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High CHT - Some thoughts

walter

walter

Well Known Member
I've been living with hight CHTs since my initial flight. Last weekend it
was pretty warm around here (70's) [don't say it, even if you do
live in WI] and I can *easily* get to 450 in a 500fpm climb at 6000'.

Several causes come to mind; one of them is the LASAR ignition which
aggressively advances the timing. But another, and I'm really starting
to suspect that *this* is the real culprit is the size of the exhaust
area of the cowl and all the crap in this area which includes the
nose gear attachment, exhaust hangers, vertical cowl attachment
(with it's flat top and bottom), and the lower firewall lip (RV8s have
a nice rounded lip dookickey. All of this junk is in the way of the
air escaping (don't tell me I should have built a TD) and, all of this
crap is either perfectly round (read: totally un-aerodynamic) or
perpendicular to the flow of escaping air.

So how to fix and test? Well I can't just add an aerodynamic leading and
trailing edge to all the round stuff. I could enhance the shape of the
aluminum parts that are perpendicular to the flow, but that would
probably not have any significant effects (cowl hanger). So I need
something else and this morning I read a post on the lycoming group
about Ron Lee adding louvers to the bottom of his cowl. He had a link
to http://www.attawayair.com/rv6a.htm and reading that link I read
that Robbie was able to drip his CHTs by 25 degrees **Celsius**,
dude that's 77 degrees F! That puts me in the high 300's, excellent.

Who else has added louvers? What was your experience with CHT and
was your speed affected?

I found this site which has two sizes of louvers, I might start with the
small ones and see what effect they have. http://www.raceace.com/


Thanks for your input.
 
Walter,

Several causes come to mind; one of them is the LASAR ignition which aggressively advances the timing.
Click to expand...
From Unision Web site

[font=ARIAL,HELVETICA]
When the engine is operated between 85% and 100% of its sea level rated power, the LASAR? System provides the same ignition timing as conventional magnetos
Click to expand...
[/font]

I seriously doubt that the Lasar is advancing the timing much past 25 degrees when at 6000' and full throttle. The spark may be hotter and the dwell time longer but that is about it. At low MP settings it will start to advance the spark past 25 degrees. Remember Lasar stands for Limited Authority Spark Advance Regulator. I would hesitate to use "Aggresive" in the same sentence as LASAR

Anyway, I digress. Your CHT's seem hot for a 6000' climb. Airspeed and fuel mixture have a lot to do with CHT's when in climb. I find that a good airspeed for sustained climbing is around 120 knots. Slower than this and there is just not enough air flow through the cowl. Mixture plays an important role too. Don't lean to aggresivly during climb and leave it a little rich once leveled off to allow the CHT's to come back down. Then you can lean as you please. Climb at 24 squared increasing the throttle to keep the MP up until your at full throtle.

Some things to check before resorting to louvers. If the cowl exit is cut so that it slopes towards the aft it is restricting the exit size. Make sure the cowl exit is cut parralel with the firewall. You could also slope it forward a little which would expand the exit a little. The old Cessnas had a lip on the bottom of the cowl exit to help scavenge air out of the cowl. You might try that. But remember more cooling airflow = more drag.

Baffles, make sure they are good and tight. No leaks!

Good luck on your CHT's

Gary
 
Baffles are as good as I've seen anywhere. Doesn't matter if you
run my engine rich as hell or LOP, doesn't affect the CHT even 5 degrees
either way. Cowl is cut parallel to the firewall. Don't want to cut
any more of the cowl away, that would create more drag by allowing
the heated air to exit more perpendicular into the airstream.

More cooling airflow does not necessarily mean more drag. If the exit
airflow is exited parallel to the aircraft and it's sped up that will
minimize the drag. Exiting perpendicular and slow are the culprits, in
a nutshell (big nutshell).

Oh, and the LASAR is good for at least 10 degrees from what I've read/heard.
That's why I don't assume it's the #1 culprit.

I'm still thinking the louvers are the way to go. 25 Deg. C? Wow.
 
