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Rv6 cylinder temperatures

dan carley

Well Known Member
I have a Rv6 with a James col
180 hp catto 68x78 prop
At 2400 rpm my cylinder temperature are
About 400 for number 3-4 I think that high
What is everyone else temperature running
Thanks
Danny carley
 
Can you give us a bit more info? Is that 400 in a 110 knot climb leaned on a hot day or 400 in cruise flight on a standard day ect..
 
How fast are you flying? If I climb out too steep on a hot day I have to watch my cylinder temps. They can get above 400, especially after idling on the ground for a while.
 
I think ~370 should be pretty normal at that power setting. Has the timing been checked recently?
 
My RV-7A temps in cruise are in the 350’s at my economy cruise power setting of 22/23 LOP, 7 Gal. Hr. Front cylinders are hotter in climb but I usually have no problem keeping them under 400 if I keep the airspeed up.
 
Well thanks for no advice
Danny carley

You are welcome.

I think ~370 should be pretty normal at that power setting. Has the timing been checked recently?

+1, 340-370 range is about right for me for ~80's OAT, but depends greatly on the A/F ratio.

Assuming you have a James plenum, where is the oil cooler, large off-engine mounted, or on the engine? You have not mentioned oil temps so they have to be in range. This leads one to assume you have a larger than stock oil cooler drawing more air. James plenums are known to yield higher CHT and oil-T issues without close attention to engine sealing and maybe inlet diffuser modifications. Some include removal of the blocker plate in front of the #1 and #2 heads to cool them this unbalances the flow and bumps up #3 & #4. Engine leakage sealing is a hard requirement for SJ cowl/plenums. Mine is SJ cowl, but my own plenum.

Lot of variables (unknowns) at play before a good answer can be offered. OAT is basic, as is airspeed. Then you will get a flood of usable information.

Lots in the archives if you use google search as [site:vansairforce.com "query"]

https://vansairforce.net/community/showthread.php?t=68241&page=01

Did you know the angle valve engines have much lower CHT's?
 
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Cht

I do apologize about pasting
No help with my post. I thought I gave
Enough information but I was wrong.

The plane is a Rv6 180 hp James cowl but no
Plemimum just regular baffling. Running a catto
68 x78 prop. I am not talking about climb I was asking
Cht heat in cruise. At 3 thousand feet on a 80 degrees
Day turning 2400 rpm’s my cht on 3-4 run at 400
Degrees my oil temperature is 190-195 and pressure is about 80 lbs.
the question I have is it ok to run at this temperature or do
I have to look for a way to reduce the temperature
I know in a climb it well go over 400
Thanks
Danny carley
 
Technically you are in range.

OK, that is much better. Technically, since 435F is the lycoming limit for continuous cruise, and around 500F for short term (climb) you do not need to do anything as an emergency. However, the system is not performing with the average of the field. Roughly if OAT was 100F then it could be ~420F for the CHT.

If you took a poll of regular RV operators, you would probably get the recommendation to do some "tuning" to the cooling system. That would mean sealing the baffle-to-cowl areas and aluminum baffle-to-case leakages. A guess, is that much of this could be done without any hardware changes and could reduce CHT 20-40F.

These leaks may not be obvious and some downright subtle, but they all add up. One area of concern could be geometry around your inlets, and how the air might flow there.

The next time you have your cowl off, if you could take pictures of the all the sealing areas around the cowl, and then around the engine, they can be easily posted here and you can get some expert comments.

Meanwhile click this and you can read a good bit about the various questions and answers. It's a forum, so add salt.

Last item, if your fuel system is carbureted, then it could be a mixture issue and ignition timing is a big factor so if you have mags, it is an easy check. Overall, being a James cowl, I would certainly start with the sealing path before anything else.
 
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I checked the timing was good
It is a carborator engine I run it about 9 gph
Possibly not using the plenum with the James
Cowl
Maybe not enough space in the back of 3-4
By the metal baffling
Thank you for answering the question
At lest I feel more comfortable about running at
400 degrees. Ned t time the cowl off I’ll take pictures

Danny carley
 
Baffling

I did a small gap in the rear baffling also
The metal baffling behind 3-4 had no
Space I put washer behind the cylinders
I’ll fly it tomorrow

Danny carley
 
Baffling

I flew today the temp did drop a little
But not number 4, right behind number 4 on
The back of the metal is where the oil cooler is
Mounted, because of this not much air goes
Around the cylinder. All other cylinders are around
380 degrees number four is 400 degrees.
It was 80 degrees outside I was at 3000 ft and rpm was 2400 rpm
Is there something I can make to help the back
Of the cylinder to force the air down or just
Let it be. Don’t think 400 degrees is that bad

Danny carley
 
Check baffling, then check timing.

