CHT's?

CHT's?

I flew my 172 today for the first time since converting it to 180 hp with a factor new lycoming engine from Air Plains.  The cht's for the two rear cyclinders were 430 degrees with the rear egt's being high as well.  I'm wondering how alarmed I should be by this.  Air Plains told me not to worry about it, but a couple A&P's said that it shouldn't be this high.  I don't know what to do.  If it's not ok, who's responsible and what should be done?  From what I've read, cht's above 400 will hurt the longevity of the engine.  I don't want it to be ok until around 1500 hours and then turn sour.  This would mean I have no warranty and their problem becomes mine.  I've also read that cht's tend to be high on a new, but usually drop as the engine breaks in and the rings seat.  That sounds logical and encouraging, but it seems that there is no way to know how long it will take the cht's to drop and to what extent they will do so.  By the way, I have new baffles, baffle seals, oil cooler, muffler, and every other moving part that could affect the engine's performance.  Any advice is appreciated!

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Re: CHT's?

Hi Paul,
   It's common for CHT's to be high during break in. It's best to keep the airplane low and high MAP to break it in correctly. Don't baby the engine but temp is the guide. It's also better to keep the mixture a bit richer than usual during the first 15-20 hours to avoid high temps, keep all climbs at higher airspeed and shallow to keep the cooling air moving. You may need to enlarge the cowl outlet or increase the lip to draw more air.
   If, after 10-15 hours the temps are still high you need to change something...either cowl opening or technique. Change the oil and filter after the first 2-3 hours of operation on a new engine and do an oil sample.  I would suggest mineral oil for no more than 15 hours...then change to regular 50 weight Aeroshell. Install the largest filter you have room for...if you have the CH48108...go to the CH48109. Ch48110....go to the CH48111...they move oil better (12 GPM v. 8 GPM for the smaller filters).
   Keep the nose down, mixture rich and stay at low altitudes with high cruise power settings during break in. I suspect your engine will start calming down in the next 10 hours or so. Your taget CHT should be 400 or less on a mature engine.

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Re: CHT's?

Greggs' advice is all good.  CHTs above 400 are not good.  I like to use 380 as a target and 400 as a redline.  At CHTs above 420, thermal runaway has been observed a number of times.  STAY AWAY FROM THERE.  420 is the DO-SOMETHING-RIGHT-NOW to get the CHTs down redline.

You pointed out that the EGTs on those cylinders were also high.  This would indicate that those are running not rich enough and would explain the high CHTs.  It is not at all uncommon to have induction leaks on a new installation and that would contribute to the problem at hand.  430 is NOT a break-in problem as they will still be too hot when they are finished breaking in.  Do not let anyone tell you this is normal or allright.  Something is not right and needs to be addressed ASAP.

The breakin period should be complete in UNDER 5 hours.  Change the mineral oil then and go to the regular oil you plan to use.  Get rid of the mineral oil ASAP.  Mineral oil breaks down at lower temperatures than AD oil and it's really not a good break in oil.  The recommendation to use mineral oil is an OLD recommendation from 60 years ago that won't go away. We have broken in the last 30 or so engines with the regular AD oil and it works quite well.

Good luck,

Walter Atkinson
Advanced Pilot Seminars

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Re: CHT's?

I have had the 180hp O360-A4M in my plane for just over 100 hours now.  At Oshkosh I took advantage of the great special offered by JPI on the EDM700.  Now I have a very accurate gauge to show me temperatures digitally.

Leaning to 50deg rich of peak I get cylinder head temp of 420deg in cruise.  I called PenYann  and they said that is fine as the redline is 500.  On steep climb outs, I can get temps in the 470’s.  I have great baffling but it is a 1968 version which allows a lot of air to sneak past around the alternator.  My #3 is the hottest so I even tried plugging the outlet for the oil cooler which is right above the #3 cylinder and saw no change in climb out temps.  I didn’t try this in cruise as I didn’t want to get the oil too hot.  By the way my oil temp is normally in the 212 range for cruise.

I have had one mechanic recommend placing some rubber baffle down the center of the cowl forcing the air to stay on the side from which it came in.  He said that he has herd that this has worked for others.

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Re: CHT's?

