C model CHT's

[bonal]

I never climb at 100 I just don't see much gain and I like getting down range as soon as possible. My CHT peeks at just under 400 but I have a crappy old Garwin cluster so who knows what is really going on under the hood. What I do know is when I was racing sprint Karts with a Yamaha KT100 I would routinely run that engine to the 490 degree range and over 14,000 rpm and twice a season it would go in for rebuild using the same cylinder and head year after year. The rebuilds were needed if I expected to make competitive horse power. That little 100cc would make 21.9HP my point is I think our engines are a lot tougher than some would give credit

Edited October 24, 2015 by bonal

[Hank]

I routinely climb at Vy = 100 - Altitude in Thousands. I have a guppy mouth closure (whose? Dunno. How old? Dunno.) and did lots of work on my doghouse the last two annuals, which gained 10-12 mph in cruise. Wednesday evening, solo with 38 gallons, I was getting right in 1000-1100 fpm. 

Where I see the most difference in climb rate is at altitude. If I hold 100 mph, vertical speed drops below 500 fpm around 6000 msl. Then I back off to 95 mph and climb rate perks back up.

then again, I earned my license and bought the Mooney in WV. Flew it there for seven years before moving back South last year. I have noticed lesser climb rates here in the summer . . . But I only have the factory gages so I can't give complete information. 

[bonal]

With me my wife full fuel I'm getting 700 to 800FPM at 120 to 125 mph good enough to clear the east mountains with plenty of room to spare. At 100mph I get better climb rate. But I prefer the faster speed using cruise climb. Hank is your oil cooler up front next to the air intake

Edited October 25, 2015 by bonal

[Hank]

I'm not sure. I'll have to check now . . . 

[Guest]

Accurate gauges are required for this discussion to be meaningful.  Both engine manufacturers provided one hole per cylinder head for a thermocouple.  You would have to come up with a way of calibrating the factory CHT system, if that's the only system you have.

Many aftermarket systems have used ring thermocouples installed under the spark plug, others use a ring thermocouple under a Tanis heating element.  Both of these provide false readings.  The bayonet thermocouple in the factory hole is the most accurate.

Clarence 

[Taracka]

Clarence,

  good point I forgot to mention. Apparently the spark plug gasket type thermocouple can read about 40 df higher so yes, the bayonet are the type we should use for comparison.

thanks,

     Rich

[Oscar Avalle]

I agree, there may be many reasons why the gauges may read wrong... but at the end it is true that the design of the cowling is not the best. The issue is, what can we do? I have tried many things, like new baffles, climbing at more than 100 mph, etc. but what else can we do? Open the cowlflaps more? It would be great if we could get a new cowling design that could help us reduce the CHTs... but it may take a while.

[Shadrach]

Rick,

If what you say is true, then why does my "guppy mouth" F model run so cool?  I have to work pretty hard time getting #3 to 370 Even at Vx. What is it that would cause a lower compression, carbureted engine withe the same ignition timing to run so much hotter than the injected engine with the same cowl? It might be uneven F/A going to each cylinder, but the fact is, many C's have all cylinders on the high side not just one or two. So what is causing the disparity? I think theres a good chance that it has more to do with the mixture rather than the doghouse.

[N601RX]

Mooney also had a 3rd fixed cowl flap option.  I've saw some planes with it.  It covers the area between the 2 adjustable flaps and sticks down about 2 inches.

[Marauder]

Mooney also had a 3rd fixed cowl flap option.  I've saw some planes with it.  It covers the area between the 2 adjustable flaps and sticks down about 2 inches.

My 1975 F has it.

Sent from my iPad using Tapatalk

[Taracka]

The reason I don't think it is mixture is I have climbed to 10000 and had cht's stay hot all the way up with the mixture rich enough  to cause the engine to begin to stumble from it being too rich.  I haven't had the opportunity to compare the "C" to an "F" to see if there are cowl design differences.  

[Hank]

On my C, the cowl flaps are fixed. Surely this also has an effect, despite the guppy mouth closure also installed. I generally start to lean at some point in the climb. Since having my various induction issues repaired, I need to redo the Target EGT climb, and then remember to use it.

gsxr, my C left the factory with the cowl flaps riveted in place. No cowl flap lever in the cabin, no mention of it in the Owners Manual. So I don't have a whole lot of choice in the matter.

Edited October 26, 2015 by Hank

[gsxrpilot]

The last time I flew my C I had cooling problems in the climb as well. It was really the first time I'd not been able to keep it below 420 in the climb. On landing I discovered my cowl flaps were fixed as well. But they were stuck CLOSED. I made some adjustments and fixed them in the OPEN position and flew it to Maxwell's for it's annual check up. Picking it up tomorrow with working cowl flaps.

