I have a newly installed MVP-50P engine (and just about everything else) monitor. Usually the EGT spread is about 85-90 degrees from hottest to coldest.

On take off last friday the EGT spread went up to 270 degrees in the climb. I levelled out at 9000 in the hope it would even out but there was still a spread of 150 degrees. After a text to my LAME I returned to Rocky. Fuel injector cleaned out we set off for Brisbane once again. At 2500' the spread was 270 degrees. left circuit to land. More cleaning checking and doing LAME things and two more test circuits failed to find the problem except #1 cylinder was about 850 degrees in the climb and then rest about 1200 degrees. #1 is usually the hottest. The enginme was running perfectly smoothly, developing normal power and the CHT's were normal across the board. When power was pulled back in the circuit the difference, or spread, became about 150 degrees.

Excluding a faulty probe next week, the LAME thinks it is a fuel supply problem and will look at the fuel distributor this week. Fortunately there was one Dash 8 departure left out of Rocky Fri night which we were able to make but at a cost that will allow Qantas to pay an extraordinary dividend this year!!

If I did not have an engine monitor I would be none the wiser as a single combined EGT probe would show a normal temp i would think. I wonder what the long term outcome of that would have been for my cylinder.

Hi MIchael,

The easiest thing your LAME could have done is to swap the neighboring EGT probes. Obviously if the problem stayes on the #1 cylinder a probe fault has been eliminated. Or you could just switch the wires to the probes to see if the fault is in the instrument.

Hi Peter,

Yes, the avionics guys said check the probe although the EI ones have a very low failure rate. To do that the bottom cowling has to come off and he ran out of time. Initially he decided it was a blocked injector and so concentrated his efforts in that direction. I am having another probe coming by air express overnight in case that is the problem althogh the LAME (who has had to leave town today/tomorrow) thinks not due to the almost normalisation of temps when the power was pulled back in the circuit after climb out.

Hi Michael,

You've obviously got too much information...

Seriously though, short of an instrumentation problem, your system just might be trying to tell you something. Can you dump and graph the data?

You have a Continental in your plane right? I'd be surprised if the fuel distribution unit was the culprit. There is nothing inside the unit apart from a spring, rubber diaphragm and filter screen. A split or cracked diaphragm would affect all cylinders. The unit must be opened and then resealed by an appropriately licenced engineer.

What is the CHT doing? Is that down as well? If the CHT was down as well I'd suspect a failing cylinder, possibly an inlet valve or exhaust valve problem.

Or a cracked cylinder. Is there any unusual grey exhaust gas staining around the edges of the cowling?

If you do have a cylinder problem, I can put you in touch with an engineering company which could repair the cylinder for a pretty fair price, which is unusual...

For what it is worth, I looked at the manual for my EI engine analyzer. The scary thing was that on the Engine Diagnostic Reference Guide pages the only faults associated with a decreasing EGT in 1 cylinder were pre-ignition, and detonation!

However, I still think it could easily be a probe or instrument error. Just swap the probes of the bad cyl and a neighboring cylinder. Go fly and you will now have a lot of information. Personally I would do that before changing the probe to a new one. Perhaps there is an error in the way the probe is installed? I'm not sure what might happen if the probe isn't properly tightened down....might leak or allow the probe to pivot in the exhaust. That would surely change temperatures.

Good luck, and keep us posted!

Peter R,

I think you are on the money. It was noted by the LAME that the probe was a bit loose but he didnt think enough to cause the changes in temps we saw.. After everything else checked out as per below he has taken a closer look at the probe and feels that it may very well ne the culprit. I am not sure how much time he took to reach this conclusion but was a bit apologetic that he had placed more emphasis on it first. At least I know eveything else is ok. However he did note a leaking fuel distributor diaphragm so that unit has been sent south for a makeover and he also noted something wrong with the nose gear rigging and wants to jack the aircraft to check that. I have attached the graph he is talking about .

They did all the usual stuff. Compression excellent, boro good, rockerboxes for broken springs etc-all good, looked at valve lifts and lifters for collape etc, etc..

They also did a cal on the probe (comparison) with No. 3 and they’re both the same up to 600F.

When we looked at the graph from my MVP data It then became clear that those very dramatic drops are NOT followed by any waver at all in the CHT. That just isn’t right. Also, looking at it that cylinder was virtually at idle power (according to the EGT). That would have been noticed as a roughness.

In short back to the idea that it is an indication problem.

We’re now thinking that the probe was in a different position in the pipe because it was loose and therefore read differently. This does happen.Probe position does alter the reading.

The little circlips that are supposed to hold the probe sit in a groove. The groove is virtually non-existent on that probe so the probe was free to float about. I’ll get a new probe and see what happens.

You can see the offending EGT #1 in thick yellow. It dips on take off and again on go around. The Fuel flow and TIT and MAP all rise with power on but the EGT dips. This might be all very straight forward for engineering types and experience drivers but I'm learning about the aircraft almost every day.

Unfortunately the LAME decided to look at the MVP graph after he had tinkered with the engine and checked all things mechanical. After he found nothing he investigated the probe more and found a groove missing / worn where a little circlip which holds it is place locks it. This allowed the proble to move about a little. He doubted the amount of movement would be the cause but it seems so. I flew it nearly 3 hrs last week and there was no problem. It would appear therefore that once again the combined wisdom and experience of the Mooney Forum has been proven correct - it was a probe problem and not the engine. Thank God!!

Sorry. Forgot I had already posted the outcome!

Looking at the graph sparked my interest. My temperature gauges are in Celcius, the graph shows the EGT at a fraction above 1500F (815C). I run at 800C max, I looked through the Lycoming data but they do not give an EGT. The closest is a range of the temperature gauge (1200F to 1700F or 650C to 925C). What should the maximum EGT be for engine longevity?

Lycoming give the CHT as 220F (104C), and the max cooling rate of 50F/min (28C/minute).

Geoff
NWF

In respect to my previous post. The oil temp is 220F (104C) and the CHT is 400F (204C). Sorry about that error, must be old age setting in

Geoff
NWF

Hi Geoff,
I believe the max figures rec by GAMI (at full power, non-turbo) are EGT 1250F & CHT 380F. This gives minimum engine wear. Doug Sprigg of Arkaroola observed these limits in his Cessna and the engine was still within new limits at TBO. He operated mainly LOP as well.

My TCM IO-550 runs somewhat hotter than this: one cyl regularly gets to 430 on T/O, but seems to be wearing OK.

During cruise the EGT can get close to 1600 at 75% power, 50f ROP.

I don't have a lot of faith in the absolute temp readings: there is a 200F discrepancy between the factory gauge and the EDM700 gauge.

Geoff,

GAMI dont seem to go much on EGT in cruise. They like them below 1300 from memory in climb. There is nothing in my TCM book which tells me what EGT to aim for or aim under. GAMI are mainly interested in keeping CHT below 380 as Peter said. My EGT tend to run between 1200 - 1300, CHT around 320 - 350 and oil around 160 winter 180 summer. TIT around 1550 at 75% power at 50 LPH which is 125 ROP. I used to run at 46 LPH ot 75 ROP but quite a few LAMES here and in the States said go to book value of 125 ROP, an xtra 4LPH is cheaper than another top overhaul...