Hottest CHT during climb

[231LV]

I had an early morning flight today and decided to push into the higher teens. During the climb to 16,500, I noted my hottest CHT (#3) went to 405 degrees and oil went over 210 (triggering the alarm). Outside air temp was 4 C as the temps pushed through 400...I was planning on picking up a pop-up clearance to climb into the flight levels but after seeing how hot things were getting I decided to stay at 16,500. This is the highest I have climbed since overhauling the engine about 5 years ago so maybe this is normal but I don't seem to recall these temps on the old GB engine (the OH was upgraded to an LB). Climb rate was about 650 fpm steady. Everything fully forward (except throttle)and full open cowl flaps...

Edited June 16, 2024 by 231LV

[EricJ]

What was your airspeed?   If it gets hot you can trade climb rate for more airspeed to get more air over the cylinders and oil cooler.   It's not unusual to lose cooling capacity as altitude increases and have to drop the nose a bit.

[Falcon Man]

I frequently climbed in my 231 LB to the high teens as my field elevation is 5,300 ft and I flew over the Sierras on most of my flights. To keep the CHT's close to 350F I had to open the cowl flaps all the way and set FF to ~ <1500 TIT and keep the climb rate ~ 500 fpm. Cylinder # 3 was always the hottest until we modified the cylinder baffles. On occasion I would fly out of Palm Springs and the climb rate was pretty low to keep CHT's good until I got into the cooler air.

[231LV]

OK it sounds like my engine is working as designed...lowering the nose would have been a prudent move.  I was also using about 82% of power available as I knew pushing up the power would increase the heat significantly. I also know that thinner air produces poorer cooling and combined with the turbo working harder equals lots of heat. I was trying to establish parameters for a sustained climb so I tried to keep the climb rate steady but clearly the rate needs to be a bit less to help with cooling. Thanks all

[hubcap]

I climb at 33” MP and 2600 RPM at 105KIAS with cowl flaps open and rarely do I see numbers above 370. When that happens I just lower the nose a bit. 

[Crawfish]

I often fly between 13-16K since I’ve had fuel flow adjusted to ~25.5GPH at full power, CHT’s don’t get about 350 on the way up. Full power all the way up, (no Merlyn so MP starts to fall off after about 13K) Cowl flaps full open, mixture full rich, 110-115IAS. At max gross gives me about 700-800Ft/min. 
 

oil temps I have yet to see get over 185 at any altitude or power setting. 

I’d start by checking fuel flow if you’re operating it the same way as me. If you don’t operate the same way I’d read the articles published by John Deakin I believe it was “operating the fire breathing turbo” and make your own decisions from there on how to operate! Best of luck! 

TSIO360 LB1B

No intercooler, no Merlyn 

Edited June 16, 2024 by Crawfish
Added details.

[Falcon Man]

Have you run a GAMI lean test? This information will help you determine much about how your engine is running. The GAMI spread information will tell you if your engine is producing balanced power in all 6 cylinders, based on the fuel flow spread. I have performed this test on all 5 of my K models (231, 262, 252's and Encore). Surprisingly only one of the aircraft had a fuel flow spread that was intolerable and GAMI fuel injectors were helpful in reducing the spread to less than  0.5 gph.  Also, several engines  were set up with too little of fuel flow at max power. Having similar fuel flow to cylinders and adjusted baffling went a long way in helping to level out the CHT's in climb to and cruise in the teens.

