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912UL EGT`s Running HOT
Posted: Mon May 11, 2009 11:00 am
by Splinter
Morning Guys.
OK I need some serious advice from the guys that know the 912ul inside out! Here is the problem….
My 912 has flown for many years without a single problem. My normal temps were as follows, anything between 82 and 90 degrees oil temp, CHT always ran about 3 degrees lower than oil and my EGT`s ran at approx 700 – 760 degrees. 760 Degrees was only reached if I was really pushing the plane and flying hard. On these temps I would be burning 10 or 11 liters per hour maybe 12 if pushing it. The motor idle was set at 1750rpm when warm and ran smoothly.
On the way from Lambertsbay routing Carnavon the two rear cylinder EGT`s started running hot at about 800 – 810 degrees. The motor was running at approx 4700rpm. I have never seen the EGT`s this high. I wouldn’t even reach these temps pushing hard, why now suddenly at reasonable cruise? Check all the other temps - Oil temp, CHT temp, Oil Press – all normal. Check for something obstructing airflow – nothing! Nurse the plane to Carnavon keeping the EGT temps just below 800. After landing the plane was suddenly at an idle of 2400rpm.
Returning to Springs and thinking this might be fuel related I filled with ulp93 only to find the EGT`s were still running hot. No changes were made to the carbs, balanced 100%, no changes to idle settings, fuel / air mixture or needles – nothing! I don’t think it is faulty EGT sensors as the chances of 2 (out of four) failing at the same time are slim, plus they were indicating temps very close to each other all the time (no erratic jumps in temps). As far as I know the rear cylinders will always run just a little hotter because of the engine layout.
What else can cause this problem if no changes were made to the motor? I have been told to have the needles pulled higher for more fuel and understand this but want to know why the current setting suddenly don’t work anymore? They have been set like this for many years.
Thanks
Splinter
Re: 912UL EGT`s Running HOT
Posted: Mon May 11, 2009 11:29 am
by Morph
EGT's measure the fuel burn and are controlled by the mix in the fuel or the loading on the motor. Now I can't see the loading suddenly changing, which leads me to fuel. Higher egt's are usually as a result of the fuel mix becoming leaner. Maybe the carbs need cleaning? look also at plugs fouled or gap reducing or fuel line sucking air.
http://www.avweb.com/news/maint/egt_and ... 791-1.html
Re: 912UL EGT`s Running HOT
Posted: Mon May 11, 2009 11:49 am
by Splinter
Morph wrote:EGT's measure the fuel burn and are controlled by the mix in the fuel or the loading on the motor. Now I can't see the loading suddenly changing, which leads me to fuel. Higher egt's are usually as a result of the fuel mix becoming leaner. Maybe the carbs need cleaning? look also at plugs fouled or gap reducing or fuel line sucking air.
http://www.avweb.com/news/maint/egt_and ... 791-1.html
Thanks Morph. Will give the fuel system a rundown this afternoon. Please explain to me why the EGT temp will run hotter if the plug is fouled or the incorrect gap is set. 
I thought about dirty carbs in flight but disregarded the option as two EGT`s on two different carbs suddenly ran hotter at the same time? This will surely be a BIG coincidence if it is due to dirt? Reading the attachment it looks like I will have to measure the cylinder preasure if I dont find anything wrong with your suggestions?
Re: 912UL EGT`s Running HOT
Posted: Mon May 11, 2009 12:39 pm
by justin.schoeman
Also check for air leaks on the inlet manifold. A small leak will result in high EGT and fast idle...
Re: 912UL EGT`s Running HOT
Posted: Mon May 11, 2009 12:44 pm
by Splinter
justin.schoeman wrote:Also check for air leaks on the inlet manifold. A small leak will result in high EGT and fast idle...
Will keep that in mind! Thanks! Keep them comming boyz, I need all the advice you can give!
Re: 912UL EGT`s Running HOT
Posted: Mon May 11, 2009 1:10 pm
by Morph
Splinter wrote:Please explain to me why the EGT temp will run hotter if the plug is fouled or the incorrect gap is set.
actually probably the other way around, if the plugs gap widdened then the spark would be longer and hotter and so would the combustion.
But the fact that it affected both sides, different carbs and differnent manifolds means there must be something in common, like fuel pipes.
Do you have EGT on the two front at well? Did they get hotter?
Re: 912UL EGT`s Running HOT
Posted: Mon May 11, 2009 1:44 pm
by Splinter
Morph wrote:Splinter wrote:Please explain to me why the EGT temp will run hotter if the plug is fouled or the incorrect gap is set.
actually probably the other way around, if the plugs gap widdened then the spark would be longer and hotter and so would the combustion.
