Back-cylinder (#1/#2) CHTs in Ovation IO-550.

[Jeff Uphoff]

I'm finally getting data dumps from the EDM-800 in my 2000 Ovation, which has a 310HP STC'd IO-550.[1]

I'd always noticed during cruise flight that my #1 CHT would read anomalously low compared to its brethren, my #2 would read anomalously high, and then my #3/4/5/6 would all read a dead straight line together. (During climb, things tend to be more jumbled, but #2 still consistently reads the highest.)

Now that I have dumps, I have plots that confirm the above pattern and that I can look at in detail rather than out of the corner of my eye while flying (when I'm busy doing other things).

My question is this: given that #1 & #2 on an IO-550 are both at the back of the engine, does it make sense that the pair are consistently the hottest *and* the coldest cylinders?!? It's quite a striking disparity--as high as 420+ in a climb for #2 while #1 may be 360 or below.

Worth swapping the CHT probes between #1 & #2 to see if the anomaly flips, indicating a sensor issue? Or...?

--Up.

[1] My EDM had to go out for service: it was recording data but wouldn't dump it until JPI fixed something during my recent annual.

[irishpilot]

Jeff, swapping a probe is an easy way of ruling out a bad probe and the temps you suspect. I fly the IO-550 in a Lancair, so the airflow is going to be a bit different, but the troubleshooting remains the same.

I had #2 high EGT compared to the rest of my cylinders. I ruled out a bad probe, then concentrated on ensuring the baffling was correct with no tears in the uppers.

If that checks good, then you can clean out your injectors. That's what ended up being the issue for mine. Speaking of injectors, do you have the TCM balanced injectors or GAMI?

Also, what power setting are you noticing this issue and is it the same ROP and LOP?

The IO-550 is an awesome engine.

-Ryan

Sent from my Pixel 7 using Tapatalk

[Jeff Uphoff]

3 minutes ago, irishpilot said:

Jeff, swapping a probe is an easy way of ruling out a bad probe and the temps you suspect. I fly the IO-550 in a Lancair, so the airflow is going to be a bit different, but the troubleshooting remains the same.

I had #2 high EGT compared to the rest of my cylinders. I ruled out a bad probe, then concentrated on ensuring the baffling was correct with no tears in the uppers.

If that checks good, then you can clean out your injectors. That's what ended up being the issue for mine. Speaking of injectors, do you have the TCM balanced injectors or GAMI?

Also, what power setting are you noticing this issue and is it the same ROP and LOP?

The IO-550 is an awesome engine.

-Ryan

Sent from my Pixel 7 using Tapatalk
 

I have GAMIs. EGTs line up nicely through all phases of flight, as do CHTs for 4 of the 6 cylinders in cruise. It's just these back two that read consistently high & low.

It's the same ROP and LOP in that I climb ROP and then cruise about 50 LOP, and the same CHT distribution usually holds in both cases; #2 is always hottest, and in climb sometimes #4 next to it is the coolest rather than #1, but in cruise #1 in back across from #2 is always the coolest. Definitely has me scratching my head and wondering about probes.

Power setting is usually full throttle and 2600 RPM for climbing ROP (blue arc EGT), and then since I usually fly high I'm still full throttle for cruise but at 2400 RPM and 40-50 LOP. LOP is smooth, with a nice, tight EGT spread and fuel flow around 12-13 GPH.

I'm relatively new to the IO-550, and I'm seeing elsewhere on the forum that it's apparently optimized to cruise at 2500-2550 RPM. I may start spinning mine faster when I'm not trying to keep the cabin quiet for pax.  

[mike_elliott]

--up

#5 is typically the "hot guy" on the Ovation and there is even a hangar elf tweak to help this. Absolutely swap probes to rule out the problem temp traveling or staying put as a first step. Where is your #1 & #2 falling on the "gami" spread in relation to each other? IOW,  Are they the first and last to peak and FF when peaked? If some hints are not discovered, ping Paul Kortopates @kortopates and get some experienced chart reading done

 

[irishpilot]

Jeff, you fly it similarly to how I do. I do 95% flying 8,500' and above, so I'm always WOT and 2500 rpm below 10k (2550 above).

Hopefully other Ovation owners can chime in regarding their temps as it may be a known airflow issue with the cowling. If not, then I'd start checking things off the list.

Sent from my Pixel 7 using Tapatalk

[Jeff Uphoff]

5 minutes ago, mike_elliott said:

--up

#5 is typically the "hot guy" on the Ovation and there is even a hangar elf tweak to help this. Absolutely swap probes to rule out the problem temp traveling or staying put as a first step. Where is your #1 & #2 falling on the "gami" spread in relation to each other? IOW,  Are they the first and last to peak and FF when peaked? If some hints are not discovered, ping Paul Kortopates @kortopates and get some experienced chart reading done

 

My GAMI spread seems pretty tight in that EGTs tend to stay close together and there doesn't seem to be consistency as to which cylinder peaks last and becomes the reference when leaning LOP.

