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RV6A CHT Problem

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jgh2(at)charter.net
Guest

Posted: Fri Jun 10, 2011 4:28 am Post subject: RV6A CHT Problem

I'm seeking advice about a CHT issue with a recently completed RV6A with 30 hours on an O-320 D1A ordered from Van's. 1.5 quarts of break-in oil has been consumed during those hours and I'm getting ready to take plane out of service for an oil change etc.



Climbing out at 120 knots produces 415 degrees F. CHT temperatures before getting to pattern altitude and cruise at around 65% power produces about 395 degrees (at ambient temperatures of 70-80 degrees F.). Oil temperatures remain below 210 degrees and both CHT and EGT temperatures are reasonably uniform across the four cylinders. Baffling (both above and below the cylinders) has been checked and the inlet area "ramps" are sealed on both the inboard and outboard ends. There is a 60 - 70 degree F. difference in EGT temperature between "full rich" and "leaned until the first cylinder peaks" during tests at 8500' (conducted without wheel pants or strut fairings). There is no fuel flow instrument but fuel pressure readings appear to be highly affected by engine temperature. On the ground it is 5 PSI (without the boost pump) but the drops to 1 PSI or less when the engine is hot.



Since the measured cruise and full power CHT values are slightly below Lycoming's "acceptance levels" for an O-320 they (politely) say:

1) they are "unable to help",

2) the engine cannot be considered broken before 50 hours, and 

3) high CHT temperatures are usually cause by airflow problems.

Van's referred me to Bart in British Columbia who recommends drilling the carb jet .006" oversize. Web search results suggest opening up the lower cowl outlet area via louvres (or simply cutting back the lower cowl) would be helpful. 



I'd greatly appreciate advice from those who have "been there done that".



jack

Kellym

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

Posted: Fri Jun 10, 2011 4:49 am Post subject: RV6A CHT Problem

If you don't have wheel pants/fairings on, the engine will run hotter, 

probably 20-30 degrees. Make sure magneto(or equivalent electronic 

system) timing is spot on. If in doubt, try retarding a couple degrees. 

Ensure you climb at full  throttle. Make sure your throttle cable is 

taking the carb to the stop. When the throttle is retarded 1/4-1/2 in. 

the carb power enrichment circuit closes and the engine will run 

significantly leaner and hotter. Ensure there is at least 1/8" gap 

between your baffles and cylinder head at front of #2 cyl and rear of 

#3. If you sealed that area tight, the intake side of the cyl head is 

not getting cooling because there are very thin to no fins there. 

Inserting a double thickness strip of baffle seal there to allow airflow 

will help.

They are correct that temps will continue to come down as you get up to 

50 hours. Until then be sure to run at least 100 degrees rich of peak 

EGT. Some of Vans cowlings are marginal in outlet area, but that usually 

also shows up with high oil temps as well as CHT.

I would not have carb main jet drilled. That takes very precision 

drills. Field drilled jets don't necessarily flow in proportion to 

expected drilling. If you want to go that route, talk to Tempest(or 

whatever they are calling the carb company now) and get a new jet of 

desired size from them. Many carbs have several different jet sizes for 

different applications. Some 180 hp O-360s have 4 different jet sizes 

resulting in different 10- numbers where the main jet is the only 

difference.

On 6/10/2011 5:24 AM, Jack Haviland wrote:

 	  Quote: 	
		   



 I'm seeking advice about a CHT issue with a recently completed RV6A with 30 hours on an O-320 D1A ordered from Van's. 1.5 quarts of break-in oil has been consumed during those hours and I'm getting ready to take plane out of service for an oil change etc.