[Shadrach]

Mooney also had a 3rd fixed cowl flap option.  I've saw some planes with it.  It covers the area between the 2 adjustable flaps and sticks down about 2 inches.

My F does not have this option nor would I want it. I have a hard enough time keeping things warm down low. When I'm on the deck (say 2500msl) flying max speed at 40 LOP I can barely keep my #1 and #4 CHTs above 300 except on hot summer days. In the winter time I have to live with 280-300.

[Taracka]

It doesn't look like the center cowl scoop was available for the "c" , only the "e" model per service bulletin m20-182.  My "C" burns 18.5 gph at full takeoff power which the experts say should be enough.  Also, I have the stock exhaust.  

   

[Shadrach]

It doesn't look like the center cowl scoop was available for the "c" , only the "e" model per service bulletin m20-182.  My "C" burns 18.5 gph at full takeoff power which the experts say should be enough.  Also, I have the stock exhaust.  

   

18.5GPH under what conditions? Shouldn't full rich FF vary a bit with DA. 18.5gph would be fine at my airport in September, not so sure it would be OK in February. The DA at my airport yesterday was -1600ft with a field elevation of 703 AGL.  Do you have an engine monitor? What are EGTs doing?

[carusoam]

Taracka,

The engineers really screwed up 50 years ago...!    Really?

What is the document that clearly states the FF at take-off for your aircraft?  The TCDS?

Try not to bash the experts, then follow it up with missing data.  The strength of aluminum at 400°F...?

The experts including the ones at the factory didn't ever think you would be this interested or be this knowledgable.  Or, even have device that could do this...

They had no idea that you would buy a four chanel CHT monitor.

They had no requirement to monitor EGT.  They couldn't predict that you would buy a four channel EGT monitor either.

Their original customer was more 1 per center than we are.

Their POH wasn't a POH!

Fortunately, we have evolved at MS. We have learned to get the most out of what we have.  We have learned what CHTs work and how to keep them controlled.

Bt the time you are done reading this thread you will understand that a FF gauge and a carb Temp gauge are normal devices to have in your M20C.  Your carb already has the port for it.

Don't bother blaming the experts for what you don't have. It can't be their fault.  You can blame the guy who owned the plane before you if you want. That probably won't help either.

Now that you have these sensors, are you looking forward to the new cowling that is nearly available for the newer C's?

Heat is a known factor for cylinder wear. Internal cylinder pressure is another. Strength of aluminum does decrease with temperature but has little to do with cylinder wear. Cooler is better.

Do a search for the modern cowling, if you are not familiar...

Best regards,

-a-

Edited October 26, 2015 by carusoam

[Shadrach]

I still think it's more fuel related given the baffling has been sealed and and is in good shape. If it's not fuel related, then I would think it's engine application related. So many C drivers seem to suffer from high CHTs but rarely do you read about an F or an E owner making the same complaints. My very stock F runs very cool even when being run very hard. Why does the surplus of air from the guppy mouth not cause cooling issues for my plane? If my hottest cylinder hit 340df in cruise, I would consider that on the high side. 360-370 in high performance climbs. The only way to see anything over 400 is to hang it on the prop after leaning aggressively. There is more to the C model cooling issue than the cowl design.

 

[mike_elliott]

 It would be great if we could get a new cowling design that could help us reduce the CHTs... but it may take a while.

http://mooneyspace.com/topic/16601-vintage-mooney-cowling-mod-completion-pictures/

I have seen Dave's cowl mod during its premier unveiling at the Mooney Summit. What a great mod he has developed and will get approved soon.  After this, who knows? maybe he will do landing gear donuts, or possibly E&F induction boot.

[DXB]

I still think it's more fuel related given the baffling has been sealed and and is in good shape. If it's not fuel related, then I would think it's engine application related. So many C drivers seem to suffer from high CHTs but rarely do you read about an F or an E owner making the same complaints. My very stock F runs very cool even when being run very hard. Why does the surplus of air from the guppy mouth not cause cooling issues for my plane? If my hottest cylinder hit 340df in cruise, I would consider that on the high side. 360-370 in high performance climbs. The only way to see anything over 400 is to hang it on the prop after leaning aggressively. There is more to the C model cooling issue than the cowl design.

 

Yeah I'd be very curious to know from the engine experts on here  if and why O-360s and IO-360s cool so differently inside the same doghouse.  

