Cylinder 3 and High Oil Temps.

[Xkuzme1]

Hey y’all.

Historically I’ve asked more questions than I’ve answered. So in an effort to be less of a non-contributing-zero, I thought I’d post about my efforts to lower my CHT#3 temps and Oil temps.

F-4 Raider
Lycon IO-360A1B6 220hp

Right now she has just a shade above 5 hours on it. So my temps are still a little high from break in. At about 4 hours nearly all my CHTs dropped 15-20% so I’m assuming that the rings have started to settle in.

My oil cooler is attached to the motor mount behind cyl 4 and air is captured off of the baffling behind cyl 3. Air was routed using a 4 inch scat tube.

Cyl 2+4 chts and egts were nearly identical. No excessive heat, exactly where I’d like to see them.

Oil temps have been as high as 225, but normally we’re 210-215. Cyl#1 typically runs 50° cooler than #3. Cyl#3 with the power pulled back and full rich, is typically 390-410° but at full power I’ve seen it spike quickly past 415°.

I know it is still early to worry about temps with only 5 hours on the engine, but being proactive, I know that a 50° spread and the abnormally high oil temps should be addressed.

What I’ve done so far:
-I’ve put an angled air damn in front of Cyl#1
- washer mod done on both sides and bump (metal formed) behind cyl 3
-RTVd all gaps to promote positive airflow over fins.
-installed an air diverter Behind cyl #3 to make sure air is directed over the cylinder (and not get robbed by the oil cooler or heater box)
-replaced the 4” SCAT with 4” SCEET to try to remove some turbulence inside journey from the air source to the oil cooler.

I know my oil cooler placement is not optimum. But honestly I’m only a little hot. If I could reduce oil temps by 10-15° and even out my CHTs on the right hand side, I’m a happy guy.

My nuclear option is to completely move the oil cooler and reduce the duct size. As of yet, I don’t see a reason to go nuclear.

Thanks for listening to my Ted Talk.

X

 

[Kyle Boatright]

I think your adjustments are appropriate. The air dam on #1 will help. One thing to consider during break-in, particularly in the warmer months, is to use tape to tape off part of the duct that feeds the heater. You need some airflow through the heat muff but taping over half of the opening is gonna help your oil temps and CHT's.

Another thing I'd look at is cylinder fin flash. Look down through the fins and see if there is any flashing you could remove to promote airflow through the fins of the hot cylinder(s). You'll need tiny little files.

So, I'd tape off half of the opening for your heater and fly 5 more hours to see how much the changes help. I'd look at fin flash too. The other thing I will note is that the temperatures on both of my airplanes slowly came down over the first 100 hours or so.

 

[D-Dubya]

It's hard to tell from your pictures, but it looks like there's a heater muff feeding from behind both of the back cylinders. If that's the case, there's a lot of air going through those muffs that's not cooling your cylinders or going through the oil cooler. It's somewhat toasty where I live, so in the warmer months I completely take off my one heater muff and block off the air inlet to it at the back baffle. Even when I'm up high, I haven't had the need for cabin heat this time of year. Of course, depending on where you live, this may not be a viable option. But if you have TWO muffs, I'd remove one for now and re-install it in the fall.

Also, have you confirmed your ignition timing is correct? Looking at the other CHTs, that's not a major concern, but it's worth checking. Lastly, if you have a standard Van's cowl, are the fiberglass "ramps" formed properly on the upper half of the cowling at the air inlets? Those really do smooth out the airflow and reduce turbulence & pressure drop.

 

[Xkuzme1]

It's hard to tell from your pictures, but it looks like there's a heater muff feeding from behind both of the back cylinders. If that's the case, there's a lot of air going through those muffs that's not cooling your cylinders or going through the oil cooler. It's somewhat toasty where I live, so in the warmer months I completely take off my one heater muff and block off the air inlet to it at the back baffle. Even when I'm up high, I haven't had the need for cabin heat this time of year. Of course, depending on where you live, this may not be a viable option. But if you have TWO muffs, I'd remove one for now and re-install it in the fall.

