AVSIG: High CHT @ High Altitude wwswsigarch.jpg (7236 bytes)

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AVSIG Discussion Sections >> Training & Proficiency

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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
High CHT @ High Altitude
      #248263 - 05/21/09 11:15 AM

Flying my Turbo Saratoga above 12000 feet or so usually results in CHT trying to go above 400F. I fly at relatively low power settings and find this difficult to manage. Last year I especially had a problem over the Rockies when the only way I could get the CHT down was to descend.

Yesterday I was flying at 12500. The usual pattern began. All is fine for some time, half hour or more of cruise, stable CHT around 380. OAT 4C. Then a slow increase begins. After another half hour or so, the CHT is pushing 400 and increasing more rapidly. OAT still 4C, all settings still the same.

After levelling off for cruise and getting up to speed, I pull MAP back to 30", RPM back to 2400, and FF to 13.2-13.6 GPH, which gives a LOP TIT around 1550 (stock injector nozzles). Yesterday I further reduced power by reducing RPM to 2200 which runs a little smoother. Everything was nice and stable for a half hour or so, then reference the previous paragraph. After reducing MAP to 28", everything stabilized again. Last year over the Rockies at 16500, I couldn't fix it by reducing power, it reduced airspeed so much, and I had to descend. Fortunately I had passed the highest terrain and the terrain was slowly sloping away from me, so a slow descent to follow the terrain worked.

Oil temp also increased, from 199F or so to 205F or a little more. This was on the factory instrumentation, my EI engine monitor showed 220+ and gave a high temp alarm.

I haven't tried running ROP in this situation, maybe that will help, but will have to be planned for in the fuel/payload.

Does anyone have any experience or advice in managing this problem?

--------------------
Best Regards,

Stan


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Dave Siciliano (ADS)
Top Gun


Reged: 05/17/04
Posts: 8469
Loc: ADS (Dallas, TX)
Re: High CHT @ High Altitude [Re: Stan Prevost]
      #248272 - 05/21/09 11:48 AM

Stan: We are running our P-Baron higher than you are running your plane and not having that problem. We consistently run about 2200 with 35" of MP at 16.5 to 17 gph and all CHTs are 380 or less. I don't understand why your CHTs are rising after 30 minutes of stable operations with no power changes. Sounds like you really need to speak with the TAT fellas about what may be going on.

I assume you checked engine baffling to be sure something didn't get moved or sealed improperly.

Have you done a GAMI lean test to see what the spread on your cylinders is? I wonder if one or more is rich when another is lean. Still, I don't understand why CHTs would rise after stabilizing. Fuel injectors could change temps if one is plugged or not performing properly. Maybe changing fuel flows in flight even through your mixture isn't changing.

Wish I could be more help. Please keep us informed.

Best,

Dave


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Scott Dyer [HPN/NY]
Top Gun


Reged: 01/11/03
Posts: 20065
High CHT @ High Altitude [Re: Stan Prevost]
      #248276 - 05/21/09 12:05 PM

Stan -- First step is to ensure that all your baffles are in good shape, no
leaks around flexible seals, etc.

I am taking as a given that your cowl flaps are nearly fully open and you
still have the temp problems over time?

--------------------
www.scottdyercfi.com


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Re: High CHT @ High Altitude [Re: Scott Dyer [HPN/NY]]
      #248339 - 05/21/09 07:50 PM

Dave, Scott -

No cowl flaps on this airplane. I actually had this same problem with the prior Saratoga, a 1980 turbo with intercooler. This one is not intercooled. Different engine variant, TIO540S1AD then, TIO540AH1A now. The increasing temp and rate of rise has always been very puzzling, like some kind of runaway process.

I have done the lean test, that's how I decided to not buy GAMIjectors. Had them on the previous 'Toga. I have had this airplane for three years. I got the EI UBG16 analyzer installed in Dec '06 or Jan '07, and set the Normalize function then. Still, in normal cruise, it looks just like it did then, I haven't changed the Normalize. All cylinders are well LOP, and the Normalize function on the EI doesn't show any cylinder EGT changing realtive to the others. Flat line across the tops. Weelll, let me think about that. It's true at 30"/2400, flat line across the top. But I have noticed that if I change the engine operating condition, like 25"/2400, or 30"/2200, the EGT distribution does change some. Sometimes the right side of the engine will have slightly elevated EGT, or the left side has slightly depressed EGT, such that alternate columns on the Normalize display are up and down a little. I have never thought much of it, and maybe it led me to overlook a small change during the temperature increasing condition.