 Climbing out at 120 knots produces 415 degrees F. CHT temperatures before getting to pattern altitude and cruise at around 65% power produces about 395 degrees (at ambient temperatures of 70-80 degrees F.). Oil temperatures remain below 210 degrees and both CHT and EGT temperatures are reasonably uniform across the four cylinders. Baffling (both above and below the cylinders) has been checked and the inlet area "ramps" are sealed on both the inboard and outboard ends. There is a 60 - 70 degree F. difference in EGT temperature between "full rich" and "leaned until the first cylinder peaks" during tests at 8500' (conducted without wheel pants or strut fairings). There is no fuel flow instrument but fuel pressure readings appear to be highly affected by engine temperature. On the ground it is 5 PSI (without the boost pump) but the drops to 1 PSI or less when the engine is hot.



 Since the measured cruise and full power CHT values are slightly below Lycoming's "acceptance levels" for an O-320 they (politely) say:

 1) they are "unable to help",

 2) the engine cannot be considered broken before 50 hours, and

 3) high CHT temperatures are usually cause by airflow problems.

 Van's referred me to Bart in British Columbia who recommends drilling the carb jet .006" oversize. Web search results suggest opening up the lower cowl outlet area via louvres (or simply cutting back the lower cowl) would be helpful.



 I'd greatly appreciate advice from those who have "been there done that".



 jack

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

carl.froehlich(at)verizon
Guest

Posted: Fri Jun 10, 2011 5:46 am Post subject: RV6A CHT Problem

A side note, a recent RV-8 builder with an IO-390 engine noted a measureable

drop in temperatures when he shifted from straight weight mineral oil to

AeroShell multi-grade after engine break in.



If you used only 1.5 quarts over the first 30 hours I'd say your break in is

complete.



Carl



--

mrobert569(at)hotmail.com
Guest

Posted: Fri Jun 10, 2011 6:09 am Post subject: RV6A CHT Problem

Tom,

  

 One other suggestion.  Have you tried using compressed air to blow out the area as you are trying to clean out everything?

  

 Mike Robertson

 

 > From: carl.froehlich(at)verizon.net

[quote] To: rv-list(at)matronics.com

 Subject: RE: RV6A CHT Problem

 Date: Fri, 10 Jun 2011 09:42:58 -0400

 

 --> RV-List message posted by: "Carl Froehlich" <carl.froehlich(at)verizon.net>

 

 A side note, a recent RV-8 builder with an IO-390 engine noted a measureable

 drop in temperatures when he shifted from straight weight mineral oil to

 AeroShell multi-grade after engine break in.

 

 If you used only 1.5 quarts over the first 30 hours I'd say your break in is

 complete.

 

 Carl

 

 --

bicyclop(at)pacbell.net
Guest

Posted: Fri Jun 10, 2011 8:22 am Post subject: RV6A CHT Problem

415 to patten altitude? That's real hot, real fast.       Do I read you to say that EGT on any given cylinder only spans 60       degrees from rich to lean? I'd expect to see a couple hundred,       maybe more. Too bad you don't have a fuel flow. Sounds like you       are lean. Check for full travel on both the mixture and throttle       arms. If they are both on the stops, your main jet is probably too       small.

       

       I wouldn't worry about the 1 psi fuel pressure, hot. Just run the       boost pump for a few minutes after takeoff and the pressure will       eventually come up as it moves more cool fuel into the carb.

       

       Pax,

       

       Ed Holyoke

     

     On 6/10/2011 5:24 AM, Jack Haviland wrote:     [quote]        	  Quote: 	
		  --> RV-List message posted by: Jack Haviland <jgh2(at)charter.net> (jgh2(at)charter.net)



I'm seeking advice about a CHT issue with a recently completed RV6A with 30 hours on an O-320 D1A ordered from Van's. 1.5 quarts of break-in oil has been consumed during those hours and I'm getting ready to take plane out of service for an oil change etc.



