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Optimal Temperatures and fuel burn

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AirMike

Joined: 27 Feb 2007
Posts: 514
Location: Nevada

Posted: Sun Oct 21, 2012 9:26 pm Post subject: Optimal Temperatures and fuel burn

Not unusually, I have a hot #6 cylinder. It consistently shows CHT at about 25-40 degrees hot compared to the other cylinders. I always keep it under 400 degrees even though Lycoming says up to 425 is ok. My EGT on #6 also runs hot at 1420 when the other cylinders are 1375. My oil is 168 in fall and 180 in winter. What do you all consider excessively high EGT? I do not want to melt my exhaust valves or pipes!



Do you folks think that I should inhibit the air flow to the oil cooler to get better cooling on #6.

_________________
See you OSH '18
Q/B - sold.

flying-nut(at)cfl.rr.com
Guest

Posted: Sun Oct 21, 2012 9:46 pm Post subject: Optimal Temperatures and fuel burn

I'd suspect an induction air leak first.  Easy to find ....

Hook up a CLEAN shop-vac so it blows instead of sucks.  Put the hose in 

the intake and stuff some rags around it to seal it. Spray soapy water 

all over the intake to #6.  Usual culprits are where the intake tube is 

swaged into the oil pan and the intake coupling hoses.

Same procedure works on a lot of oil leaks too ..... pressurize the 

crankcase breather.

Linn



On 10/22/2012 1:26 AM, AirMike wrote:

 	  Quote: 	
		   



 Not unusually, I have a hot #6 cylinder. It consistently shows CHT at about 25-40 degrees hot compared to the other cylinders. I always keep it under 400 degrees even though Lycoming says up to 425 is ok. My EGT on #6 also runs hot at 1420 when the other cylinders are 1375. My oil is 168 in fall and 180 in winter. What do you all consider excessively high EGT? I do not want to melt my exhaust valves or pipes!



 Do you folks think that I should inhibit the air flow to the oil cooler to get better cooling on #6.



 --------

 See you OSH '13

 Q/B - flying 3 yrs.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=385771#385771





 -----

 No virus found in this message.

 Checked by AVG - www.avg.com

Bob Turner

Joined: 03 Jan 2009
Posts: 885
Location: Castro Valley, CA

Posted: Sun Oct 21, 2012 9:57 pm Post subject: Re: Optimal Temperatures and fuel burn

What are the EGTs relative to peak EGT, on each cylinder?

E.g., if #6 is 50 rich of peak and the others are 100 rich of peak;

Or, of #6 is 50 rich of peak and the others are 50 lean of peak, 



Either way you would expect #6 CHT to be hotter than the others.

_________________
Bob Turner
RV-10 QB

TimRVator(at)comcast.net
Guest

Posted: Mon Oct 22, 2012 1:57 am Post subject: Optimal Temperatures and fuel burn

Mike Busch's free webinars (hosted by EAA, link from 

https://www.savvymx.com/index.php/webinar) address several points from 

the post:



"The EGT Myth" addresses concerns about excessively high EGT: 

http://www.eaavideo.org/video.aspx?v=1316946190001 (1420 is not "too hot.")

"Troubleshooting Engine Problems" has a wealth of good info: 

http://www.eaavideo.org/video.aspx?v=972961455001

"Flight Test Profiles" from January 2012 Sport Aviation includes mixture 

distribution test and an airborne induction leak test (page 61).



I don't think 25-40 degree CHT spread is a problem.  Depending on phase 

of flight, my CHT temps are spread that high or higher.



Tim



-- 

Tim Lewis -- HEF (Manassas, VA)

RV-6A N47TD -- 1104 hrs - sold

RV-10 N31TD -- 350 hrs



AirMike said the following on 10/22/2012 1:26 AM:

 	  Quote: 	
		   



 Not unusually, I have a hot #6 cylinder. It consistently shows CHT at about 25-40 degrees hot compared to the other cylinders. I always keep it under 400 degrees even though Lycoming says up to 425 is ok. My EGT on #6 also runs hot at 1420 when the other cylinders are 1375. My oil is 168 in fall and 180 in winter. What do you all consider excessively high EGT? I do not want to melt my exhaust valves or pipes!



 Do you folks think that I should inhibit the air flow to the oil cooler to get better cooling on #6.