[Fritz1]

Check cowl baffles, replace dead pieces, don't count on ram air pressure to close them tight

[Fly Boomer]

12 hours ago, 231LV said:

don't seem to recall these temps on the old GB engine

As someone else suggested, you should read these articles again and again.  If you are not familiar with John Deakin, according to John, at one time he had more hours in a 747 than anyone else (39,000).  These should be required reading for anyone who flys behind a turbocharger:

https://www.avweb.com/features_old/pelicans-perch-31those-fire-breathing-turbos-part-1/

https://www.avweb.com/features_old/pelicans-perch-32those-fire-breathing-turbos-part-2/

https://www.avweb.com/features_old/pelicans-perch-33those-fire-breathing-turbos-part-3/

https://www.avweb.com/features_old/pelicans-perch-34those-fire-breathing-turbos-part-4/

https://www.avweb.com/features_old/pelicans-perch-35those-fire-breathing-turbos-part-5/

https://www.avweb.com/features_old/pelicans-perch-36those-fire-breathing-turbos-part-6-and-final/
 

[anthonydesmet]

+1 fit making sure your fuel flow is set accurately. Your temps do seem high….assuming your throttle and airspeed are set for cruise climb.  You should see about ~22.5gph to 23.5gph maybe 24gph fuel flow at your red line during climb.  I also climb at red line to high teens and not cruise climb.  Better fuel flow, performance and air and better on engine.  Did you have baffles replaced at annual?  Also the inter-cylinder baffles and sealing? I had this years annual dine at Dugosh and he found a half dozen places that weren’t sealed after my overhaul. Between the baffles and my fuel flow being set correctly during mid-summer (34c to 15c in the climb) at red line I see all temps around 360 at 120knots, ~700fpm and 23gph.

[231LV]

I have been flying this plane for about 20 years so well aware of flying behind a turbo BUT all suggestions are gratefully accepted (as OLD dogs CAN actually learn new tricks). I will have my baffles checked and have the FF adjusted up by another .5 gallon....running around 23.5 gph full throttle with intercooler and Merlyn. I posted on here because I suspected I was running hotter than I should have and since I haven't pushed it up this high, I was operating in a new environment for this engine. My old GB I took to FL220 a few times and I don't recall the temps getting as high as I saw yesterday but that was many years ago before the Merlyn was installed. I am very familiar with Deacon and his articles and have read them over a couple times and yes, I do run LOP during cruise. I think I will try another climb with the nose lower and see what that yields and will report my findings back here. Regarding the GAMI spread, yes I have run it a couple times and all cylinders are very closely matched...in fact, they will all nearly simultaneously flame out if I go too lean. I am suspecting my culprits are climbing too steep, poor fitting baffles and a fuel flow setting a bit on the lower side.

[Crawfish]

@231LVYou might even have them bring it up by a full Gallon per hour. The guys at SAVVY recommend 24.7GPH as the bare minimum. 
 

 

[hubcap]

2 hours ago, Crawfish said:

@231LVYou might even have them bring it up by a full Gallon per hour. The guys at SAVVY recommend 24.7GPH as the bare minimum. 
 

 

During my takeoff roll I get ~24 GPH fuel flow. When climbing out at 33” and 2600 RPM I get a little over 18 GPH, which is plenty to keep the CHT’s cool.

Not enough fuel will definitely increase the CHT’s.

[231LV]

10 hours ago, Crawfish said:

@231LVYou might even have them bring it up by a full Gallon per hour. The guys at SAVVY recommend 24.7GPH as the bare minimum. 
 

 

good to know, thanks

[rickseeman]

On 6/16/2024 at 7:29 AM, Fly Boomer said:

As someone else suggested, you should read these articles again and again.  If you are not familiar with John Deakin, according to John, at one time he had more hours in a 747 than anyone else (39,000).  These should be required reading for anyone who flys behind a turbocharger:

https://www.avweb.com/features_old/pelicans-perch-31those-fire-breathing-turbos-part-1/

https://www.avweb.com/features_old/pelicans-perch-32those-fire-breathing-turbos-part-2/

https://www.avweb.com/features_old/pelicans-perch-33those-fire-breathing-turbos-part-3/

https://www.avweb.com/features_old/pelicans-perch-34those-fire-breathing-turbos-part-4/

https://www.avweb.com/features_old/pelicans-perch-35those-fire-breathing-turbos-part-5/

https://www.avweb.com/features_old/pelicans-perch-36those-fire-breathing-turbos-part-6-and-final/
 

