Van's Air Force
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CHT
- Thread starter Selma
- Start date
Johnnybgoode
Well Known Member
Good question...
Most of the current mechanic writers out there now are espousing anything under 400 all phases of flight. Above 400 it's time to do something right now to lower the temps. Lycoming's number has remained unchanged throughout the years at 500.
In my Mooney I try to stay below 400 except in initial climb - I don't pull back until 1000-1500' and usually see about 435 max - under 400 in cruise. In the RV, same motor as yours, I don't have instrumentation but I usually climb pretty slowly, using the speed to cool the motor.
Not an official answer - don't think there is one, except 500. Research the difference in strength of the materials at between 400 and 500 degrees and decide your technique based on that research. For me, minor excursions over 400 are acceptable until an altitude when I feel better giving up power for temps.
Patrick
Most of the current mechanic writers out there now are espousing anything under 400 all phases of flight. Above 400 it's time to do something right now to lower the temps. Lycoming's number has remained unchanged throughout the years at 500.
In my Mooney I try to stay below 400 except in initial climb - I don't pull back until 1000-1500' and usually see about 435 max - under 400 in cruise. In the RV, same motor as yours, I don't have instrumentation but I usually climb pretty slowly, using the speed to cool the motor.
Not an official answer - don't think there is one, except 500. Research the difference in strength of the materials at between 400 and 500 degrees and decide your technique based on that research. For me, minor excursions over 400 are acceptable until an altitude when I feel better giving up power for temps.
Patrick
400 F
Patrick, thanks. I experienced the same temps in my M20J as you did. And that is what makes me scratching my head. The RV9 is significantly higher in the initial climbout. Later or higher when pulling back the throttle and in the cruise I saw 390 and a bit lower. Are these temps usually and regularly normal for an O320 in a RV9?
Pit
Patrick, thanks. I experienced the same temps in my M20J as you did. And that is what makes me scratching my head. The RV9 is significantly higher in the initial climbout. Later or higher when pulling back the throttle and in the cruise I saw 390 and a bit lower. Are these temps usually and regularly normal for an O320 in a RV9?
Pit
ColoRv
Well Known Member
Your temps look high to me, but I also do not subscribe to the "do something immediately if over 400" theory. I've never heard it said by anyone I considered smarter than a Lycoming engineer. 460 would worry me though
Look into baffle sealing around the engine. If that's not it, check timing.
Look into baffle sealing around the engine. If that's not it, check timing.
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Mahlon Russell was at Mattituck in LI for many years. He has stated that he has never seen any evidence that 425 hurts a cylinder. My 0 320 with 10-1 pistons runs 375 in cruise. During break in in ambient temps ranging from 90-110 F. I had to pull the power back at 500' on takeoff and level off to keep the temps at 400. I have a very tight cowling with small inlets and outlet. At present I have a fixed cowl flap which is 75% open all the time. I believe the cowl flap is very effective. Not an RV. I do have a plenum and absolutely believe in the plenum. All CHT measurements taken on cylinder #3 with the cooler mounted aft of 3.
Kyle Boatright
Well Known Member
What is the truth with CHT on a Lyc.O320 / 160 HP in a RV9? Is 460 F really too much in a long climb up to the flightlevels? Is 360 - 390 good in the cruise ?
Thanks for your advice!
Pit
I don't think you'll find anyone who is comfortable with 460 F, even during a climb. Unless you're climbing at a really low airspeed, there is no reason your temperatures should be that high.
So, what speeds do you climb at? Can you post some pictures of your baffles and seals? Is your engine's mixture properly set (at a 1,000 rpm idle, if you slowly lean it, do the RPM's increase by at least 25 before it dies?).
dougknight
Well Known Member
Selma:
Numbers seem high to me. My 9A o-320 160hp runs 375 F (highest cyl) on a 90 knt climb on a 80 F day. Cruise (same cly) runs 325 F in cruise. I'll show 13-15 gal/hr on climb and I lean to 7 gph in cruise which gives me around 1200-1300 EGT.
What do you have for instruments? I have the cheap vans steam gauges and had to change my CHT gauge out the other day when it was getting up to 450-500F. It was also showing 250F with just the master switch on before even starting the engine. The gauge change out cured all ill's.
doug
9A
kit #625
650 hrs
Numbers seem high to me. My 9A o-320 160hp runs 375 F (highest cyl) on a 90 knt climb on a 80 F day. Cruise (same cly) runs 325 F in cruise. I'll show 13-15 gal/hr on climb and I lean to 7 gph in cruise which gives me around 1200-1300 EGT.
