VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.


Go Back   VAF Forums > RV Firewall Forward Section > Traditional Aircraft Engines
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 05-07-2019, 12:00 AM
msaltzman14 msaltzman14 is offline
 
Join Date: Mar 2017
Location: New York, NY
Posts: 57
Default High CHTs? Going into Condition Inspection, Looking for Ideas

Hi All-

I have an RV9A, bought not built. I've had her about 2 years and put 250 hours on so far.

My CHTs are consistently higher than I'd like, but some associates with RV experience have told me they're warm, but nothing to worry about.

That said, I'm starting to not love what it means for performance, let alone potential safety factors or engine lifetime.

On spring days here in Northern California, I climb out at 105 KIAS and get about 420 CHT on my O-320, 1 p-mag and 1 mangeto. When I come back to 65% power in cruise around 7500, I'm seeing temps like 390. Last week I did a red-line (2700 rpm for fixed pitch) test at 8500 and the temps came up to 416.

I've tried to stay under 400 in cruise always, which can mean I'm not going as fast as I want, especially at altitude. I know the Lyc book says 500 and below is fine, but it just feels totally wrong. Even on climbs to high altitudes, I'm reducing power and climbing flatter to keep the temps below 430.

Anyway, I'm going into my inspection this week and working with a local A&P and I wanted to hear what people think about these temps.

In terms of baffling, there isn't any obvious defects.

Really appreciate thoughts here- is this way warmer than most engines? Something to be concerned about?


Mike
__________________
Mike Saltzman
Flying -9A N7KR
Reply With Quote
  #2  
Old 05-07-2019, 12:25 AM
Lars Lars is offline
 
Join Date: Nov 2005
Location: Davis, CA
Posts: 1,189
Default

A PMag could have more advanced timing than the engine needs, which could make it run hot. But, start with the basics. Remove cowl (upper and lower). In darkened hangar, shine flashlight up from bottom of engine. If you can see light inside the baffled area other than around the fins, you have leaks that need to be plugged. Silicone RTV is your friend. Next verify that the baffle seals are actually contacting the upper cowl, and are facing inward (opposing direction of airflow, so that plenum pressure holds them against the inner cowl surface). That may seem self-evident but I've encountered an overheating RV where all seals were facing away from the airflow. Flipping them inward solved that overheating problem.
__________________
Lars Pedersen
Davis, CA
RV-7 Flying as of June 24, 2012
1120+ hours as of August 17, 2021.
Reply With Quote
  #3  
Old 05-07-2019, 06:12 AM
titanhank titanhank is offline
 
Join Date: Aug 2007
Location: Friendswood, Tx
Posts: 476
Default

Good advice so far, check baffles, check timing. If this does not get it done, if equipped, pull the carb and drill the jet. My rv6 with a 320 always ran a little hot. I pulled the carb and it had a #42 main jet. I drilled it to #37 and it runs perfect now. I went one drill bigger than recommended due to the port/polish job and 10-1 compression. Most 320’s will need a #38. My fuel flow went from 10gals/hr at takeoff to 14gals/hr. I also changed from a fixed pitch to constant speed prop. The fixed pitch prop will mask the problem due to the lower rpms at takeoff requiring less fuel. As it unloads in the climb, the fuel requirements will increase to more than is available through the jet hence the higher temps.

Here is the link to the document to support the change.

https://drive.google.com/file/d/0B-S...ew?usp=sharing
__________________
Harmon Rocket #1
IO-540
10-1 pistons

1959 Piper PA22-150 Tri-Pacer

Rv7a sold
Rv6 sold
Rv4 sold
Rv3 sold
Reply With Quote
  #4  
Old 05-07-2019, 07:06 AM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,322
Default

Good advice on the timing check, also on checking the baffles, and carb. Basics, do these and know definitively what they mean.

Timing, leaks and mixture are the the three huge factors and all can be easily managed/repaired to yield a well performing cooling profile.

Mike, regarding your baffles, it does not take much, and many of those add up quickly. The full speed at 8500 is the most revealing. Speed should provide all the cooling you could need, but it did not.

Leaks, take a 2" piece of soda straw (material does not matter ) blow through as hard as you can, and feel the blast. Imagine a dozen of these.

Don't think about it, just seal all the cracks, gaps and holes that leak. NO gaps are acceptable. It will make a huge difference assuming the timing and mixtures are in range.

Good luck, do some research and post some pictures for comment. Comments will help tune your sight picture.

When you report CHT, do also report ambient temp too. The cat-ambient delta is key for comparing different conditions.
__________________
Bill

RV-7
Reply With Quote
  #5  
Old 05-07-2019, 07:10 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 10,356
Default

This is a Lycoming cooling chart for the 320. It assumes typical cylinder and head baffling (the wraps) and 25BTDC ignition timing.

I've plotted two examples. In red, the difference between the upper and lower plenum pressures is 4" of water, and air density is standard for 5000 feet. If OAT is (ballpark) 57F, the air at the engine face will be about 60F, so the chart tells us to expect 435F CHT at 75% power and best power mixture (0.51 BSFC). Mass flow is about 1.5 lbs per second.

In green, same altitude, but now 6" deltaP. CHT will be somewhat lower at the same OAT and power setting. Mass flow is 2 lbs per second.

Advanced timing and lean mixtures can push CHT upwards, but the majority of cooling issues are just failures to supply enough mass flow in contact with hot metal.