WOW I liked those charts. Thanks

[jlunseth]

I see you base in Sedona AZ. The “high, hot” climbs out of western airports in the summer are the most challenging as far as CHTs are concerned. Rather than reducing your power, you might try a full power/full rich climb. Strong fuel flow is the best way to keep cylinders cool in a high hot climb (or any other climb for that matter). The POH spec calls for 22.5-24.0 GPH at full power. It is actually best, if you can persuade your A&P to do it, to set the fuel flow for about 25 GPH. You can always reduce fuel flow with the red knob but the biggest problem I have run into is that A&Ps persistently set the fuel flow too low, so a full power, full rich climb will be at, say, 21.0 GPH. Too little fuel, cylinders will run hot. 

Also, in both my 231 engines (I replaced one in the past year) I have noticed that there is a fuel flow bump as the engine approaches full power. In other words, in the area of cruise settings you will see a more or less linear increase in fuel flow as you change settings, but as you approach full power the fuel flow will bump up more rapidly in the last inch or so of manifold pressure. You really want that full fuel flow, so even though it may seem counterintuitive, full power is the way to get the best fuel flow and actually will keep the engine cooler than a reduced power climb in my experience.

Lastly, what is “full power” in the 231? If you don’t have an intercooled engine the answer is simple, 40” MP/2700 RPM/24.0GPH . In the intercooled engine it is a little bit of a moving target. If you look at the STC instructions for setting fuel flow with an intercooler, there is a table that the mechanic is supposed to use, which says what MP will provide full power at what OAT. Most of us think of full power as 36” with the intercooler. It is actually a little closer to 37” and varies with OAT. I generally use 36” for full power climbs, but on takeoff it does not offend me if the MP gets up to 37. The important thing is to use an MP that gets you to full fuel flow, which is the way to keep the engine cool.

Two more things. One, if you want full power, and I think you do, you have to use 2700. A lower setting will reduce the fuel flow. Two, I climb at 500 fpm. Yields good airspeed and cooling. I can climb at over a thousand in the winter here in MN, but not in summer temps.

Final thought: The baffling in my old engine was not ideal. I would see temps like your 405 in high hot climbs quite often. When I had the new engine installed I was a little more demanding about the new baffling, insisting that all the leaks, seams, and wrinkles needed to get sealed. The temps in the new engine are quite a bit cooler, I mean by about 20 degrees, and also more consistent between the cylinders, so in the old engine the difference between hottest and coolest was around 85 degrees, now it is around 45. In the new engine with the new baffling if I see a temp climbing over 400 on a cylinder it is a fuel flow issue that I can adjust for rather than a systemic problem that I could not adjust for as was the case with the old baffling.

[Will.iam]

On 6/16/2024 at 7:29 AM, Fly Boomer said:

As someone else suggested, you should read these articles again and again.  If you are not familiar with John Deakin, according to John, at one time he had more hours in a 747 than anyone else (39,000).  These should be required reading for anyone who flys behind a turbocharger:

https://www.avweb.com/features_old/pelicans-perch-31those-fire-breathing-turbos-part-1/

https://www.avweb.com/features_old/pelicans-perch-32those-fire-breathing-turbos-part-2/

https://www.avweb.com/features_old/pelicans-perch-33those-fire-breathing-turbos-part-3/

https://www.avweb.com/features_old/pelicans-perch-34those-fire-breathing-turbos-part-4/

https://www.avweb.com/features_old/pelicans-perch-35those-fire-breathing-turbos-part-5/

https://www.avweb.com/features_old/pelicans-perch-36those-fire-breathing-turbos-part-6-and-final/
 