Last edited:
Huh?

top.jpg


I'm sorry...what were you talking about? :)
 
Plenum

I built an aluminum plenum for my O-360 6A. Engine was used, not new. I've not seen CHT's over 400 degrees yet after 9 hours of test flights. Below 40 degrees OAT, I had to completely seal off the airflow to the oil cooler to keep the oil temp's up. I'd say the problem is in the baffle seals.
 
I'm using essentially a one piece baffle made of red silicone baffle material.
No gaps = no loss. I've got a clear indication of scuffing on the top cowl
all the way around and on the baffles themselves with no gaps.
I've got red silicone on absolutely every possible gap larger than a hair
width. In short, my baffles are NOT the problem. I don't have any
flashing between the cooling fins either. And all my CHT's are within
15 degrees of each other.

Have you seen how much crap is *directly* in front of the lower cowl
exit on an A model? Have a look, and this is not a good picture, some
of the crap is not in the picture or missing.

http://rv7-a.com/Img_5103.jpg

Please, is there anybody out there that can comment on the CHT drop
(or not) that they experienced using louvers? Maybe I need to pose
this question to the Rocket folks...
 
cylinder fins clean?

Someone recently posted regarding some metal residual that plugged the space between some of the cooling fins on Lycomings. After the excess metal was removed, the problem was solved. Worth checking.

What type engine, prop, pistons? Lots of horsepower means lots of heat to dump. My O-360/catto/std compression pistons doesn't have a problem with overheating.

New engine?

have you checked your CHT calibration?

Climbing at 500fpm at 6000' with OAT 70F and you're overheating? Sounds odd. Is that 500fpm with nose pointed straight up or just above horizon in cruise-climb?... just asking.
 
CHT's/Oil Temps

Hi Walter,

I have a new ECI IO360 with 19 hours on the new 7. The first couple of flights I had high oil temps but the CHT's were excellent. I cleaned up the baffling and double checked to insure a good seal and no holes in the system. I found a couple and plugged them.

Robbie Attaway has been my guidance on this endeavor and he recommended that I cut the tunnel forward to increase the exit air. This dropped the oil temps into acceptable levels. I cut another 1" off and also built a small dam on the bottom of the tunnel. The temps came down even more. It is raked forward and looks kind of cool.

I suspect as the engine gets more broken in and I get the pants and fairings on the temps will improve more.

I will post a couple of pictures later. I would look at the exit air for sure could be the same issue.

Darwin N. Barrie
Chandler AZ
RV-7 N717EE
 
I don't have the flashing problem.

New, Injected O-360, standard lycoming stuff, nothing weird.

All CHT's are within 15 degrees, by this measurement
I'm assuming that they are either all wrong or all right.

Mid power or high power or low power climb at 500fpm
all keep the CHT's well into the 400's. Higher power =
higher CHT.

I'm pretty darn sure it's an exhaust size issue
or rather an exhaust blockage issue.

For the sake of arguments, let's assume that is the
issue, nothing else, let's just talk louvers. Anybody have
any experience with louvers?

btw, cafefoundation.org is non-responsive and they
have some info I seek. Anybody have a copy of
localflow1.pdf, localflow2.pdf, localflow3.pdf handy???
 
RV7Guy said:
Robbie Attaway has been my guidance on this endeavor and he recommended that I cut the tunnel forward to increase the exit air. This dropped the oil temps into acceptable levels. I cut another 1" off and also built a small dam on the bottom of the tunnel. The temps came down even more. It is raked forward and looks kind of cool.
Click to expand...

Hey Darwin,

I sent an email to Robbie earlier, perhaps he'll have some time to respond.
I thought about cutting it off more forward too. If the louvers, or
perhaps even a reverse scoop or pressure lip doesn't seem appealing from
an aerodynamic perspective I will have to cut the tunnel back.

How's that baby flying?
 
walter said:
Hey Darwin,



How's that baby flying?
Click to expand...

