CHT issues

[ghostflyer]

I am having a issue with CHT,s that for some time I didn’t know I had . Originally when the 180 hp 4 banger was fittted I had only 1 CHT probe on the hottest cylinder . That being no.3 . The single probe EGT was fitted to the cylinder opposite . Every thing appeared to work well . Then another STC had to be fitted . This was the EI 4 probe CHT. The ground run after fitment was satisfactory. I then had to do a flight under some very trying conditions and decided to keep a close eye on CHT,s and see what was happening to the other cylinders . Shock!!! . There was a difference of 100 degs between the hottest and coldest cylinder . The coldest was 293degs and the hottest was 393 degs . Normally at altitude [7500ft] and at 2550 rpm the hottest cylinder would run running at 340 degs. It was a extreme day for flight ,hot and massive turbulence and engine power was constantly being changed . [and altitude]
My ‘BLUE’ silicone baffle seals are as in new condition and seal well. The pressure in the lower cowl is constant with the exception of near the out let . I have heard stories from others that the intakes are not correctly designed. So my question is ..... has any body else with the 4 banger up front had any issues similar to mine . I have some radical ideas , [george is rolling his eyes again ] . So the research has now started .

[c170b53]

Absolutely , or at least with mine temps are all over the place until I dial in the EGT: I can tell when I’m close to the best lean point, rich of peak, all the EGT’s start to line up and subsequently the head temp differences narrow. 0-320 B3B

[GAHorn]

I am having a issue with CHT,s that for some time I didn’t know I had . Originally when the 180 hp 4 banger was fittted I had only 1 CHT probe on the hottest cylinder . That being no.3 . The single probe EGT was fitted to the cylinder opposite . Every thing appeared to work well . Then another STC had to be fitted . This was the EI 4 probe CHT. The ground run after fitment was satisfactory. I then had to do a flight under some very trying conditions and decided to keep a close eye on CHT,s and see what was happening to the other cylinders . Shock!!! . There was a difference of 100 degs between the hottest and coldest cylinder . The coldest was 293degs and the hottest was 393 degs . Normally at altitude [7500ft] and at 2550 rpm the hottest cylinder would run running at 340 degs. It was a extreme day for flight ,hot and massive turbulence and engine power was constantly being changed . [and altitude]
My ‘BLUE’ silicone baffle seals are as in new condition and seal well. The pressure in the lower cowl is constant with the exception of near the out let . I have heard stories from others that the intakes are not correctly designed. So my question is ..... has any body else with the 4 banger up front had any issues similar to mine . I have some radical ideas , [george is rolling his eyes again ] . So the research has now started .

Look at the TCDS for your engine and compare your readings with the limitations posted. http://rgl.faa.gov/Regulatory_and_Guida ... Rev_25.pdf

The typical IO-360 has an upper cylinder limit of 500-degrees Fahrenheit. If the hottest you observe is 393 you are in good shape (although some baffling might still be questionable if the spread amongst cylinders is great.)

[DaveF]

My O-360 usually runs hottest on number 3, but no more than 50° difference between hottest and coolest. Normally about 20 in cruise. I rarely exceed 380° and absolutely never exceed 400.

After the engine overhaul I was seeing CHTs of 400-420°, but they came down over about the next 100 hours, and have continued to decline slowly, now at 350 hours. I spent a lot of effort trying to fix the baffling, but it made no difference at all. I think the biggest effect on CHT is mixture, specifically, maldistribution among cylinders. I think the Avcon carb airbox in my airplane is a poor design that puts a nonuniform air flow into the carb, so small changes in throttle position have a large effect on how the fuel is atomized and distributed. For example, takeoff at full throttle gives EGTs and CHTs much higher on 3 and 4 (rear cyls running lean) than 1 and 2 , but pulling the throttle back 1/4" evens out the temperatures a lot, with no loss of MP. I know, I should let the economizer do its job, but the JPI shows that this works. Also, rolling back the RPM to 2500 helps. Back in the '60s Mooney and Piper put a set of flow-straightening vanes in their O-360 airbox outlets, and a bunch of RV guys have reported improved cylinder uniformity doing the same. I haven't tried it.

Something else to try is converting the carburetor from a 10-3878 to a 10-3878M, or swap to a 10-4164-1. The 3878M is the 3878 with an improved main jet, and the 4164 is the factory-new designation. All are approved for the O-360. The conversion kit (Marvel-Schebler p/n 666-660) was introduced in the 1960s in response to Mooneys running high CHT, hence the "M". I haven't tried this, either.

When I was first troubleshooting the CHTs by fixing baffling I tried blocking off the cabin air inlet. It's a 3-inch hole in the baffle wall behind cyl 3. You'd think that closing a 7 sq. in. hole in the baffling would make a difference, but it didn't at all! I'm guessing, because I haven't measured it, that the lower cowl pressure is too high and there's not enough delta-P across the cylinders, but the upper side has plenty of pressure, so messing with the upper side won't fix it. I might need a larger lower cowl lip to lower the outlet pressure.

I've also found that in climb, my CHTs are lower at 65mph indicated than at 80. Counterintuitive, but I assume the change in deck angle influences the upper/lower pressure delta. Works for me, though, because I get much better rate of climb at 65 than at 80. I also found that the MT propeller gives lower CHTs in climb than the Hartzell did. I don't know if it's an airflow difference or just due to the improved ROC, but I can do landing and instrument approach practice on the hottest days in the summer without exceeding 400.

Ghost, I know you've done some fancy cowl mods, and I'll be interested to see what you find.

[ghostflyer]

Thankyou gents for the update and advice. Firstly the engine baffling fits really well and seals excellent. Initially I placed a very strong light in the intakes [done in a dark hangar] and checked for light escaping on joins and sealing surfaces. Then I placed a very small camera in the intake looking at all the seals and went for a fly .all good . . NOW, these seals are BLUE so they keep up with the aeroplane . . I will look at my main jet but I am very happy with my carburettor and it’s operation at the moment. I will try your leaning process.
My heater intake is before the LH intake to the engine so it doesn’t upset the airflow that much . On the other intake [RH] I have a small 1.5ins in Dia duct the runs to the back bearing on the alternator .
However no1 cylinder is in direct blast of air from the Lh intake and no3 cylinder gets what’s left over . I have been talking to a friend at cessna he suggested I have a look at the new Cessna 182,s intake [ I have been looking at it before he mentioned it] . The duct rapidly curves upwards and runs about 8ins rearwards. I also feel my lower cowl is working well also.

[NB. My friend who works at Cessna only advises me in his free time for entertainment reasons only , he is a qualified aeronautical engineer . He has worked for a number of aviation companies on some big projects and some of his ideas are just rubbish ,I love to tell him that ,we are always having a go at each other. . He is a very funny guy when he has a few beers under his belt . ]

[GAHorn]

Cessna specifies Lip PN 0552001-60 on all floatplanes.

[n2582d]

Years ago Lycoming issued Service Bulletin 258 for the O-320. I’ve read that diameter between the intake manifold and the carb is doesn’t match on the O-360 either. Something to consider for more even fuel flow?