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Yet another “my engine is running hot” thread

00Dan

Well Known Member
BLUF: my CHTs are running high in both climb and cruise, and my oil temperature is running almost up to redline.

Rather than piggyback on my detonation thread I figured I’d start over with a new baseline of what I’ve tried so far. Today I flew and tried a 3500’ 2400 RPM lean test I read about in another recent thread about carb nozzle size.

https://apps.savvyaviation.com/beta/shared/flight/6985417/be3f4097-6137-4041-8f38-5053deca4858

You can see the results of that test between 13-15 minutes.

The CHTs at climb out are easy to see in that entire graph. After the lean test I tried a climb to 11,500’ and had to terminate that at about 10,000’ due to oil temperature reaching redline.

What I’ve done so far:

New silicone baffle strips sealed as best I can using a dark hangar with the top cowl on and a borescope to see how it is all sealing up.

Every hole I could find on the baffles sealed with RTV. I used a shop light underneath the engine and hit anything that wasn’t through a fin.

Fiberglass RTV baffle wraps - including checking that I didn’t inadvertently block any fins.

Taping off the gaps between my cowl and the baffles around my Cessna style airbox, at the inlets, and blocking the blast tubes pointed at my magnetos.

Reamed the carb main jet to .1065” and validated float height.

What I haven’t done yet:

Investigate the vernatherm.

Instrument the cowling for pressure differential measurements.


Some basic info for reference:

O-320 with 10:1 pistons

7 row oil cooler mounted on the firewall fed by a 3” SCAT hose tapped from the back baffling wall above cylinder #4. The oil lines are AN-8s.

MA-4 10-3678-32 carburetor with 47-862 nozzle reamed to .1065” diameter.


What am I missing here? I’m banging my head against a wall trying to find a smoking gun and even my incremental changes aren’t yielding results.
 
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thanks for posting the Savvy graph. From that I saw the ground temp was 91F.

Well, anyhow... Notable that really they ALL are running hot. My guess is you are missing a biggy somewhere.

Common biggies:
  • upper cowl Ramps - fully missing, or providing a route to fully bypass the engine
  • seals at the front of the engine - between cowl and baffles in the flywheel and inlet areas
  • no seal between the chin air inlet (assuming you have one) and the airbox, allowing lots of air into the lower cowl, pressurizing it, preventing good down flow through the engine
 
Have you tried adjusting the mag timing?
After going thru all the steps you mentioned, plus cleaning up the outflow area, and measuring pressure differentials, the last big increment of improvement was changing the mag timing. I reconfigured the harness to fire all of the bottom plugs with the right mag, and all of the top plugs with the left. Then ended up with the right mag at 24BTC and the left at 22BTC. Now, climb CHTs are all right at 400, and cruise at 360
 
thanks for posting the Savvy graph. From that I saw the ground temp was 91F.

Well, anyhow... Notable that really they ALL are running hot. My guess is you are missing a biggy somewhere.

Common biggies:
  • upper cowl Ramps - fully missing, or providing a route to fully bypass the engine
  • seals at the front of the engine - between cowl and baffles in the flywheel and inlet areas
  • no seal between the chin air inlet (assuming you have one) and the airbox, allowing lots of air into the lower cowl, pressurizing it, preventing good down flow through the engine

Upper cowl ramps are present, and the baffles around the front of the engine all seal up as best as I can tell. There was a gap between my air filter and the lower cowl that I used tape to seal.

Have you tried adjusting the mag timing?
After going thru all the steps you mentioned, plus cleaning up the outflow area, and measuring pressure differentials, the last big increment of improvement was changing the mag timing. I reconfigured the harness to fire all of the bottom plugs with the right mag, and all of the top plugs with the left. Then ended up with the right mag at 24BTC and the left at 22BTC. Now, climb CHTs are all right at 400, and cruise at 360

I have two slick mags that are timed to 20* BTDC.
 
I would recommend changing your magneto timing to 19° to 17° BTDC since you're running 10:1CR.

edit: What happens at 00:20:37? Can you export IAS/GS/ALT/DALT, etc? Also, the RPM is all over the place -- are you adjusting it or ????
 