To steal a line from Dan Checkoway..... SAWEEEET!!!!!

Also I have the EMag PMag set up that is working great!!

Darwin
 
At least its not just me

.7 hrs on the the bird and on climb out # 3 reached 475 before I got to pattern alt. I was told its not my engine but I need more air through th cylinders, I was also told it is not uncommon to cut up to 2" off the cowl exit. I thought about the louvers also, let me know how you make out.

CHT probes were tested, no leaks but I think I can reduce the oil cooler area as I only got the oil upto 150. But what will happen in the summer. There is also another discusion going on in the engine group about the same problem. Seems like a lot of people have the same problem.

John
 
Cafe docs

I tried this will limited success, but thought I'd pass it along. You can search with Google for filenames too, just put the localflow1 or localflow1.pdf in google.

It mostly will find the cafe links, which don't seem to be working. However, if you enter that name without the pdf extension, it will come up as the first search result. if you click "view at HTML", at least you'll be able to read the "cached" copy. Won't have pictures, but might be some value.

Alan
 
I finally got the files. Office computer was playing games with me.
(I was working and not surfing, honestly).

Several ideas come to mind about fixing this problem. Some of these
ideas are noted in the localflow2.pdf document which is an interesting
read. I either need to increase the negative pressure (sucking power)
of the exit or simply make the hole bigger.

1. Exit deflector plate
2. Build an air extractor or two (bluff bodies)
3. Louvers
4. Open the cowl bottom more

It should be quite easy to create a bluff body and tape/glue it on and
test it. The easiest might the the deflector plate or deflector lip which
should also be easy to test. These two are the two non-destructive
items I'll probably try first.
 
High CHTs

This is all very interesting. I don?t think I?ve ever seen a post on high CHT and in the last few days I think there have been at least three threads dealing with high CHTs. I just marked my lower cowling at 11/2 & 2 inches forward of the exit area to be cut off. I plan on making a couple of flights tomorrow to document temps before and after.
I?ll keep everyone posted. I have also thought about adding a lip to the cowl at the exit area to create a lower pressure. I?ll see how things go.

Roger Ping
RV-9 no A
90869
TT: 63 hours
 
walter said:
I either need to increase the negative pressure (sucking power) of the exit or simply make the hole bigger.
Click to expand...

Careful with the later, it's not the panecea that you might think. Early mooney's had too large of an opening, not only bad for cooling, but also create drag due to the reverse airflow back out of the baffles/plenum.

There seems to be a optimum opening for a given flow of air, with the high pressure at the opening and the low at the exit.

Alan
 
Well How did it go?

Roder / Walter

Did you make any alts to your cowl? If so how did they turn out, any flight testing yet. Pic would be great as I need to do something before my next flight. I am thinking about luovers or cowl flaps myself, just not sure yet. Hate to cut holes in the cowl after I spent hours fixing and preping unless I have to.
 
So far I have two confirmations that cowl louvers do
**SIGNIFICANTLY** reduce CHT temps. I am more and
more tempted to install them. If fact, if I had a set of
louvers in my hands today, I would install this weekend.

I think that a few mph lost due to cooling drag is much
less, much less significant that an engine that is running
at the correct temps versus running on the verge of
heat stroke. Moving CHT from 450 to the mid to high
300's sounds like the plan.
 
Cowl Mod

I did fly yesterday and documented temps, 448f. I will cut my cowl today and fly Saturday to document any changes. I have been told of positive results by other builders and Van's.

Stay tuned for the results with pics...


Roger Ping
Rv-9 90869
TT: 63 hours
 
High CHTs

Walter
Been watching your thread for a while, before you alter your RV check to make sure your engine has the inter-cylinder baffles and deflector plates installed. Its a long shot but worth looking into. How about posting a picture of your engine installation.
Good luck
Tom
RV3 2000 hours,
pumped up engine,
no cooling problems.
 
walter said:
If fact, if I had a set of
louvers in my hands today, I would install this weekend.
Click to expand...

