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Temperature control on O-360

Mtherr

Well Known Member
Patron
Lycoming recommends not exceeding 400F CHT for continuous operations and Mike Bush, recommends not exceeding 400F CHT, period. Max cooling rate should also not exceed 50F per minute.

Well, no matter how hard I try, seems I cannot always respect those limits; especially when doing circuits.

On first takeoff, after warm-up and run up, I will get temperature on no 3 cylinder reaching 415 to 430F. This with reduced throttle and decreased angle of climb (faster speed) (90-110KT).

While I seem OK to control cooling rate on descent and landing, I cannot get much less than 55F/min doing circuits, after climb and when turning downwind.

Interestingly, i can keep CHT lower than 400F when climbing doing circuits, but the rate of ascent is not what I was dreaming about with a RV.

Any tricks? Opinion?
 
It is not a slow speed airplane. Some cool better than others and while you can help that with some attention to the cooling, operation is important too. When working in the pattern, throttle back early and climb with lots of horizon showing. Cooling increases with the square of the speed. Heat is generated with higher engine rpm and power. Assuming always rich in the pattern. Adjust accordingly and if your bird is exceeding temps compared to others, then look for cooling improvements.

I have CS prop and reduce to 2500 at 200ft and throttle back more for patterns than for normal climb. The thermal mass of the system helps slow temperature rise, but find it necessary to go to a near by airport in lean cruise to cool it off before doing more circuits.

You can lower temps up to 20-30F if the cooling system has leaks. You likely do. Timing plays a big part in heat generation, so be sure it is not advanced at your altitude and speeds. Throttling back is less helpful if the timing advances. It sounds like cooling improvement is something you need to address. Do some research using google to search the site, and post pictures for feedback on specific areas of interest. Details greatly matter in sealing the baffles, small holes, gaps between baffles and case etc. There are many opportunities for air to bypass the fins.

Have fun in developing your plane and procedures.
 
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Your #3 cylinder is running hot, while 1,2, and 4 are OK.

The casting of the cylinder from the factory on the Rear of #3 creates an air dam preventing proper airflow if the baffling is installed IAW the vans baffle kit instructions. There are ways to create a gap to open up the dam and allow airflow to pass over this area. That might help.

Read this thread.
https://vansairforce.net/community/showthread.php?t=37835
 
...
Interestingly, i can keep CHT lower than 400F when climbing doing circuits, but the rate of ascent is not what I was dreaming about with a RV.

Any tricks? Opinion?
What kind of prop do you have? A 360 should get you some really good climb performance - if you are not getting that, might need to check some things.
 
What is your fuel flow and RPM during the climb where you see the high cht's? Carb/injected? Mixture plays a dominant role in CHT's. Also please report the OAT, since CHT will track that.
 
Try a higher speed climb. Try 120 knots, that helps significantly with mine.

Outside air temp plays a big roll too. If OAT is 60 degrees or less, I have no issues. If it's warm out, I have to pay attention and keep the speed up.

Lots of threads on trying to get the back cylinder to cool. I have the same issue in mine. I've worked my baffeling alot and it has helped, I still have a little more work to do.

I live in a very hot area, I'm planning on adding a cowl flap just to help with temps in the hot summer.
 
Bcone, thanks! I will look into this. Great information

Mickey. Sensenich FP 72X85. I was still climbing above 1000fpm, but to control temperature, I was reducing throttle significantly.

Alex. I have to go back and pay attention. At full throttle, I was above 60 litres per hour (17gph), full rich. My engine is not injected (O-360-A1A). It is not yet hot here in East Canada. Yesterday was 16C (60F) when I was flying.

From the various responses. Should I understand that it is not normal to go into the 400s on initial climb?
 
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From the various responses. Should I understand that it is not normal to go into the 400s on initial climb?

It isn't preferred, but depending on how good your baffling is, timing, how aggressive you climb will all effect your CHT. It will be a bigger problem in the summer and when the plane is heavier.

