"Baffled" by High CHTs

[Seanhoya]

Ladies and Gents,

 

I have a recurring problem in the summer that I have not been able to crack.  I have high CHTs on takeoff.  Yesterday I got up to 413 or so on one cylinder for about 5 minutes before it cooled off.  I normally run around 350-360 each cylinder in cruise flight.  But on hot, high DA days, there seems to be nothing that I can do to cool down the engine - I even pulled flaps early and climbed at 120 MPH to try to increase engine cooling.  But still the high CHTs.  I have brought this up on the forum before, but I still have this problem.

 

I installed the LASAR cowl modification - this did nothing to cool my engine.  I rebuild the oil cooler - this did nothing.  I had my mechanic check the baffling - this did nothing.  It seems like Mooney recognized that this was a problem - my 1968 POH tells me that I should run full rich on the ground for engine cooling - they didn't really think about how bad this would fowl the plugs, though.  

 

Are high CHTs on takeoff in the summer indicative of a greater engine problem?  What else can I do?

 

Clear Skies!

 

Sean

[Marauder]

What are you flying behind? Carb or fuel injected? On my IO-360 A1A, I will normally climb at 110 KIAS on hot summer days and this will keep my temps well below 380 (usually in the 360 to 370 range). At Vy, I will see some temps go above 380 but only on really hot days.

Also do you pull back power during the climb? I leave the throttle full forward. I thought I was once told that there is an enrichment feature only at full throttle. I do lean on the ground aggressively and my temps stay well below 300 at idle.

Sent from my iPad using Tapatalk

[carusoam]

Sean's G has the carburetor...

Similar to my C, but, I only had the ships EGT and single CHT, and full guppy mouth.

At annual, I would empty the lead BBs out of the bottom spark plugs.

See if Hank has more specific CHT data from his O-360 set up...

Best regards,

-a-

[Hank]

The only thing I've been able to do with my C, with the factory single-point gauges, is watch the CHT and adjust climb speed accordingly. In summer, that is my limiting factor. I always depart and climb to cruise altitude, be it 3000 or 10,000 msl, WOT and Max RPM. In the summer, I climb at a faster airspeed which lowers climb rate, engine load, CHT and oil temp.

 

I expect to learn more about that this summer. Living on the bank of the Ohio River is humid and can be warm, but nothing like living here in Lower Alabama. So far it hasn't been too bad . . . But if memory serves correctly from living here many moons ago, July and August are generally the hottest. Back then, though, I wasn't worried about climb performance, engine preservation or even flying, I was worried about finishing homework, taking finals and getting gas for the truck.

 

P.S.--lean heavily on the ground. I generally pull it back at least halfway. I recently visited another field for the day and parked in the grass; cranked up, leaned, and when I gave it extra throttle to start taxiing in the grass to get back to the runup area, the engine sputtered badly and I reduced throttle, richened it some and tried again. I also lean again after landing, and once killed a Cessna and had to restart it turning off the runway by leaning it on the rollout like I do my Mooney. It saves fuel and keeps the plugs clean for better performance all the time.

[takair]

Check out the recent thread, O-360 Engine Help....some of that advice would apply.

[DS1980]

I have never heard of leaving the mixture full rich on taxi for engine cooling, and while I am not advocating deviating from the POH, there have been breakthroughs in the understandings of engines and spark plugs since 1968. I would suggest you explore the writings of Mike Busch and John Deakin. You are not producing enough power to worry about CHTs.

What CHTs do you eventually see if you aggressively lean for taxi?

 

If your mechanic's work was correct, I would say you're not climbing out fast enough. There are many views on airman ship, and while most are perfectly safe, there are some tricks to take advantage of the Mooney airframe. In Vegas, I would climb at Vy until I was at an altitude that I could either turn back or pick a spot in case the engine went south, I would then transition to a cruise-climb. This would put me about 120 mph. I would be climbing at 500 fpm at the same speed the Cherokees were cruising.

 

Maybe you're already doing this, and maybe you need to speed up a bit on climb out. I can't remember, what are your cowling flaps? I think they're fixed?

[lamont337]

Here's a great thread on the subject by Dan H. over at VAF: http://www.vansairforce.com/community/showthread.php?t=37835

 

I had the same problem and even though my baffles all looked correct, I still think I had the same symptom he describes (not enough air flowing from the top of the cylinder down to the bottom due to fin depth on the rear side and baffle placement).

 

I ended up spacing the baffle out a little behind my #4 which brought the climb temps down somewhere between 10-15 degrees.

 

Btw, is it just one cylinder? If so, which one?

[BigTex]

The older O-360's with the doghouse baffling just doesn't do a good job cooling on takeoff. You might want to make sure that the baffling around the nose it tucked up into the top half of the cowling. Mine was worn and kept flopping down causing air to be routed over the top of the dog house.