But the fact that it affected both sides, different carbs and differnent manifolds means there must be something in common, like fuel pipes.
Do you have EGT on the two front at well? Did they get hotter?
Yes i have 4 EGT readings at any given time. The front two were also running a bit hotter but nowhere near the 800 mark. If i remember correctly they were both running approx 60 degrees less than the back two readings so around 740 - 750.
Re: 912UL EGT`s Running HOT
Posted: Tue May 12, 2009 8:10 am
by Splinter
Thanx Demon, will keep that in mind! At that stage I could still control the EGT by trimming the wing slower and throttling back. Now that you brought up the subject of fuelflow meters I remembered, the fuel consumption went for a ball of "burger residue" 
and climbed according to the meter, but closer inspection of the tank showed that I used less fuel than indicated by my flow meter. I swiched on the elecitric fuelpump (series), thinking it could be fuel, but this also did not seem to make any diff. Will keep you guys posted........ Hold thumbs
Re: 912UL EGT`s Running HOT
Posted: Tue May 12, 2009 3:04 pm
by Smiley
Check your choke, I think it's stuck and doesn't close properly...
Re: 912UL EGT`s Running HOT
Posted: Tue May 12, 2009 8:15 pm
by Boet
You have a dirty filter or a partial blockage of some kind. The engine is getting less fuel, therefore= higher EGT. Running leaner. What type petrol filter do u use??
Re: 912UL EGT`s Running HOT
Posted: Wed May 13, 2009 8:14 am
by Splinter
Boet wrote:You have a dirty filter or a partial blockage of some kind. The engine is getting less fuel, therefore= higher EGT. Running leaner. What type petrol filter do u use??
Use the normal transparent Merc filter. It was replaced about 60H ago with the last service. Will check all possibilities anyway and keep you updated! Never know what you find!
Re: 912UL EGT`s Running HOT
Posted: Wed May 13, 2009 3:44 pm
by Thatchman
Not sure if this my point is valid cause I am just an accountant and not a mechanic.
There are four cylinders and each side, two exhaust outlets and one carb per side. So if one carb feeds each side of the engine, would it not mean that any fuel or mix problem in that carb would then effect both the front and back EGT on that side and not just the back? Or does it mean that filter blockage or partial blockage effects them all but the back ones more?
Why not change plugs and check.
Also swop probes around and see if the answer changes. You can then rule the plugs and probes out for sure.
Re: 912UL EGT`s Running HOT
Posted: Thu May 14, 2009 2:37 pm
by Splinter
Thatchman wrote:Not sure if this my point is valid cause I am just an accountant and not a mechanic.
There are four cylinders and each side, two exhaust outlets and one carb per side. So if one carb feeds each side of the engine, would it not mean that any fuel or mix problem in that carb would then effect both the front and back EGT on that side and not just the back? Or does it mean that filter blockage or partial blockage effects them all but the back ones more?
Why not change plugs and check.
Also swop probes around and see if the answer changes. You can then rule the plugs and probes out for sure.
You are entirely correct! Fuel "shortage" will cause a leaner mixture and cause all four EGT`s to run hotter. This did happen, but keep in mind that the layout of the inlet manufold causes the rear EGT`s to always run hotter than the front ones! Thats why I was only worried in flight about the rear EGT`s as they were the ones closest to, and most likely to reach the max allowed temp! Ruled the probes out in flight as all the EGT`s were climbing (front less than rear) and keeping the normal variance in temp between them.
Checked the fuel supply yesterday (fuelflow included) and replaced the fuel filter while I was at it. (Pease remember that your AP also has a part to play and that you cant just do maint as you wish). Flew the plane afterwards and all four EGT`s were lower but not there yet. At least they were opperating well within the allowed temps at any rpm.
Will keep you informed if we find anything else that makes a diff! Thanks for the help so far!
Cheers
Re: 912UL EGT`s Running HOT
Posted: Sun May 24, 2009 6:08 pm
by Dobbs
Having read this thread I took a bit more notice of my EGT's today and they peaked at 800, only measure number 2 and 3 (ULS)
I have always ensured that they remain below the max. as highlighted on the instrument of 820.
Went through the Rotax CD tonight and cannot find any reference to EGT, unless I have missed it - can anyone help?
Re: 912UL EGT`s Running HOT
Posted: Mon May 25, 2009 10:57 am
by Trikenut
Can someone please explain to me the difference between CHT's and EGT's and also tell me how they work? This topic has now sparked an interest but I'm also a bit confused!?
Why do some people have 4 EGT readings and some people, with exactly the same engine, only have two??
Finally, can you have 4 CHT readings??
Sorry if it seems like I am hijacking thread... I don't think I am though, as this is about engine temps!
Thanks
Ross