#5 CHT Ovation

[PMcClure]

My 2002 Ovation has about 1100 hours on it and I bought it in November last year. Now that the outside temps are higher, I am getting a persistent problem with #5 CHT. I can now barely keep a 500 fpm climb (OT at 30+ C) and can not lean to desired cruise settings without the CHT climbing above 390 at 65% power 10,000 ft. A few more facts/questions:

 

1. I am trying to keep CHT under 390 (prefer 280). Other CHT's are well in line at about 350. Next highest CHT is #6.

2. EGT on #5 is usually slightly below rest of cylinders. 

3. Performance seems fine otherwise, oil consumption is normal. 

4. Baffles look fine. I tweaked them a little and will try it again. 

5. The alternator set-up seems to give very good flow (no need for Pixie hole amendment).

6. Getting some lead or oil fouling consistently on #5 plug (L)

 

I am going to replace the plug in the morning and borescope and test compression in the morning and have the AP double check the baffles. Any other suggestions or thoughts?

 

PS - Am babying it to shoot for 380? Alarm is set at 450 from the factory and I believe the engine manual allows up to 465?

[BorealOne]

Operationally, you should be aiming for 120 IAS in climb to keep temps <390 in warmer OAT but you shouldn't see >390 in cruise under any circumstance at 10'000.

 

What do you mean by 'normal' oil consumption in your bird? 

 

Everything else being equal, I'd start to be thinking 'valves' - and perhaps be setting aside some AMU's for getting that cylinder replaced...

[PMcClure]

Couldn't hold 120, which is my usual in cooler temps. I haven't had the plane long enough to establish a real evaluation of oil consumption. But If I am using a quart every 5 hours I would be surprised, although there is enough belly oil residue to notice. Wouldn't a valve show up with higher EGT?

[Cruiser]

My 2002 Ovation has about 1100 hours on it and I bought it in November last year. Now that the outside temps are higher, I am getting a persistent problem with #5 CHT. I can now barely keep a 500 fpm climb (OT at 30+ C) and can not lean to desired cruise settings without the CHT climbing above 390 at 65% power 10,000 ft. A few more facts/questions:

 

1. I am trying to keep CHT under 390 (prefer 280). Other CHT's are well in line at about 350. Next highest CHT is #6.

but do you know what the temps were for the first 1100 hours?

2. EGT on #5 is usually slightly below rest of cylinders. 

3. Performance seems fine otherwise, oil consumption is normal. 

4. Baffles look fine. I tweaked them a little and will try it again. 

5. The alternator set-up seems to give very good flow (no need for Pixie hole amendment).

The high temp problem with this cylinder is well documented. Why do you think yours is not effected ?

6. Getting some lead or oil fouling consistently on #5 plug (L)

probably from the excessively high temp in the area directly behind the alternator has "oil coked" the rings in the piston and you are getting blow by.

 

I am going to replace the plug in the morning and borescope and test compression in the morning and have the AP double check the baffles. Any other suggestions or thoughts?

 

PS - Am babying it to shoot for 380? Alarm is set at 450 from the factory and I believe the engine manual allows up to 465?

and engines run this way get cylinders replaced in 800 - 1000 hours or less.

[PMcClure]

 

I have seen the pixie hole pictures here on Mooneyspace and set out to hire a pixie but when I looked closer, the set-up is a little different. I'll have to post some pictures. I am sure #5 would still be the hottest CHT but don't see any good place to put a hole for more air. Someone would have to cut the cowling open to place a hole. Blow by is a possibility but last compressions and trend have been good? 

 

[carusoam]

Oil loss of the IO550 is much lower than an IO360, by nature...

Definitely measure what rate you are replacing it at.

-a-

[BorealOne]

And the verdict is...?

[PMcClure]

I don't quite have the verdict yet. The borescope indicated the valves were in good shape as was the cylinder wall. There was some oil pooling right at the plug. We checked compressions and was good. We decided to swap #3/#6 CHT probe and L/R plugs after cleaning them and do a test flight. But the mag test failed on #5L again and after pulling the plug found it was oil fouled. 

 

The plan is to do do a lead test on #5L wire today and replace the plugs with fine wire plugs and see how it works. I assume the oil is coming from around the rings but not sure it is related to the #5 CHT.  

 

I do keep a log of added oil/hours. But I am still learning the trends. Adding oil above 6qts seems to blow right out. After reaching 6 the oil loss rate does not seem linear. The oil loss comes in large (1/2-1Q) increments. Sometimes I can fly it for 4-6 hours and not add any oil. Sometimes shorter flights tend to eat more oil. I just haven't taken the time to calculate the usage.

 

All of it points to rings for me. Not sure it is related to the CHT or not, Any thoughts appreciated. 