Thanks for this list of links. I thought i had read everything he had talked about in LOP operations but somehow missed this set. The amazing points i got were LOP power can equal ROP power from the charts and it winds up being about 3” more MP to do so. Also LOP high power does not hammer the piston as much as the ROP side power of the same setting. I tried his LOP climb and to my amazement first tine in the Texas 100 degree heat days and ISA +15 had my cylinder heat temps all below 360 in the climb! Where as ROP I’m pushing 395. My climb rate went from 800ft per min to 500ft per min but my fuel flow was 12 gallons compared to 24! As i got up to 8k i could close the cowl flaps to the first notch also giving me back 4 knots from less drag on the way up to 12kft. My limiting factor was trying to keep my turbo inlet temp below 1550. It hovered around 1565 but once level and accelerating it dropped below 1550. And i settled in for 9.5 ff  For a 2 hour flight normally i use close to 30 gallons due to the climb fuel but this flight it was just over 22 gallons used. It’s my new favorite way to climb by far. 

[Bigdaddie]

On 6/15/2024 at 6:09 PM, Falcon Man said:

I frequently climbed in my 231 LB to the high teens as my field elevation is 5,300 ft and I flew over the Sierras on most of my flights. To keep the CHT's close to 350F I had to open the cowl flaps all the way and set FF to ~ <1500 TIT and keep the climb rate ~ 500 fpm. Cylinder # 3 was always the hottest until we modified the cylinder baffles. On occasion I would fly out of Palm Springs and the climb rate was pretty low to keep CHT's good until I got into the cooler air.

I also have the #3 cylinder problem.  What is the baffle modification?

[Falcon Man]

In my case I wanted to raise the temp on #5 and reduce the temp on #3, so we raised the baffle in front of #5 by adding more material and cut down the baffle material from the top of # 3, to create more down flow of cooling air. We adjusted these a couple of times before finding the correct amount of adjustment. We were able to perform these modifications by removing the induction tubes over cylinder #3 and #5 as I recall.

Related, I had run a GAMI lean test and found a 0.3 gph difference between cylinder and #3 was not the leanest.

[231LV]

As a quick followup, I took the plane out this morning after I had my mechanic turn up the fuel flow. I climbed to FL190 at 500 fpm steady, full rich, full prop(2640 rpm), cowl flaps open, 100% power. Hottest CHT was 350, oil temp 173, oil pressure 53psi. The fuel flow "only showed 22 gph" but I assume closer to SL it registers higher (23.5 gph). The only "issue" was the CDT which went over 280 at FL190 and 100% power. I pulled back the power a bit and leveled off and it dropped down to around 275...I am wondering if I need a bit more fuel cranked in to cool the CDT...everything else looked fine.

Edited July 24, 2024 by 231LV
corrected word

[Shadrach]

7 hours ago, 231LV said:

As a quick followup, I took the plane out this morning after I had my mechanic turn up the fuel flow. I climbed to FL190 at 500 fpm steady, full rich, full prop(2640 rpm), cowl flaps open, 100% power. Hottest CHT was 350, oil temp 173, oil pressure 53psi. The fuel flow "only showed 22 gph" but I know closer to SL it registers higher (23.5 gph). The only "issue" was the CDT which went over 280 at FL190 and 100% power. I pulled back the power a bit and leveled off and it dropped down to around 275...I am wondering if I need a bit more fuel cranked in to cool the CDT...everything else looked fine.

Why would being close to sea level matter if you’re making 100%?

[jlunseth]

I don’t remember if you have an intercooler or not. I think not?

If you have an intercooler, then CDT is basically irrelevant. The CDT redline is in the POH for the original factory engine to protect against detonation caused by too hot induction air. If you have the intercooler, then the relevant temp for that purpose is Induction Air Temp (the temp after the intercooler). CDT is the temp before the intercooler. The difference between the two varies depending on the flight regime, but even in a climb with lower airspeeds the temp difference will be around 80 dF and you won’t have to worry about detonation.

However if you do not have an intercooler, then CDT is definitely an important redline. I have the intercooler, but I see both CDT and IAT on my JPI930 and can confirm that somewhere around 17-19,000 you will run into the CDT redline in the non-intercooled engine.