Next time I go up I'll make a note as to FF when it peaks.

Thanks Mike.  

--Up.

[GeeBee]

My #1 is consistently the lowest, #2 is second lowest the rest are all close together.

[Jeff Uphoff]

1 minute ago, GeeBee said:

My #1 is consistently the lowest, #2 is second lowest the rest are all close together.

I'm not worried about my #1 being the lowest in cruise (and often in climb)--it's the #2 reading what seems to be anomalously high in both that has me concerned enough to troubleshoot this. Were #2 low, too, I'd be a happy clam.  

--Up.

[exM20K]

How are the baffles, and are all the through-the-firewall grommets in place?

definitely swap two probes to confirm it’s not an instrumentation issue.

If the baffles are old and floppy, they can make a poor seal against the top cowling at the rear of the engine compartment, spilling cooling air out the back. Mine is currently a bit bimodal: #1, which is indicating cooler than #2, has excursions up and down about 15* as the baffle sags and goes Back to its seated position.  It has done this for a long time, doesn’t keep me up at night, and I’ll eventually replace at least the rear baffle.

 

How big is the delta between #1 and 2, and do they track each other and the other CHTs?

-dan

[GeeBee]

#2 is by the oil cooler. So a baffle leak will create more pronounced issues. Obviously the baffle seals are the first suspect.  Also check the seal between the engine and the aluminum baffle itself as well as the positioning of the inter-cylinder baffles which are often installed incorrectly. Finally make sure the probe is accurate.

[StevenL757]

4 hours ago, Jeff Uphoff said:

My GAMI spread seems pretty tight in that EGTs tend to stay close together and there doesn't seem to be consistency as to which cylinder peaks last and becomes the reference when leaning LOP.

Next time I go up I'll make a note as to FF when it peaks.

Thanks Mike.  

--Up.

2550RPM and 40-50LOP is your sweet spot on your engine.  Running with iridium finewire plugs is an even better option to keep things humming nicely.  Bob Minnis backs all of this up with data from several tests and experiences on the IO550's 310hp upgrade.  He's also the original STC holder for the upgrade, and knows a thing or two.  :-)

55 minutes ago, GeeBee said:

#2 is by the oil cooler. So a baffle leak will create more pronounced issues. Obviously the baffle seals are the first suspect.  Also check the seal between the engine and the aluminum baffle itself as well as the positioning of the inter-cylinder baffles which are often installed incorrectly. Finally make sure the probe is accurate.

+1

[Jeff Uphoff]

I think I just found my possible best clue! Looking at a couple of engine starts (immediately after reinstallation of my fixed EDM-800) for short runs during my annual (for things like oil-leak and fuel-setup checking), where the time scale is stretched out more in the plot, you can see #2 starts out much hotter than all the other cylinders--even before there's any notable power being generated by the engine or significant airflow for cooling. The orange line at the top is #2, and there's really no way it's that much hotter than the other cylinders right out of the gate and at idle power. This is really looking like a sensor issue....

(Note: the flat blue line in the left plot is fuel flow.)

[hypertech]

Mine are routinely similar to yours in cruise.  #5 is the hottest on the ground but once you get going it itsn't.

Baffles have all been replaced.  No holes to speak of.  #1 is the coolest ~305 in cruise.  # 2 is the hottest ~345 in cruise.  I have assumed this is because #1 is getting all the air pushed down over the fins from the back baffle and #2 probably has less because its exiting through the oil cooler.  #3 and 5 ~315.  #2/4 ~330

 

I keep it under 400 in the climb.  Add fuel or increase airspeed.

[Jeff Uphoff]

So it turns out a couple of things were in play here:

- I learned this week that the #2 JPI probe on the IO-550 isn't the same as the others! Because the factory CHT probe sits in #2, the #2 JPI probe is a gasket probe around the spark plug rather than a bayonet probe into the cylinder like on the other five. The factory CHT for my #2 reads normal: by its indication, my #2 cylinder isn't really getting too hot. The JPI gasket probe on #2 appears to have started reading higher recently, so I'm considering replacing it.

- A bit of RTV was added to some gaps near the recently overhauled oil cooler behind #2, and that appears to have lowered the temperature slightly. The baffling appeared fine, so any airflow issue was probably related to the gaps, though it appeared to be only a secondary cause.

Thanks to everyone who provided hints, suggestions, and analysis above!

--Up.