ENGINE: CHT Cooling

[gderamel]

I'm trying to troubleshoot why at altitude (4,500'), running LOP (60% power), my #3 CHT is running so much cooler (~75 degrees cooler) than the other cylinders, but at 1-2,000' they're all even. And if I run the fuel ROP, at 4k, the CHTs all stack up nicely. It only happens during LOP, >4k'.

I did a mag-check (dual Lightspeed Electronic Ignition) at altitude and both sides ran fine, and non of the cylinder EGTs temps fell.

Does it have something to do with the carburetor? Any suggestions?


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[DRL]

What were the EGT's?

It doesn't sound like a cooling problem. An induction leak, indicator connections, ignition elements all affect EGT, CHT in different ways. We haven't had much luck getting LOP with a carburetor. There have been a number of carb mods to get better fuel distribution, but so far no one seems to have solved the problem. The old lean until it runs a little rough and slightly enrich works for us. We are using a Skyview EMS, it gives us a lot of information, but we look for change, not so much the absolute numbers.

[gderamel]

What were the EGT's?

I'll take a picture of the EGTs next flight, but recall them being abnormal, or #3 peaking a lot lower.

Where would one check - in a carbonated system - for an induction leak?

I'm guessing, the low #3 CHT is just a fact of life trying to run LOP in a carborated system.


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[Pete D]

CC340 induction leaks would be either top end of the induction tube where it connects to the head or bottom end where it has shrink tube (older airplanes) or hose connection to the oil sump. See SB00032 for photos and an idea of what it looks like.

http://legacy.cubcrafters.com/techni...tions/116/view

[DRL]

I'll take a picture of the EGTs next flight, but recall them being abnormal, or #3 peaking a lot lower.

Where would one check - in a carbonated system - for an induction leak?

I'm guessing, the low #3 CHT is just a fact of life trying to run LOP in a carborated system.


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If enriching the mixture raises the #3 CHT to match the others, it is likely to be running too lean. One cause for this could be uneven fuel distribution, but it also could be an induction leak. In that case, the EGT would initially be higher as the mixture is leaner than the others until the mixture is so lean that the combustion process diminishes resulting in low CHT on that cylinder. I would guess the first reason. In any case, it is worth while to ensure the induction service bulletin was accomplished.

[gderamel]

CC340 induction leaks would be either top end of the induction tube where it connects to the head or bottom end where it has shrink tube (older airplanes) or hose connection to the oil sump. See SB00032 for photos and an idea of what it looks like.

http://legacy.cubcrafters.com/techni...tions/116/view

Yes, I completed SB00032, but I'll check that the hose clamps are good and tight.

Here's a screen shot from my G3X Touch Engine page... granted #3 CHT isn't as dramatically cooler than what I described at 4,500', but you get the point.

IMG_3132.jpg

[Springloaded]

Here some screen shots of couple different airplanes. I couldn't find any that I was that high. 7.7 gals a hr seems like a lot to me. I average roughly 500hrs a year in these planes and have never seen over 7gals a hr at my cruise which is usually 2280-2350 6-6.4 gals a hr. I found one were I was at 2440 ( I was flying someone else plane following them so I ran it like they wanted)which in my opinion is a waste of fuel. I haven't found a few miles a hr for the fuel burn worth it to me. Sometimes when you get higher it takes some FINESSE but I always end up around the same as these. I have flown with a few people who were use to burning 7.5-8 gals a hr and showed them this works. I usually push it to 2350 start leaning then just adjust throttle mixture till I end up here. Sometimes you have to play with throttle little more little less, It seems 90% of the time I end up at 2280 6.2 gal hr.
If that's any help?
Easy fix is just don't fly that high Unless there's a mountain 😀

[gderamel]

Thanks!

I'll try your power settings. I'm brand new to the Cub - just 225 TT!

I'm running a Catto Propeller, 80" 50 Pitch NLE (2-Blade) in case that makes a difference. Obvious the 2180 Clamars floats I'm slinging off to Cub, effects the true airspeed!

[Springloaded]

Yes 80-50 standard prop. Those pictures were actually 3 different planes the last one had a 3 blade on it. You gonna be in Greenville in Sept? I plan on being up in Lake Placid on a set of Aerocets Labor Day weekend then up to ME for seaplane flyin then back to FL.
Chuck

[gderamel]

Yes. Planning on going to Greenville. Clair (owns Clamar) asked me to go to show the CC on the 2180 floats.




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