 --------

 See you OSH '13

 Q/B - flying 3 yrs.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=385771#385771

bill.peyton

Joined: 19 Sep 2010
Posts: 198
Location: St. Louis, MO

Posted: Mon Oct 22, 2012 4:24 am Post subject: Re: Optimal Temperatures and fuel burn

I have the same issue with number 5 CHT.  It started out way to hot and slowly came down during break-in.  One of the things I did to help cool number 5 was to loosen the outer lower baffle wrap-around and to add a 960-10 washer under the rear baffle attachment screw.  This created about a 1/4" gap around the back of the cylinder and dropped my #5 CHT by 10 degrees.

Just for a data point.  My #6 is the last to peak and it peaks at the highest temp.  It is also one of the coolest CHTs.

How many hours do you have on the engine?  Go to Tim Olson's web site where he has a little write-up on what he did to cool the CHTs.  Also, check for that leak in the intake tube as previously posted.

_________________
Bill
WA0SYV
Aviation Partners, LLC

Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Mon Oct 22, 2012 6:00 am Post subject: Optimal Temperatures and fuel burn

What is your peak EGT, and which cylinder is 1st to peak? What is the 

spread of fuel flow from 1st cyl peak to last cyl peak?

EGT is NOT an absolute value and should not be treated as such.  You 

need to know where you are operating relative to peak. If running rich 

of peak you should be 100 degrees rich of the 1st cyl to peak. If you 

run lean of peak(and it doesn't sound like you are) you need to base 

your lean of peak range from the LAST cyl to peak.  If the spread from 

1st to last to peak is more than 0.5 gph, you have either induction 

problem or injector problem. If you get the mixtures balanced between 

cylinders, and baffles are good, CHT issues will go away.



On 10/21/2012 10:26 PM, AirMike wrote:

 	  Quote: 	
		   



 Not unusually, I have a hot #6 cylinder. It consistently shows CHT at about 25-40 degrees hot compared to the other cylinders. I always keep it under 400 degrees even though Lycoming says up to 425 is ok. My EGT on #6 also runs hot at 1420 when the other cylinders are 1375. My oil is 168 in fall and 180 in winter. What do you all consider excessively high EGT? I do not want to melt my exhaust valves or pipes!



 Do you folks think that I should inhibit the air flow to the oil cooler to get better cooling on #6.



 --------

 See you OSH '13

 Q/B - flying 3 yrs.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=385771#385771






	


-----

No virus found in this message.

Checked by AVG - www.avg.com

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

rv10flyer(at)live.com
Guest

Posted: Mon Oct 22, 2012 6:06 am Post subject: Optimal Temperatures and fuel burn

I have battled a similar issue. I have discovered that if you look at the 

Lycoming manuals, "key operations" it will tell you that 400-435F is 

"normal" for performance and takeoff, 400F for cruise. It will also tell you 

that having a CHT spread of 100F is fine and not a bit issue. Most Lycomings 

come pretty close to being able to lean them out of the box. I made one 

tweak and mine engine is where GAMI says good enough.

Forget EGT's they mean nothing except for Leaning and engine 

troubleshooting.

My #3 cylinder is 40F cooler than any other cyclinder. Was told by Eci that 

is just fine.

My oil, more like 189-203 for me most of the time, but within the green arc 

and below 220F, so once again told it's fine and normal.



Don't fret it, believe me, I have ! BTW if you listen or read a Mike Busch 

article or webinar- IGNORE his if its at 400F do something now.. that is 

just an unneccessary stress inducer, may be an issue for his Continental, 

but both Lycoming and Eci told me it was NOT an issue at all.

Everything is within "normal" tolerances that you are seeing.

Pascal



--

Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Mon Oct 22, 2012 6:20 am Post subject: Optimal Temperatures and fuel burn

Lycoming is not known for good advice regarding engine management. These 

are the same folks that say pilots are too inattentive/stupid to run 

lean of peak.

Lycoming and TCM cylinders are made from the exact same alloy. The main 

difference is that Lycoming uses sodium filled exhaust valve stems, and 

TCM uses solid valve stems. Lycoming specifies approx 5 ft/lbs higher 

spark plug torque, for no know reason.