The Pmag unquestionably contributes to higher CHT. As for mixture, there is no point in drilling a jet until after establishing full rich EGT in relation to peak EGT.

__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #6  
Old 05-07-2019, 08:18 AM
titanhank titanhank is offline
 
Join Date: Aug 2007
Location: Friendswood, Tx
Posts: 476
Default

Quote:
Originally Posted by DanH View Post
This is a Lycoming cooling chart for the 320. It assumes typical cylinder and head baffling (the wraps) and 25BTDC ignition timing.

I've plotted two examples. In red, the difference between the upper and lower plenum pressures is 4" of water, and air density is standard for 5000 feet. If OAT is (ballpark) 57F, the air at the engine face will be about 60F, so the chart tells us to expect 435F CHT at 75% power and best power mixture (0.51 BSFC). Mass flow is about 1.5 lbs per second.

In green, same altitude, but now 6" deltaP. CHT will be somewhat lower at the same OAT and power setting. Mass flow is 2 lbs per second.

Advanced timing and lean mixtures can push CHT upwards, but the majority of cooling issues are just failures to supply enough mass flow in contact with hot metal.

The Pmag unquestionably contributes to higher CHT. As for mixture, there is no point in drilling a jet until after establishing full rich EGT in relation to peak EGT.

Dan is right. You should have 150-200 degs from full rich to peak available with the mixture knob. My engine, with a #42 jet was already at peak. After drilling to #37, i now have 170degs from full rich to peak available. Your engine will never run cool with the stock jet in a carb.
__________________
Harmon Rocket #1
IO-540
10-1 pistons

1959 Piper PA22-150 Tri-Pacer

Rv7a sold
Rv6 sold
Rv4 sold
Rv3 sold
Reply With Quote
  #7  
Old 05-07-2019, 10:06 AM
Toobuilder's Avatar
Toobuilder Toobuilder is offline
 
Join Date: Jul 2009
Location: Mojave
Posts: 4,841
Default

The Pmag aggressive timing curve hurts, but since you only have one it softens the effect quite a bit. Is the jumper in or out? Assuming timing is correct, you have enough mixture control, and the intake tubes are not leaking (if they aren't, they will), then you are down to baffling. Many people have no idea what is required. They must be tight. This means more than the rubber against the cowl. This means the factory installed intercylinder baffles are bent to make contact with the case and cylinder bases and sealed with RTV. Cylinder 2 & 3 need the bypass ducts. The inlet ramps need to seal the cowl inlets perfectly. The baffle tin needs to be sealed with speed tape and RTV so there are no gaps. In short, any air that comes in the cowl MUST pass through cylinder fins before it can be allowed to escape. This takes a bunch of time but will pay off.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
Reply With Quote
  #8  
Old 05-07-2019, 11:48 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,721
Default

I agree that baffling is the likely issue here. I run aggressive timing and still have 360* CHTs at cruise in warm weather (2700 RPM cruise, LOP) and likely not the best baffling. If I were to advance my timing more at cruise, power would fall off and so would the CHT's (they may spike a small amount before declining). If the red knob is anywhere other than full in, your main jet is not the issue. Titanhawk is correct, that you will need a bigger jet to get good fuel flow at full rich in high power demands, such as low altitude climb. However, once you start pulling the red knob back, you are restricting flow before the jet, so jet size is not an issue. Your main jet only restricts flow at full rich. Generally speaking, once you start pulling the red knob, the mixture control valve is restricting flow, not the main jet. I do concur that you will likely need to drill the main jet to get your CHTs down in the t/o and climb, but it won't help your 8K cruise.

A well baffled 320 should deliver well less than 415* in cruise at 8K'

Many good posts here to search as you undergo efforts to improve your baffling.

Larry
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019

Last edited by lr172 : 05-07-2019 at 11:57 AM.
Reply With Quote
  #9  
Old 05-07-2019, 12:04 PM
sglynn's Avatar
sglynn sglynn is offline
 
Join Date: Mar 2008
Location: Anacortes, WA
Posts: 833
Default CHTs and leaks

I'm just 10 hours into Phase I with IO360 and CS Prop. My CHTs are running 380 - 390F. they will go 420+ on full RPM climb out. So I'm reading this thread with eye on sealing leaks. I have not used RTV to seal leaks because the few leaks I have are very small especially compared to the two holes I have for tubing that blows air on the mags and the large hole that sucks air for the heater. Are cooling tubes for Mags really needed? Would moving the heater inlet hole to the engine inlet ramp make much difference. I guess I'll tape over these and see.

What are "normal" CHTs on a 70F day at 25x25 square climb at 110kts 1000 - 3000' msl.?
__________________
Steve Lynn
Built RV-7A
Flying It
Anacortes, WA
www.mykitlog.com/sglynn
Reply With Quote
  #10  
Old 05-07-2019, 12:51 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 10,356
Default

Quote:
Originally Posted by sglynn View Post
Are cooling tubes for Mags really needed? Would moving the heater inlet hole to the engine inlet ramp make much difference.
Don't get me started on blast tube requirements.

As for results, Bobby Looper (then working at ECI-Titan) once posted that a 1" diameter hole would drop deltaP by 1" of water. I have not confirmed it independently, but I have no reason to doubt it. According to the Lycoming cooling charts, every inch counts. Two or three inches deltaP is a Big Deal.

Moving the inlet to the ramp would make no difference. It's still a leak, trying to equalize the upper and lower pressures.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 10:53 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.