Problem solved: High CHT on #3 Cylinder

[Kent Wien]

I wanted to share a modification that works beyond my expectations. Ever since I put the belly pod on my Husky, I’ve had a difficult time climbing to 900 feet before the CHT on #3 cylinder would exceed 400 degrees.

So after learning that Aviat has recently redesigned the baffling behind the number 3 cylinder to accelerate the flow over that cylinder, I decided to try it. The easiest way would be to buy the right rear baffle and bypass channel as a complete set that’s riveted together. It is listed as Aviat part: Right Rear Baffle P/N 35380-504.


After this change, upon reaching 1000’ my #3 cylinder is now at 370 instead of 400-410. In cruise the #3 cylinder is the second coolest. This is on an airplane using a Powerflow Exhaust, Auto Fuel STC and a cargo pod.

Just wanted to pass this along. I believe this baffle works on all Huskies.

Kent

 

[belloypilot]

Interesting. I installed that last winter and certainly noticed an improvement but not as significant as you report. I now have the front blocking baffles, the #3 modification, and Thomas’s new larger lower cowl cooling lip. On a warm day, (ISA +15 C) my #3 will still get to 405-410 during a prolonged Vy climb. If I drop the nose a bit and indicate 80-85 I can get it back to 400 or lower. In cruise #3 is the second hottest behind #4, but all good. Coldest is usually 330. Hottest about 355. I have standard exhaust.

 

[Snowbirdxx]

Here is the plan for the cup

 

[dogday]

Belloypilot
Look for flashing that lycoming missed and remove it. Flashing is the aluminum at the parting line that can sticks out of a sand casting. It can/will block the airflow past the cooling fins if it still fhere.. Use a jewelers file for the parting area around the spark plug.

 

[belloypilot]

Belloypilot
Look for flashing that lycoming missed and remove it. Flashing is the aluminum at the parting line that can sticks out of a sand casting. It can/will block the airflow past the cooling fins if it still fhere.. Use a jewelers file for the parting area around the spark plug.

Will do. Thanks for the tip!

 

[harry harper]

I wanted to share a modification that works beyond my expectations. Ever since I put the belly pod on my Husky, I’ve had a difficult time climbing to 900 feet before the CHT on #3 cylinder would exceed 400 degrees.

So after learning that Aviat has recently redesigned the baffling behind the number 3 cylinder to accelerate the flow over that cylinder, I decided to try it. The easiest way would be to buy the right rear baffle and bypass channel as a complete set that’s riveted together. It is listed as Aviat part: Right Rear Baffle P/N 35380-504.


After this change, upon reaching 1000’ my #3 cylinder is now at 370 instead of 400-410. In cruise the #3 cylinder is the second coolest. This is on an airplane using a Powerflow Exhaust, Auto Fuel STC and a cargo pod.

Just wanted to pass this along. I believe this baffle works on all Huskies.

Kent

View attachment 5073 View attachment 5074

How proud $$$ of that baffles is Aviat?

 

[Kent Wien]

I think $300.

 

[dogday]

When you drop the outlier/highest CHT down 30 degF all of the other mods to lower CHTs become less important/critical. I think that if you start with the #3 baffle mod to drop the CHT on #3 and then add the short baffles/dams in front of 1 & 2 to raise the front CHTs, most folks in cooler climates could stop there with getting their CHTs under control.

 

[Kent Wien]

When you drop the outlier/highest CHT down 30 degF all of the other mods to lower CHTs become less important/critical. I think that if you start with the #3 baffle mod to drop the CHT on #3 and then add the short baffles/dams in front of 1 & 2 to raise the front CHTs, most folks in cooler climates could stop there with getting their CHTs under control.

Yep, that’s what I now have. Love it!

 

[chrispo]

Thanks for posting, Kent.

I can't quite picture what the modification is. Is it essentially a scoop in the leading edge of the baffling that ducts air back toward the #3 cylinder?

I've experimented with both blocking some of the airflow from the #1 and from the oil cooler inlet in attempt to push a little more air over the #3, all with limited success.

 

[Kent Wien]

Thanks for posting, Kent.

I can't quite picture what the modification is. Is it essentially a scoop in the leading edge of the baffling that ducts air back toward the #3 cylinder?

I've experimented with both blocking some of the airflow from the #1 and from the oil cooler inlet in attempt to push a little more air over the #3, all with limited success.

Imagine two golf ball sized holes cut in the back of the baffling, both just behind the #3 cylinder, one on the top part and one on the bottom. Then put a channel over the two holes to direct air out of one hole and back in through the other (bottom) hole. It speeds up the air around the cylinder. Basically matches up #3 temps with #4.

 

[Snowbirdxx]

This is how it looks and how it can be made

 

[TheFlyingMouse]

Hi All,

Figure I would tack onto this thread rather than make a new one. I live in a predominantly warm climate (CA) and my #4 temps tend to be much higher than the others, quickly getting to 450 degrees in 5-10 minutes of climb on hot days. Other than checking for stray flashing and the usual pilot tricks like step climbs, etc., is there anything you all know about that will specifically improve the cooling on #4? (The next hottest is #3 and 1/2 are distant equals.)

