High cht's

[Flygirl1]

From day one I have been having problems with high CHT’s—30 degree spread from Cyl # 1 to Cyl #4. Also for some reason 70 degree spread at altitude. My #4 has been consistently at 419 and above, especially on take off, up to 430 at altitude. I'm using 75% power and fuel burn at 10.6 and upwards of around 11.2 to keep the CHT’s down. The Dynon has a lot of information in this area, maybe too much, but it’s there and I look at it. Some changes happened when we took the baffle off the front of # 2. At that time it was the highest. That made #4 the highest and #1 the coolest. Our most recent change has been adding some tape on the bottom, engine side, of the door hinges. A lot of light showing there and I had about 1/4 inch of cowling inside the fiberglass cowl lip that we cut off. This produced an Unbelievable amount of change. At 75% power and 10 GPH fuel burn all cyl are within 7 to 10 degree’s of each other and now #3 is the hottest at around 395 degree’s with a 58 degree outside temp. As far as at altitude, I’ll let you know. So it appears the cowling outlet is most likely the area to pay attention to if your having high CHT’s.

[jaredyates]

If you want to get scientific about cooling, measure the pressure differential with a manometer. I'd ship you mine, but you could make your own for less than the cost of the postage. Route the lines through the cabin heat valve after you temporarily remove the scat duct that comes into the cabin heat box. Then, rather than guessing about whether your pressure is adequate, you'll know. And rather than guessing about which improvements really make a difference, you'll have quantifiable data.

[Battson]

In my experience over many different aircraft, a spread in CHTs is completely normal. I would say that finding an aircraft with even CHTs on all cylinders is the exception to the rule.

Practically 9 times out of 10, it's the baffling which leads to high CHTs. Every little hole lets air escape and adds considerably to the overall drag profile.

A good rule of thumb is, every hole big enough to let a pencil through needs to be closed - this inclues every place air can escape, the baffle fabric, around the prop, everywhere. It's easy to close small holes with red RTV liquid gasket.

If your baffles are already in great shape, then you can increase the tunnel opening area, or add a small lip to the firewall to tunnel interface to increase airflow.

[Ed.Meyer]

I have been making outlet changes too. Opened it a fair amount and put on about a 2 inch lip made out of 025 aluminum. Had a smaller lip which helped but wanted more. Initially I was occasionally seeing temps up to about 430 which I did not like all and leveled out to mitigate. I also retarded the timing some at high power settings (thanks to Bill for that tip) and blocked part of oil cooler with tape, oil temp still 180, all of which incrementally seemed to help. I am able to lean quite agressively and can cruise at about 55% power and less than 7 gph with chts about 350 and within 10 of each other. If I lean less aggressively chts run higher. Still working on figuring out the rich side of things for climb. Real warm outside yesterday with 82 oat and about 370 chts. Didn't climb very high but never got over 400. Fixed pitch prop is keeping power setting pretty low at 2350 to 2400 rpms. Would like to eventually be able to climb several thousand feet at full power and not exceed 400. Still testing...

[JimParker256]

A good rule of thumb is, every hole big enough to let a pencil through needs to be closed - this inclues every place air can escape, the baffle fabric, around the prop, everywhere. It's easy to close small holes with red RTV liquid gasket.

If your baffles are already in great shape, then you can increase the tunnel opening area, or add a small lip to the firewall to tunnel interface to increase airflow.

The engine experts at the Advanced Pilot Seminars (www.advancedpilot.com) told us to plug any baffle leaks bigger than the lead in your pencil. One smart-a$$ pulled out his mechanical pencil with the tiny lead, and asked "You mean like this?" To which the instructor replied "Yep - if you can see a hole that size, plug it up!" They told us not to bother doing anything else about CHTs until that is complete.

Suggestion: get a friend to reach up under your exhaust area, and shine a flashlight toward your cowl / baffle intersection from behind, while you look into the cowl inlets. Any visible light means work to seal that hole... As Battson said, it makes an amazing amount of difference!

[Mark Goldberg]

Lots of time increasing the outlet area of the cowl bottom is very helpful with high temps. I seem to recall that the outlet area should be 1.3-1.5 of the inlet area in front at least. You might try to calculate what you have and see how the outlet area compares to the inlet area. Mark

[Battson]

I am not sure what the inlet area is off-hand, but my outlet area is between 100 and 130 square inches depending on the cowl flap setting - with no lip outside the cowl. With ambient temps around freezing, 100 sq.in is too large and the engine runs too cold. But that said, I was pedantic about our baffles, and we run lean of peak ALL of the time.

I would certainly stop the air leaks before increasing the outlet area, otherwise it's going to increase the total drag of the cooling system.