[carusoam]

I would expect that you are seeing serious oil loss compared to other IO550s. 8qts should stay as well as 6qts, I believe.

This is a reference to io360s that blow the 7th quart out the vent.

High time io550s may get cylinder work or exchanges depending on how they have been run.

A mechanic should be able to do compression tests or detect broken oil rings.

Wet spark plugs in a particular cylinder are a pretty good sign that the cylinder is talking to you.

Observations of PP... Not a mechanic...

Best regards,

-a-

[PMcClure]

Update - replaced the #5 lower plug with a fine wire plug and did a test flight. The engine ran much smoother and the CHT was 20-40 degrees cooler. It was slightly cooler today in Alabama, but still 30C on the ground. I am suspect that the plug would make a difference on CHT. I have a flight to Norfolk planned for Wednesday and will test it in cruise. 

 

PS - i reviewed the log for oil use and think I am pretty good. In over 75 hours, I have added less than 8 quarts, including a couple of times when I added above 6. So the use looks like 1qt every 7-8 hours. 

[Cris]

In my experience the oil consumption is high and I too watch the cht on climb out when it hits 400 on the Moritz factory gauge which it will do easily on a warm day at 2700. I am keeping the mixture rich and the airspeed at 120-130. Go find the Pixie. It definitely works. At altitude 330-350 max CHT's are what I see. You didn't say but I'm thinking you are running 50 degrees ROP. Try 50 degrees lean of peak at altitude and see if that doesn't make a difference. One last point is the Moritz gauge pkg. I have an Insight G2 engine monitor. I find the CHT and EGT's are substantially differant and lower on the G2 engine monitor and I believe are more accurate. As a example my EGT's will easily hit 1650 on the factory gauge but be 100 degrees cooler on the G2. Obviously the probes are in differant areas but those cyls. would have been cooked long ago if the Moritz system was reading true. Do you have an engine monitor system. If not get one.

[PMcClure]

The AP adjusted my baffles which seemed to help. In flight, I was about 15-20 cooler but still #5 was higher and limiting my leaning. I will try LOP and look up the pixie mechanic.  I have a JPM 700 factory installed and don't even pay attention to the panel CHT and EGT gauges. 

[PMcClure]

Lop operation helped keep #5 below 380 this last trip. Still over 390 in climb. Any comments on how the pixie drills the hole. Mechanic says he would have to remove alternator and plate to drill hole. Not that big of a deal I guess.

[Cris]

No need to remove alt. Search the forum for the discussion and the pictures including measurements on where the hole goes.

[PMcClure]

Thanks everyone for the help. We added the hole last week and I flew 15 hours xc in the heat. I am running cooler on #5 but still hotter than I like. @ 75% power, I am seeing 385-388 50 degrees lop and 390-395 at 50 rop. Others are running 340-350. Any other suggestions? Baffles look good and after some tweeking, already saw a drop (before adding the hole).

[FAST FLIGHT OPTIONS LLC]

I would opine that your going to kill your engine using 50 RoP setting. Be careful with that and beware of the red box

[PMcClure]

Update  - out of annual and replaced all 12 plugs. Standard Champion's on the top and fine wire on the bottoms. They were about 400-500 hours. The CHT's are all lower now and #5 is no longer the hottest (#3 and 6). #5 is running 40F cooler than before in cruise. OAT is about 20F cooler at altitude than before. Anyone believe or explain why new spark plugs can affect CHT. 

 

As a side note, I was running rough at 50-100 LOP now able to easily get to 75LOP and just noticeable rough at 100 LOP now. 

[ghovey]

I had a similar experience with my IO550 (2005). 1478 hours. Just overhauled all the cylinders (1st cylinder replacement). The real issue you are going to have is the oil. The rings are failing, you will continue to use oil. The oil will start to get dirty shortly after an oil change. The biggest pain is washing the bottom of the airplane. I never lost much power but compressions did start to fall. Cylinders and valves always looked good on boroscope. Eventually oil use became unreasonable. And yes I also found oil usage occasionally intermittent. Always had high CHTs on climb out (over 400) and had to reduce rpm to 2400 which always kept peak CHT under 400. Started using Camguard around 1200 hours and frankly have no idea if I got any benefit. It certainly did not fix the piston rings (which was obviously impossible). But I did suffer a starter adaptor slippage shortly after I started using the Camguard and had to overhaul the starter adaptor when I did the cylinders- the shaft was out of tolerance and had to be replaced, cost about $2700. Also replaced the Iskra starter- gained 1.4 lbs useful load.

I have been running fine wires top and bottom and gami injectors. The Gamis made the biggest improvement. Lowered fuel flow about 1/2 gal per hour overall and could run LOP without issue.

[ghovey]

I also never run 50 degrees ROP. Usually 100-125 ROP if I am below 8500', otherwise always LOP higher.

