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Old 04-11-2018, 02:47 PM
WingnutWick's Avatar
WingnutWick WingnutWick is offline
Join Date: Jun 2013
Location: Fresno, CA (KFCH)
Posts: 272
Default RV-8 O-360 Temps and Fuel Flow issues

Hello all,

Just wanted to push out to all of you to see what you guys think about some of the engine issues I have. O-360, fixed pitch, dual P-Mags, Dynon D10 EMS. CYL #3 runs VERY hot even on cold days, even in cruise with CYL 2, 4 not too far behind. CYL 1 runs much cooler than the others. You can see some temps I see on climb and cruise taken on a winter day at altitude. Anything slower than a 100 KT climb will have my #3 CHT shoot to above 430 rapidly.

Also on climb out and WOT I will see my fuel pressure typically drop quickly from a nominal 3-4 PSI to .5 and 0 PSI which sets off the alarm. I've noticed this is often accompanied by an increase in fuel flow. Turning on the electric pump will push these up to 4. Securing the electric pump, the PSI will gradually decrease again to .5-0. Once throttling back to cruise settings the fuel pressure will climb back to nominal.

I am wondering if any of you have any ideas on the fuel flow and the over heating. What's a good way to check the baffles? Are there any good plenums out there for my configuration that has shown good success in cooling so I can do away with worrying about baffles? Searching through the threads it seems adding a washer helps with cooling but I'm not quite sure where that washer is being added....any photos to show this?

Otherwise the motor runs nicely and no noticeable performance issues associated with the drop in fuel PSI.

Any input is greatly appreciated!

F-18E/F, Mk.58, CF-5
Own: RV-8 & RV-10

Last edited by WingnutWick : 04-11-2018 at 05:10 PM.
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Old 04-11-2018, 04:12 PM
drill_and_buck's Avatar
drill_and_buck drill_and_buck is offline
Join Date: Feb 2005
Location: Bridgewater, MA - KPYM
Posts: 479

I have a similar setup with the exception of the prop (Hartzell). Here are my observations.

On a cold day, if I climb with a high angle of attack, my fuel pressure (not fuel flow) will occasionally drop to zero. My fuel flow remains healthy and all other engine parameters are in the green. Turning on the electric boost pumps remediates this. I think the problem may be with the sensor or could be air in the line.

I tend to climb out at 120kts. Anything slower and CHTs will rapidly rise. Due the angle of your climb you have a significant reduction in airflow over the cylinders. High power + reduced flow = high chts.

Your CHT spreads indicate that you most likely have some improvements to make in the baffling. There are plenty of suggestions in the forums on checking your baffles. Here is an example: Look for others. There is no one magic bullet. Collectively they can significantly reduce CHTs. You should do whatever it takes to keep your CHTs below 400.

After you have implemented all the baffle fixes you can always add a cowl flap on the bottom of the cowl. This will allow you climb at a higher angle of attack or join the 90 Kt conga line to KOSH without overheating.
Mike Draper
RV-8 N468RV
First Flight 11/13/2011
TMX0360, Dual Pmags, CS
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Old 04-11-2018, 04:42 PM
BillL BillL is offline
Join Date: Sep 2007
Location: Central IL
Posts: 6,328

Two suggestions (if not done already & assuming you have checked for mixture issues)

1. Progressively block the front of #1 to warm it up and deflect air back to #3.

2. Open up the back side of #3 where the fins are too shallow. Search for the "washer trick" but better to make a proper chute for it. Many example here. Email me if you want a template for the chute, and a picture of the install. (also here on VAF)

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Old 04-11-2018, 05:18 PM
WingnutWick's Avatar
WingnutWick WingnutWick is offline
Join Date: Jun 2013
Location: Fresno, CA (KFCH)
Posts: 272

Mike and Bill,

Thanks for the info and suggestions. Bill, you mention mixture issues: what do you mean in particular? Running it too lean? Even at full mixture it'll drop the CHT's a little but not by much. I would love a template for the chute if you don't mind sending it my way!


