Van's Air Force
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Lycoming 0-320 CHTs
- Thread starter tbonepac
- Start date
BH1166
Well Known Member
What r u looking for…… data ? Mine runs in 300’s always. Only time 400+ is in steep or slow climbs at departure due to speed and airflow. Nose over a little speed increases, cooling improves. 400f and nothing happens, 425f nothing, sustained flight above 400f isn’t best per Lycoming.
Since the Constant Speed prop allows the engine to make more power, there is more waste heat than what Butch sees. My RV-6 with 320 CS has been flying 26 years and almost 3,600 hours landing in 49-states. Taking off on a hot day after a fuel stop at KSJN, I can see 420 CHT on climb out but like Butch says, slowing the rate of climb / increasing airspeed and the temperature will drop. Typically at high altitude high power cruise, I will see 390 as my highest CHT. Flying in the southeast now, 350-370 CHT is more common in cruise. Lower cruise power also has lower CHT.
Dugaru
Well Known Member
I have this setup in a -9A. My hottest cylinder, #2, runs as high as 420 on climbout on a hot day, cooler if I close the oil cooler shutter. It’s right around 400 in cruise if it’s hot outside.
Both Lycoming and Mike Busch consider these numbers to be perfectly acceptable.
I have not seen that in Lycoming manuals, but I’m certainly ready to sit corrected.
Busch thinks 400 is a “comfortable target” for Lycoming cylinders, and pictures a mental “yellow arc” between 400 and the “mental redline” of 420. But as he notes,
“Keep in mind there’s nothing magic about any of these numbers. Nothing terrible will happen if a CHT runs in the ‘mental yellow arc’ or if there are brief exceedances above the ‘mental redline.’ I’m offering them only as suggestions, not commandments or operating limitations.”
carolsyracuse
Well Known Member
Vic spoke about CHTs in Lycomings in the video below at approximately the 2 minute mark.
He also wrote an article about CHT's and EGTs for the Jan 2024 magazine
I have a 6A with a 320 (160 hp) and FP prop. However, I climb at 2500 and likely you do also making this comparable. My climbs are done around 140 mph TAS. Climbs are done around 150 ROP, so a bit rich of best power. But not the 250-300 flithy rich many use. If I climb to 8000, my CHTs stay beliow 380 until around 6K where they start climibing, due in part to my ignition advancing and to the air getting thinner. By the time I get to 8K, I am about 405. If I retarded the ignition back to where a mag would be, I get to 400 or a bit less. All of that is summer and winter temps are lower. My 10 behaves very similar.
Key here is baffle sealing quality. Large range of quality out in the fleet and will see a lot of variability on temps based upon variability in sealing quality.
Larry
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Roadjunkie1
Well Known Member
This might be my opportunity to brag about the -4. 
I think the RV-4 cools better than the other models except, maybe, the -3 which has similar cowling.
O-320, fixed Bernie Warnke wooden prop with the Landoll balancer. I invested a lot of time with my baffling to make sure everything was sealed as well as I could get it. The markings of the baffling material (which is black) on the inside of the cowl tell me the baffling is well-sealed. I pull my oil cooling off the back of the shroud behind cylinder #4 but with an air dam to direct most of the air around the cylinder, and cabin heat from behind cylinder #2. Full-throttle climb out to, as an example, 8,000, (3k AGL, by the way), running 50-100 ROP, I might get into the mid to upper 300 range. Once at cruise, typically 2400/20 running 50 ROP (carburetor) CHT 280-320 with temps usually not over 300. Looking at my previous flight logs, upper 200's is typical.
There is a recent series of articles on engine cooling in Kitplanes magazine and stresses many factors including air entering the cowling (VERY well-designed intake by Vans), baffling and seals, and air exiting the cowling and taking the heat with it. I think this is one place that could possibly be improved by many builders. My oil temperatures are on the lower side, in the 180-200 range and that is with the oil cooler gate closed and the air intake partially blocked off, the amount depending on OAT.
Just some reference numbers from a well-designed cowling and paying a lot of attention to air flow over the cylinders. Can the engine be too cold? Yes, but that is usually not the problem. I do block some air entrance when Winter arrives.....
IMHO YMMV
I think the RV-4 cools better than the other models except, maybe, the -3 which has similar cowling.O-320, fixed Bernie Warnke wooden prop with the Landoll balancer. I invested a lot of time with my baffling to make sure everything was sealed as well as I could get it. The markings of the baffling material (which is black) on the inside of the cowl tell me the baffling is well-sealed. I pull my oil cooling off the back of the shroud behind cylinder #4 but with an air dam to direct most of the air around the cylinder, and cabin heat from behind cylinder #2. Full-throttle climb out to, as an example, 8,000, (3k AGL, by the way), running 50-100 ROP, I might get into the mid to upper 300 range. Once at cruise, typically 2400/20 running 50 ROP (carburetor) CHT 280-320 with temps usually not over 300. Looking at my previous flight logs, upper 200's is typical.
There is a recent series of articles on engine cooling in Kitplanes magazine and stresses many factors including air entering the cowling (VERY well-designed intake by Vans), baffling and seals, and air exiting the cowling and taking the heat with it. I think this is one place that could possibly be improved by many builders. My oil temperatures are on the lower side, in the 180-200 range and that is with the oil cooler gate closed and the air intake partially blocked off, the amount depending on OAT.
Just some reference numbers from a well-designed cowling and paying a lot of attention to air flow over the cylinders. Can the engine be too cold? Yes, but that is usually not the problem. I do block some air entrance when Winter arrives.....
IMHO YMMV