So here's my data point for whatever its worth, in my '68C with non-adjustable cowl flaps: I just got the JPI-900 and now have accurate data on what my engine is doing. Taking off from 21ft AGL with temps in the low 60s this past weekend, the CHT for #3, which presumably has the worst airflow, shoots up to past 400 shortly after rotation, hits 430 climbing  at Vy up to 500 AGL.    Feeling anxious about it, I drop the nose and climb at 120mph or even a bit faster and it stops the rise, settling it in the 420s.   When I've persisted at Vy in the past, it can hit 440.   As far the as the other cylinders #2 is leanest and peaks in the 410s.  #1 and #4 barely touch 400 or stay cooler than that. In cruise there's no issues at all  - #2 is leanest and runs the hottest, but stays well below 400 even with aggressive leaning.  #3 runs in 360s under these conditions, again suggesting its issue is airflow and not mixture related.  This is corroborated further when I ground run with the cowl off after an oil change to look for leaks- with the airflow altered, #2 now runs the hottest. A final observation: though folks seems to advise against this, when I pull power back from WOT to 25-squared during climb above 500agl, I get a very favorable drop in CHT- could this mean the auto-enrich at WOT isn't working right?

So at annual in a couple months I plan to obsess over the doghouse.   The real question is how much further should I go- looking at oil cooler/vernatherm?  Maybe the oil cooler relocation mod? Surreptitiously reduce mag timing advance from 25 to 23 (as Mike Busch suggests)?    "Cooler" plugs? If you believe him, CHTs in the 430s should be taken very seriously.  If you believe much of the Mooney community, my experience is par for the course and no big deal.  I want to get this sorted out before the 90 degree days next summer...

[N601RX]

There are some internal engine differences that may affect cooling.  The 200hp engines have piston oilers that squirt oil on the bottom of the piston to help with cooling.  The angle valve cylinders are heavier and seem to have more cooling fins. I think I also remember reading the valves are larger also.  The C and E cooling may not be a simple comparison.

[Hank]

What is the document that clearly states the FF at take-off for your aircraft?  The TCDS?

Try not to bash the experts, then follow it up with missing data.  The strength of aluminum at 400°F...?

 

Do a search for the modern cowling, if you are not familiar...

Anthony, maybe he was looking in the Owner's Manual. Here's my Performance Chart for sea level, with the highest fuel flows.

I'd love to see a chart of strength vs. temperature for aluminum, especially if it had been done with an aircraft engine instead of a dogbone.

Sabremech's new cowl is very interesting, although he is being coy with pricing until after STC approval. This is quite reasonable to me. I wonder if he has a target price in mind?

[Schinderhannes]

 I can speak from experience that mixture played a significant role in excessive CHT's (especially #3) in my M20B.  My Mooney sports an aftermarket ( I am keeping names out of this) "tuned"  exhaust with polished and ported heads.  Previously my engine temp peaked at 480+ degrees almost instantaneously after take off full throttle and full rich..  I had to reduce climb rate and prop RPM to lower the power.  I kept it full rich yet couldn't keep temps below 430 in cruise which limited me to 22" and 2200 RPM.  A call to Don Maxwell said that 410-420 in cruise is typical and #3 is always hottest.  When I told him what I was running hotter, (and lacking any other mechanical problems) he said the only thing it can be is mixture...not enough fuel.  

So I made a call in to Marvel-Schebler and told the tech of my problems.  The VERY FIRST thing the tech asked me was, "What exhaust do you have?"  I told him that I have (Brand X) tuned exhaust.  He told me that he hears this all the time and to send the carb in so he can do a bench test, inspect and REPAIR the carb as needed.  He told me that the Mooney engine does well with +9 lbs/hr fuel flow increase with that particular exhaust.  You can only do this with a REPAIR, as overhauls must be brought to within specs, whereas there is a bit more flexibility with a repair.

No kiddin'!!  Climb temperatures MAX out at 420 and cruise maxes out at under 390 degrees.  Fuel flow went up a bit, but I can opt to lean as much as I need to keep it happy.   I barely even look at the CHT gauge anymore.

Phil Mc.

Do you have before / after fuel flow data?

[Oscar Avalle]

I hear you. I have obsessed over my doghouse. I even purchased a new doghouse which I plan to installed as soon as I am back in the US in December. I really don't know what else to do, but to move to a colder climate :=), which I will be doing soon.

Now, in the meantime, I looked into my cowlflaps and I decided to open them a bit more. Hopefully that will help. 

I also heard from Don Maxwell about the carburator. Once I am back I will look into that too.

Cooler plugs... may be also an option. But I agree I want by CHTs down from 440 during climb.

But at the end of the day I believe that the design of the cowling does not help...so I am looking forward to the new cowling. 

 

Oscar 

[Schinderhannes]

Oscar – Similar to you I have done a lot of work to improve my cooling and still not where I would like to be.  Changing the plugs didn't help. Obviously being based in the desert amplifies the problem. Do you have a powerflow exhaust and what is your fuelflow during takeoff / climb.  Also my 1970 model (Serial number +61 compared to yours) doesn’t have the channel on the aft side of the cowling, where the lower baffling strip rests – does yours?  

 

Frank