What do you have for instruments? I have the cheap vans steam gauges and had to change my CHT gauge out the other day when it was getting up to 450-500F. It was also showing 250F with just the master switch on before even starting the engine. The gauge change out cured all ill's.
doug
9A
kit #625
650 hrs
erikpmort
Well Known Member
I've done everything in the book and I still see up to 430 on hot lower alt climbouts but I still have to reduce mp big time. I am still unhappy about this. When it's 80-90 degrees I am very unhappy with my setup. I've heard you can get the wrong carb with an Rv... That's all I have left to try. I'm always under 400 in cruise but that's up high. If I lived at sea level I would have to make a change
Kyle Boatright
Well Known Member
Have you had an experienced (successful) builder take a look under your cowl? I've known a few bright folks who missed fairly obvious things on the baffling and seals.
The truth ....
The truth is in the operations manual you got with your engine from Lycoming. Pretty much anything else is educated opinion.... and probably good opinion but Lycoming built it !
Can't speak for the O-320 but the O-360s run hotter than most think and the manual calls for under anything under 400 in cruise. I think peak is 450. I found this in a generic O320 Lyc Manual. My O 360 manual has something similar and I frequently see 425 F on a hot day in slow climbs.
SECTION 3 0-320 10-320 SERIES
Manual leaning may be monitored by exhaust gas temperature
indication, fuel flow indication, and by observation of engine speed
and/or airspeed. However, whatever instruments are used in monitoring
the mixture, the following general rules should be observed by the
operator of Avco Lycoming aircraft engines.
GENERAL RULES
Never exceed the maximum red line cylinder head temperature limit.
For maximum service life, cylinder head temperatures should be
maintained below 435 F. (224 C.) during high~perfornzance cruise
operation and below 400 F. (205 C.) for economy cruise powers.
Again, read the manual for your engine. Also note that A models just tend to run a little hotter in climb due to congested air flow around the engine/nose gear mount.
Hope this helps.
The truth is in the operations manual you got with your engine from Lycoming. Pretty much anything else is educated opinion.... and probably good opinion but Lycoming built it !
Can't speak for the O-320 but the O-360s run hotter than most think and the manual calls for under anything under 400 in cruise. I think peak is 450. I found this in a generic O320 Lyc Manual. My O 360 manual has something similar and I frequently see 425 F on a hot day in slow climbs.
SECTION 3 0-320 10-320 SERIES
Manual leaning may be monitored by exhaust gas temperature
indication, fuel flow indication, and by observation of engine speed
and/or airspeed. However, whatever instruments are used in monitoring
the mixture, the following general rules should be observed by the
operator of Avco Lycoming aircraft engines.
GENERAL RULES
Never exceed the maximum red line cylinder head temperature limit.
For maximum service life, cylinder head temperatures should be
maintained below 435 F. (224 C.) during high~perfornzance cruise
operation and below 400 F. (205 C.) for economy cruise powers.
Again, read the manual for your engine. Also note that A models just tend to run a little hotter in climb due to congested air flow around the engine/nose gear mount.
Hope this helps.
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Could not agree more. Only Lycoming has decades of data and is financially accountable.
That being said, how to ensure your installation achieves the Lycoming published limits is completely up to builder/owner and has many opinions and options.
Can't end without my opinion; temperature, like a lot of stuff, is not a hard and fast limit but if it gets up in the "hot" range (insert your definition of hot) to many times you can expected you are paying a price in engine life (TBO) and therefore $$$. Therefore I listen to the educated opinions and personally keep my CHTs below 380 in cruise and 425 in climb. Your mission may vary if your priorities are more performance driven and less economy driven.
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Set aside the opinions and consider the question this way...are you running hotter than the most of the similar installations? If so, then something is not as it should be.
My opinion? I could not accept 460F. I think a good, normal parallel valve installation in an RV reaches a little over 400 in climb and probably cruises about 350.
460 is too high
I agree that 460 is too high. However, all of the RV-9A's with fixed pitch props I have flown seem to have high CHT's on climb out, peaking around 435 before starting to settle back down as the altitude increases. Cruise is also higher, in the 370's. I use a cruise climb at 120 KIAS or better and still see very respectable climb rates approaching 1000 FPM.
As Dan mentioned, do check to see that the cylinders are sealed really well all around the baffling with RTV, especially the front of the engine, the washer is in place behind cylinder 3, the ramps on top of the cowl are closed on both ends, and the rubber baffling is laying properly across the lower cowl ramps when the colwing is on.
Also, make sure the FAB box is properly sealed with rubber baffling to the lower cowl. Any pressurization of the lower cowl will prevent airflow from the top and result in higher temps.