Mr. Atkinson or anyone else, what do you recommend doing to troubleshoot this high temp problem.  Air plains and Lycoming said they won't agree to do anything until the engine has been run ten hours.  They said that if the temps haven't come down then, they will send another new carb.  Is this a sensible plan, or should I dispute it?  Lycoming said that the max temp is 500 and the top end of the normal (safe) operating range is 435.  I agree with you saying that these numbers are too high, but I don't what I can make them do with my numbers being in their normal range.  It seems that unless my numbers rise above their range, I'm riding on their grace when it comes to help.  Any suggestions?

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Re: CHT's?

Hi Paul,
   I would pull the cowls and do the following....remove the scat hose for the carb heat at the carb airbox. Get a good shop vac and some duct tape....put the shop vac hose in the outlet side of the vac so it's blowing air. Duct tape the other end of that hose to the airbox opening for the carb heat. In the cockpit, open the carb heat and the throttle wide open. Get a squirt bottle with water and dishwashing liquid...about 3-4 teaspoons of soap to a squirt bottle full of water. Turn on the shop vac so it's blowing air thru the induction system and start squirting that soapy bubble stuff around the carb gasket, induction tube couplings and the flanges where they mount to the cylinders. Also check to see the primers are installed tightly and no hex plugs are missing or loose on the cylinders. Broken or loose primers and primer lines can cause the engine to run lean...Any bubbles are a sign of a leak and need to be looked at. On a new engine with a new carb I wouldn't suspect a bad carb but it can happen. That would probably be the last thing I would look at. Just make sure the mixture cable allows the mixture arm to hit the stops on both sides....if it isn't adjusted correctly it could cause some problems but that is an obvious inspection item during install and should be okay.
   Shine a flashlight inside the cowl openings with the cowls installed and make sure the baffle seals are tight against the upper cowl so they'll send the air where it belongs. Other than that, your ignition timing can be a bit too far advanced and that'll make it run hot so check that too. 25 degrees before top dead center is where you want it.....
   Let us know what you find.
       Gregg Horrell

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Re: CHT's?

Paul
You say that the rear cylinders were running at 430 degrees... What were the two front cylinders reading????  How much difference????  What was the outside air temprature?????

                      Steve

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Re: CHT's?

The two front cyclinders were at 380 (50 degrees cooler than the rear), and the oat was around 80 degrees.

Paul

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Re: CHT's?

Curt:

* Leaning to 50deg rich of peak I get cylinder head temp of 420deg in cruise.  I called PenYann  and they said that is fine as the redline is 500.  On steep climb outs, I can get temps in the 470’s.*

1) 50dF ROP is the mixture setting which results in the hottest possible CHTs.  Is that really where you want to run your engine?  At the HOTTEST possible mixture setting?

2) Any recommendation allowing 470dF is criminal.  It is contradicted by all of the known engineering data.

3) The engine redline was set on an engine test stand with as near perfect cooling with forced air as could be accomplished.  That cooling air cooled the cylinders evenly all the way around, keeping them round during this extreme heat.  The installation of the engine into an airframe changes all of that.  Cylinders in an airframe do not cool evenly.

4) Thermal runaway has been demonstrated to occur at temps as low as 420dF.

5) Aluminum loses 50% of it's strength at 400dF.  The strength-temperature relationship is not linear and strength is lost very quickly as temperature increases above 400dF.

Owing to these and other factors, I very strongly recommend that you not allow CHTs to get above 420 and do whatever it takes to get CHTs to run below 380 as a matter of routine.  470dF is very dangerous and will very likely result in shortened cylinder life and quite possibly catestrophic failure.  I am stunned that any good engine builder has made the statement that 420dF is acceptable.  They should know better and if they don't, they might take the opportunity to become better educated.

I have the engineering graphs from TCM, Lycoming, and other engine manufacturers to support these statements and we show these routinely in the Engine Management Seminar.

Walter Atkinson
Advanced Pilot Seminars

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Re: CHT's?

Gregg's recommendations on a plan of action all make sense.  It's very likely not the carburetor.  If it were, ALL of the clyinders would be running not rich enough and would all be hot.  If it were timing, they would all be running hot, not half of them.

This is likely from two possible sources.

1) the induction leaks Gregg thinks are likely, or

2) improper baffling.

Both could be contributing factors.

Run FULL RICH and keep it as cool as you can until this is addressed.

Walter Atkinson

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Re: CHT's?

Two other items I think should be addressed. 

1) Are your temperature readings accurate?  What is the accuracy of the setup? 