 

[dogday]

If your Husky has a 4 channel CHTs & EGTs you can determine quite a bit from the data. First, have you checked the accuracy of your #4 CHT to ensure the displayed output is correct? This could be as simple as switching the CHT probes between 2 cylinders and seeing if the hot cylinder moves accordingly. Then check the mixture on #4 by ensuring that it is running at least 150 degF rich of peak by momentarily leaning to peak during a climb. How is the cylinder leakage on #4, is there blow by past the rings? Has the engine be recently overhauled where things are still breaking in?

I assumed that you have already checked the baffeling and have found no issues.

 

[rnorty]

Hi All,

Figure I would tack onto this thread rather than make a new one. I live in a predominantly warm climate (CA) and my #4 temps tend to be much higher than the others, quickly getting to 450 degrees in 5-10 minutes of climb on hot days. Other than checking for stray flashing and the usual pilot tricks like step climbs, etc., is there anything you all know about that will specifically improve the cooling on #4? (The next hottest is #3 and 1/2 are distant equals.)

What power / prop / mixture settings are you using?

On a hot day (in the desert), I have to work to keep it below 385, to hear people have problems keeping it below 400 is concerning to me.

 

[TheFlyingMouse]

Haven’t checked the baffles yet. I’m looking for things to dig into. Plan to pull the cowling this weekend and have a look around for the source of an oil drip and want to start sorting out the cooling at the same time. The engine is an unknown to me as I purchased the airplane last month. Prebuy inspection didn’t find any issues on borescope. Last overhaul was about 490 tach time ago for prop strike tear down.

This was my return flight back from Colorado. High desert, 85F or hotter mid day and there’s no way I could climb at 2500 rpm and WOT (20-21 MP at altitude) without busting 450, mixture full rich. I was able to cruise climb at 2350/WOT from 10k-12k around 75mph IAS to keep temps right about 400 on 3+4. This was all fully loaded with dudes and gas though, so maybe that’s also part of the difference. Might just be asking too much from the engine.

Good call on swapping the CHT probes to see if it’s just that. I have a VM-1000 with full temp probes installed. I’ll run the mixture test next as well. I do get the 18gph fuel flow that folks have been talking about down at sea level, so that’s at least good to go.

 

[rnorty]

Haven’t checked the baffles yet. I’m looking for things to dig into. Plan to pull the cowling this weekend and have a look around for the source of an oil drip and want to start sorting out the cooling at the same time. The engine is an unknown to me as I purchased the airplane last month. Prebuy inspection didn’t find any issues on borescope. Last overhaul was about 490 tach time ago for prop strike tear down.

This was my return flight back from Colorado. High desert, 85F or hotter mid day and there’s no way I could climb at 2500 rpm and WOT (20-21 MP at altitude) without busting 450, mixture full rich. I was able to cruise climb at 2350/WOT from 10k-12k around 75mph IAS to keep temps right about 400 on 3+4. This was all fully loaded with dudes and gas though, so maybe that’s also part of the difference. Might just be asking too much from the engine.

Good call on swapping the CHT probes to see if it’s just that. I have a VM-1000 with full temp probes installed. I’ll run the mixture test next as well. I do get the 18gph fuel flow that folks have been talking about down at sea level, so that’s at least good to go.

When it's hot I pull the throttle back to 19.5-21.5 and leave the prop at 2500 during the climb. This always pushes the temps down for me. I push the nose down and it'll still give me 3-400.

 

[TheFlyingMouse]

I’ll have to play with it some more, but anything like 2500 rpm while climbing was easily making temps over 450 that day above 10k ft. Manifold pressure was down below 20 environmentally by the time we got up to altitude. It sounds like I might have an issue with the #4 cylinder or its probe to dig into specifically then.

It’s hard to compare apples to apples here though. We were quite heavy for the entire adventure. The plane has quite a bit more performance margin with just me and half gas at sea level compared to full gross at 10-12k, and that probably means lower AOA in climb.

 

[rnorty]

I’ll have to play with it some more, but anything like 2500 rpm while climbing was easily making temps over 450 that day above 10k ft. Manifold pressure was down below 20 environmentally by the time we got up to altitude. It sounds like I might have an issue with the #4 cylinder or its probe to dig into specifically then.

It’s hard to compare apples to apples here though. We were quite heavy for the entire adventure. The plane has quite a bit more performance margin with just me and half gas at sea level compared to full gross at 10-12k, and that probably means lower AOA in climb.

Another thing I noticed - and this could be anecdotal - if the CHTs get high on the ground, like 350-360, it's very hard to cool it down. If I take off and they're 330~, I never have to worry about them in the climb.

 

[TheFlyingMouse]

Another thing I noticed - and this could be anecdotal - if the CHTs get high on the ground, like 350-360, it's very hard to cool it down. If I take off and they're 330~, I never have to worry about them in the climb.

Oh interesting. I get CHTs over 380 almost immediately after takeoff on #4 even if I pull the rpm back pretty quickly to 2500. I’m going to put in a gopro to record the instrument panel on the next flight so I can log the data and see what I’m really dealing with.