High CHTs

Any DA40 related topics

Moderators: Rick, Lance Murray

User avatar
Rich
5 Diamonds Member
5 Diamonds Member
Posts: 4592
Joined: Mon Aug 30, 2010 12:40 pm
First Name: Rich
Aircraft Type: DA40
Aircraft Registration: N40XE
Airports: S39 Prineville OR
Has thanked: 145 times
Been thanked: 1180 times

Re: High CHTs

Post by Rich »

hoyaj wrote: Frankly, our numbers correlate to excessive air pressure loss around the number 3 cylinder, keeping it nice and cold, some evidence of which we found on the baffle "bra" (1 inch of play/give behind the number 3 cylinder). Adjustment to the baffle assembly to tighten the attach points reduced the give, but did not result in evening out the temps.

The temp probe from 3 was swapped, with no change. Remember also that the used oil is now confirming that something is causing excessive ring wear. My read of Deakin and Busch says heat is likely the culprit.
No argument that excessive heat is being generated. Just trying to figure out why. Remember, also that CHT probes measure temperatures at a specific point on each cylinder head. I'm wondering if the excessive heat is being generated in some portion of the cylinder barrel (which also needs cooling) and is perhaps more severe than the CHT probe alone indicates. I assume the baffle that sits between 1&3 looks ok?
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
User avatar
hoyaj
2 Diamonds Member
2 Diamonds Member
Posts: 46
Joined: Wed Oct 19, 2011 1:38 pm
First Name: Bob
Aircraft Type: DA40
Airports:
Has thanked: 3 times
Been thanked: 3 times

Re: High CHTs

Post by hoyaj »

Rich wrote:
Just trying to figure out why. ... I assume the baffle that sits between 1&3 looks ok?

Thanks! Overall, it appears that the baffling is in good shape. The only thing left in my mind is whether there is a decent/good seal between the cowling and the top end engine baffles. Will have to look at that to see. The cyl probes are on the bottom, so the top side of the cylinder wall where the air flow is greatest and coolest would likely be cooler in theory. I guess we'll have to continue to look at it as an air pressure disruption of some kind.
User avatar
Charles
5 Diamonds Member
5 Diamonds Member
Posts: 638
Joined: Thu Aug 26, 2010 5:36 pm
First Name: Charles
Aircraft Type: DA40
Aircraft Registration: C-FLEV
Airports: CYHU
Has thanked: 27 times
Been thanked: 96 times

Re: High CHTs

Post by Charles »

Based on what I saw a Cessna owner do to his plane, you can fix the seals by applying a bead of silicone on the baffles where they're supposed to contact the cowling, putting wax paper over the top, and installing the cowling. Let it cure, remove the cowling and the wax paper and voilà! Perfectly shaped baffles.

It's probably quicker to do that if you have any doubt that there's a gap than to try to find where the gap might be.
User avatar
Lance Murray
5 Diamonds Member
5 Diamonds Member
Posts: 1163
Joined: Tue Jul 06, 2010 11:25 pm
First Name: Lance
Aircraft Type: DA40
Airports:
Has thanked: 7 times
Been thanked: 118 times

Re: High CHTs

Post by Lance Murray »

On one of my Airplanes I sealed up all the possible air leaks with black RTV. It did make an obvious difference. Perhaps you have air leaking.
User avatar
Lance Murray
5 Diamonds Member
5 Diamonds Member
Posts: 1163
Joined: Tue Jul 06, 2010 11:25 pm
First Name: Lance
Aircraft Type: DA40
Airports:
Has thanked: 7 times
Been thanked: 118 times

Re: High CHTs

Post by Lance Murray »

Here is some light reading on the subject. Skip to the conclusions.

http://www.n91cz.com/Interesting_Techni ... CR3405.pdf
User avatar
rwtucker
5 Diamonds Member
5 Diamonds Member
Posts: 1283
Joined: Thu Feb 21, 2013 11:24 pm
First Name: Rob
Aircraft Type: DA40
Aircraft Registration: N831BA
Airports: KFFZ KEUL
Has thanked: 100 times
Been thanked: 110 times

Re: High CHTs

Post by rwtucker »

My DA40 is a December 2007 assembly. I generally have to watch CHTs to keep them under 400 on the climb out (worse with the winter baffle). After that, they settle into the 370-380 range at 75%. LOP CHTs are really impressive though. They average 300 with the low barrel typically 298 and the high one 305. The problem with LOP is that I drop down to 122 kts or so at 5.5. gph and I'm not that patient.
User avatar
BlackMammoth
4 Diamonds Member
4 Diamonds Member
Posts: 318
Joined: Mon Jun 20, 2011 5:50 pm
First Name: Phil
Aircraft Type: DA40
Aircraft Registration: N29PG
Airports: KPSP
Has thanked: 5 times
Been thanked: 23 times

Re: High CHTs

Post by BlackMammoth »

122 @ 5.5 GPH? What RPM are you running?

We typically cruise @ 2450 which will lead to LOP fuel flows 8-7.2 depending how high we are flying. Cruise speeds are 135+ and we don't have a particularly fast airplane.

Back on topic with CHTs...
We operate from KTRM which is in the Palm Springs region. Aside from Phoenix, there aren't a lot of other places which consistently have HOT weather. Taking off in 115+ heat, BELOW sea level our SOP is to keep mixture @ takeoff EGT and hold 90 knots through the climb. CHTs stay below 400 (although 395 does pop up occasionally).