Climbing out at 120 knots produces 415 degrees F. CHT temperatures before getting to pattern altitude and cruise at around 65% power produces about 395 degrees (at ambient temperatures of 70-80 degrees F.). Oil temperatures remain below 210 degrees and both CHT and EGT temperatures are reasonably uniform across the four cylinders. Baffling (both above and below the cylinders) has been checked and the inlet area "ramps" are sealed on both the inboard and outboard ends. There is a 60 - 70 degree F. difference in EGT temperature between "full rich" and "leaned until the first cylinder peaks" during tests at 8500' (conducted without wheel pants or strut fairings). There is no fuel flow instrument but fuel pressure readings appear to be highly affected by engine temperature. On the ground it is 5 PSI (without the boost pump) but the drops to 1 PSI or less when the engine is hot.



Since the measured cruise and full power CHT values are slightly below Lycoming's "acceptance levels" for an O-320 they (politely) say:

1) they are "unable to help",

2) the engine cannot be considered broken before 50 hours, and 

3) high CHT temperatures are usually cause by airflow problems.

Van's referred me to Bart in British Columbia who recommends drilling the carb jet .006" oversize. Web search results suggest opening up the lower cowl outlet area via louvres (or simply cutting back the lower cowl) would be helpful. 



I'd greatly appreciate advice from those who have "been there done that".



jack 



	
     [b]

Doug Gray

Joined: 10 Jan 2006
Posts: 112
Location: Sydney, Australia

Posted: Fri Jun 10, 2011 4:43 pm Post subject: RV6A CHT Problem

On Fri, 2011-06-10 at 08:24 -0400, Jack Haviland wrote:

  	  Quote: 	
		       3) high CHT temperatures are usually cause by airflow problems.

     

 	
 My experience paralleled yours almost exactly (same engine RV6 sens prop) except my CHT remained below 400 at a 120 knot climb.  This was fine except after holding for traffic on the ground for an extended period.  In cruise the temps dropped to 333 341 372 367.

 

 I thought my baffle seals were fine because they were wide and fit the cowling well.

 

 Except: I hand tried to minimise the number of breaks in the fabric obviously to 'improve' the seal. But what I ended up doing was causing some MINOR puckering away from the cowl surface at the reverse bends in 4 places.  Above the inlet ramps and  above the rear cylinders.  I expected air pressure would force these puckers against the cowling.  

 

 I was thinking that perhaps during climb the increased angle of attack air at the puckers above the inlet ramps was causing the front seals to flip down and allow air to escape past the seal,  then in cruise the seal fabric would settle back where it should be..

 

 Only several weeks ago I was determined to solve the issue and drastic action was necessary so I popped the cowling off and slit the material at these puckers to allow them to lay flat flat on the cowling.

 

 The test flight following this surgery I was able to climb full power to 6500 at about 90 knots and the temps remained below 400.  In cruise the temps dropped to 325 342 360 357, ie about 10 degree drop all round.  Also my oil temp dropped (another!) 8 degrees.

 

 I am happy with the change.  Possibly I need a deflector on cyl 1 to even the temps between 1 and 3.

 

 Good luck,

 Doug Gray     [quote][b]

jgh2(at)charter.net
Guest

Posted: Sat Jun 11, 2011 11:38 am Post subject: RV6A CHT Problem

To: Kelly and All Others Who Were Kind Enough to Provide Helpful Comments,



A 20 to 3- degree drop from putting the wheel pants and strut fairing on would make an enormous difference! I never would have predicted a decrease of more than a few degrees but I'm going to put them on and try it. Almost all of the baffling and carb linkage related suggestions have previously been investigated and judged acceptable.



I'll also obtain a richer carburetor jet (rather than drilling one out with number drills on a lathe) as soon as I can find one. One last question on that topic. Is a "full-rich to first-cylinder-to lean EGT differential less than 150 degrees F.'" really a "recognized" way of detecting lean carburetor jetting? The Lycoming representative said he had never heard of it but I found references to it during web searches and talking to two engine rebuilders.



Thanks for all the help! It is very much appreciated.



jack

On Jun 10, 2011, at 8:46 AM, Kelly McMullen wrote:



 	  Quote: 	
		   If you don't have wheel pants/fairings on, the engine will run hotter, probably 20-30 degrees.

