High CHT's on Takeoff

[jetdriven]

Im not sure about a C model, but the J fuel pump is delicate becasue the seal will wear and leak. There is more info on BT but it has a carbon seal which overheats and goes bad easily.  We ruined a new OH fuel pump in one flight leaving it on for takeoff and landing practice. After asking around,  lots of M20J pilots use it for starting only, and keep in mind the first sign of fuel pressure fluctuation or engine problems, turn it on.  At that point it is an operational decision. Running the pump continuously is hard on it, but flying the plane througn trees, water, dirt, or a mountain is ever harder on it.

[Oscar Avalle]

Ever since installing my EDM-700 I've been fighting/obsessing over really high CHT's on take-off. As soon as I take off, my CHT's spike to an alarming 450 degrees for about 3-4 minutes. As soon as I can back off on power and gain climb out airspeed (~ 120mph) all of my CHT's come back down in the 350-380 range. Any thoughts or techniques on how to keep down or better manage CHT's on take-off?

 

Gary

I had a similar problem with my M20C. My CHT 3 always went through the roof as soon as I took off. Once I even aborted a take off and declared an emergency. 

 

After consulting a lot and listening to advice from our friends on this Board, I was able to figure out what was going on. The cowl flaps in my M20C are fixed and they were closed. So I opened them to about an inch and a half and the temperatures at take off went down. I also changed my climb procedure, as soon as feasible I let the plane speed up to 120 mph and use that climb speed. It may take a little longer to get to my 8 or 11 k that I have to use around here, but the CHT stay where they should be. Hope this helps...

[Alan Fox]

Was your engine monitor a new install , or a upgrade from a gem.......On my beech I did a gem upgrade , and the JPI reads the gem (insight) probes about a hundred degrees hot , even if programmed for the gem probes.... I replaced the probes and the temps went down 100 degrees or so....

[rbridges]

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[jimosborn]

Hi again, Gary:
 
It's curious that all the logical remedies suggested to cure your high CHT problem have thus far yielded so little improvement, which indicates some underlying problem not yet identified.  So the challenge endures!  Perhaps clues may be found in the data collected by your JPI; my question then is whether or not you've downloaded and/or analyzed all the trip data since the JPI was installed.  If so, can you upload some of these to this thread (or else numbers from your notes or memory) for our neophyte analyses? 

 

What interests me, specifically, is peak EGT & CHT for each cylinder under the following conditions (IAS is not important for this exercise - just needs to be steady under each scenario):

 

CLIMB   -  WOT, Full Rich (specify FF) @ Max RPM

CLIMB   -  WOT, Full Rich @ your preferred climb RPM (please specify RPM and FF)

CRUISE -  WOT, Full Rich @ your preferred cruise MAP/RPM/ALT (specify each + ALT)

CRUISE -  Your preferred MAP/RPM/ALT - mixture leaned either ROP or LOP (specify each parameter)

[BigTex]

Hi Jim, I believe I have made some progress by adjusting my climb out and fighting up the Doghouse. I uploaded my last flight and posted it on the "strangest failures" thread. I plan on doing some of the recommendation made here. Namely WOT/2600 rpm on climb out and see if that changes my temperature profile.

[jetdriven]

Hi Jim, I believe I have made some progress by adjusting my climb out and fighting up the Doghouse. I uploaded my last flight and posted it on the "strangest failures" thread. I plan on doing some of the recommendation made here. Namely WOT/2600 rpm on climb out and see if that changes my temperature profile.

Im not sure what the aversion to 2700 RPM is, but runing WOT and 2600 RPM increases cylinder pressure over that of 2700 RPM. Both are probably within limits, but why give up 200 FPM in climb only to run more cylinder pressure? There is no benefit.

[BigTex]

Actually... That was a typo... I meant to say 2700.

[jimosborn]

Hi Jim, I believe I have made some progress by adjusting my climb out and fighting up the Doghouse. I uploaded my last flight and posted it on the "strangest failures" thread. I plan on doing some of the recommendation made here. Namely WOT/2600 rpm on climb out and see if that changes my temperature profile.

 

Gary, glad to hear of some progress.  You sure had an interesting experience with the separated MAP line... appreciated seeing #25 JPI download, about which I posted a few thoughts.   BTW, what was your cruise FF and altitude during that event?