One of the tricks is to get to 120 MPH ASAP and then climb out at that speed or even faster if you still have cooling issues. I also on occasion (many disagree with this) I'll reduce RPMs to around 2500 at around 1000 AGL and monitor temps. When temps come down you can bring RPMs back up.

[jamesm]

I am having  similar  problems with my '67C  (Lyc O360A1D carbureted ) for me it is left side Cyl #2 & #4 on a 3 year overhauled engine.

Sometimes  I see 420 degrees f  breifly on inital climb out  and it has been driving me crazy. I have checked baffling on the ground to ensure no light leaks, on which there are none. I am not sure how else  to check engine baffling for leaks while prop is spining or if somehow engine baffles move in such a way to create holes/gaps while engine is running causing the high CHT's. I have put rubber baffle material between front baffles and the engine cyclinder to keep the cylinder cooling fins rubbing through engine baffle like it did prevously over time.

I have been pulling prop back rpm back  to 2500 rpm /25 in   immediately after take-off  ,sooner than I would have normally would have  ( yeah I know it is probably not recommended) but I wanted  to  see if that help the High CHT's prolbem . it  helps a little.

Though I operate in mild climates most of the time I have not noticed too much differece that OAT has play on my CHT's and not too sure why that would be. 

Someone here on  MooneySpace posted article about this done by Mooney Test pilot ( I think it was) talking  about cooling talking about this problem. I don't have link to it.   But like you.... I don't remember hearing/seeing a solution to this High CHT(s) problem.

For my case  ....

•  I am not sure if the answer is because I  installed Insight G3 Engine monitor which the Airplane never  had before cauing me to worry about high CHT(s) which I would have never known about CHT before I installed the Engine Monitor.
• or
• if this is  way it is  and going over 400 degree  on CHT for short periods time is "normal" for this configuration. According to Lycoming's TCDS  for my engine model max CHT is 500 degrees F to  which I hope never ever come close to. I don't recall reading/seeing some sort of engine derate like they have for engines on the  airliners.
• or ????

Sorry for my ramblings, I don't think I am helping you. Other than we may have similar CHT problems. would be curious to hear what you tried and would happy to share what I have done so far.

Good luck.

 

James

'67C

[BigTex]

One additional thing I did was to adjust the cowl flaps so that they open up more than what is called for. In fact they are almost twice what they were originally. I saw about a 5 degree drop after making this adjustment.

[carusoam]

As Gary pointed out....

The dog house in it's best condition...

- all holes, filled.

- all cracks, fixed.

- all seals replaced. (Silicone would be nice)

- all tiny screws with matching receivers (tinnermans) replaced with SS screws.

Is still missing the airflow that is found in modern cowlings. The square box and large mouth are anti-engineering for good flow...

Having the JPI would certainly be helpful.

Cruise climb at 120 seems to be the best compromise between vertical speed and cooling. Kias or mph depending on what you have...

Took me several years without MS to grasp all this...

Best regards,

-a-

[John Pleisse]

There was a previous thread where a gentleman owned a 'D" model with similar problems. He mentioned a MSC IA said higher temps were normal and that he routinely ran at high CHT's (440-460).

[Seanhoya]

James - I have has precisely the same thought-process.  I never worried about this issue until I got an Aerospace Logic 4-probe CHT sensor and could see what was happening in my engine.  Maybe what has changed is not the engine temp - maybe it is my knowledge of the temp!

 

I climb at 100 MPH (About Vy) until 1000', and then at 120 MPH (basically the cowl on the horizon).  I keep full throttle until 1000', then 25" and 2500 RPM.  I don't know which cylinder is hottest, but I seem to remember #3.  I will check the next time I fly.  My 1968 M20G is a carbuerated model and the cowl flaps are fixed.

 

On the day in question, I departed from Greensville, SC in the afternoon.  It must have been 90 plus degrees out.  I lifted off, and immediately went to 120 MPH and pulled up the flaps - I know, this isn't recommended, but I wanted to see if aggressive flying helped.  It didn't.  One cylinder stayed about 400 degrees for 5 minutes - I think it was #3.

 

I will ask the guys at Air Mods in Jersey what they think during my annual, but this isn't until November.  In any case, the plane is flying great, I just don't like to see these high numbers, and yes - OAT matters immensely. I hadn't seen over 400 degrees all winter, and I did a lot of flying.  I am using 100W oil - should this matter?

 

Sean

[scottfromiowa]

Try full power max rpm and 120. I have the same set-up and still see very good climb, I can see better and I am covering more ground. 100% agree on the importance of having dog house repaired. I have never seen a cylinder temp above 380 with this profile in climb. If still hot I would climb at 130MPH. Should still be 500FPM. I think the laser cowl closure makes a big difference in cooling with older vintage guppy mouths. Keep the throttle full....You will like the result...and you get to altitude quicker. I leave cowl flaps open for a couple minutes when I level off and wait to reduce fuel flow/prop too.

