. It was pretty worn out and I didn't want to use it, and I can't replace it. I could make a new one. So I tried both of them. The cylinder ran about 5 deg cooler with the short one like you have. So I left it on.

If you want to take it off and totally violate the TC for the plane  Loosen the right screw and remove the two outboard screws so you can swing it out of the way a bit, then replace the screw in the outboard hole before removing all the screws. If you take them all out at the same time the lower cylinder baffles will fall off and it is a PITA to get them back together.

[N201MKTurbo]

3 minutes ago, alextstone said:

 

I agree compleatly!

[Fly Boomer]

14 minutes ago, alextstone said:

?

Your post must have dropped into the bit bucket. 

[Shadrach]

That is on the hot side. I would not remove the plate but would instead focus on ensuring all baffle parts and seals are properly oriented. 

[Fly Boomer]

2 minutes ago, Shadrach said:

That is on the hot side. I would not remove the plate but would instead focus on ensuring all baffle parts and seals are properly oriented. 

I see lots of engines with RTV goobered all over everything.  Does that help?

[EricJ]

5 minutes ago, Shadrach said:

That is on the hot side. I would not remove the plate but would instead focus on ensuring all baffle parts and seals are properly oriented. 

^^This.    The issue is more likely to be leaky baffles than that plate in the front, which pretty much every M20J has.

An easy trick is to open the oil filler hatch and shine a flashlight in the front cowl openings and see where the light is coming through.    Similarly you can shine a light in the oil filler hatch and see where it comes around the baffles by looking in the front openings.   That'll help get an idea of whether the baffle gaskets are sealing well or not.    It is also useful to just inspect around the baffle attachements and see if there are gaps that can be tightened up.

Also look underneath the cylinders and make sure the engine baffles that attach underneath the cylinders are there and properly attached.

Sometimes people think that opening up airflow will make it cooler, but it doesn't always work that way.   The cowl is designed to slow air down so that it flows from the high-pressure side (top) across the cylinders to the low pressure side and out the flaps.    The more time the air spends there the more heat it can absorb, so there's a tradeoff between flow and heat removal.   Opening up gaps to make more air flow may wind up making the cylinders hotter.   The best bet is to make sure everything is where it is supposed to be per the original design, which is pretty good.

[A64Pilot]

What is your cruise altitude? MP and RPM? Fuel flow?

I ask as if I’m ROP and high MP/ RPM down lower my temps will get up higher than I like requiring full open flaps, and I believe my baffling is in good shape.

But if I’m 23 squared and 8 GPH (LOP) my temps are right in the middle of the green flaps closed or trailing on a hot day.

But as was said this is a pressure cowl and the way to build pressure is to slow airflow.

Next time your around a King Air etc take a good look at its engine intake, their purpose is to build pressure of course, if you look hard the opening is a reverse funnel meaning the opening is the smallest cross section of the intake, I know it seems a funnel meaning a big opening and then narrowing down would “pack” more air in and build pressure, but that’s not what would happen.

A carburetor for example narrows down thereby increasing air velocity which causes a vacuum that sucks the fuel out, well actually the lower pressure actually allows the higher ambient air pressure to push fuel into the venturi, but you get what I mean.

So bottom line, there were smart people that designed the thing, and they did a lot of testing, there is no easy improvement available, and the way it works isn’t intuitive.

[GeeBee]

All the above is correct. Lycoming requires 4" of a H2O manometer to properly cool the engines (That is about 105 mph pressure on your pitot system). Flow is important but so is pressure. I've used everything from light in a dark hangar to theater smoke to seal up baffles. On Lycomings often the "dog house" area surrounding the starter wheel is leaky as is the rear baffle by the mags.

[Shadrach]

1 hour ago, Fly Boomer said:

I see lots of engines with RTV goobered all over everything.  Does that help?

No RTV anywhere on my baffles. My CHTs reflect healthy airflow through the engine compartment.  Cruise CHTs are always under 340°  In the hot summer months low 300s in winter. Can be difficult to keep number one and number four above 300° at sub 35° OAT.

[Shadrach]

Also, if the rear baffle seal is not dressed forward (airflow should push it against the cowl) than CHTs will be much higher. 

[N201MKTurbo]

Yes, but you have one of those fish mouth F’s. They always run cool, I owned one for 19 years.

[Shadrach]

On 4/7/2023 at 8:06 PM, N201MKTurbo said:

Yes, but you have one of those fish mouth F’s. They always run cool, I owned one for 19 years.

The design is supposedly inefficient from a cooling perspective compared to the 201 as it’s been said much of the airflow reverses direction and spills out e front. The “fish mouth” Cs don’t run cool.

[A64Pilot]

1 hour ago, N201MKTurbo said:

Yes, but you have one of those fish mouth F’s. They always run cool, I owned one for 19 years.

I think it’s primarily from running LOP.

Winter time in Fl which means temps close to but not below freezing at my normal low power cruise I have to either increase MP or enrichen to keep temps in the low green.

LOP for whatever reason, really seems to reduce Cyl head temps.

And yes, the “fish mouth” inlets are less efficient as in don’t cool as well.

Again these pressure building inlets aren’t intuitive.

‘I was heavily involved in the design and testing of this “pitot inlet” AKA pressure recovery cowling who’s purpose is to increase pressure on the suck side of the engine so that at higher altitudes the engine inlet is at a much lower pressure altitude than the aircraft, increasing HP.

‘As you can see the inlet is much smaller than the rest of the induction system.

‘I copied the photo from the Archangel’s website, it’s not my photo.