 

Further to musing your CHT issue, if you are inclined to post them I'd like also to see JPI data from the two previous flights, plus #26 if and when that comes about... including FF and ALT for those as well. 

 

Cheers!

[Seanhoya]

Hey guys - I am new to this forum.  I just wanted to chime in that I have experienced nearly the same issue - I put in a four-plug CHT probe, and immediately realized that my #3 cylinder peaks at around 420 on takeoff.  With my old CHT sensor, its position never really alowed me to see it well enough to tell if it was above 400 (given the effects of paralax).

 

Of course, lowering my pitch, shortening the time from engine start to takeoff both help.  But when you fly out of an airport surrounded by small mountains, and in the goo at that, you have to pitch for Vy regularly.  I fly out of Monterey.

 

I replaced my oil cooler - that helped speed oil cooling once I level off.  I had my mechanic check baffling - that may have helped with about 10 degrees.  I changed my carbuerator - dont know if that helped at all.  I put in Lasar's engine-cowl speed mod - that didn't help at all with temperature.

 

Frankly, I think that older Mooneys simply run a bit hot, and when we put in these after-market CHT gagues, we realize that they are running hot!

 

If anyone has any other advice, I would love to hear it.  Of course, in the back of my mind, I wonder if my 500-hour engine is going to need an overhaul - I am getting slightly rising iron levels, but I had to let the plane sit for quite a while last year.

 

I can't change my cowl flaps - they are fixed, from what I understand with a 1968 M20G.  Someone mentioned moving the oil cooler - that strikes me as drastic.

 

Any recommendations are apprecated - but I am not going to pul back on power, or forgo Vx climbs simpy because I get a hot cylinder temperature - I saw temps once as high as 450 degrees in Truckee Taho, but my option was to plow into the side of rising terrain, so I accepted the hot temp for a few minutes.

 

Regular takeoff temps generally run around 410 or so for one cylinder - usually #3.  It's frustrating, but I am not going to limit engine power to fix it.

 

V/R,

 

Sean

[BigTex]

Hi Sean, Welcome! You mentioned that #3 is 40-50 degrees hotter than the rest. That's the cylinder that the original CHT gauge is connected. If you use the spark plug probe, you will see that kind of delta. Does the original CHT gauge agree with your engine monitor?

[Seanhoya]

Hey Gary,

 

I replaced the original CHT probe with a TSO/STC'd Aerospace Logic 200 series four-cylinder bayonette probe system.  It's kind of funny, because I think my mechanic commented that the probe that he took off my engine was actually a Cessna CHT ring-probe attached to my Mooney gague - one of many issues I have discovered with my engine over the last four years.  The gague actually went bad on the original Mooney 6-pack, and rather than search for a used gague, I elected to go with an aftemarket solution.  Overall, I have been very happy with Aerospace logic's equipment, although getting the part through customs proved to be a hastle.  So after I installed the CHT probe, I noticed the issue with temperature.

 

One thing I haven't done is installed a newer air-filter system.  I have the Bracket-style air filter, which once got so clogged when flying in Mexico that I couldn't even turn over the engine.  I have toyed with installing one of those automotive-style air filters (another Lasar Mod),  which could help with temperature theoretically.  But I am somewhat loathe to do anything else, having already tried a number of tricks to lower CHT temperature.  BTW - the engine runs at 340-350 degrees straight-and-level.

 

One more thing - you probably know this, but the M20G has a normally aspirated IO-360.  So in my mind, when it comes to temperature, its really an issue of fuel, oil, and air.  I put in a remanuafactured carbuerator, put in a newly rebuilt oil cooler, and put a mod on the cowling to try to improve air pressure through the engine cowling.  None of these changes really helped, though.

 

V/R,

Sean 

[danb35]

One more thing - you probably know this, but the M20G has a normally aspirated IO-360.  

Actually, the G has an carbureted O-360--an IO-360 would be fuel-injected.

