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Old 02-24-2016, 10:38 AM
bluebrear bluebrear is offline
Join Date: Feb 2013
Location: Bethel
Posts: 32
Default High CHT's

I've been reading about excessive oil temps, of which, happily, I have none. Oil temp is, at highest 169 degrees, and at cruise steady 143 degrees. But, after 5 hours in my RV9A, we are still experiencing CHT's, with OAT's 16-26 F, @450 at TO for #1, being the highest. At cruise 2100 RPM, we're 370 for #1, the others are lower, but not by alot. We have a rebuilt O-320 B1A with chrome cylinders, conical mount. The prop is a metal Sensenich recommended by Van's (79") pitch. Two IA's have looked at the baffling and didn't find any obvious causes for the high temps. We have RTV'd waste areas and lowered a small amount of the intake dams on both sides of the intake per recommendation of the IA. Seemingly no change. I removed two small fiberglass rectangles from the exit of the lower cowl thinking that that would increase airflow. Still no change. VAN's tech said they have not experienced temps that high. It's built per the plans, no mods. I'm not seeing squawks from any of the 1100 or so 9 builders. Does anyone have a clue here? We're at wits end. EIS with GRT HXr.
Thanks to all.
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Old 02-24-2016, 11:34 AM
RVbySDI's Avatar
RVbySDI RVbySDI is offline
Join Date: May 2005
Location: Tuttle, Oklahoma
Posts: 2,655

A lot of questions. Not so many answers.

You do not mention quite a few things that may help in anlysis:
  1. what kind of fuel flow gets that 450 Deg?
  2. What mixture settings during climb/during cruise?
  3. Are these temps while running Full Rich, ROP (how far), LOP (how far)?
  4. What is your climb rate when seeing the high temp (Vy, Vx, cruise climb)?
  5. What is your airspeed during this high CHT time?
  6. What is the RPM, MP during these high temp readings?
  7. Where/How are your CHT probes installed?
  8. When the high temps occur what do you do to bring them down?
  9. You state your cruise CHT temp on #1 is 370 with the others not far off that. How far off are the others? The GRT should give you all cylinder readings. What are they during this high temp rate?
  10. If they are close, how close?
  11. Do they move in unison with each other when they do move?
  12. I assume the reported temperature is while running somewhere ROP but not full rich. Have you attempted to run with various differing mixture settings to see what that does to the temps?
Ok, enough with the questions. Well, maybe one other. That may also lead to a 'WHY' answer. Have you checked the induction tubes, fittings, rubber, etc? It is possible there could be an induction leak somewhere? Just one possible answer.

Maybe there are others with questions, and answers, but these are the ones I have now.

Live Long And Prosper! 🖖🏻
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Old 02-24-2016, 12:10 PM
krw5927 krw5927 is offline
Join Date: Aug 2010
Location: Wichita, KS
Posts: 1,990
Default A couple ideas

1) Check timing. Advanced timing can cause this. Do you have electronic ignitions or mags?

2) Get rid of the #1 and #2 cylinder dams. They can be added back later after you solve other issues and determine the right height by experimenting with different widths of aluminum tape.

3) What is your climb profile like? Where in the climb are you seeing these temps? You're unlikely to be able to climb unlimited at 85 kts without the CHTs going high. Vy to safe altitude (1000' AGL or so) then lower the nose for cooling.
Kurt W.

Last edited by krw5927 : 02-24-2016 at 12:18 PM.
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Old 02-24-2016, 12:31 PM
bluebrear bluebrear is offline
Join Date: Feb 2013
Location: Bethel
Posts: 32

Hi Steve,
I'm the builder/owner/pilot. My test pilot friend has flown the hours.
I can answer most of your questions.
1. Fuel flow has not been calibrated yet.
2. Mixture is full rich at climb out/cruise is leaned somewhat.
3.Temp at Full Rich TO was 455 for #1, I'm not sure of exact changes ROP/LOP
4.Climb rate at Vx was 1800 fpm
5. Airspeed at high temp was 100 kts
6. Probes are in Lycoming wells, bayonet type.
7.To lower temp, lower ROC
8.At high temp: 1/455, 2/454, 3/442, 4/409 Cruise: 1/368, 2/345, 3/333, 4/331
9. Unison; Yes
10. High temp report at full rich.
Any clues?
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Old 02-24-2016, 12:56 PM
vic syracuse vic syracuse is offline
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Join Date: May 2005
Location: Locust Grove, GA
Posts: 2,724
Default Lower the nose

My experience has been that the RV-9's will cool much better with a climb rate around 120 KTS. Even with a fixed pitch prop climb rates are usually around 900-1000 FPM. Climbing at VX for any length of time will cause high temps.

Vic Syracuse

Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, Just Superstol, DAR, A&P/IA, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES/RW
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Old 02-24-2016, 01:08 PM
BobTurner BobTurner is offline
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,911

Get the fuel flow calibrated. Looks like flow may be too low at full power/full rich.
Small issue: I think your oil temps in cruise are on the low side, you may need a plate over the cooler for winter use.
Just to double check, since I see you have chromed cylinders:
Were the correct (not standard) piston rings installed?
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Old 02-24-2016, 01:23 PM
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Dbro172 Dbro172 is offline
Join Date: Apr 2012
Location: West Fargo, ND
Posts: 1,076

What carb? What plane does that engine/carb combo come from? Most likely jetted too lean
Derek Hoeschen
EAA Tech Counselor
RV-9A #92103 - N803DK
G3X, Superior XO-320, Dual Pmags, Catto 3B

1974 Bellanca Super Viking - N16AW - Flying
RV-8 #83565 - N184DK - building
1968 Mooney M20C - N6801N - Sold
1956 C-182 - N744W - Sold
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Old 02-24-2016, 01:43 PM
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N941WR N941WR is offline
Join Date: Jan 2005
Location: SC
Posts: 12,887

Originally Posted by krw5927 View Post
1) Check timing. Advanced timing can cause this. Do you have electronic ignitions or mags?
This is more common than you think.

Even more so if you are running P-mags without the jumper installed.
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
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Old 02-24-2016, 03:29 PM
bluebrear bluebrear is offline
Join Date: Feb 2013
Location: Bethel
Posts: 32

The engine is completely rebuilt Lycoming O-320 B1A S/N L901. Carb was never used (new condition) Marvel-Schebler MA4SPA.
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Old 02-24-2016, 03:30 PM
bluebrear bluebrear is offline
Join Date: Feb 2013
Location: Bethel
Posts: 32

There are Bendix Mags. We'll check the timing.
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