Make yourself a set. Nothing says they have to be out of alum. Make em out of fiberglass. Build up a simple mold and layup some glass. :) In fact there are probably a bunch already pre-made out there. The Long-ez guys have been using them for awhile, and so do some of the models of other composite airplanes.

Alan
 
Intercylinder baffles and everything else has been inspected and
confirmed to be in excellent order.

Would build my own but since vans louver (P/N F10109) costs
a whopping $4.60 each it's not worth the time and hastle.
Ordered a pair today and will install next week. Stay tuned for
the results. I suspect it will help *significantly*, plus it will
look pretty neat. I called today to order and get the dimensions,
here they are;

Length: 7"
Top/Front Width: 3.5"
Bottom/Aft Width: 4.5
Made from .020 AL

Now if I can just decide whether I want to go ahead with the
F1 rocket kit purchase. Gotta have something else to work on
when not flying... :eek:
 
Walter:

When are you going to be at your plane again? I'd like to take a look at the installation. Before doing anything with louvers, you should evaluate the differential pressure you are getting between the top and bottom of the engine. I bought an air speed indicator for doing exactly this, since there are published tables which show Lycoming's requirements for pressure differential that yields adequate air for cooling. If you really do have a problem with exit air, it will manifest itself as insufficient differential, i.e., the pressure below the engine is not low enough to allow the high pressure above to flow through the cylinder cooling fins. This would be absolute rock solid evidence that this is the cause of your problem. Would have to rig a couple of temporary hoses back into the cockpit attached to the ASI but it should not be very difficult. I suggest this is a logical next step.

Bill Marvel
 
Hi Bill,

That's a great idea. I have to work tomorrow but should be at the
airport (KCNO) Sunday unless the skies decide to dump on us (unlikely).

Are you going to fly out? If so, perhaps I could ride shotgun...

Also have to think about how to run the tubing.

Give me a call if you like (310) 345-8925
 
CHTs Not much change

Here's the numbers...
The flight the other day was 441F not 448. Ambient temp was 70f.
I cut the cowl forward 2 inches which opened it up 1/2 inch.

The highest CHT was 436 and ambient temp was 74f.


Net gain was 9f.

Not much time...gotta go.

Roger
 
Walter,
In one of your initial notes, you stated:

"Doesn't matter if you run my engine rich as hell or LOP, doesn't affect the CHT even 5 degrees either way."

It would seem that even assuming a less than ideal airflow pattern, an engine with a correct mixture range setting should not behave in that fashion. Do the EGT values follow expected patterns as you go from full rich to various lean settings?

Hawkeye
RV-3
 
Test Results Are In.

Folks, I want to thank Bill Marvel for initiating and helping me with the
pressure differential testing we did today. The results were, well, a little
different than I had expected. I did a partial writeup tonite for your pleasure.

I received a bunch of emails from many of you experiencing the same high
CHT issue and I want to thank you for your correspondence.

The preliminary results can be found here:

http://rv7-a.com/phase_1_page2.htm#1/15/05
 
Cerminil and breakin

Walter,

I had a thot after your first post. I wondered... HMMM, is the engine not broken in...?

Couple of things. Most people will tell you that Ceramic breaks in the quickest. Usually in the first 5 hours.

Break in in a nut shell - you always want to run with Max manifold pressure to keep the pressure of the rings to the cylinders. And it is critical to not let them generate a bunch of heat. Below is a break in guide and is good reading on the topic.

http://www.highrf.com/Rockets/035tech.pdf

To give credit where due, this is from the Cessna Pilots Association and is copyright information - now don't get me in trouble.

Alan
 
Were back ?????? High CHT,s

Last week I put a pair of louvers in the bottom of the cowl. Blocked 95% of the oil cooler back, sealed every thing I could and check the baffle, every thing looks good. Took the RV6A up again today. Flys great but my CHT,s are still high. Climbed out at 130 mph #3 when to 495!! and was still climbing. Backed off to 2000 and managed to climb to 3500 feet. Levelled off started adding power and got her up to 150 mph but the temps still went to 480 on #3. I am going to pull the probes and check the again but other than that I am lost. Cant fly it like this. Any more thoughts. Here what the readings looked like. Engine sounds good ? Got 1.1 hrs on her now.