[Seanhoya]

Dan, Thanks for the note. The reason that I mentioned that I fly a carbuerated aircraft is that normally-aspirated engines cool differently than fuel-injected engines. Fuel cools a cylinder, and a carbuerated engine is less precise in terms of how much fuel is added. My experience has been that the vast majority of Mooney pilots and mechanics are now working with fuel injected engines, which don't behave precisely the same way as the old O-360s. So we have to be careful when comparing anecdotal evidence, because what works in an F model may not apply to a G model, and vice-versa. My overall point is that there is some evidence that there was a design flaw with the older Mooneys that the folks at Mooney were well aware of - that they run hot. My 1968 POH actually recommends to taxi at full-rich in order to avoid overheating. If I did that, I would never get off the ground due to fouled plugs! In the original configuration with the 6-pack of gagues, the CHT gague is located on the right side of the dash, and consists of a simple analog indicator. It is somewhat difficult to see the gague, and certainly is difficult to determine is an engine is running 20 degrees over 400. Now that many of us are beginning to install modern CHT probes and gagues, we have a level of precision that was never available in the original aircraft. My broader point is that what has changed may not be overheating engines, but rather pilots who are now aware of them! Or not - it could be a problem with my engine. But I suspect not. Appreciate your advice and thoughts. What about putting in tuned exhaust - will that cool an engine? My sense is that as an engine progresses through its 2000 hour TBO, it will begin to run hotter - any thoughts? V/R, Sean

[Seanhoya]

I just had a realization - I think that my engine is running way too lean.  Apparently, Mike Busch recommends that your full-throttle EGT should be 200-250 degrees rich of peak.  Mine is somewhere around 100 - I think this may be why I am occasionally seeing above 400 degrees CHT on takeoff.  It seems remarkably simple, but I need to try this out.

Does anyone know what Lycoming recommends with regard to tuning an engine?  Is it similar to Mike Bush's recommendation?  I just need something to reference with my mechanic. 

 

V/R,

Sean

[jimosborn]

Sean: I think you're right about way too lean!

 

I don't have actual specs but can vouch for Mike's 250 ROP recommendation as being bankable. Too, target EGT at that point should be somewhere in the 1250^o to 1300^o range. 

 

Now all this is predicated on proper fuel flow setup, which for your engine @ SL, WOT, 2700rpm should be about 18 gph - or a bit less but not less than 16 gph .  Do you  have a FF indicator to validate that?

 

Symptoms at first-glance suggest low fuel flow as the prime suspect  But conflictingly your comment about fouled plugs during taxi  suggests FF being amply rich.  If amply rich, we are then alerted to the possibility of magneto timing being too far advanced, which will always be reflected in higher than normal CHT and lower than normal EGT.

 

TCDS E-286 specifies 25^o BTC for the O-360-A1D engine.

Cheers 

[Seanhoya]

Jim,

Thanks so much for your comments. My problem is that my mechanic thinks that the mixture is good - I actually can see a 25 RPM rise when I shut down the engine with mixture control (I hold 1000 RPM, then pull out the mixture control, and see a rise of 25 RPM - this is supposedly a good indication of proper mixture). But full-rich EGTs generally run around 1380 on climb, and peak EGT is usually around 1480-1500 degrees.

I don't have an engine analyser, I just have a four-probe 100-series Aerospace Logic EGT sensor, and a 4-probe 200-series CHT sensor. So I have good info about temperatures, but I can't download it. I don't have a fuel flow sensor, but I think that full-rich fuel flow is more like 12 gallons (anecdotal evidence only - I generally cruise at 22"and 2400 RPM and lean). But even when I cruise at 24"/2400 and don't lean, I don't think I have ever experienced more than about 12 GPH fuel burn.

Yes - my plugs do foul if I don't lean. And my plugs also have a bad tendency to go bad - I think I replaced two at my last annual, and two just a few months before that. I have heard that the fine-wire-type plugs are better for Lycomings.

I am not familiar with target EGT - what does this mean exactly?

V/R,

Sean

[danb35]

But full-rich EGTs generally run around 1380 on climb, and peak EGT is usually around 1480-1500 degrees.

Absolute EGT values don't mean much, but this does sound pretty high.  If full rich for you is only 100 degrees ROP, you're definitely running too lean, and my understanding of the design of the carburetors is that the idle mixture doesn't really have anything to do with the full-throttle mixture.

 

Fuel flow instrumentation and a good recording engine monitor are very valuable tools for all operators, not just those who run LOP.

 

Target EGT is a method of leaning in the climb.  It involves noting the EGT at full rich, full power, and sea level (or close to sea level), and leaning in the climb to maintain that EGT.  Most people seem to find that the target EGT is around 1250 degrees F, +/- 50 degrees.