Kellym

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

Posted: Sat Jun 11, 2011 1:46 pm Post subject: RV6A CHT Problem

On takeoff from a sea level airport the EGT should be 150 to 200 degrees 

less than a normal peak EGT. 1200-1300 on most engines is a safe takeoff 

EGT. You don't want to see much over 1300. But keep in mind the power 

enrichment circuit is supplying maybe 1/3 of that extra richness, so you 

won't see that big a spread from full rich in cruise with less than full 

throttle to peak in cruise. Probably more like 100 degrees generated by 

the mixture control.

On 6/11/2011 12:34 PM, Jack Haviland wrote:

 	  Quote: 	
		   



 To: Kelly and All Others Who Were Kind Enough to Provide Helpful Comments,



 A 20 to 3- degree drop from putting the wheel pants and strut fairing on would make an enormous difference! I never would have predicted a decrease of more than a few degrees but I'm going to put them on and try it. Almost all of the baffling and carb linkage related suggestions have previously been investigated and judged acceptable.



 I'll also obtain a richer carburetor jet (rather than drilling one out with number drills on a lathe) as soon as I can find one. One last question on that topic. Is a "full-rich to first-cylinder-to lean EGT differential less than 150 degrees F.'" really a "recognized" way of detecting lean carburetor jetting? The Lycoming representative said he had never heard of it but I found references to it during web searches and talking to two engine rebuilders.



 Thanks for all the help! It is very much appreciated.



 jack

 On Jun 10, 2011, at 8:46 AM, Kelly McMullen wrote:



> If you don't have wheel pants/fairings on, the engine will run hotter, probably 20-30 degrees.

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

vanremog(at)aol.com
Guest

Posted: Sat Jun 11, 2011 1:59 pm Post subject: RV6A CHT Problem

Best way in my opinion, to verify that you have the correct main jet, is to confirm max fuel flow at WOT as you are climbing out full rich flat pitch max rpm as near MSL as possible.  Do you have an engine monitor that logs fuel flow?

  

 If so, then you can confirm this with the formula (0.48 * maxhp)/6 = fuel flow at WOT.  For example this would be approx 14.4 gph with a 180 hp aircraft engine.  Until you get this, you are not flowing enough fuel.

  

 Then work from there as needed with your oil cooler, intakes, exit and baffling to maximize the cooling effects for your installation.

  

 -GV (RV-6A N1GV flying 972hrs)

  

  

  

  

  

 In a message dated 06/11/11 12:39:12 Pacific Daylight Time, jgh2(at)charter.net writes:

 [quote]   .aolmailheader          {font-size:8pt; color:black; font-family:Arial} a.aolmailheader:link    {color:blue; text-decoration:underline; font-weight:normal} a.aolmailheader:visited {color:magenta; text-decoration:underline; font-weight:normal} a.aolmailheader:active  {color:blue; text-decoration:underline; font-weight:normal} a.aolmailheader:hover   {color:blue; text-decoration:underline; font-weight:normal}  --> RV-List message posted by: Jack Haviland <jgh2(at)charter.net> 



To: Kelly and All Others Who Were Kind Enough to Provide Helpful Comments, 



A 20 to 3- degree drop from putting the wheel pants and strut fairing on would make an enormous difference! I never would have predicted a decrease of more than a few degrees but I'm going to put them on and try it. Almost all of the baffling and carb linkage related suggestions have previously been investigated and judged acceptable. 



I'll also obtain a richer carburetor jet (rather than drilling one out with number drills on a lathe) as soon as I can find one. One last question on that topic. Is a "full-rich to first-cylinder-to lean EGT differential less than 150 degrees F.'" really a "recognized" way of detecting lean carburetor jetting? The Lycoming representative said he had never heard of it but I found references to it during web searches and talking to two engine rebuilders. 