Outside Air 50 - 55 F
Speed 150 mph indicated
Full power
RMP - 2550 - 2575
Oil Temp 185 F
Oil Press 75 psi
Fuel Press 5 psi


#1 - 435
#2 - 440
#3 - 480 & climbing
#4 - 445

What do I do next????????????????? BTW the EGT,s all ran around 1400 - 1425
 
Last edited:
High CHTs

John, I?m sure your temps will go down when the cylinders break in. How much is the big question. Are you able to get up to 7,500 or 8,500 feet and level off? That should give you 75% power with plenty of extra fuel for cooling, cooler ambient temp and plenty of air flow in level flight.
I have high temps on climb out but once I get some altitude the temps come down. I recently cut the lower cowl forward 2 inches which opened up the clearance 1/2 inch (6 square inches) and that brought my temps down 10f. I have since put a 1 inch lip across the lower cowl that hangs out and should create a low pressure to draw more air through the cowl. I will fly tomorrow and report back.
The only other thing I can think of is the wrong rings have been installed. Basically, iron rings go in chrome cylinders and chrome rings go in iron cylinders.

Good luck and I hope I have some good news for you tomorrow.
 
walter said:
Baffles are as good as I've seen anywhere. Doesn't matter if you
run my engine rich as hell or LOP, doesn't affect the CHT even 5 degrees
either way.

Walter, this would seem to be a clue to the problem - as another posted, mixture should have a large effect on CHT's. Do you have a fuel flow meter? If so, it will be a great diagnostic tool, together with EGT's. If you have fuel flow and multi EGT/CHT instrumentation, I'll post what I think would be helpful to try.

Some other things to check:
1. The gap between curved portions of the baffles which are drawn together under each cylinder should be the same. I don't recall, but this is something like an inch or so. My baffles were all different in this regard, and I evened them up.
2. Put a series of tiny drops of oil on the fuselage belly, immediately aft of the firewall, from side to side in the cooling air exit area. Go fly and have a look. A couple of the drops on my 6A actually showed forward flow! I am going to tuft the whole lower cowl sometime and see what is going on.
3. I put a firewall to belly fairing in similar to the 8's.
4. Most builders do indeed cut off an inch or inch and a half from the lower cowl.

Mixture, mixture, mixture! It is a key. Good luck!

Alex
Click to expand...
 
Hight CHT

[email protected] said:
(snip). Climbed out at 130 mph #3 when to 495!! and was still climbing. Backed off to 2000 and managed to climb to 3500 feet. Levelled off started adding power and got her up to 150 mph but the temps still went to 480 on #3. I am going to pull the probes and check the again but other than that I am lost. Cant fly it like this. Any more thoughts. Here what the readings looked like. Engine sounds good ? Got 1.1 hrs on her now.

Outside Air 50 - 55 F
Speed 150 mph indicated
Full power
RMP - 2550 - 2575
Oil Temp 185 F
Oil Press 75 psi
Fuel Press 5 psi


#1 - 435
#2 - 440
#3 - 480 & climbing
#4 - 445

What do I do next????????????????? BTW the EGT,s all ran around 1400 - 1425
Click to expand...

Wow
:eek:

A couple of thoughts--do you have fuel flow instrumentation? You should be running about 200 degrees rich of peak at takeoff power, which is about 19 GPH for a 200HP engine, or 17 GPH for a 180. It's possible that you are running way too lean for takeoff, and near peak EGT , which would explain your symptoms.

EGT is really only useful as a relative, not absolute, number in normally aspirated airplanes, but in most planes I've flown EGTs run around 1100 or so on takeoff, and peak somewhere in the 1350-1500 range. It's possible that your probes are close to the exhaust valves and read that high on takeoff, but it's unusual in my experience.