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CHTs look okay. I'd look at the vernatherm. You can put it in boiling water to make sure its working. Doesn't take too long.
 
Peak FF looks a little low at only 12 GPH. HP values don't seem to be set right - is it possible that the EDM needs calibration?
 
The vernatherm "moving" in response to boiling water is one thing - getting the plunger to properly seat and force all the oil through the cooler is quite another.

The addition of the viscosity valve is a cheap and easy way to ensure all the oil goes through the cooler.
 
You are in MS….warm in winter … heck Id remove vernatherm and fly, no change put it back in ( you’ll need a plug) Which Slick mags #s , left and right. What does mag data plate states timing setting should be. Vendor of your EIS? I run o320, slick, 8:5:1 160 HP@2700rpm. Does topping off tend to agree with EIS FF ? Mine within a quart:). With your info, and my knowledge ( limited) , I feel like it is a mag timing issue. Nothing seems amiss from baffling….so lowering the nose gives nothing noteworthy , gotta be timing or TOO MUCH HP ( never tight ) Looking forward to hearing your solution when you get there. Try the in-air mag test Savvy offers on their site too.
 
Upper cowl ramps are present, ...

OK, that answers half of my question. I'll be more detailed... do your side baffles have scalloped out curves to seal against the bottom of the upper cowl ramp? Or are the ramps cut short on the outboard side and the side baffles run up to touch the cowling alongside the ramps?

See this post https://vansairforce.net/community/showthread.php?t=57495

There is an opportunity for top cowl air to get into the ramp 'tunnel', and depending on how things are done, the other end of the 'tunnel' may be a direct path bypassing the upper cowl!
 
I would recommend changing your magneto timing to 19° to 17° BTDC since you're running 10:1CR.

edit: What happens at 00:20:37? Can you export IAS/GS/ALT/DALT, etc? Also, the RPM is all over the place -- are you adjusting it or ????

Not sure what event you’re seeing at that time stamp. As for RPM, it’s a fixed pitch prop and I flew in the heat of the day.

Peak FF looks a little low at only 12 GPH. HP values don't seem to be set right - is it possible that the EDM needs calibration?

The HP function specifically is not calibrated. Everything else is.

You are in MS….warm in winter … heck Id remove vernatherm and fly, no change put it back in ( you’ll need a plug) Which Slick mags #s , left and right. What does mag data plate states timing setting should be. Vendor of your EIS? I run o320, slick, 8:5:1 160 HP@2700rpm. Does topping off tend to agree with EIS FF ? Mine within a quart:). With your info, and my knowledge ( limited) , I feel like it is a mag timing issue. Nothing seems amiss from baffling….so lowering the nose gives nothing noteworthy , gotta be timing or TOO MUCH HP ( never tight ) Looking forward to hearing your solution when you get there. Try the in-air mag test Savvy offers on their site too.

I don’t have the mag model #s off hand but can get them - they came with the engine. Last time I calibrated the k-factor the totalizer agreed with the pump within 1/10th of a gallon.

OK, that answers half of my question. I'll be more detailed... do your side baffles have scalloped out curves to seal against the bottom of the upper cowl ramp? Or are the ramps cut short on the outboard side and the side baffles run up to touch the cowling alongside the ramps?

See this post https://vansairforce.net/community/showthread.php?t=57495

There is an opportunity for top cowl air to get into the ramp 'tunnel', and depending on how things are done, the other end of the 'tunnel' may be a direct path bypassing the upper cowl!

See photos.

RV4 ?…..thanks. Are you burning 100LL ?

Yes and yes.
 

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Assuming you have the inter-cylinder baffle in place, all the baffles looks like they are pretty effective, and probably not your problem. I'd have to agree with OK, Butch, and Brian that you might want have someone look at your timing.
 
Here’s my flight today:

https://apps.savvyaviation.com/beta/shared/flight/6990741/cbfd4bc2-0f5d-44e1-b73f-75b82717b692

I cruised at 7500’ just slightly LOP. Anecdotally, I’m not sure if the oil cooler is getting much air. My cabin heat is tapped off the oil cooler exit (it’s a door that switches the outlet between either the lower cowl plenum or into the cabin at my feet). When I open it I don’t feel much air coming out, whereas on the old installation I could.

