Is this typical? re: cht's at cruise

[haymak3r]

Hey all! 

Curious if what I normally see regarding my CHT's are typical for other J owners. I am noticing that my #3 cylinder is always the hottest by 20 or more degrees. Here is a pic with the cowl flaps adjusted to be a little more open than they used to be ~1" to 1.5" opening on the right side now. Other side is right at 1" open. 

 

Everything seems to be running just fine, but was curious about this. My baffling is definitely not new, and so perhaps I am getting some leakage around it back there on the right side that could be contributing to this? Or this one just runs a little hotter, and I should not think about it until the current norm changes.

 

[RoundTwo]

8 minutes ago, haymak3r said:

Hey all! 

Curious if what I normally see regarding my CHT's are typical for other J owners. I am noticing that my #3 cylinder is always the hottest by 20 or more degrees. Here is a pic with the cowl flaps adjusted to be a little more open than they used to be ~1" to 1.5" opening on the right side now. Other side is right at 1" open. 

 

Everything seems to be running just fine, but was curious about this. My baffling is definitely not new, and so perhaps I am getting some leakage around it back there on the right side that could be contributing to this? Or this one just runs a little hotter, and I should not think about it until the current norm changes.

 

Same here. ‘88J

[A64Pilot]

I think a max spread of 20 degrees is pretty normal, yes you will have a hottest cylinder, that’s the one the factory sensor should be on.

Personally I’d return the cowl flaps to the factory recommended setting and open as necessary to maintain 380 or lower CHT, otherwise come winter you may not be able to keep them warm enough.

[EricJ]

Fairly similar.   What was your OAT?   On mine that seems to make a big difference.

[OR75]

#3 should be the hottest for Lycoming engines based on the airstream and by the book

Continental engines are numbered differently 

[0TreeLemur]

Similar to mine:

 

[MB65E]

Make sure there is a small gap/washer/spacer at the rear of the No.3 cyl baffle attachment that helps. But other than that Keep them under 400 any you’ll be fine. Shine a flashlight through the oil dip stick door to make sure you don’t see light from the front of the cowl. 
-Matt

[haymak3r]

16 hours ago, A64Pilot said:

I think a max spread of 20 degrees is pretty normal, yes you will have a hottest cylinder, that’s the one the factory sensor should be on.

Personally I’d return the cowl flaps to the factory recommended setting and open as necessary to maintain 380 or lower CHT, otherwise come winter you may not be able to keep them warm enough.

Agreed, but that was after the small adjustment. Before, cyl3 would creep up over 400 in that same man/rpm config. also my oil temp would be in the high 190's too. In these cases, I had to open the flaps just a little. I could pull the lever out about an inch and the temps would come down. So, making the adjustment, I didn't need to pull the lever out slightly anymore. I definitely plan to re-adjust the flaps as the temps come down.

[haymak3r]

13 hours ago, EricJ said:

Fairly similar.   What was your OAT?   On mine that seems to make a big difference.

I believe on this leg, OAT was +5C

[A64Pilot]

4 hours ago, haymak3r said:

Agreed, but that was after the small adjustment. Before, cyl3 would creep up over 400 in that same man/rpm config. also my oil temp would be in the high 190's too. In these cases, I had to open the flaps just a little. I could pull the lever out about an inch and the temps would come down. So, making the adjustment, I didn't need to pull the lever out slightly anymore. I definitely plan to re-adjust the flaps as the temps come down.

What’s wrong with opening the flaps just a little?

This time of year for me in the morning I cruise full closed at 60% LOP and the knob pulled out quite a bit to the overcenter point in the afternoon, the over center point while it’s a lot of travel on the knob I believe only opens them about an inch. One setting won’t cover me for the cool morning and the hot afternoon, both woukd be in the green, but I shoot to keep them at the F mark on the factory gauge.

Be careful of two things if you adjust them more open than the factory recommends, first that full open isn’t too far open and secondly that there are enough threads left in the fitting at the cowl flap

Edited June 27, 2023 by A64Pilot

[haymak3r]

Nothing wrong with having them slightly open. I may just move them back to where they were, and continue slightly opening them. But now I know that 1. the cht diff is not concerning to others, and it also not abnormal to need to run them less than half out to control the temps. I would rather do that, and then not worry about it in the cooler months, than always having to adjust. 

 

Thanks all for the responses as always.

[gmonnig]

What kind of probe is on your #3? If it's a spark plug mounted probe, those will be 25degrees warmer than the threaded CHT probes. I believe the factory probe location was on #3 because it's the hottest cylinder and it's a spark plug probe. 

[M20F]

On 6/27/2023 at 10:26 AM, haymak3r said:

I believe on this leg, OAT was +5C

+/- ISA is what matters if you are flying at 5C ambient that by me (KLZU) is @ 12000 feet and that currently shows ISA +13C.  In other words a lot hotter than it should be hence a lot hotter cylinders. 