[Bob - S50]

Update  - out of annual and replaced all 12 plugs. Standard Champion's on the top and fine wire on the bottoms. They were about 400-500 hours. The CHT's are all lower now and #5 is no longer the hottest (#3 and 6). #5 is running 40F cooler than before in cruise. OAT is about 20F cooler at altitude than before. Anyone believe or explain why new spark plugs can affect CHT. 

 

As a side note, I was running rough at 50-100 LOP now able to easily get to 75LOP and just noticeable rough at 100 LOP now. 

 

I am not a mechanic!  What I think I know is only what I've learned from listening to Mike Busch webinars and reading John Deacon (?) in his Pelican's Perch articles.  I also tend to be wordy.  It's the engineer in me.

 

From what I understand, the higher the internal pressure in a cylinder, the higher the CHT.  For any given power setting, the closer the peak pressure comes to TDC, the higher that pressure will be and the higher the CHT will be.  So what can cause the peak pressure to occur closer to TDC?

 

1.  If you had one flame front (one plug firing) and now have two flame fronts (both plugs) the fuel will be burned quicker, peak will occur sooner, and CHT should, if anything go up.  This is the opposite of what you saw.

 

2.  Reduced RPM.  Normally (from what I remember) ignition is set to fire about 20 to 25 degrees BTDC so that peak pressure occurs about 16 degrees or so ATDC.  The flame front does not care how fast the engine is turning so a lower RPM will rotate the engine fewer degrees before peak pressure has occured.  That will place peak pressure closer to TDC.  This is not normally a problem for us because by the time we do this we are down below 75% power.

 

3.  Mixture.  Apparently right around 30 degrees ROP is the ideal mixture for the quickest flame front.  All other factors being equal, that will place peak pressure as close to TDC as you can get.  Leaner or richer than that provides less than ideal mixture and has the effect of retarding the peak pressure point until further ATDC.  That's why we run full rich for takeoff.  We are running full power creating the maximum internal pressure so we run very rich to provide far from the ideal mixture to keep the peak pressure occuring well after TDC.

 

With all that said, is it possible that you are now running leaner than you were before?  Maybe #5 was running effectively on one spark and the engine would run rough when you tried to lean.  Maybe that caused the #5 to actually be slightly ROP while the others were LOP putting #5 right near peak pressure.  Since you got the plug replaced, the cylinders are now more evenly matched, you can run leaner, and #5 is actually LOP now.

 

If you have an engine monitor that can download data, you can go to the savvyanalysis website, sign up for the free service, upload your data and then look at it.  Look at a couple flights before you replaced the plug and see if #5 actually went LOP or if it was still ROP.  Then do the same for after you replaced the plug.

 

When you say you run 75 LOP, is that the leanest cylinder or all cylinders?  If I don't have all cylinders LOP I don't consider myself to be running LOP.  Usually I end up with one cylindar about 30 LOP and the other 3 about 10 LOP.

 

Interestingly enough, the next Mike Busch webinar is supposed to be about "Flying Efficiently in a World of $7 Avgas".  It was last night but is not yet available for viewing on line.

 

Enjoy your now properly working engine.

 

Bob

[PMcClure]

Bob, 

 

Thank you for your post. The only thing missing is a diagram or two!! Most engineers can't talk without a pencil in hand and a diagram to refer too (me included!!)

 

Everything you say makes sense to my engineer side as well. Your comments sparked a thought. In annual, we also replaced the tach generator which required removal and retiming of the left mag. So the timing could have been the culprit of the high CHT. EGT's are more even (perhaps due to new plugs) and CHT's are all lower and #5 is no longer the hottest. This could be due to previous incorrect timing. 

 

I am sure I am LOP, I use the EDM which has a LOP leaning procedure. So 75 would be the last cylinder to peak ( I think this is correct). Also, I watch the EGT all rise and reduce. I am running leaner in cruise now but CHT is lower at all mixtures. Even at 100 ROP, 50 ROP and peak EGT,  my CHT's were acceptable. Where as before, I couldn't keep these settings for very long at 75% cruise, 9,000'. 

 

I don't think I was running on one spark plug as this would have showed in my mag check? I never did a in flight mag check though.You also gave me a few more references and resources to check. Thanks again. 

[Cruiser]

In a normal operating engine, the biggest (maybe sole) effect on CHT will be timing.

I suspect you are seeing the effect of a timing change from previous setting. Only a degree or two can make a huge difference as you have noted.

[Bob - S50]

Glad I gave you some ideas.  Even happier you can trust your plane again.

 

Bob

[Txbyker]

#5 Post impixination. I like it.

Russ

[carusoam]

Russ,

Do you have the before picture to go with that? (High CHT #5)

The final nail in the coffin.

Best regards,

-a-