It is preferred to keep your CHT below 400, but short periods of time in the lower 400's aren't a big problem in my opinion. You will likely need to do some work with the baffling to try too cool the rear cylinder more. I will admit that I routinely hit 400-430 on initial climb in the summer, but I work really hard to keep it below that. I have perfect temps in cruise. Its just an airflow issue. You likely need to seal gaps and try to get more airflow to those back cylinders to bring the temps down. Its a lot of trial and error.
 
Michel, the folks saying climb at a higher airspeed are entirely correct. Dynamic pressure is the source of the pressure differential which forces cooling mass (air) down through the fins. Available dynamic pressure increases by roughly 50% when going from 100 to 125 knots.

RPM reduction is also effective. The old NACA papers said "Cooling demand is proportional to mass flow". Our engines are air pumps with mass flow roughly proportional to RPM.

Having boosted cooling mass flow and reduced combustion mass flow, the next job is to increase heat transfer. You want every molecule of air which passes through the cowl to carry away as much heat energy as possible. This is where effective baffling and zero leakage come into play. Cowl exit air temperature is a pretty good yardstick. Some guys with hot engines have rather cold exits.
 
I noticed a fairly large opening 1 inch wide by almost 1 inch deep at the base of the cylinder no 3. The baffle is straight, but where the cylinder has no more fins, all that area is open. Should I close this? Seems that this is useless....

Outside of this, I do have a conduit to the oil cooler behind that cylinder (a 3 inch SCAT) and a 1 inch conduit (or 3/4 inch) to cool the magneto.

I also check about increasing the clearance behind the fins (with a washer)... seems not relevant for the O-360 I have; perhaps this mod is more useful for the IO-360.

What do you think?
 
I noticed a fairly large opening 1 inch wide by almost 1 inch deep at the base of the cylinder no 3. The baffle is straight, but where the cylinder has no more fins, all that area is open. Should I close this? Seems that this is useless....

...
The way you describe it, it does sound useless. Do you have a photo? This seems kind of strange. As DanH said, all air that comes into the cowl should be passing by some part of the engine where it's picking up heat and sending it out the bottom of the cowl. That's the principle. If any air passes through without picking up heat, it's wasted.
 
Pics needed! For example, this is a pusher engine but see the between-cylinder baffle. All air must be forced to go through the fins. If it can take an easier (open) route from top to bottom it will. If it can go through a gap, crack or hole anywhere else, some of the flow will go there and bypass the fins. That's wasted energy, unnecessarily increases cooling drag, and allows the engine to run hotter
 

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Thanks Kent. I can see the area I am talking about on your picture (top right). This area is perfectly closed on your installation and totally open on mine. This gives me a good idea of what needs to be done.

Trying to attach pictures, but I have difficulties. (And i consider myself quite computer litterate)...

I also have cooling draft tubes to the magnetos... I am wondering if this is needed at all (I did not have those on my previous aircraft and all was good).
 
My cabin heat intake is behind the cylinder no 3, stealing a lot of air from going down the fins, I imagine. Would it be better to have this intake on the cyl. No 1 baffle? I also have my oil cooler air intake on the cyl 3 baffle.
 
I noticed a fairly large opening 1 inch wide by almost 1 inch deep at the base of the cylinder no 3. The baffle is straight, but where the cylinder has no more fins, all that area is open. Should I close this? Seems that this is useless....

Yes, absolutely. And you'll find the same opening at the no-fin base of #4.

I seem to recall the baffle kit as having a tab there, which should be bent to close much of the gap. The rest is sealant.

Outside of this, I do have a conduit to the oil cooler behind that cylinder (a 3 inch SCAT) and a 1 inch conduit (or 3/4 inch) to cool the magneto.

(Opinion warning) 3" is too small for an oil cooler, and blast tubes are wrong as a soup sandwich. This is 2021. Anything on the accessory case which won't operate without the very marginal cooling of a blast tube is either a bad design or way out of date.