Thanks for all t      

  [quote][b]

jgh2(at)charter.net
Guest

Posted: Sat Jun 11, 2011 3:56 pm Post subject: RV6A CHT Problem

On Jun 11, 2011, at 5:56 PM, vanremog wrote:

 	  Quote: 	
		  Do you have an engine monitor that logs fuel flow? 	
Unfortunately I elected not to install a fuel flow sensor - an error I'm regretting.

 	  Quote: 	
		   1200-1300 on most engines is a safe takeoff EGT. You don't want to see much over 1300.

One more thing to worry about! My EGTs at full power typically run around 1350 to 1375 F. 
	


I had attributed that to the sensors being installed only about 2.25" from the exhaust flange. 

I'm also considering the suggestion to deliberately retard the mag timing slightly.  

Thanks again for the advice. I'll post my findings after making some progress on the problem

jack

 



 [quote][b]

denis.walsh(at)comcast.ne
Guest

Posted: Sat Jun 11, 2011 6:07 pm Post subject: RV6A CHT Problem

On Jun 11, 2011, at 3:56 PM, vanremog wrote:

[quote] Best way in my opinion, to verify that you have the correct main jet, is to confirm max fuel flow at WOT as you are climbing out full rich flat pitch max rpm as near MSL as possible.  Do you have an engine monitor that logs fuel flow?

  

 If so, then you can confirm this with the formula (0.48 * maxhp)/6 = fuel flow at WOT.  For example this would be approx 14.4 gph with a 180 hp aircraft engine.  Until you get this, you are not flowing enough fuel.

  

 Then work from there as needed with your oil cooler, intakes, exit and baffling to maximize the cooling effects for your installation.

  

 -GV (RV-6A N1GV flying 972hrs)

  

  

  

  

  

 In a message dated 06/11/11 12:39:12 Pacific Daylight Time, jgh2(at)charter.net (jgh2(at)charter.net) writes:

  	  Quote: 	
		     .aolmailheader          {font-size:8pt; color:black; font-family:Arial} a.aolmailheader:link    {color:blue; text-decoration:underline; font-weight:normal} a.aolmailheader:visited {color:magenta; text-decoration:underline; font-weight:normal} a.aolmailheader:active  {color:blue; text-decoration:underline; font-weight:normal} a.aolmailheader:hover   {color:blue; text-decoration:underline; font-weight:normal}  --> RV-List message posted by: Jack Haviland <jgh2(at)charter.net (jgh2(at)charter.net)> 



To: Kelly and All Others Who Were Kind Enough to Provide Helpful Comments, 



A 20 to 3- degree drop from putting the wheel pants and strut fairing on would make an enormous difference! I never would have predicted a decrease of more than a few degrees but I'm going to put them on and try it. Almost all of the baffling and carb linkage related suggestions have previously been investigated and judged acceptable. 



I'll also obtain a richer carburetor jet (rather than drilling one out with number drills on a lathe) as soon as I can find one. One last question on that topic. Is a "full-rich to first-cylinder-to lean EGT differential less than 150 degrees F.'" really a "recognized" way of detecting lean carburetor jetting? The Lycoming representative said he had never heard of it but I found references to it during web searches and talking to two engine rebuilders. 



Thanks for all t      

   	  Quote: 	
		  



href="http://www.matronics.com/Navigator?RV-List">http://www.matronics.com/Navigator?RV-List

href="http://forums.matronics.com/">http://forums.matronics.com

href="http://www.matronics.com/contribution">http://www.matronics.com/contribution



	


	


[b]

Kellym

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

Posted: Sat Jun 11, 2011 7:36 pm Post subject: RV6A CHT Problem

That is too hot for full power EGT. You need more fuel flow. My probes 

are 1.5" from exhaust flange and I keep rich enough for 1325 or less on 

takeoff, normally closer to 1250.

On 6/11/2011 4:52 PM, Jack Haviland wrote:

 	  Quote: 	

 On Jun 11, 2011, at 5:56 PM, vanremog wrote:

> Do you have an engine monitor that logs fuel flow?