[jimosborn]

Jim,

Thanks so much for your comments. My problem is that my mechanic thinks that the mixture is good - I actually can see a 25 RPM rise when I shut down the engine with mixture control (I hold 1000 RPM, then pull out the mixture control, and see a rise of 25 RPM - this is supposedly a good indication of proper mixture).    Sean, sounds like your idle FF is just fine, but keep in mind that idle mixture is independent of the mixture control.

 

But full-rich EGTs generally run around 1380 on climb, and peak EGT is usually around 1480-1500 degrees. 

This depends on power setting.  If full throttle and 2500-2700 RPM, target EGT should be somewhere in the 1250^o to 1300^o range.  Else suspect FF set too low.

 

Any throttle reduction in climb tends to lean the mixture by disabling a full throttle auto-enrichment feature designed into the carburetor to prevent detonation at max power.  To a lesser degree, some leaning takes place upon RPM reduction due to slowing of the mechanical fuel pump (thus less fuel pressure), but if FF is set up to spec this has very little impact.

I don't have an engine analyser, I just have a four-probe 100-series Aerospace Logic EGT sensor, and a 4-probe 200-series CHT sensor. So I have good info about temperatures, but I can't download it.  Good enough!   I don't have a fuel flow sensor, but I think that full-rich fuel flow is more like 12 gallons (anecdotal evidence only - I generally cruise at 22"and 2400 RPM and lean). But even when I cruise at 24"/2400 and don't lean, I don't think I have ever experienced more than about 12 GPH fuel burn.  Depending on altitude, your full-rich12 gph FF sounds okay at cruise .  But for this exercise we're addressing only TO & CLIMB FF, so without a way to measure that at the panel it will be necessary to have your Mooney savvy AP/IA check the fuel flow setup for proper settings.

Yes - my plugs do foul if I don't lean. And my plugs also have a bad tendency to go bad - I think I replaced two at my last annual, and two just a few months before that. I have heard that the fine-wire-type plugs are better for Lycomings.   Are you running Champions?  There's been quite a lot of chatter over on Beech Talk about bad Champion plugs now and recent past.  The consensus among pilot and mechanics alike is that modern Tempest plugs are the answer to most such issues.  

I am not familiar with target EGT - what does this mean exactly?   See dand35's excellent definition above.

Sean

Cheers.  Jim Osborn

[kurtsnyder]

Well, I am having the same exact problem. I have an Insight G2 and can't figure out why I'm getting such high CHTs on climbout. I hit 490 on #4 cyl last summer on a really hot day. I was panicking! I always climb at WOT, full rich and I normally use 2500 RPM. I also climb at 120MPH+. That day, I leveled off, tried climbing faster, pulled out power, increased power, played with the RPM. I tried everything and it just wouldn't cool down until I was leveled off in cruise. Then #3 and #4 are my hottest and run anywhere from 340-370 in cruise.

 

I got 430 deg on #4 cyl climbing out today. It was about 43 degrees outside, I was climbing full rich, WOT and max RPM at 120mph with cowl flaps open. Couldn't get the temp down until level off. That's way too hot for such a cool day. I talked with my mechanic and we're going to check the timing of the mags. I'm also wondering about my WOT fuel flow and maybe that it's too lean. I can't remember off hand what it is, but I'm thinking about 14gph. Oh, and the oil temp always seems to be fine. The engine runs great. I just don't want something to fail prematurely because of such high CHTs.

[jimosborn]

Wow Kurt, those extremely high CHTs are horrible; no wonder you were near panic.

 

14 gph, full rich, WOT for a 180 hp engine is quite low; should be more like 16 -18 gph.  Too, a properly set up fuel delivery system should yield EGTs in the neighborhood of 1200^o - 1300^o F.  What kind of EGTs were you seeing both today and in those earlier scenarios?

 

Good that you are having timing looked at.  Surprisingly small advances in mag timing affects CHT adversely, yet timing seems a too frequently ignored troubleshooting item.

 

Hope you get it all straightened out soon.... and please share your findings.

 

Cheers

[bd32322]

What about a bad probe? Can timing affect temps in one cylinder only?

[jimosborn]

What about a bad probe?  Certainly a bad probe is one consideration.  My personal experience is that they either work or they don't. YMMV

 

Can timing affect temps in one cylinder only?   NO!

 

Cheers!    Jim

[DonMuncy]

My personal experience is that they either work or they don't.

I had a bad probe that read high.

[DonMuncy]

Sorry, that was not Jim's quote.