Also, have you confirmed your ignition timing is correct? Looking at the other CHTs, that's not a major concern, but it's worth checking. Lastly, if you have a standard Van's cowl, are the fiberglass "ramps" formed properly on the upper half of the cowling at the air inlets? Those really do smooth out the airflow and reduce turbulence & pressure drop.

I did forget to mention that… the ramps are currently being formed to smooth out the air.

Yes, there are heat muffs in both sides. I may put a “Y” fitting in there and just cap off the one in the right hand side. At least tape it up for now. Right now I have both of those scat tubes connected to fresh air for the cabin. (Each vent has two separate ways to isolate the air coming from the engine bay).

I did open and close those vents to see if it had any effect on oil temp or CHTs and it didn’t seem to make any difference. But I do plan on making some adjustments to them.

 

[D-Dubya]

My bigger concern would be the oil temps. It appears you have plenty of oil cooler surface area back there, but it's just not able to do its job.

The added air diverter behind #3 may be disrupting air to the oil cooler more than it's directing air to the #3 cylinder fins. My next few suggested moves would be to remove that deflector, block off the 1.5" SCAT tube opening behind #3, and possibly install a slightly larger dam at the front of #1. Your #1 cylinder appears to be cooler than all the other cylinders, and a larger dam may allow more air to go to the back. And yes, install the ramps on the top cowling. You will likely have to rework your flexible baffle seals at the front to make all of that work effectively.

Not sure how you are controlling the fresh air coming in through those SCAT tubes...when you close off the air to the cockpit, is the airflow completely dead-headed or does it just divert to the firewall forward area? If it's the latter, that would explain why you didn't see a change when closing the vents. The high pressure air above the cylinders would just be going elsewhere rather than going into the cockpit or cooling the engine. You stated that it's an F-4 Raider, so I'm not familiar with how they typically duct fresh air into the cockpit. RV's use remarkably efficient NACA duct inlets on the side of the fuselage to get fresh air into the cockpit. They have very low drag, a low risk for air contamination, and they don't rob air from engine cooling.

 

[Xkuzme1]

My bigger concern would be the oil temps. It appears you have plenty of oil cooler surface area back there, but it's just not able to do its job.

The added air diverter behind #3 may be disrupting air to the oil cooler more than it's directing air to the #3 cylinder fins. My next few suggested moves would be to remove that deflector, block off the 1.5" SCAT tube opening behind #3, and possibly install a slightly larger dam at the front of #1. Your #1 cylinder appears to be cooler than all the other cylinders, and a larger dam may allow more air to go to the back. And yes, install the ramps on the top cowling. You will likely have to rework your flexible baffle seals at the front to make all of that work effectively.

Not sure how you are controlling the fresh air coming in through those SCAT tubes...when you close off the air to the cockpit, is the airflow completely dead-headed or does it just divert to the firewall forward area? If it's the latter, that would explain why you didn't see a change when closing the vents. The high pressure air above the cylinders would just be going elsewhere rather than going into the cockpit or cooling the engine. You stated that it's an F-4 Raider, so I'm not familiar with how they typically duct fresh air into the cockpit. RV's use remarkably efficient NACA duct inlets on the side of the fuselage to get fresh air into the cockpit. They have very low drag, a low risk for air contamination, and they don't rob air from engine cooling.

The air damn and diverter that are on the right hand side (cyl 1&3) have not been tested yet. Those were made and plan to test those on my next flight.

The air ducts for the scat tubes are for cabin heaters that I have rerouted the ducts to get fresh air into the cockpit. The system is exactly the same as an RV-8 or RV-4. Right now, the scat tube goes from the back baffling straight to the heater box on the firewall (it’s bypassing the exhaust pickup). There is an electrically controlled rheostat door on the firewall.

 

[clam]

How is this going? The baffle seals look a little ”scalloped” in a few places. Possible leak paths.