So, the same thinking regarding CHT applies to both brand engines. The 

hotter you let the cylinders get the weaker the metal gets and the more 

it fatigues. Also, hotter cylinders are more prone to valve sticking and 

excess valve guide wear. Prime example...Mooney TLS in first couple 

model years had cylinders losing compression and other valve problems at 

200-300 hours. Problem was that Mooney designed the cowling to provide 

the pressure differential and CHT Lycoming said were OK.  This engine 

was the same as the RV-10 engine, with lower compression and a 

turbo-charger added, for 270 hp rating, same parallel valve cylinders.

The fix was to incorporate positive oil flow to the outside of the valve 

guides to cool them. Engines now do fine, but are very pricey to overhaul.

So, to make long story short, pay attention to what Advanced Pilot 

Seminars, GAMI and Mike Busch have to say. They have test data to back 

them. Lycoming recommendations are likely to lead to shorter engine life.



On 10/22/2012 7:05 AM, Pascal wrote:

[quote] 



 I have battled a similar issue. I have discovered that if you look at 

 the Lycoming manuals, "key operations" it will tell you that 400-435F 

 is "normal" for performance and takeoff, 400F for cruise. It will also 

 tell you that having a CHT spread of 100F is fine and not a bit issue. 

 Most Lycomings come pretty close to being able to lean them out of the 

 box. I made one tweak and mine engine is where GAMI says good enough.

 Forget EGT's they mean nothing except for Leaning and engine 

 troubleshooting.

 My #3 cylinder is 40F cooler than any other cyclinder. Was told by Eci 

 that is just fine.

 My oil, more like 189-203 for me most of the time, but within the 

 green arc and below 220F, so once again told it's fine and normal.



 Don't fret it, believe me, I have ! BTW if you listen or read a Mike 

 Busch article or webinar- IGNORE his if its at 400F do something now.. 

 that is just an unneccessary stress inducer, may be an issue for his 

 Continental, but both Lycoming and Eci told me it was NOT an issue at 

 all.

 Everything is within "normal" tolerances that you are seeing.

 Pascal



 --

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

partner14

Joined: 12 Jan 2008
Posts: 540
Location: Granbury Texas

Posted: Mon Oct 22, 2012 10:09 am Post subject: Optimal Temperatures and fuel burn

Only thing I can add to my good frieeeeend Pascal's comments... and noone else seemed to answer your question.... Your oil temps are plenty low... so yes, you could block off some of the flow to the oil cooler.  Best way is a butterfly fly valve.  That emables you to be right on top of the entire temp issue all year long.  Especially since 168 is low and not good on the engine.  If it came down to a choice of running a cht at 400, and oil temp at 168 to 180...  vs.  cht at 385 and oil temps at 180 to 200.... I'd take the latter any day.

My 5 cents worth

 

Don McDonald



      

  From: Pascal <rv10flyer(at)live.com>

 To: rv10-list(at)matronics.com 

 Sent: Monday, October 22, 2012 9:05 AM

 Subject: Re: Optimal Temperatures and fuel burn

  

 

 --> RV10-List message posted by: "Pascal" <rv10flyer(at)live.com (rv10flyer(at)live.com)>



I have battled a similar issue. I have discovered that if you look at the Lycoming manuals, "key operations" it will tell you that 400-435F is "normal" for performance and takeoff, 400F for cruise. It will also tell you that having a CHT spread of 100F is fine and not a bit issue. Most Lycomings come pretty close to being able to lean them out of the box. I made one tweak and mine engine is where GAMI says good enough.

Forget EGT's they mean nothing except for Leaning and engine troubleshooting.

My #3 cylinder is 40F cooler than any other cyclinder. Was told by Eci that is just fine.

My oil, more like 189-203 for me most of the time, but within the green arc and below 220F, so once again told it's fine and normal.



Don't fret it, believe me, I have ! BTW if you listen or read a Mike  Busch article or webinar- IGNORE his if its at 400F do something now.. that is just an unneccessary stress inducer, may be an issue for his Continental, but both Lycoming and Eci told me it was NOT an issue at all.

Everything is within "normal" tolerances that you are seeing.

Pascal



--

_________________
Don A. McDonald
40636

AirMike

Joined: 27 Feb 2007
Posts: 514
Location: Nevada

Posted: Sun Oct 28, 2012 8:10 pm Post subject: Optimal Temperatures and fuel burn

Thanks all of you for the comments especially Don. I think that I will try a flow restrictor on the oil cooler air intake.

_________________
See you OSH '18
Q/B - sold.

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