I also check about increasing the clearance behind the fins (with a washer)... seems not relevant for the O-360 I have; perhaps this mod is more useful for the IO-360.

It is relevant for your parallel valve cylinder, just like the angle valve cylinder.

The "washer trick" is not a great way to address it. It allows some flow to the lower fins on the intake side of the head, but it also allows a leak to an area of no fins (photo below, section on the right), which is useless. The best approach is a bypass duct, which is not a new idea. You can find them on quite a few baffles in certified GA. I've attached photos of a Grumman Tiger's bypass on #3, and two photos from my own 390.
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Cooling

Michel, I haven’t read the responses so this may have already been said. I placed a washer between #3 cylinder and rear baffle. On the 8, there is a screw that secures baffle to cylinder and a washer or two goes on that screw to increase the space between cylinder and baffle. This let my #3 run cooler by around 15*f.
 
I have to say a big THANK YOU to all who provided information. This really helped. I modified my baffle to integrate a bypass duct behind cylinder no 3. I also sealed all openings I could see. I flew today climbing at an aggressive angle and I was able to stay under 400F (!). Very happy with this now.
 

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I have to say a big THANK YOU to all who provided information. This really helped. I modified my baffle to integrate a bypass duct behind cylinder no 3. I also sealed all openings I could see. I flew today climbing at an aggressive angle and I was able to stay under 400F (!). Very happy with this now.
Félicitations, great to hear that it's better!
 
I have to say a big THANK YOU to all who provided information. This really helped. I modified my baffle to integrate a bypass duct behind cylinder no 3. I also sealed all openings I could see. I flew today climbing at an aggressive angle and I was able to stay under 400F (!). Very happy with this now.

Mike,

Thanks for sending me over here from my other post. Interesting solution. That would definitely coincide with what I am seeing with my #4 CHT being the coolest.

Right now, #1, #2, #3 are my "hot" cylinders. Even with EGTs within 10* of each other.
 
blast tubes are wrong as a soup sandwich. This is 2021. Anything on the accessory case which won't operate without the very marginal cooling of a blast tube is either a bad design or way out of date.

I have blast tubes on my magnetos. In your opinion, they are unnecessary. Is this the general consensus? I'm wondering if I am giving up valuable cooling air.
 
Seems there is no consensus on the use of blast tubes. I have them on mine and now cooling does not appear to be an issue..,, we will see during the hotter season. The main issue seems to be that there is no space to let air get to the lower fins on cylinders 2 and 3. I do not have cooling issues with no 2 on mine so the duck to create a space behind no 3 really helped. More details on links provided earlier in this thread
 
If understand correct standard ignition timing is 25 degrees BTDC? I also heard Mike Busch on a webcast saying that reducing by even 2-3 degrees can dramatically reduce temps, anyone tried this?
 
If someone has no cooling on his mag, and its fine it doesn't tell you anything about your magneto in your cowling.

You can discover the actual temperature of your Magneto (and other accessories, like Alternator?). Monitor it via a thermal crayon or a Strip Thermometer in the most extreme atmosphere you operate. Once you know how hot it gets, and you know the magnetos' temp limitation the question of a blast tube in you cowling is solved.

Thermal crayons are made in very specific temperatures from 100F to 2000F. When they hit a temp, the mark will melt. Place a mark on the magneto and see if it melts.

Another way it to use an Adhesive strips thermometers that are non-reversable. When a high temp is reached, its indication will stay there.

https://www.thermometersite.com/thermax-10-level-strips-irreversible-labels-2
 
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#3 Bypass Chute Template

I did fin and flow area calculations many years ago for the one like Stu shows. Phase I measurements confirmed success. Easy to make. Here is the template, just make a cardboard (white board) sample, bend and understand the fit. Then cut one from .032, bend to fit. The circle is 4" dia as a reference to confirm your printer is dimensionally correct.