Do have the recommended carb recommended for Vans i think its 10-4161-1 ?
I just put one in my RV7 and it dropped CHTs 25 degrees
 
Carb

I fixed all the baffling and timing is correct
Unless I can figure out something with the oil cooler I guess
Not much can be done. Not sure about the carb
Seems to work well
I’m just looking for the answer if running 400 degrees
On number 4 is ok
Lycoming says at normal cruise any where between
375 to 435 is ok

Danny carley
 
I fixed all the baffling and timing is correct
Unless I can figure out something with the oil cooler I guess
Not much can be done. Not sure about the carb
Seems to work well
I’m just looking for the answer if running 400 degrees
On number 4 is ok
Lycoming says at normal cruise any where between
375 to 435 is ok

Danny carley

You need to check the carb. This common source of cooling problems.
I added an electric antisplat cowl flap in addition.

Lycombing has a red line of 500 degrees. This is for a catastrophic failure.

Most experts will tell you that cylinder life is significantly effected over 410-420 degrees. Lycombings tolerate hotter temps but if you getting hot in cruise you probably really pushing limits in the climb.

I try to keep it under 420 always.
 
Baffling

Thanks for the answer
If I cruise at 2350 instead of 2400
Number 4 cyl would be about 390
That’s at 3000 ft who much is a new carb?

Danny carley
 
I fixed all the baffling and timing is correct
Unless I can figure out something with the oil cooler I guess
Not much can be done. Not sure about the carb
Seems to work well
I’m just looking for the answer if running 400 degrees
On number 4 is ok
Lycoming says at normal cruise any where between
375 to 435 is ok
Many RV-6s including mine have the oil cooler there without it resulting in high temps on #4.
I'm no authority but from what I read you want to keep it under 400 or at least 410 whatever Lycoming says. With your temps, I'd fly but keep working on it.
 
This topic is LONG in the Tooth.... Asked 1000's of times. Please search the forums going back decade or more for pearls of wisdoms.

Your immediate fix is full rich at least to 8,000ft MSL and STEP CLIMB. You lower your lose, increase your airspeed, even level off if needed, to cool. Than continue climb. You do that as needed.

The list of things that can cause this is LONG. It is not SJ cowl or plenum flaw or weakness per se'. It is working as designed (assuming it is installed properly). However the cooling has been optimized to provide adequate cooling for cruise with min drag. Also the word optimized in airplane design, means compromises, which all things in aircraft design are. There are trade offs. If you want better climb cooling at loss of cruise (cooling) efficency, open up the exit air in your cowl. If you want to be fancy (at more the expense of added weight and complexity and cost) add adjustable cowl flaps.

Because you are not over cooled and draggy in cruise there is less extra cooling margins for climb. Not as forgiving. Even factory planes Piper, Cessna, Mooney, Beech, all get hot in the summer on a long climb.

VERY HIGH AMBIENT Temps and steeper and or long climbs will expose any weakness or flaw or needed improvements in your engine, cooling baffles and cowl (exit air).
How are your OIL TEMPS. A bigger more effective oil cooler will lower CHT's, or just improving airflow in and out of cooler will help. These engines are both AIR and OIL cooled.

There is a long list of things to look at and fine tune or improve: Timing, main jet if carb'ed, baffle spacing on the back side of right rear cylinder, exit air, baffles in general and on and on. Again search to forum. This is the 1000th time this has come up.

Last 400F CHT is HOT. However Lycoming allows that for short periods. I like to never get too near 400F but sometimes in extremes, ambient conditions, gross weight, need to climb for mountainous terrain, you get up there, close to or at 400F. Again I use a step climb if I am high, hot, max gross. Back in the old days before 1990's very few planes had full digital engine monitoring. You were lucky to get one analog CHT gauge on #3 (right rear jug), typically the hottest cylinder (but not always).
 
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Last 400F CHT is HOT. However Lycoming allows that for short periods. .

Not accurate, at least according to the folks who design and produce the engines we use.

Here's a lycoming document for O-360's.

https://www.peter-ftp.co.uk/aviation/misc-euroga/201603-LycOperatingManual.pdf

It lists the CHT redline at 500F.
It lists a high power cruise recommendation of <435F for maximum service life.
It lists an economy cruise recommendation of <400F for maximum service life.

Synopsis: Cooler is better, but 400F isn't a serious concern.
 
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