Vic
I agree that 460 is too high. However, all of the RV-9A's with fixed pitch props I have flown seem to have high CHT's on climb out, peaking around 435 before starting to settle back down as the altitude increases. Cruise is also higher, in the 370's. I use a cruise climb at 120 KIAS or better and still see very respectable climb rates approaching 1000 FPM.
As Dan mentioned, do check to see that the cylinders are sealed really well all around the baffling with RTV, especially the front of the engine, the washer is in place behind cylinder 3, the ramps on top of the cowl are closed on both ends, and the rubber baffling is laying properly across the lower cowl ramps when the colwing is on.
Also, make sure the FAB box is properly sealed with rubber baffling to the lower cowl. Any pressurization of the lower cowl will prevent airflow from the top and result in higher temps.
Vic
MikeyDale
Well Known Member
I took off on my first flight, nervous as ****, got about 400' off the ground, looked down and saw 405 on my #1 and almost crapped my pants! This was a used engine with 75hrs since OH. I reduced power, brought the nose down, and got it coming down after it reached about 415. By then, a couple of the others had reached 400....So began several months of experimenting. I also learned from reading these forums, that 415 on climb out will not cause you to fall out of the sky! I worked on the baffles and sealed gaps, didn't help much but a little. I increased my cowl exit by 1", helped a little but not enough. I resisted trimming more because it will slow me down, and eventually it was gonna turn winter again and I didnt want to be up there cruising with excess cooling. I installed antisplat cowl flap and that helped a little, especially when doing all my slow flight maneuvers in phase 1. Then, after 30-40 hours, I believe, my baffle seals finally got hot and broken in and all of the sudden, I wasn't having any problems anymore! It could have been, my engine loosened up a little since it was overhauled back in 2006 and was run only 75hrs the next few years and my first flight was in 2015. Also, this is the first time I've ever had such good engine monitoring (Skyview) on a plane. My old 59 tri-pacer could have hit 500 and I'd never knew it!
N941WR
Legacy Member
During testing of the Van's RV-9A, the CAFE foundation recorded a CHT of 462 while performing a climb test.
Mu question is, were you full throttle and full rich during your climb? Apparently our carbs have feature that adds more fuel when wide open to help cool the cylinders.
Mu question is, were you full throttle and full rich during your climb? Apparently our carbs have feature that adds more fuel when wide open to help cool the cylinders.
N941WR
Legacy Member
No picture, just a description.
On the aft side of #3 (that is the right rear cylinder as you sit in the plane), there is a 1/4 - 20 bolt (it looks like a hardware store bolt) that screws into the cylinder head just above where the baffles start to wrap around the cylinder. The washer goes between the cylinder head and the baffle.
The cooling fins are not very deap in this area, which is why the extra cooling air is helpful. (There is a corresponding bolt on the front of #1 but no washer is needed there because the incoming air keeps that cylinder cool.)
WA85
Well Known Member
Be careful in assessing fuel flow when operating with a fixed pitch prop. Fuel flow is somewhat proportional to engine RPM. If you have a FP prop and are in a low speed climb condition with low engine RPM (due to loading the prop), fuel flow is going to lower. Fuel flow is proportional to mass air flow, which is directly related to how fast that engine cylinders can pump air through the engine.
By increasing your climb speed, the FP prop may have less load on it, turn faster, allowing the engine to flow more air and fuel, and higher airspeed means more cooling air. Its a balancing act.
Adding a #10 thick washer between the #3 baffle and the cylinder does have a significant impact on cooling the #3 cylinder. I just did this on a 9A and it took the climb CHTs from 415 down to 390, almost amazing. Did the same thing on my IO-320 powered 8 and it was 20 degree delta after adding the washer.
If you have an AeroSport O-320, which may have an O-360 oil sump, another mod I just did was adding the tapered insert in the sump opeing above the carb per Lycoming SB 258. This also had a significant impact on the rear cylinder CHTs. The #3/#4 CHTs in climb used to be 20 deg hotter than the front cylinders. After adding the insert, the aft cylinders are 5 degrees cooler than the front.
By increasing your climb speed, the FP prop may have less load on it, turn faster, allowing the engine to flow more air and fuel, and higher airspeed means more cooling air. Its a balancing act.
Adding a #10 thick washer between the #3 baffle and the cylinder does have a significant impact on cooling the #3 cylinder. I just did this on a 9A and it took the climb CHTs from 415 down to 390, almost amazing. Did the same thing on my IO-320 powered 8 and it was 20 degree delta after adding the washer.