[Steve W]

Ensure your baffle sealing rubber is not too long and not the soft red/black silicone stuff. It should be fairly stiff and just long enough to stay in position when pressurized. If it's too long it can and will get caught in the force of the incoming air before it builds enough pressure to hold it in place. It will bend down to unseal against the upper cowl. The area around the flywheel and starter is usually neglected which allows a large area of leakage. The metal baffling must wrap and cover a fairly large amount of the bottom portion of the cylinder and head area, forcing the majority of the fin area to receive cooler air and remove all heated air. I understand that 2 square inches of leakage is all that's allowed for a properly functioning baffle. That really ain't very much!

[Flygirl1]

It's obviously important to have the the proper sealing and exit air flow. I'm also sure the way the air flows through the cyl can have a huge effect. So if your temps are good, good for you!! Not an easy accomplishment. As far as sealing the cowling, I'm curious about what people are using on those holes in the cowling from the cowl door hinges. Ours are "outies" and not inies. Right now I have aluminum heat duct tape, but it's not holding up to all the opening and closing.

[Mark Goldberg]

I have never tried to seal the hinges themselves on the cowl doors. For the little holes everywhere I used Hi Temp RTV. Mark

[Battson]

I didn't bother sealing the hinges either.

[jim.mclaughlin924]

Donna
Did you have the taper fin ECI cylinders? If so, how did you deal with the gaps? I am trying to modify the Van's baffle kit, but it is kind of a pain.

[Flygirl1]

We made a new piece that fit up against the tapered fins. I'd post a photo, but I'm not home. We are on our way to OSH and are overnite in Spearfish. On our way for a well deserved bruesky. Very nasty bumpy ride over the big hills, but the plane held together just fine. ( A testament to the quality of the kit, and the builders. 😁)

[Flygirl1]

Jim, wondering what your airport identifier is. We might be able to stop in on the way home. I thought a photo of the two birds together would be nice.🌞 Donna

[JimParker256]

And for most of us, this probably falls into the "Duh!" category, but... Be sure your baffle seals (the flexible seals where the baffle meets the cowling top) are bend "inward" rather than "outward"... If you imagine the airflow coming in through the inlets, it should force those seals up into the cowl, thus tightening the seal at the cowl.

You'd be surprised at how often our local DAR finds the bent outward, which simply allows all the air to blow past those seals, resulting in terrible overheating issues!

[Bdflies]

Donna, something you said got my attention. You mentioned that you had 1/4" cowling inside the lip. I'm understanding that your lip is on the outside of the cowl. My temps were uncomfortably high, at first. The cooling lip solved my problem. One difference is that I put the cooling lip on the inside. Once again, I copied the way it's done on my previous plane. See picture attached. Mine is aluminum. I screwed it, rather than rivets, so I could modify it or build another if it didn't work. The bent lip, on the inside, eliminates the sharp edge at the transition from cowl to lip. At least that's my story! More seriously, you and I have similar engines in similar planes. My exit area is probably too small. My lower cowl is wrapped pretty tight to the bottom of the fuselage. I'm flying in OAT's in the mid 80's. All this and my temps are fine and yours are high. Puzzling, to say the least.

Bill

[Flygirl1]

I agree, a bit puzzling! We modified the Vans baffle kit. Wondering what you did?

[Bdflies]

I also used the Vans kit. The only modification was to cut it down to fit the top of the cowl. Well, thinking about it, I also made some 'transition pieces' to better fit up to the nosebowl.

[Pat Fagan]

As for sealing the piano hinge, I tried the aluminum tape also but as you have found, it doesn't hold up to the opening and closing. I then tried some weatherproofing from Lowes that has worked well. It is a 1/2" wide hollow tear drop shape. I taped it to the opening hinge and it smooshes against the stiffener angle when closed. It blocks the air out of the hinge. I still have high CHTs but every little bit helps.

[Flygirl1]

We left Cottage Grove this morning at 6:30' flew all day and are now in Spearfish S Dakota. The gorilla tape has held up just fine.🌞

[Bdflies]

Here are a couple of pics of the pieces I made, to transition the baffling to the nosebowl. You might need to zoom in to get detail. If you'd like more details, I can take shots of what you like.

Bill

[Flygirl1]

Looks like you did just exactly what we did. Also to clarify, it was not cowling material we cut, but a reinforcing strip for the fiberglass cowl lip, which "is" on the inside like yours. Sorry, I misspoke. D.

[Rorch]

I thought I'd weigh in here because I fought high CHT problems for two years with an 0-360 in a carbon cub. It finally all boiled down to more air over the cylinders. We tightened all baffling which helped and we put the air dam lip on the exit side which helped. We finally moved the oil cooler out of the top of the baffle box and mounted it below the motor picking up air from front much like a stock cub. This allowed all input air to flow over cylinders. This really helped. Finally we used Cessna louvered vents in cowling to get more air out. It turned out it wasn't air in but rather air out. None of these things were silver bullets but they all helped a little. My question on the patrol is has anyone tried mounting the oil cooler anyplace but high in the back of the baffled portion of intake?