[Wildhorsetrail]

Your temps are pretty similar to mine. In hot weather I have to keep my cowl flaps open just a little with similar fuel flow at 8 or 9 thousand. And I have new baffle material.

Sent from my SM-A326U1 using Tapatalk

[haymak3r]

On 7/1/2023 at 10:25 AM, gmonnig said:

What kind of probe is on your #3? If it's a spark plug mounted probe, those will be 25degrees warmer than the threaded CHT probes. I believe the factory probe location was on #3 because it's the hottest cylinder and it's a spark plug probe. 

All new probes for the garmin EIS system that was installed in November. I do not have factory probes anywhere anymore.

[haymak3r]

On 7/3/2023 at 3:41 PM, M20F said:

+/- ISA is what matters if you are flying at 5C ambient that by me (KLZU) is @ 12000 feet and that currently shows ISA +13C.  In other words a lot hotter than it should be hence a lot hotter cylinders. 

Yep. It was way warmer than it usually would be. But even at 7500 on Sunday the temps were generally the same spread. Not saying there is an issue here, just wanted to come by and compare with other people's 'numbers' If there is a wild change from this 'norm' then I'll investigate further.

[M20F]

On 7/5/2023 at 10:07 AM, haymak3r said:

Yep. It was way warmer than it usually would be. But even at 7500 on Sunday the temps were generally the same spread. Not saying there is an issue here, just wanted to come by and compare with other people's 'numbers' If there is a wild change from this 'norm' then I'll investigate further.

Less than 385 and over 300 is generally what is agreed that matters. If a cylinder runs +/- 30 degrees beyond normal without crazy weather swings (i.e. AZ in summer and ND in the winter) probably worth looking at. 
 

Gauges today are wildly accurate on an engine with 175 degree operating range (io360).  It’s like people fixating over oil burn.  Generally much to do about nothing.

Let’s all compare EGT #’s next, it’s a slow week at work and I need entertainment. 

[haymak3r]

LOL. right? My instructor has asked me a couple different times now about egt's as I start leaning the engine. Old school thinking. CHT's are primary. EGT's just give you a point of reference.

[jaylw314]

On 6/26/2023 at 7:46 PM, OR75 said:

#3 should be the hottest for Lycoming engines based on the airstream and by the book

Continental engines are numbered differently 

I thought #4 is supposed to be the hottest (rearmost and loses air to the oil cooler)?

@haymak3r What OAT were you at?  My CHT's started out around 360F, but now are down about 320-340F in cruise after cleaning up the baffling. My #3 is the hottest, but I have a piggyback probe on the factory probe.  The other cylinders vary by about 20 degF between them

Edited July 7, 2023 by jaylw314

[201Mooniac]

1 hour ago, jaylw314 said:

I thought #4 is supposed to be the hottest (rearmost and loses air to the oil cooler)?

In my J, #1 is always the hottest (about 15 degrees hotter) but I have the Lopresti Cowl so maybe that makes a difference.

[haymak3r]

11 hours ago, jaylw314 said:

I thought #4 is supposed to be the hottest (rearmost and loses air to the oil cooler)?

@haymak3r What OAT were you at?  My CHT's started out around 360F, but now are down about 320-340F in cruise after cleaning up the baffling. My #3 is the hottest, but I have a piggyback probe on the factory probe.  The other cylinders vary by about 20 degF between them

I think it was around +5C at 10500... So quite warm. It was a couple weeks ago when we were having the pretty warm weather. Though I think I took the pic when we were in northern cali on our way back home. But still super warm.

[haymak3r]

I have also thought about really looking at the baffling and maybe getting new. 

[kris_adams]

I think it is pretty common to adjust cowl flaps to be open an inch or so even when they are closed.  I haven't done that.  I just run them in trail as needed on the hottest days and temps easily stay below 380.

[haymak3r]

Even ROP?

[Bolter]

46 minutes ago, haymak3r said:

I think it was around +5C at 10500... So quite warm. It was a couple weeks ago when we were having the pretty warm weather. Though I think I took the pic when we were in northern cali on our way back home. But still super warm.

I also flew over Oregon this past weekend, and it was much warmer than standard day at altitude, and I was also seeing warmer CHT's on my Ovation.  Enough to prompt adjusting mixture and RPM until it got happy again.  In these warm cruise conditions with my J, I would have cowl flaps in "trail" position.  I never made a summer-winter adjustment of the cowl flap gaps.  Climb was fully open cowl flaps, from engine start.

On the standard J, the #3 cyl has the factory gauge, and threaded into the CHT.  Typical analyzers are therefore a spark plug ring for the #3 cyl only, threaded sensor for the othes, but that spark plug ring reads hotter than the threaded location would.  If your analyzer is a primary installation, then they probably put the sensor threaded into the cylinder, and you have the best apples to apples comparison of temps between each cylinder.