Have you checked your ignition timing?

James Freeman
 
Too High

I am starting to believe I am running to lean as when I shut down I did not get the 25 - 50 rpm rise that aparently is normal. Is there a way to ricen up the mixture , an adjustment? Some pic or a scan of the manual would help. If not I think I will be sending my carb in to be checked and rebuilt if needed. I did originaly have high EGTs at 1500 - 1800 rpm so maybe this is a hint.

Just tring to avoid another $500 - $600 bill.
 
The mixture adjustment is on the aft side of the carb and there is a notation stamped on it for R or L. (I think it is counterclockwise for Rich and clockwise for Lean.) Anyway, you have to do this in conjunction with the idle setting, which is the stop on the throttle link on the side of the carb.
It may take several attempts to get it right, but I believe the OH manual says to set the idle at about 600 to 800 RPM, engine warm. Then see how much RPM rise you get at shut down. If none, richen the adjustment about 1/8 turn and try again. If your idle starts to go up, you will need to adjust it back down. Keep at it until you get the idle in the appropriate range and you get the RPM rise at shut down. When checking the idle, the manual says to run the RPMs up to 1800 (?) momentarily before shut down. (I got to where I could make the adjustments on my RV6 with out taking off the cowling, but it does get hot down there. Keep an Aloe plant nearby!)
 
Found it

I rebuilt the carb and did not remember the adjustment. Cowls off and I think I will start real rich and work my way back. Too windy to do much now so I guess I will give it a test Sunday.

Thanks
 
mixture adjustment

The mixture control screw is only for adjusting idle settings, has nothing to do with full power settings. The fuel nozzle controls the amount of fuel/air mixture getting to the engine, the mixture control (little red knob) controls the amount of fuel getting to the fuel nozzle. A check of your spark plugs should be a quick and dirty way to determine rich or lean operation.
Good luck
Tom
RV 2000+
 
This is from the Cardinal Flyers Online. Something that helps with #2 & #3 with the C177's.

Cylinder Cooling
Improving #2 and #3



I'm going to let Paul do the talking on this one.. explaining some work that has been done to improve cooling flow in our engines. Remember that in spite of what may be discussed here, your engine and airframe manuals, and the advice of your certified mechanic, remain the sole authority on proper configuration and maintenance of your aircraft. Webmaster

For general information on other things you can do to cool the cylinders, please see this page.
cylnfin1.jpg
If you look at the Lycoming cylinder, whether parallel valve (O360) or angle valve (IO360), you'll note that on one side, the right if you're facing the valve cover, the cooling fins extend all the way from the top to the bottom of the cylinder (from sparkplug hole to sparkplug hole).

However, on the left side [of the head part of the cylinder], the cooling fins diminish to nothing as they approach the midline of the cylinder. The fins then reappear as you descend further down the cylinder.

What happens when you place the metal baffle right against the cylinder, or worse yet, seal it against the cylinder, there's no path for cooling air to exit the upper fins, and no source of cooling air for the lower fins.

gem.jpg
What this causes, at best, is uneven cooling around the cylinder, making it egg shaped as it expands differentially due to the uneven temperature, which is thought to be the reason Cermichrome cylinders didn't work well on Cardinals (and Lycoming powered Mooneys).

At worse, the cylinder runs hot, due to the lack of cooling air on the left side.

Webmaster's note: The picture to the right shows a common situation, as indicated on my GEM. Things are pretty flat, but #2 and #3 are just a titch higher in cylinder head temps. The GEM shows 25 degrees per bar, so both #2 and #3 are 25-50 degrees higher. This indication is on my '76 RG without the mods mentioned here, running at 65% power lean of peak, 4500 feet and 50 degrees ambient.

cylnspacer.jpg
The proposed solution is to create a controlled gap between the metal baffle and the cylinders where this is a problem, #2 and #3 (which oddly enough, are the ones that often run warmest). On #1 and #4, these funny shaped fins are faced toward the intra-cylinder gap, where they receive lots of cooling air.