One thing I tried, out of guesswork, was to increase RPM from 2200 to 2300, to maybe reduce peak cylinder temp and pressure a little. It increased CHT.

I haven't gone back through the recorded data to see if all cylinders are following the same pattern, I need to do that. But I suspect so, since the oil temp is tracking along, to a lower degree.

Oil analysis is always good, no metal in filter. Oil/filter change at 30/35 hours. Spark plug cleaning, inspection, and rotation every other oil change (despite Walter's ridicule <g>).

--------------------
Best Regards,

Stan


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Sean Franklin
Top Gun


Reged: 08/15/04
Posts: 2566
Loc: Eureka Springs, Arkansas
Re: High CHT @ High Altitude [Re: Stan Prevost]
      #248357 - 05/21/09 11:31 PM

Nothing like that on my end, including multiple 3+ hour flights at 17,000+. I also have stock injectors but the GAMI lean test showed that LOP is not a good solution for me with these injectors, so I fly ROP. That changes everything, of course, but I will say that I see very stable temps even over multiple-hour flights.

--------------------
Eureka Springs, Arkansas


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Re: High CHT @ High Altitude [Re: Sean Franklin]
      #248360 - 05/21/09 11:46 PM

Thanks for the info, Sean.

My temps are stable at lower altitudes.

Next time I will have to try going ROP and see how that does. I'm dubious of crossing the Rockies again until I get a handle on this. I did one Rockies crossing two years ago with no problem.

--------------------
Best Regards,

Stan


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Re: High CHT @ High Altitude [Re: Dave Siciliano (ADS)]
      #248362 - 05/22/09 12:54 AM

Quote:

We consistently run about 2200 with 35" of MP at 16.5 to 17 gph and all CHTs are 380 or less.




Dave -

Off topic, but my Lycoming charts don't show anything higher than 34" for 2200RPM for TIO-540-S1AD or -AH1A. What engine do you have?

--------------------
Best Regards,

Stan


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Nigel Thompson(1D2)
AVSIG Member


Reged: 04/30/04
Posts: 610
Loc: Ann Arbor, MI
Re: High CHT @ High Altitude [Re: Stan Prevost]
      #248371 - 05/22/09 08:21 AM

Stan, do you have recording engine monitor? If so, if you look hard at the data for the flights in question you may be able to find some clues.

If it is as you say, stable for a period of time, and then rising, something has changed. The number of variables are not large. Most likely culprit is fuel flow, if ambient temp, IAT, MP and IAS are the same. Much less likely is ignition timing drifting at high altitude (for which offhand I cannot think of a failure mode). If you are running fairly close to peak on the lean side, small FF excursions in the rich direction will give the symptoms you describe (as would ignition timing advancing).

What mags are installed? When was the timing last checked?

Do the old analog instruments track the same trend? We need to eliminate power supply or other common mode problems in the engine monitor.

I don't think I have ever flown a turbo Saratoga, but my various TN Bonanza's have never exhibited this problem up to 23000.

Nigel.


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Stan Prevost
Public Guest


Reged: 06/02/04
Posts: 773
Loc: Huntsville, Alabama
Re: High CHT @ High Altitude [Re: Nigel Thompson(1D2)]
      #248397 - 05/22/09 11:47 AM

Nigel -

I am going to try to get out today and download the data from the engine monitor and generate some plots. Although, it doesn't have all the parameters, notably fuel flow, manifold pressure, OAT and RPM. This airplane has a combo analog/digital panel, and data can be recorded from the digital part, but it doesn't store data. I can't deal with the in-flight distraction of having the laptop hooked up and recording the data, and the batteries won't last out the flight anyway. Then there is the problem of time syncing with the EI.

Mags are stock original. They are pressurized at upper deck pressure but the pressurization has never been checked, requiring a tester not found in most shops. Timing checks are just the normal timing checks done at annual (coming up again in about three weeks).

CHT and oil temp on the panel followed the trend.

--------------------
Best Regards,

Stan


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Joe Budge (W29)
Top Gun


Reged: 04/30/04
Posts: 7423
Re: High CHT @ High Altitude [Re: Stan Prevost]
      #248493 - 05/22/09 09:57 PM

Stan,

I haven't flown a turbo Toga so this is probably worth even less than you paid for it: have you tried more power? CHT is a function of heat generation by the engine balanced by airflow. LOP ops generally give low heat generation so maybe more airflow is what you need. My experience with LOP ops on the NA engine is that airspeed is very sensitive to FF; CHT not so much so. Maybe more airspeed, and hence more airflow, might work for your engine?

Regards,
Joe

Edited by Joe Budge (W29) (05/22/09 09:58 PM)


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