‘Look at the size of a Mooney’s ram air, intuitively you would expect it to be large, which it would be if velocity was desired, but it’s not, pressure is, so it’s small.

 

[Fly Boomer]

1 hour ago, Shadrach said:

Also, if the rear baffle seal is not dressed forward (airflow should push it against the cowl) than CHTs will be much higher. 

So the goop doesn't help.  Are your temps so low because your baffles and baffle seals are in factory-new condition?

[Shadrach]

34 minutes ago, Fly Boomer said:

So the goop doesn't help.  Are your temps so low because your baffles and baffle seals are in factory-new condition?

I can’t say. Those baffles and seals date to 2000. I stripped, painted and wet sanded  the two pieces that cover the front cylinders back in 2013 (you can see I was too aggressive on the rt piece). I did not replace the baffle seal material as it is still in good shape. Over all we have good seals and well fitting baffles, but’ I’m not trying to make it water tight. We’ve been well instrumented for over two decades. Temps have been consistent over that time. That being said, if the rear baffle is not properly oriented when the cowl is installed, everything runs significantly hotter. #3 and #4 in particular.
I asked for max permissible fuel flow when the the servo rebuilt which means even on hottest days Vx climbs are doable (for as long as you’d ever want) without over temping.

[Fritz1]

as everybody said closing gaps where air blows through makes a big difference, a couple of pieces of new baffle material, a couple of pop rives and some RTV go very far, RTV closes the smallest gaps where air blows through, switch the CHT thermocouples between cylinders, clean the connectors, maybe things are not as hot as they appear

[PT20J]

Before I would spend a lot of time chasing CHT variations, I would get an infrared thermometer and do some checking. I had a JPI EDM 700. When we replaced the engine, I installed new CHT probes. I also had fuel flow added to the EDM and the factory checked it out and calibrated it. The left side was always hotter than the right side with #2 the hottest of the bunch which seemed strange because it's out in front. Then I got a G3X with EIS installed using the same probes and wiring. Now all the temps run within 10-15 degrees of each other, the left side isn't hotter than the right, and #2 is no longer the hottest.

Whenever something doesn't measure right it's always a good practice to verify the accuracy of the measurement.

Skip

[OR75]

to answer the OP question:  no baffle plate in mine  

 

[carusoam]

The extra tall baffle plate sure looks odd…

Walk the line of Mooneys at the airport and see if anyone else has the extra plate there…

Compare to the other side….  Extra sheet metal on that side too?

Check the maintenance and parts manual… does it show all of the baffling?

 

The M20J has four cylinders that are being cooled in the top down fashion…

But air has to get in the top first…

Don’t be afraid to show the rest of the pics… if you want a more complete answer… 

baffle seals are important… starters and alternators need to be sealed properly…
 

Got an engine monitor with that?

The M20R is known to have a warm cylinder, because a piece of sheet blocks a small amount of flow into the cowl…

PP thoughts only, not a mechanic…

Best regards,

-a-

[PT20J]

[bruce.m]

On 4/7/2023 at 5:27 PM, N201MKTurbo said:

That plate is there so the air flows around more of the fins. You have to remember that these are pressure cowls. The idea is to build up pressure in the top plenum which causes the air to flow around the cylinders and down to the lower pressure area in the lower plenum. 

I know it looks like the air would blow on the cylinders more if it wasn't there, but I think it may stagnate there and you would get a hot spot.

That being said, When I replaced my baffling a couple of years ago, I got that plate, but the STC for the turbo indicates a replacement plate that covers the barrel all the way to the top of the cylinder. It was pretty worn out and I didn't want to use it, and I can't replace it. I could make a new one. So I tried both of them. The cylinder ran about 5 deg cooler with the short one like you have. So I left it on.

If you want to take it off and totally violate the TC for the plane  Loosen the right screw and remove the two outboard screws so you can swing it out of the way a bit, then replace the screw in the outboard hole before removing all the screws. If you take them all out at the same time the lower cylinder baffles will fall off and it is a PITA to get them back together.

Thank you and after mentioning the pressure differential, it makes complete sense.  

[bruce.m]

On 4/7/2023 at 6:01 PM, EricJ said:

^^This.    The issue is more likely to be leaky baffles than that plate in the front, which pretty much every M20J has.

An easy trick is to open the oil filler hatch and shine a flashlight in the front cowl openings and see where the light is coming through.    Similarly you can shine a light in the oil filler hatch and see where it comes around the baffles by looking in the front openings.   That'll help get an idea of whether the baffle gaskets are sealing well or not.    It is also useful to just inspect around the baffle attachements and see if there are gaps that can be tightened up.

Also look underneath the cylinders and make sure the engine baffles that attach underneath the cylinders are there and properly attached.

Sometimes people think that opening up airflow will make it cooler, but it doesn't always work that way.   The cowl is designed to slow air down so that it flows from the high-pressure side (top) across the cylinders to the low pressure side and out the flaps.    The more time the air spends there the more heat it can absorb, so there's a tradeoff between flow and heat removal.   Opening up gaps to make more air flow may wind up making the cylinders hotter.   The best bet is to make sure everything is where it is supposed to be per the original design, which is pretty good.

I’ve looked at the baffling and all looks good to me, but never thought of the light trick.  I’ll try that to see if shines some light on something I’m just not seeing.

[carusoam]

32 minutes ago, bruce.m said:

I’ve looked at the baffling and all looks good to me, but never thought of the light trick.  I’ll try that to see if shines some light on something I’m just not seeing.

How old is the silicone seals around your cowl?

If original… they make new ones.

We can find our silicone guy for you…

Best regards,

-a-