The current thinking-in-progress is to glue a double layer of thin baffle seal to the metal baffle, inboard and outboard of the cooling fins themselves. This holds the metal baffle a uniform distance away from the cylinder across the entire area.

Of course, this purposeful "leak" must be accompanied with good sealing of the rest of the upper baffle and seals, to maintain the required (5" WC?) pressure differential across the engine for good cooling.

In our preliminary tests, Jeff and I have noticed that #3 and #2 run noticeably cooler, to the point that in cruise flight, #2 is now my hottest cylinder, when #3 was always at least 40 degrees warmer, previously (4 cylinder CHT, JPI).

Let me caution anyone considering this mod... unless you have good instrumentation, and good historical data, proceed very cautiously. You don't want to undermine your engine cooling!!

It's also important to make sure the baffle springs, all four of them, are the correct ones for your engine (Cessna changed these around from year to year for no obvious good reason) and properly installed, with the springs free to spring.

Our thanks to George Braly, principal engineer at GAMI, the balanced fuel injector folks. He pointed out this anomaly to us, and suggested the solution.

Paul
Click to expand...
The general gist is, don't tuck the baffles in too tight into the cylinder cooling fins. Keep a small, 1/8 inch or so gap between them.
 
Some Improvement

Spent 6 hr filing the flashing from between the cooling fins on all four heads. This seemed to help a little #3 still gets up to 475 on climbout so I have to back off, but not quite as far as I have had to in the past. Got the plane up to 6000 ft 2500rpm and heres what I get>

CHT EGT (These might be a little high as my probes are only 1.5 inch from the flange.)

#1 - 395 1205
#2 - 400 1235
#3 - 458 1410
#4 - 436 1400

It looks like the back 2 are running lean. I did notice a 5 - 10 deg drop in CHT aft about 45 mins of 70%-75% power. Managed to get 1hr on her today. And boy does the ground go by fast when you have a 25 mph tail wind, ground speed 186 mph and I have no wheel fairings yet.

Thanks everyone for your help. We will keep on plugging at it.
 
John, I flew this weekend but did not record any numbers. Ambient temp was 20 degrees cooler from my other referenced flights and I was unable to climb due to class B airspace. I did however notice in cruise flight that if I backed off the throttle by .2 inches of MAP, EGTs and then CHTs really evened up. You may want to play with throttle plate position to see if you can optimize your fuel distribution to your cylinders.
Glad to see you are gaining a little on your temps.

Roger Ping
 
As I reviewed this thread this morning I noticed this stupid statement that I made earlier. It is not what I had intended to write and should be stricken from the books; "Doesn't matter if you run my engine rich as hell or LOP, doesn't affect the CHT even 5 degrees either way."

Of course the amount of richness affects the CHTs. This past Saturday I was running WOT at about 3000 ft and the highest CHT was 411. Climbing to 5000 feet at 500 fpm increase the CHTs to 425. Leaning to 50 degrees ROP allowed the temps to climb into the high 440's, this on a slightly warmer than usual day. Still too hot. Oil consumption is hardly measureable.

So next weekend I plan to do the following:

1. Verify the CHT probes are accurate by testing.
2. Provided #1 is ok, cut two 2" diameter holes in the bottom of the cowl. I'll fly before I do this and after to get a differential reading of CHTs.
3. If #2 doesn't do anything then I must begin to look at things like improperly installed rings and other engine related issues.
 
CHT EGT (These might be a little high as my probes are only 1.5 inch from the flange.)

#1 - 395 1205
#2 - 400 1235
#3 - 458 1410
#4 - 436 1400

It looks like the back 2 are running lean. I did notice a 5 - 10 deg drop in CHT aft about 45 mins of 70%-75% power. Managed to get 1hr on her today. And boy does the ground go by fast when you have a 25 mph tail wind, ground speed 186 mph and I have no wheel fairings yet.
Click to expand...