2) Temperature elements only tell you how hot the temperature element gets, not the average cyclinder temperature.  So since engine cooling may not be uniform, could the installation of the temperature sensors or some other obstruction be blocking air flow near the temperature elements creating a local hot spot?

my 2 cents...

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Re: CHT's?

FROM Lycoming

Although the smaller four cylinder engines of the low compression, low horsepower variety do not generally use a cylinder head temperature gage, the higher powered, more complex powerplants require a cylinder head temperature gage in order to prevent unwitting abuse by the pilot. If head temperatures are higher than normal during flight, it should not be ignored because there is some reason for it. It may be caused by hot ambient temperatures, a lean fuel metering device at higher than cruise power, bad baffles or leaking cowling, or malfunctioning of the ignition system. Even old and tired engine mounts that allow the engine to sag slightly may cause a change in the air-flow pattern and an abnormal increase in CHT. It is also possible that a mechanical problem may be developing in the engine.

When higher than normal cylinder head temperatures are showing on the gage, the pilot should take steps to bring the temperatures down to the normal operating range in order to keep the remaining flight safe. Head temperatures may be reduced by:

1. Enriching the mixture

2. Adjusting cowl flaps

3. Reducing power

4. Any combination of the above

We suggest that in order to help the mechanic diagnose the problem, the pilot or some member of the crew should make a written record of the engine instrument readings during the above flight condition and present it to the maintenance people.

A first step in diagnosing abnormal cylinder head temperatures would be insuring that the gages are providing accurate readings. If they are, the mechanic can then proceed to check engine baffles that may have deteriorated, proper flow of the fuel metering device, and then other more time consuming checks for ignition or mechanical malfunction.

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Re: CHT's?

Walter

I use 50deg ROP because that is what I have read to use.  What is the best to use?  I searched the Lycoming Publications just now and found for best power to use 100deg ROP. 


FROM LYCOMING
8. For maximum service life, maintain the following recommended limits for continuous cruise operation:
(a) Engine power setting - 65% of rated or less.
(b) Cylinder head temperatures - 400oF. or below.
© Oil temperature - 165oF. - 220oF

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Re: CHT's?

Just curious, what is thermal runaway?  Should there be concern if the CHT routinely goes above 420oF?  the Owner's Manual for the 172d with the O-300-D lists the CHT normal operating range from 350of - 475of with the max/redline at 525oF.  From this discussion, these limits seem high.  What would be the optimal CHT in cruise for this engine?  Thanks!

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Re: CHT's?

OK, I have some new info regarding this engine headache I've acquired.  After being told to moniter the feul burn, I ran the plane today for 1 1/2 hours.  First my mechanic and I visually checked all the lines, seals, and baffles for leaks.  We took the plane up to 6500 and ran it to the firwall at full rich.  The front two cyclinders were at 350, cyclinder #3 was at 400, and cyclinder #4 was at 415.  The numbers were all fifteen degrees or so lower than the first flight.  The big kink in all this is that the engine burned 23 gallons in an hour and a half.  If my math is right, that's around 16 gallons an hour.  If I'm not mistaken the new operating info says that it should burn 10 1/2 gallons an hour max.  I can't figure out how in the world it can burn this much fuel, and still run so hot.  It seems to me that with this much fuel burn, the cyclinder temps should be very low.  The fuel flow showed it burning 12 1/2 gallons even after pulling the throttle back a bit.  By the way, I did cross check the fuel flow by refueling the plane after the flight.  All I know to do is be happy that everything is under warranty.  Thaks for all the advice!

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Re: CHT's?

Hi Paul,
   If you now have 2-3 hours on the new engine I would go ahead and change the oil, take a sample, install the bigger filter and clean the plugs.
   16 gph on a new engine isn't unusual for a 180 HP Lyc. at full rich. That thing has a lot of internal friction going on right now and will show higher numbers until it's broken in.
   If the timing, baffles and cowl geometry are all good you just need to keep your speed up to force more air in it during break in. The temps will come down....just keep an eye on it.
   415 isn't bad for a virgin engine. I would select an altitude lower than 6500 for break in if you can. You want thicker air to keep manifold pressure high and to drag heat off the cylinders.
   Sounds like you're doing it right...just watch that monitor and you'll be surprised when it starts to come down...it will do it one cylinder at a time but they'll all come down within the next 10 or so hours.
   NO TOUCH AND GOES DURING BREAK IN!!!
   Gregg Horrell

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Re: CHT's?