Even if you do not have an instrument like the 930 that shows both temps, the original intercooler came with a differential temp gauge, needed to be able to use the charts that tell you what MP to use. With a little mental math you would be able to read the CDT and convert it to IAT.

Putting in more fuel flow is unfortunately not going to reduce CDT. CDT is a function of how hard the turbo is working to produce a given MP, plus the lack of cooling at high altitudes. It has to run harder at higher altitudes because there is less ambient air to compress. Running into the CDT redline is unfortunately an issue with the non-intercooled engine. The solution would be to install an intercooler, which cools the induction air by quite a bit.

I have to say though, it is excellent that you are finding that higher fuel flow and full power makes the engine run cooler in a climb. That is as it should be. But you are always going to see that CDT redline problem around 17-19k so long as you do not have an intercooler. The intercooler gets you to about 22,500 (depends on day temps) before you reach Critical Altitude where the MP begins to fall off even with the MP knob full in.

[231LV]

On 7/25/2024 at 6:09 AM, jlunseth said:

I don’t remember if you have an intercooler or not. I think not?

If you have an intercooler, then CDT is basically irrelevant. The CDT redline is in the POH for the original factory engine to protect against detonation caused by too hot induction air. If you have the intercooler, then the relevant temp for that purpose is Induction Air Temp (the temp after the intercooler). CDT is the temp before the intercooler. The difference between the two varies depending on the flight regime, but even in a climb with lower airspeeds the temp difference will be around 80 dF and you won’t have to worry about detonation.

However if you do not have an intercooler, then CDT is definitely an important redline. I have the intercooler, but I see both CDT and IAT on my JPI930 and can confirm that somewhere around 17-19,000 you will run into the CDT redline in the non-intercooled engine.

Even if you do not have an instrument like the 930 that shows both temps, the original intercooler came with a differential temp gauge, needed to be able to use the charts that tell you what MP to use. With a little mental math you would be able to read the CDT and convert it to IAT.

Putting in more fuel flow is unfortunately not going to reduce CDT. CDT is a function of how hard the turbo is working to produce a given MP, plus the lack of cooling at high altitudes. It has to run harder at higher altitudes because there is less ambient air to compress. Running into the CDT redline is unfortunately an issue with the non-intercooled engine. The solution would be to install an intercooler, which cools the induction air by quite a bit.

I have to say though, it is excellent that you are finding that higher fuel flow and full power makes the engine run cooler in a climb. That is as it should be. But you are always going to see that CDT redline problem around 17-19k so long as you do not have an intercooler. The intercooler gets you to about 22,500 (depends on day temps) before you reach Critical Altitude where the MP begins to fall off even with the MP knob full in.

I am intercooled...great info and very appreciated!

[anthonydesmet]

On 7/23/2024 at 1:57 PM, 231LV said:

As a quick followup, I took the plane out this morning after I had my mechanic turn up the fuel flow. I climbed to FL190 at 500 fpm steady, full rich, full prop(2640 rpm), cowl flaps open, 100% power. Hottest CHT was 350, oil temp 173, oil pressure 53psi. The fuel flow "only showed 22 gph" but I assume closer to SL it registers higher (23.5 gph). The only "issue" was the CDT which went over 280 at FL190 and 100% power. I pulled back the power a bit and leveled off and it dropped down to around 275...I am wondering if I need a bit more fuel cranked in to cool the CDT...everything else looked fine.

Beautiful!  I’d have him dial it up a little at next oil change but sounds like things are running cooler.  Yeah, climbing at red line is where it’s at.  I still pump 23.5 through the climb.  

[231LV]

On 7/26/2024 at 2:03 PM, anthonydesmet said:

Beautiful!  I’d have him dial it up a little at next oil change but sounds like things are running cooler.  Yeah, climbing at red line is where it’s at.  I still pump 23.5 through the climb.  

Will do, sir!