 Unfortunately I elected not to install a fuel flow sensor - an error 

 I'm regretting.

 > 1200-1300 on most engines is a safe takeoff EGT. You don't want to 

 see much over 1300.

 One more thing to worry about! My EGTs at full power typically run 

 around 1350 to 1375 F.

 I had attributed that to the sensors being installed only about 2.25" 

 from the exhaust flange.

 I'm also considering the suggestion to deliberately retard the mag 

 timing slightly.

 Thanks again for the advice. I'll post my findings after making some 

 progress on the problem

 jack

 *

 *

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

Bill Schlatterer

Joined: 09 Jan 2006
Posts: 195

Posted: Sun Jun 12, 2011 1:46 pm Post subject: RV6A CHT Problem

I suppose everyone has read this (My Engine Runs HOT)  off the Vans factory

site but here is the link anyway:



  http://www.vansaircraft.com/pdf/Hot_engines.pdf   This lines up with my

Lycoming manual as well.



I am running a new Aerosport O-360 in A RV7a and also have had warm CHTs

during break in.  I am running the larger Positec oil cooler and never have

oil temps more than about 190 but CHTs are warm.  Running straight mineral

oil. This is what I found on the CHTs:



1) Some change - Adding a shim to the rear of the #3 baffle to increase flow

there (although not through the cyl fin) helped a little bit.  Easy to do

but little gain.



2) Some change - Sealing around the baffles helped a little, they were

already tight but I have three 3/4 blast tubes plus the cabin heat in the

rear baffle.  Thinking about reducing the flow there a little.



3) Big Change - Putting a baffle in front of the #1 cyl helped a LOT!  I

went from a 30 degree spread between #1 and #3 with #3 running up as high as

440 in continuous climb, normally about 390 in cruise, to completely

reversing the spread with a 1 1/2 inch baffle.  Cutting the baffle back to

about 1 inch made #1 and #3 almost even although they still run about 15

degrees hotter than 2 and 4. By changing the baffle size, you can change

easily the temps on both #1 and #3. I worked the baffle height until they

were about equal. Took 4 flights to check.



4) Big Change - adding the intersection fairing between the front gear leg

and the cowl was good for 10-15 degrees over all cyls.  I had a pretty large

2 inch wide gap that runs up the front of the lower cowl to make getting the

cowl off easier over the front leg.  See plans.  I think that in climb, high

pressure air entered the lower cowl through that large gap facing the

airstream and pressurized the lower cowl area which lowered the pressure

difference between the upper cowl area and the lower.  The pressure

differential is one of the major determinants of airflow through the cyl

head fins.  If the pressures are equal (never are) then no air would move at

all.



5) Big Change - Initial break in was with the front gear fairing and wheel

fairing only.  No intersection fairings at all and the lower cowl leg slot

wide open. (someone said draggy helps... Don't think so)  Temps were much

more controllable once all leg and gear fairings were on as it was much

easier (less draggy) to climb at a higher airspeed, take off with no flaps

helps or get them up quick.  Drag adds heat!  Airspeed adds cooling air!



Now I have set my "Hot" limit to 420 degrees and see that on #3 in climb

occasionally/frequently.  Full power climb at 110 will have all cyl running

410+ quickly on a hot day.  It's not hard to control but you have to be

watching.  GRT system makes it easy. Push over to 130 mph and they are all

well under 400 in a minute or two.



With 50 hours on the engine, I have virtually 0 oil consumption but I still

have to quickly reduce TO power back to 23-4/2400 and climb about 130 -140

if the outside temp is high.  23/2400 will show all cyls about 375 +/- 10 in

cruise.



Not sure full power climbs are "cooler" if you have a CS prop as that

equates to 2650 RPM and that makes a lot of heat compared to 2400, (my

opinion)  In my ride today, getting the RPMs back to 2400 quickly and higher

climb airspeed is the easiest way to control the heat!



Hope this helps!



Bill S

7a Got the Grin

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