On timing, when I first installed the engine I timed it to 25* and experienced detonation at WOT. I then turned it back to 20* and reamed the jet, which solved the thermal runaway. I haven’t checked the timing again since I last adjusted it. I did use new star washers so I would think it hasn’t shifted but who knows.
 
What is your IAS in climb for all the graphs?

Depending on climb, the CHTs don't seem really bad, although may be a little high. The cruise oil temps on the last graph are around 190ish. Not so bad either.

Airspeed is not known here and that will generate the pressure for cooling mass flow. Clearly that will affect the temps.

What are you expecting for the CHT's? For climb (IAS?) and cruise?

Do you have a photo from the front with cowl on looking straight at the cooling inlet? I have a visual perspective confusion when looking at the bottom of the cowl due to lack of depth indication and shape of the cowl underside.
 
What is your IAS in climb for all the graphs?

Depending on climb, the CHTs don't seem really bad, although may be a little high. The cruise oil temps on the last graph are around 190ish. Not so bad either.

Airspeed is not known here and that will generate the pressure for cooling mass flow. Clearly that will affect the temps.

What are you expecting for the CHT's? For climb (IAS?) and cruise?

Do you have a photo from the front with cowl on looking straight at the cooling inlet? I have a visual perspective confusion when looking at the bottom of the cowl due to lack of depth indication and shape of the cowl underside.

120-130 IAS for most of the climb. For climb I’d like to get the CHTs well below 400 in a 120 kt climb. At a LOP cruise at 40*F I’d expect less than 350*. My goal would be to get enough margin that I could conceivably turn the timing back to 25*.

I’ve attached some pictures of the inlets (I’ve since fixed the curl on the lip baffles.)
 

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Yes, would agree you have something that could be addressed with these temps and a 120kt climb. Nothing jumps out on the inlets from the photo.

The only other item is the exit area and/or internal stuff. It looks like you are on the right track.

Maybe you can find an experienced RV guy in the region to consult and get some eyes on it.
 
OK Dan, thanks for the ramp pictures. It looks like those are all good. Tick that off the list.

I do note that you don't have the "conical gussets" installed in the baffles. These are located on the inlet (lower) ramps, outboard between the ramp and the side baffle. They are roughly conical in shape (or at least a 45 degree) and helps smooth the air flow. In you picture I can see a hard 90 degree joint on both left and right outboard. It isn't going to gain you 20F, but it will help a little. Sometimes it is just a bunch of little stuff.

PS, with 10:1 I don't know that you'll ever get the timing back to 25 degrees on mags.
This is where electronic ignitions are handy... set at 20 for default full power, and will auto-advance as you climb and the % power goes under 70.

More thoughts... let's see your spinner prop blade cut-outs. And what kind of prop is fitted? Fixed I'm guessing?

-Bryan
 
I flew over to another builder’s hangar today and we looked at my baffling together. As best as he could tell, the top baffling is sealed up properly. We shortened the SCAT tube running from the baffling to the oil cooler in an attempt to minimize any flow losses on the tubing ridges. We also removed my carb heat muff to airbox scat hose on the theory that it may have been slightly throttling exit area due to how it was run. I only flew 20 miles back to my hangar after but I didn’t see any changes that marked either of those items as a silver bullet.

I have a vernatherm on my old engine that I know was working when it was last used; I may try swapping it in just to try and eliminate an error source for the oil temperature. Beyond that may involve figuring out if I need to upsize my cooler (not sure if there is a science to that)


OK Dan, thanks for the ramp pictures. It looks like those are all good. Tick that off the list.

I do note that you don't have the "conical gussets" installed in the baffles. These are located on the inlet (lower) ramps, outboard between the ramp and the side baffle. They are roughly conical in shape (or at least a 45 degree) and helps smooth the air flow. In you picture I can see a hard 90 degree joint on both left and right outboard. It isn't going to gain you 20F, but it will help a little. Sometimes it is just a bunch of little stuff.

PS, with 10:1 I don't know that you'll ever get the timing back to 25 degrees on mags.
This is where electronic ignitions are handy... set at 20 for default full power, and will auto-advance as you climb and the % power goes under 70.