If you have an AeroSport O-320, which may have an O-360 oil sump, another mod I just did was adding the tapered insert in the sump opeing above the carb per Lycoming SB 258. This also had a significant impact on the rear cylinder CHTs. The #3/#4 CHTs in climb used to be 20 deg hotter than the front cylinders. After adding the insert, the aft cylinders are 5 degrees cooler than the front.
Pictures here, other methods, discussion, etc:
http://www.vansairforce.com/community/showthread.php?t=37835&highlight=bypass
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Kai, I have been working the same issue on a -9A for the past two months. This particular -9A belongs to a friend that recently purchased the aircraft. It was built with a factory new Lycoming O-320D1A and a Sensenich fixed pitch metal prop. During climb if you maintained at least 120 KTS the CHTs would quickly reach 460-475 then slowly continue to rise.
A quick inspection revealed lots of cooling baffle leaks and three intake tube gasket failures, but even after these induction and cooling air leaks were fixed the engine still ran way too hot.
The owner and I took a low altitude flight to check the temps with very little change. After leveling off at 1500 MSL I slowly leaned the engine in cruise to capture EGT and CHT data on the G3X system. I analyized the data and determined that the fuel flow peaked at only 11.8 GPH and from full rich to peak EGT was only about 45 degrees. This confirmed that the carb was way too lean!
The owner called Marvel-Schebler and talked to Mark Keeney. We were initailly going to try and rejet the carb, but Mark said that our carb was so lean and needed so much more fuel flow that more parts were required to be changed than just fuel jets. Mark recommended installing carb P/N 10-3678-32. We ended up ordering a Rebuilt 10-3678-32 from Spruce and installing it. A subsequent flight revealed much improved peak fuel flow of 13.1 GPH and somewhat cooler EGTs and CHTs, but still too lean and still too hot with a mixture spread of only 190 degrees during cruise, and running approximately 10 degrees rich of peak at full throttle.
We got in touch with Mark at MS again and asked him for some guidance. Mark researched the documentation for the rebuild of our replacement carb and said the flow bench data indicated that the carb fuel flow was set to the mid range and that it was possible to increase the fuel flow to the upper limit. So we sent the rebuilt carb back to MS and after recieving it back we flew the airplane around the pattern and now we can climb out at 80 KTS to pattern altitude without breaking 400 degrees CHT. We still need to fly a mixture flight to capture some data and see exactly where we stand, but that will have to wait until next week after installing a new audio control panel.
You may want to call Mark at Marvel-Schebler and see what he reccomends.
His contact information is:
Mark Keeney Jr.
Marvel-Schebler A/C Carburetors
125 Piedmont Ave.
Gibsonville NC 27249
[email protected]
(336)446-0002 Office
(336)446-0007 Fax
1 855-672-2272 TF
A quick inspection revealed lots of cooling baffle leaks and three intake tube gasket failures, but even after these induction and cooling air leaks were fixed the engine still ran way too hot.
The owner and I took a low altitude flight to check the temps with very little change. After leveling off at 1500 MSL I slowly leaned the engine in cruise to capture EGT and CHT data on the G3X system. I analyized the data and determined that the fuel flow peaked at only 11.8 GPH and from full rich to peak EGT was only about 45 degrees. This confirmed that the carb was way too lean!
The owner called Marvel-Schebler and talked to Mark Keeney. We were initailly going to try and rejet the carb, but Mark said that our carb was so lean and needed so much more fuel flow that more parts were required to be changed than just fuel jets. Mark recommended installing carb P/N 10-3678-32. We ended up ordering a Rebuilt 10-3678-32 from Spruce and installing it. A subsequent flight revealed much improved peak fuel flow of 13.1 GPH and somewhat cooler EGTs and CHTs, but still too lean and still too hot with a mixture spread of only 190 degrees during cruise, and running approximately 10 degrees rich of peak at full throttle.
We got in touch with Mark at MS again and asked him for some guidance. Mark researched the documentation for the rebuild of our replacement carb and said the flow bench data indicated that the carb fuel flow was set to the mid range and that it was possible to increase the fuel flow to the upper limit. So we sent the rebuilt carb back to MS and after recieving it back we flew the airplane around the pattern and now we can climb out at 80 KTS to pattern altitude without breaking 400 degrees CHT. We still need to fly a mixture flight to capture some data and see exactly where we stand, but that will have to wait until next week after installing a new audio control panel.
You may want to call Mark at Marvel-Schebler and see what he reccomends.
His contact information is:
Mark Keeney Jr.
Marvel-Schebler A/C Carburetors
125 Piedmont Ave.
Gibsonville NC 27249
[email protected]
(336)446-0002 Office
(336)446-0007 Fax
1 855-672-2272 TF
