High Exhaust Temp

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Hans
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High Exhaust Temp

Post by Hans »

Yesterday, coming back to my home base, Grand Strand, I got an exhaust temp on cylinder 2 that went to the top of the bar graph, 1600 plus. The CHT remained fine and the plane ran smooth at 2400 rpms...however, at a lower rpm it ran very rough...I landed and the cylinder head temp on 2 now read 154 while the other CH temps were 295,296,267....and a run-up was very rough on both mags.....sooooo, I will probably need a good mechanic to look at it, first real problem with my 40 in ten years, love this plane. Could it be carbon build on a plug ?...also, does anyone know a mechanic in the Myrtle Beach area ?
Thank you, this forum has always been a great resource !!
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krellis
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Re: High Exhaust Temp

Post by krellis »

If it's a fouled plug, you can sometimes clear it by running a fairly high rpm and leaning to create some heat in the cylinder.

My bet is a leaking intake gasket, however. Not at all uncommon on a Lycoming.
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Re: High Exhaust Temp

Post by Hans »

Question;
I can fix foul plugs...is a leaking intake gasket a big job ??
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Re: High Exhaust Temp

Post by krellis »

Not too difficult, although I don't remember if you will have trouble accessing the pipes on the DA40. If you have easy access, it should be less than an hour to replace the gasket. A universal drive socket (3/8" or 7/16" if I recall correctly) will make it easier to get to the rear bolt. Double check the part number but Lycoming 71973 or Superior SL71973 is the likely replacement. Torque value for the 1/4" diameter coarse thread bolt is 96-106 in-lbs.

I'm not an A&P so please don't hold me to this information. Good luck with your repair and please post once you are fixed!
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Rich
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Re: High Exhaust Temp

Post by Rich »

I would not immediately jump to any conclusions. It doesn't sound like a fouled plug, but there are several other things it could be. Naturally, this has to happen on a holiday weekend, but given the symptoms I would at least eliminate the potential big problems with low-cost diagnosis:

- Pull a #2 plug, check compression. If OK, you've eliminated the worst case. If not, further investigation as to cause. A stuck or unseated valve can possibly be remediated.
- Pull the other #2 plug. Condition of plugs can tell you about the combustion process.
- Check for a clogged fuel injector - consider a "bottle test". This last is a bit of a hassle and you might do this after other things.

Some of the intake pipes are more of a hassle than others. In any case there are two gaskets/seals to be replaced. Worst case here is a broken/stripped stud.
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
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Charles
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Re: High Exhaust Temp

Post by Charles »

I would think a failed intake gasket would cause a decrease in EGT. Poor ignition, however, would cause an EGT increase. So would a burned exhaust valve.

Here is a good reference on the subject: https://resources.savvyaviation.com/und ... and-egt-2/
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Re: High Exhaust Temp

Post by Rich »

Charles wrote:
Thu Nov 25, 2021 8:00 pm
I would think a failed intake gasket would cause a decrease in EGT. Poor ignition, however, would cause an EGT increase. So would a burned exhaust valve.
If the intake leak is bad enough, you'd be pulling in more air in that one cylinder than the others and this would tend toward a leaner mixture. I would think this would be more pronounced with partial throttle, as you're in more of a vacuum situation in the intakes than with WOT. Keep in mind MAP pressure in this engine is off #4 cylinder and wouldn't reflect situations like this in the other cylinders. But I'm thinking this would have to be so bad you'd see a problem just by eyeballing and trying to move #2 intake by hand.

The last section seems to indicate that at the end of this flight, #2 wasn't firing at all at idle, on either mag. So plug/mag, etc. isn't a prime suspect in this case.
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Re: High Exhaust Temp

Post by pietromarx »

I would also look at a cracked exhaust. When that happened to me (a long time ago in a galaxy far far away), the symptoms were the same.
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Re: High Exhaust Temp

Post by Hans »

After many hours of removing and testing the mags, we traced it to a piece of rubber that had clogged in the port in the fuel distibutor going to cylinder number 2...thats why at low idle we had the exhaust temps running very hot on cylinder 2, not getting any fuel....anyway thx for all the help, now on to where that piece of rubber came from...very, very small piece...
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