[scottfromiowa]

My number two probe has always been 50 degrees hotter than other cylinders...I had the bayonet on it. I changed it and it still reads higher in all phases. Maybe check your probe placement too?

[Marauder]

Sean - what would probably help you understand if this is normal would be if other owners would give you access to their downloaded data for the critical engine temps and the OAT. If you are flying a similar profile, the temps others experience should be close. The lower cowl enclosure didn't make of a temp change on my F model but I have heard for others that it did help a bit with their planes. I would also do some experimenting to see what it would take to keep the temps under 380. Try different air speeds and power settings. After 23 years of ownership, I have a sense of what is normal for my plane and I do fly it a bit differently in the winter and summer months. Sent from my iPad using Tapatalk

[jamesm]

Hi Sean,

I am not sure what effect striaght weight oil has in comparison  to multi viscosity wieght oil  regarding cylinder cooling.  other than I would  think that a  straight weight oil heat up quicker to engine oil operating temperature,  since the engine has no way know what type oil is in  it and we don't have to change temperature ranges for the oil viscocity we run in our engines.  I am using a multi viscosity oil 20W50   mainly because ECI and Engine overhauler recommened it. To which oil better that is debate that will probably never  be resolved.  I suppect the problem at least in my case is too much volume of air comming in to the engine and the way/ lack of  the air control and directed around the engine cylinders is the prolblem. Insteresting to hear that you don't see 400 degree plus on the your CHT's in winter months with me It seems not matter what the OAT I can hit 400 plus I am probably less likey in winter months but still can happen hit over 400 degrees in winter months if I am not careful.

Of course not being able to "leaglly" modify baffling kind of sucks  because when you look at some of these experimental
guys they some nicely and tightly cowled  airplanes and no high CHT problems.  I am the PNW we rarely see 100 degree days for more than several days period of time.  Last Annual  we   boroscoped  Cyl #2  no problems found. Not too sure what to make of this.

By no means am I knowledgeable about this subject but sometimes wonder if the magical 400 degree number was convenient rule of thumb that someone came up with to cover several different engine manufactures CHT's operating limits that stuck over period of time.   After all these are "heat" engines  aren't that efficient maybe 15% to 30% at best. So essentially we are throwing away about 80% of the energy produced by these  interal combustion engines.

 

James '67C

[Super Dave]

As others have suggested, leave the throttle full forward, and if field length permits, try no flaps on the takeoff.

[Guest]

400 degrees is not dangerously hot. My RV4 with an IO 320 will top 400 on a long climb at full power on a hot day. My IO 720 in my Comanche 400 will have some of the 8 cylinders bump into 400 under similar conditions.

Eliminating any and all holes and leaks in your baffling will help, seal it as tight as a bulls butt in fly season.

Clarence

[Hank]

As others have suggested, leave the throttle full forward, and if field length permits, try no flaps on the takeoff.

This is my normal procedure at my 3000' home field, unless loaded near gross (4 adults, or loaded for vacation with the wife). I never have any concerns about clearing the trees at the end, nor do I fly in ground effect--just straight down the runway, rotate at 70 MPH and accelerate to Vy. In the summer, I need to lower the nose some, with one eye on CHT & Oil Temp after passing through 2000-3000' agl.

On those heavy flights, I use Takeoff flaps, retracting after I watch the trees pass below. Gear up always after verifying positive rate, usually around treetop level.

[garytex]

It's hot in Texas, I almost always have to climb at 130 mph to keep cyl temps low.  I also cheat like mad when I'm light and it is  hot, and lean to 8.5 GPH.  CHTs drop like mad, and I have to slow to 120 to keep climbing.  That works on injected engines, but you might also try it on carbonated ones and see.

[pinerunner]

I heard of that enrichment feature too. It was given as the reason it is dumb to take off at reduced power settings to "take it easy" on the engine. Dumb because without full throttle you're not getting to that extra enrichment zone and might not be rich enough. 

What are you flying behind? Carb or fuel injected? On my IO-360 A1A, I will normally climb at 110 KIAS on hot summer days and this will keep my temps well below 380 (usually in the 360 to 370 range). At Vy, I will see some temps go above 380 but only on really hot days.

Also do you pull back power during the climb? I leave the throttle full forward. I thought I was once told that there is an enrichment feature only at full throttle. I do lean on the ground aggressively and my temps stay well below 300 at idle.


Sent from my iPad using Tapatalk

[pinerunner]

As others have suggested, leave the throttle full forward, and if field length permits, try no flaps on the takeoff.

Oh God, here we go with the "flaps on take-off"

[mooniac15u]

Oh God, here we go with the "flaps on take-off"

 

Aren't takeoff flaps required by the POH?  Surely everyone uses flaps on takeoff...

[Marauder]

Here we go again "flapping" our mouths off...

To flap or not to flap, that is the question. Whether 'tis nobler to flap one's take-off or let it be flap free, that is a question for all Mooneys...

Sent from my iPad using Tapatalk