- We don't have the "Arizona Baffle" (although we probably should)
- We have caulked all of the gaps in the baffling shut
- We are running very closely matched GAMI injectors.
- Two blade Hartzell (not sure if that makes any difference)
User avatar
rwtucker
5 Diamonds Member
5 Diamonds Member
Posts: 1283
Joined: Thu Feb 21, 2013 11:24 pm
First Name: Rob
Aircraft Type: DA40
Aircraft Registration: N831BA
Airports: KFFZ KEUL
Has thanked: 100 times
Been thanked: 110 times

Re: High CHTs

Post by rwtucker »

I'm usually running 2,250 for the 5.5 gph. It runs LOP at higher powers but I don't see the same ROI. I can get into the mid-140's ROP at 8.9. I'm running the toy wooden prop. Seems more efficient but a constant worry that someone will bump it and snap off a tip. (I saw it happen with the same prop on an RV.)

Did you notice any difference when you caulked the baffles?

What is your lean largest EGT variation with the GAMIs?
User avatar
BlackMammoth
4 Diamonds Member
4 Diamonds Member
Posts: 318
Joined: Mon Jun 20, 2011 5:50 pm
First Name: Phil
Aircraft Type: DA40
Aircraft Registration: N29PG
Airports: KPSP
Has thanked: 5 times
Been thanked: 23 times

Re: High CHTs

Post by BlackMammoth »

EGT before the GAMIs was a nightmare... could be 40 degrees different at low airspeed / high power. Actually this was what caused us to get the GAMIs in the first place. We were having problems with high EGTs on one cylinder, so we did the "GAMI Lean Test" and found a large spread between where each cylinder peaked... especially cylinder #4 (for us). We ordered GAMIs and immediately things were better, and our FFs were lower since the "hottest" cylinder on the VM1000 was closer to the coldest.

Before we ordered GAMIs, we did the following:
- Retimed the mags (no difference)
- Pulled all plugs, cleaned and resintalled (no difference)
- Pulled stock injector nozzles and ultrasonically cleaned (slight difference)
- Measured newer DA40 to determine if we had the update baffle (we don't) and considered spending the $$$ to have it installed.

In the end we decided to start by dealing with the fuel flow issue and ordered GAMIs. We "tweaked" them three times until they are damn near dead even today. John-Paul @ GAMI was great about sending out updated injectors after each lean test.

Now that the fuel flow is closer between the cylinders, we haven't had high CHT issues and we dropped the idea of installing the Arizona Baffle.

We caulked the gaps in the baffling a couple of annual's ago and it made a slight difference. The main reason we closed up the gaps is that they were HUGE and I saw no reason for them to be there.
User avatar
Gasser
5 Diamonds Member
5 Diamonds Member
Posts: 703
Joined: Fri Feb 10, 2012 6:22 pm
First Name: Jeff
Aircraft Type: DA40
Aircraft Registration: N415AM
Airports: KADH
Has thanked: 16 times
Been thanked: 44 times

Re: High CHTs

Post by Gasser »

BlackMammoth wrote:EGT before the GAMIs was a nightmare... could be 40 degrees different at low airspeed / high power. Actually this was what caused us to get the GAMIs in the first place. We were having problems with high EGTs on one cylinder, so we did the "GAMI Lean Test" and found a large spread between where each cylinder peaked... especially cylinder #4 (for us). We ordered GAMIs and immediately things were better, and our FFs were lower since the "hottest" cylinder on the VM1000 was closer to the coldest.

Before we ordered GAMIs, we did the following:
- Retimed the mags (no difference)
- Pulled all plugs, cleaned and resintalled (no difference)
- Pulled stock injector nozzles and ultrasonically cleaned (slight difference)
- Measured newer DA40 to determine if we had the update baffle (we don't) and considered spending the $$$ to have it installed.

In the end we decided to start by dealing with the fuel flow issue and ordered GAMIs. We "tweaked" them three times until they are damn near dead even today. John-Paul @ GAMI was great about sending out updated injectors after each lean test.

Now that the fuel flow is closer between the cylinders, we haven't had high CHT issues and we dropped the idea of installing the Arizona Baffle.

We caulked the gaps in the baffling a couple of annual's ago and it made a slight difference. The main reason we closed up the gaps is that they were HUGE and I saw no reason for them to be there.
I just had a conversation with George B, the main engineer at GAMI and he is going to go up with me in my Diamond in the next couple weeks and see if they can improve my plane. I'm on there home field so ill be able to have good turn around getting mine tuned up. He walks around our airport every day so he stops in to talk on a regular basis.
The two things we discussed is my high CHT in cylinder 4 on climb out and also the fact that both 2,4 tend to be 30 degrees hotter than the other two. He thinks we can tune some of that out and we will also look closely at my baffling to see of we can improve some things there as well. Ill report if we find any improvement to be had.
Jeff

PRIVATE PILOT, IFR
2005 DA40 SOLD
2006 SR22, A/C, TKS, AVIDYINE PFD/MFD, IFD 540/440, AXP322 remote ADS-B TRANSPONDER, AMX240 AUDIO PANEL, MLB100 ADS B in.
168 KTAS 9,000' msl @ 13.6 gph LOP. 1005 pound useful load.
Post Reply