Paul

Just a thought.

Were all the baffles and springs put in the properplaces? There are different springs even though they may look similar.

All leads routed properly and being the same length and matched, to the gage. Did you also try moving the lead and probes from the front to the rear cylinders and see if you get the same readings. And verify probe/sensor/lead.

Bill

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Re: CHT's?

Curt:

For ROP peak EGT operators:

80dF ROP is the Best Power mixture.  The recommendation to be 100dF ROP is better on CHTs by a degree or two.  At power settings above 65%, I think 125-150dF ROP is a MUCH better mixture setting to use since it runs cooler under lower internal cylinder pressures.  Below about 60% power, it really doesn't make a lot of difference where the mixture is run. You can't hurt anything at the lower power settings.

The recommendation you posted from Lycoming is good advice.  Keep 'em under 400.  I like to keep 'em under 380.

For LOP operators:

At 75% power, be 35-40dF LOP.
At 65% power, be 10-15dF LOP.

We never let the CHTs get above 380dF.

Now for the eye-opener.  I frequently run above 80% power at 70dF LOP and the engine loves it.  So far, we have over 1500 hours on the engine, all at above 80% power (generally in cruise we operate at 83% power but some above 90% power) and the engine show no signs of any problems whatsoever. No jugs changed.  Oila analysis completely normal.  At 1000 hours, we did a tear-down inspection and ALL parameters were still within NEW limits, not servicable limits—NEW LIMITS.

As it turns out, it's not how hard you run the engine, it's how you run the engine hard.

Walter Atkinson
Advanced Pilot Seminars

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Re: CHT's?

Jim:

Thermal runaway is that condtion whereby the CHT will continue to rise, no matter what the mixture is.  When noted, the only response is to go to idle power IMMEDIATELY.  We think the phenomenon is related to the cylinder getting out of round and the round piston scuffing the the oval hole.  It has also been obswerved from a broken ring scuffing the cylinder.  We had an IO-520 which would undergo thermal runaway routinely as soon as the temps got above 420.

We have not observed this below 420dF.

We feel like there is ample engineering data whch supports an operating CHT below 380 which results in few deliterious effects with an operational redline  of 400dF with a DO-SOMETHING-NOW redline of 420.  My personal operational target max CHT on normally aspirated airplanes is 360dF and 380 on TC'd airplanes.

Walter Atkinson.

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Re: CHT's?

Gregg:

Of the last 30 or so engines I have broken in, not one of them wasn't fully, completely broken in by 5 hours MAX.  Most are finished with the breakin at about 3.5 hours.  It has been my experience that if it takes longer than that, something is wrong.

I would recommend doing this at as low an altitude as possible with the mixture full rich at MAX power.  That's what I do on engines that will not run smoothly LOP.  If they will run smoothly LOP, the entire breakin except for the first 15 minute flight is done WOTLOPSOP.  They break in cooler, cleaner, and quicker.

Walter  (WOTLOPSOP = wide open throttle, lean of peak, standard operating procedure)

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Re: CHT's?

Paul:

There has been a lot of information provided in this series; most of it pretty good.

At this point it appears that things are OK, however high temperatures can be caused by several things, most of which have been touched on in the various replies to your question; intake leak, baffle leaks, mixture control, mag timing.

New or freshly overhualed engines will run hotter than an engine that is broken in, so as you continue the break in process your temperatures should come in line.  The engine was provided with several important pieces of information; Engine operators manual, and Service Instruction 1014 & 1427(oil recommendations and break in procedures).  If you pay attention to the information provided in these publications you should not have any trouble.

In regard to your comments in your post of 10/22 that the temperatures were coming down but you flew the aircraft for 1 1/2 hours and burned 23 gal of fuel.  I don't know why this is such a surprise; the engine will burn 14 - 15 gal per hour at full throttle, so if you multiply these figures by 1.5 you get right in that ball park, give or take a gallon (normal tolorance).

Ray Crist

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Re: CHT's?

Paul.
I would like to know how you finally fix the CHT's
I have a 172 w/180 airplains with the same problem.
Thanks

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Re: CHT's?

I'm new to the small airplane world (77 Cessna 180)and have heard discussion of installing louvers in the cowling to help cool the engine in cruise. This 0-470U motor runs about 420 deg. a cruise and running with the Cowling flaps partcally open cools the engine but causes vibrations.  Where is information on the benefits of the louvers and are they cost effective?

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