What makes you believe that higher EGT's mean they are running leaner? If you have a fuel flow meter, start way rich of peak and record EGT's as you gradually go leaner. Adjust the mixture for about 1/10 of a gallon less flow, and after 20 seconds or so, record the EGT's. Keep doing this until the engine is running rough on the lean side of peak. You will get four curves, one for each cylinder. Fuel flow will be along the bottom of the chart, with EGT along the vertical. Only this way can you know if there is a mixture imbalance. This can't be done too easily without fuel flow information.

Alex
 
I was just reading my latest issue of Light Plane Maintenance, and they have two articles that discuss high CHT, especially on a single cylinder. Assuming that your CHT gauge is correct, the most common causes are:
partially clogged fuel injector causing lean mixture, bad baffling, an air induction leak, advanced timing, fuel system not set up within specified limits, pre-ignition or detonation.
LPM is a great investment if you plan to maintain your plane and I recommend it.
 
a little at a time

Well we moved the rear baffel back 1/4 inch and it did help but not much. At lower rpm,s the temp seems to ballance between cylinders some what. The egt,s do balance if I play with the power a little, the carb plate position does make a big differance. We are still running temps in the 440,s on climb out with #3 reaching 480. I was informed this week that the prop I have is too low of a pitch. I have a wood prop 68 long 69 pitch. I was told that I should have a 68/76. What pitch are you guts running. If I increase the pitch I will not get full rpm,s the way thing are running now. This leads me again to the idea I am running too lean and not producing full power. The engine shop told me to drill out the carb jet, +3 thou at a time. Not sure I want to do that but might try. I would rather have a shop with a flo bench do it. Any one know any shops which do this kind of work?

Anyway 3.5 hrs on the meter and my transponder seems to be eratic now?> What else???
 
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high chts

Are you using lycoming bayonet style probes? (If they are continental style that fit between the sparkplug and the cylinder head they read 50 to 75 degrees higher. I dont think your prop pitch has much to do with it. Decide what rpm you want to run FF at lets say 8000' and pitch accordingly. BTW my engine people (Lycon) say the 4 cylinder lycs will run 28-29k rpm all day long. Not that you'd want to run 2900 at cruise but you have a little to play with. FWIW my 0320/prop combo will pull 2820 @ 3000'. I normally cruise at 2620 rpm (sweeet spot for my engine/prop combo) Oil changes every 25 hours, oil analysis every 100, everything is fine.
Tom
RV3 2000+ hours
 
Just do it!

Not all fun and flying.
John, I have been sick this week and also working many hours so I have not been able to fly at all. Now I have caught a cold? Dang.
Anyway, what is the abient temp when you are flying? I?d say if you?re in 70f weather then just continue flying untill your engine breaks in. Get on up to at least 8500 feet or higher and set up cruise and the temps should be mid/high 300s. Once your engine breaks in your temps should be low 300s. Remenber, Vans RV-9 tested about 465F during climb and that engine is broken in. Just take it easy during the climbs for know and have some fun with your new plane.

Roger
 
High CHT,s Maybe not????

I went to the airport with the intention of pulling the carb but got thinking, something I apparently don?t do much of. I pulled the CHT probe from #3 and placed in a can of oil with a new candy thermometer as well as a separate thermocouple. I then heated the can to 212 Deg F as I had with water before and all match within 10 Deg I then heated to 400 Deg and all but the RV,S instruments matched. At 400 degs the gauge in the plane indicated 525 Deg!!!!! Check the oil temp with a laser thermometer and it was 400 Deg.
The CHT gauge I have is programmable so I changed the type of probe in the program and now it reads within 15 Deg of all others. Looks like I have actually been running in the mid 300,s all this time. I will be checking this one more time with a laser thermometer from work to verify. And then go fly.

Thank everyone and Roger I hope your feeling better.
 
wow!

Way to go, that is excellent news... let us know what you changed, and what you had it set to before, so others don't fall down the same trap.

Alan
 
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