F-18E/F, Mk.58, CF-5
Own: RV-8 & RV-10
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Old 04-11-2018, 08:30 PM
Dreamin9 Dreamin9 is offline
Join Date: Aug 2016
Location: Near Buffalo, NY
Posts: 71
Default Full Power FF

If the problem still persists after messing with baffle seals and other airflow solutions, check your FF at full power.
It seems some RV engine installs run lean. My O-320 160 was showing 11.8 gph at 98% power. The Lycoming manual says it should be about 13.9. Some say FF should be .9gph for each 10 hp at full power.
I recently had my carb jet reamed going from 42 to 40 and FF went to about 12.8. Further testing is needed to look for CHT improvements.

Good luck with the hunt.
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Old 04-11-2018, 09:54 PM
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Dbro172 Dbro172 is offline
Join Date: Apr 2012
Location: West Fargo, ND
Posts: 1,076

Can you post some pictures of your baffles and cowl inlets? I chased this with every suggestion and when i finally switched to McFarlane cowl saver baffle seals and made sure that they were fully tucked behind the sides of the inlets I saw a drastic improvement in temps, like 30-50 degrees. Now my #3 actually runs coolest, even without the washer...
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 04-12-2018, 05:55 AM
humptybump humptybump is offline
Join Date: Feb 2011
Location: USA
Posts: 3,181
Default Fuel pressure drop with fuel flow rise

I've seen my fuel pressure drop and fuel flow climb (signifantly). I see this when I'm running a tank to empty. In my airplane it indicates I'm getting air in my fuel.
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Old 04-12-2018, 07:44 AM
Toobuilder's Avatar
Toobuilder Toobuilder is offline
Join Date: Jul 2009
Location: Mojave
Posts: 4,845

The zero fin depth issue on #3/5 and #2 is a well understood cause of most of these temp issues. The bypass duct solution is a proven fix for the deficient baffle design.

As often as this question comes up, perhaps its time to collect the various "bypass duct" threads and make a sticky? If Vans is not going to fix their baffles, at least this site can provide an easy resource for builders/operators to do so on their own.
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
1940 Taylorcraft BL-65
1984 L39C
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Old 04-12-2018, 09:35 AM
Raymo's Avatar
Raymo Raymo is offline
Join Date: Nov 2014
Location: Richmond Hill, GA (KLHW)
Posts: 2,340

You mentioned dual P-Mags. Make sure you have the jumper installed between 2 and 3 on the connector or, better yet, connect your computer and drop the Adv Shift to 0 or -1.4 and your Max Adv to 36.x.

If set via computer, you don't need the jumper installed.
RV-7A - Slider - N495KL - First flt 27 Jan 17
O-360-A4M w/ AFP FM-150 FI, Dual PMags, Vetterman Trombone Exh, SkyTech starter, BandC Alt (PP failed after 226 hrs)
Catto 3 blade NLE, FlightLines Interior, James cowl, plenum & intake, Anti-Splat -14 seat mod and nose gear support
All lines by TSFlightLines (aka Hoser)
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Old 04-12-2018, 11:20 AM
Red Rooster Red Rooster is offline
Join Date: Feb 2017
Location: savannah
Posts: 11

I have the same issues w/ CHT & FF, but.........

One P-mag on a 0-230-D2B w/ Vetterman exhaust RV6 TD. Installed a JPI EDM 830 w/ FF and P-mag at the same time with the jumper . Tons of power, and high CHTs. #3 would reach 425 in climb and full power cruse no matter the altitude. Powering back to 2200 RPM reduced CHT temps.

But.... was able to have low CHTs, after building the harness for the Eicad and setting -1.4 for the shift and 36.4 for the max.Though it feels like some power was lost.

My FF is also low, 11.6 on take off and 12. 8 on climb out. Cruse is high 11's.
Not sure whats up with this. The FF gauge that the JPI replaced was showing 13 something on climb out. The carb was sent to the manufacture 4 years ago for a overhaul. They said the carb was bench flowed at 14 gph.

Both gauges are pretty accurate with fuel used / fuel remaining in reference to how much fuel I put in when at the pump.

I would think more fuel would equal for power / heat?

Any insight is welcomed
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