View attachment RR_Baffle_Template.pdf

I have blast tubes on my magnetos. In your opinion, they are unnecessary. Is this the general consensus? I'm wondering if I am giving up valuable cooling air.

I measured my mag temps per the location recommended by Slick and they were under the limit for all conditions including high ambients. How high - 95-100F. The mag temps were not even close to the recommended limit, 185F IIRC. It is here on VAF somewhere - may be 5-8 yrs ago. ;)
 
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I have blast tubes on my magnetos. In your opinion, they are unnecessary. Is this the general consensus? I'm wondering if I am giving up valuable cooling air.

There is plenty of air available. You're giving up deltaP, which determines velocity through the fins, which in turn affects the degree of turbulence at the fin surfaces, thus affecting heat transfer. You're also accepting unnecessary cooling drag, which is mass x loss of velocity. Flowing additional mass in order to carry away very little heat is inefficient. Heat transfer between the mag and the blast tube stream is very poor...no signficant surface area, low turbulence in the boundary layer, and not much deltaT.

If someone has no cooling on his mag, and its fine it doesn't tell you anything about your magneto in your cowling.

You can discover the actual temperature of your Magneto (and other accessories, like Alternator?). Monitor it via a thermal crayon or a Strip Thermometer in the most extreme atmosphere you operate. Once you know how hot it gets, and you know the magnetos' temp limitation the question of a blast tube in you cowling is solved.

No it's not.

A crayon or strip only tells the maximum temperature, which is usually when parked, just after engine shut down, and the blast tube is doing absolutely nothing. Put another way, blast tube or no blast tube, maximum temperature will be the same.

To learn inflight temperature you'll need a live indicator, a thermistor or some other kind of sensor.

Or you could install an ignition which couldn't care less.
 
Baffling question

I am having a cooling issue with #2. I took a look at my baffling today, and I came up with a few questions. Should there be RTV along the front of the cylinders (see pic)? It seems to me that air should be allowed to flow around the front of the cylinder. Also, should the gaps in the second picture be sealed with RTV?

IMG_6500.jpg

IMG_6496.jpg
 
If understand correct standard ignition timing is 25 degrees BTDC? I also heard Mike Busch on a webcast saying that reducing by even 2-3 degrees can dramatically reduce temps, anyone tried this?

25° for 8.5:1 Lyc.s, 20° for 8.7:1...And Yes, and Yes.

My engine is an IO-360-A1B6 (200HP, 20BTDC, Angle Valve). I initially installed Dual Lightspeed Engineering Plasma III with timing ring magnets installed at 22°.

I flew the aircraft for 75 hours, recorded a ton of data at various MP/RPM/Altitudes/OATs. Changed timing magnets to 20° and CHT's dropped ~20° across the board...
 
Smithfly…

That RTV in front of Cyl 2 in the area of aluminum fins is not good in my opinion. This is where a section of the fins are not deep enough already. The body of the cylinder is almost against the baffle already. That prevents air from reaching the lower fins in that area. I have friends that created an opening right in front of that section to direct the air to the lower fins. I think just having enough clearance between the baffle and the fins should be OK. I have to say I do not have a no 2 cylinder issue on my RV6 and the fins in that area are about 3/16 inch deep in that area on my engine. For the bottom fin opening. I would seal it as would not want air to escape on the side without going trough fins.
 
Smithfly…

That RTV in front of Cyl 2 in the area of aluminum fins is not good in my opinion. This is where a section of the fins are not deep enough already. The body of the cylinder is almost against the baffle already. That prevents air from reaching the lower fins in that area. I have friends that created an opening right in front of that section to direct the air to the lower fins. I think just having enough clearance between the baffle and the fins should be OK. I have to say I do not have a no 2 cylinder issue on my RV6 and the fins in that area are about 3/16 inch deep in that area on my engine. For the bottom fin opening. I would seal it as would not want air to escape on the side without going trough fins.

That’s kind of what I was thinking. Thanks!
 
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