More thoughts... let's see your spinner prop blade cut-outs. And what kind of prop is fitted? Fixed I'm guessing?

-Bryan

Correct, no conical gussets. I think these baffles predate those being added to the plans. I’m running a 3 blade Catto with a 12” Catto spinner, so the cutouts are factory. Picture attached.
 

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Temps

You need at least 4" duct for your oil cooler. Better yet would be to mount the cooler behind cylinder #3 tilted back as much as possible with a sheet metal bracket which also serves as duct.
I have 0 320 10-1 on my Wittman Tailwind I started out with 22 degree timing and am now at 25. I have a plenum and cowl flap and climbing 1t 130 knots keeps the CHT at around 375, never over 400 as long as I keep the speed up.
 
Correct, no conical gussets. I think these baffles predate those being added to the plans. I’m running a 3 blade Catto with a 12” Catto spinner, so the cutouts are factory. Picture attached.

Yeah, well, they (the gussets) got added for a reason. Worth installing. No silver bullet but will help a little and is an easy afternoon's work.

Those cut outs in the spinner are HUGE!!! And there's no filler (that I can see) on the back side of the blade, between the blade and the backplate. That all leads to very messed up airflow right as you are trying to get it into the cowl inlets. Take a look at the first two pictures HERE: http://www.dualrudder.com/rv7/category/prop-spinner/

The large gap can be filled with some leather so that air doesn't flow around the blade inside the spinner.
 
The other day flying a short hop I climbed to 3000’ and let the plane accelerate at full rich and WOT. At almost 2800 RPM I noted that CHTs had settled in around 410 with a fuel flow of just over 13 GPH. Airspeed was around 165 knots indicated.

I’ll pull the monitor data next time I’m at the plane but I gotta wonder if I’m still running to lean down low. I’ve already opened up the main carb jet once and based on my research I have the richest possible carburetor for a 320. I previously checked my fuel system delivery at the carb inlet and measured 23 GPH with just the electric pump.
 
The other day flying a short hop I climbed to 3000’ and let the plane accelerate at full rich and WOT. At almost 2800 RPM I noted that CHTs had settled in around 410 with a fuel flow of just over 13 GPH. Airspeed was around 165 knots indicated.

I’ll pull the monitor data next time I’m at the plane but I gotta wonder if I’m still running to lean down low. I’ve already opened up the main carb jet once and based on my research I have the richest possible carburetor for a 320. I previously checked my fuel system delivery at the carb inlet and measured 23 GPH with just the electric pump.

Something to consider is that with 10:1 compression and 2800 RPM, you *should* be using more fuel than a stock 160 HP O-320 running 2700 RPM. So even if you have the richest O-320 carb, it may not be enough for your configuration.
 
Perhaps something I missed in the thread above, but have you confirmed that you are getting full throw on both the throttle and mixture levers at the carb?
 
The other day flying a short hop I climbed to 3000’ and let the plane accelerate at full rich and WOT. At almost 2800 RPM I noted that CHTs had settled in around 410 with a fuel flow of just over 13 GPH. Airspeed was around 165 knots indicated.

I’ll pull the monitor data next time I’m at the plane but I gotta wonder if I’m still running to lean down low. I’ve already opened up the main carb jet once and based on my research I have the richest possible carburetor for a 320. I previously checked my fuel system delivery at the carb inlet and measured 23 GPH with just the electric pump.

Not enough data. What was the MAP? I will say again, the determining variables for appropriate fuel flow requires BOTH RPM and MAP. If we assume 27" of MAP, a 320 should be fed a bit over 13.5 GPH at 2700 to stay on the conservative side set by Lyc. Chart does not go to 2800 as it is beyond redline, but can interpolate that at a bit over 14. These are conservative and speculate that 13 GPH is near or slightly richer than best power (~ 80* ROP). Generally speaking, CHTs are highest mid way between best power and peak EGT. MINIMUM fuel flow at 100% power for a 320 (8.5:1) is just over 13.5.
 
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Looking at your earlier photos... it looks like the blue silicone on the right side inlet is cut just about even with the baffle metal ramp. I can actually see a bit of a gap there. In flight the inlet air pressure is probably pushing the blue baffle down, so that there's a big leak from the inlet directly into the lower cowl.
 
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