M-4 High CHT Temps

[Flyjohnny]

Hey all,I am running a '68 M-4 210C and have recently installed a JPI engine monitoring system. I have been totally surprised how warm the engine is actually running in climb and cruise. Often on an 80 degree day I am struggling to keep some of the cylinders under 420 degrees even with climbing at 110mph and full rich. In cruise front cylinders are cool but the back ones are still staying around 380 degrees. Maybe I have watched to many of Mike Busch's webinar's but this is high according to him. What numbers are other members finding on their planes? Also wondering if anyone has any mods that have helped or have dabbled in the world of cowl flaps on their planes. I have attach a picture below of a flight on the weekend in cruise at 8000ft.

Appreciate any help you can pass on.

Thanks

John

[andy]

Have you confirmed that the engine baffle seals are correctly installed against the front cylinders instead of under them?

[Flyjohnny]

Yes, all the baffling was changed fairly recently and AME says it all looks good.

[Mog]

Franklin runs hot for sure. But mine never runs that hot. If I see 400° I’m starting to panic a bit. I have heard people here claim they see 230°ish but I seem to cruise in the 320°ish range.

There is a baffle divider piece that is supposed to help the rear most cylinders, but I currently do t have that and still have ok temps. There is also a a kit to add static “flaps” to the bottom of the cowl to help pull more air. It also keeps the lower cowl from collapsing.

[Flyjohnny]

Franklin runs hot for sure. But mine never runs that hot. If I see 400° I’m starting to panic a bit. I have heard people here claim they see 230°ish but I seem to cruise in the 320°ish range.

There is a baffle divider piece that is supposed to help the rear most cylinders, but I currently do t have that and still have ok temps. There is also a a kit to add static “flaps” to the bottom of the cowl to help pull more air. It also keeps the lower cowl from collapsing.

I have a friend that also has the IO-360 and has to watch the temps but apparently not as high as mine.

I have the fiberglass upper and lower cowling. Are there cases of the lower fiberglass cowling collapsing?

[Mog]

If you do not have the extra aluminum lip flap or whatever you want to call it then yes the cowl could be collapsing in flight. As well, the flap creates more negative pressure to draw in more air. My cowl was extremely floppy in this area before installing the flap.

[yanknbank]

The lower fiberglass definitely contorts in flight. I've been considering reinforcing it. I know because it just about drained all my oil from the pan after I installed a push drain valve on it, and in flight the cowl was pushed against the valve and opening it.

Honestly, I don't think your temps are that bad though. 420 in a climb, then under 400 in cruise is just fine. If you really want to chill it down on the io360, your most effective move might be to get gami injectors and run lop in cruise.

Rop, mine runs about 400 on the hottest jug in cruise. Id like it cooler, but I don't believe it's going to cause that cylinder to quit first. Mine is missing the center baffle, some baffles over the oil cooler, and needs rtv, so it would probably come down to your temps once those are finished.

[Flyjohnny]

The lower fiberglass definitely contorts in flight. I've been considering reinforcing it. I know because it just about drained all my oil from the pan after I installed a push drain valve on it, and in flight the cowl was pushed against the valve and opening it.

Honestly, I don't think your temps are that bad though. 420 in a climb, then under 400 in cruise is just fine. If you really want to chill it down on the io360, your most effective move might be to get gami injectors and run lop in cruise.

Rop, mine runs about 400 on the hottest jug in cruise. Id like it cooler, but I don't believe it's going to cause that cylinder to quit first. Mine is missing the center baffle, some baffles over the oil cooler, and needs rtv, so it would probably come down to your temps once those are finished.

The numbers in the photo is the plane is in cruise and LOP. My AME is fairly happy with the numbers in cruise other than the large temp spread on them. He is suggesting injector cleaning and I have been saying that sometime in the future I would like to get the gamijectors.

Like I mentioned I have watched a lot of Mike Busch's webinars and he has struck fear in me stating that any time you are running at 400 degrees and up it equals 500 hrs on your cylinders.

I will take a good look at the bottom cowl and see if it needs re-enforcing.

Man, I really appreciate this group!

[TimB]

If you don't have GAMIjector installed yet do so in for this series of engines, Continental IO-360's, it will level out the temps.

[yanknbank]

I don't think Mike ever suggested you're doing damage over 400⁰. If I remember, he prefers 380 in cruise, which would suggest the climb would be at 400+, but he sets his personal red line at 400. Though he's altered his words because people are getting worried and now says 400 is more of a yellow arc to 460.

Frankly, I think he'd suggest your 5 and 6 are too cold even.

If you're capable of 7.6gph, you probably have a decent gami spread. #2 seems to run richest on mine too, so that's why you're seeing it at 380. Improve your gami spread with gami injectors and that 380 will drop to 350 or less in cruise.

In climb out, I wouldn't bat an eye at 420 on a hot day.

Consider that the main reason we care about cht is that it's a proxy for inter cylinder pressure. That's the thing that destroys engines. The problem is, there is more than one way to raise cht, so you don't always know if the cht is high because cyl pressure is high, or just because of poor baffling on a hot day. If you ran consistently above 400 in climb, but you're doing everything you should be, such as running fairly rich mixture, you're not doing damage to the engine. I'll get some push back, but I'd even suggest that if you ran 420⁰ in cruise, but your power setting is below continental's max cruise power setting of 24" and 2500 rpm, you'd make tbo if not for any other unrelated issues. Detonation margins are high, and in that realm, cht isn't really a destructive element below the max.

[Flyjohnny]

I don't think Mike ever suggested you're doing damage over 400⁰. If I remember, he prefers 380 in cruise, which would suggest the climb would be at 400+, but he sets his personal red line at 400. Though he's altered his words because people are getting worried and now says 400 is more of a yellow arc to 460.

Frankly, I think he'd suggest your 5 and 6 are too cold even.

If you're capable of 7.6gph, you probably have a decent gami spread. #2 seems to run richest on mine too, so that's why you're seeing it at 380. Improve your gami spread with gami injectors and that 380 will drop to 350 or less in cruise.

In climb out, I wouldn't bat an eye at 420 on a hot day.

Consider that the main reason we care about cht is that it's a proxy for inter cylinder pressure. That's the thing that destroys engines. The problem is, there is more than one way to raise cht, so you don't always know if the cht is high because cyl pressure is high, or just because of poor baffling on a hot day. If you ran consistently above 400 in climb, but you're doing everything you should be, such as running fairly rich mixture, you're not doing damage to the engine. I'll get some push back, but I'd even suggest that if you ran 420⁰ in cruise, but your power setting is below continental's max cruise power setting of 24" and 2500 rpm, you'd make tbo if not for any other unrelated issues. Detonation margins are high, and in that realm, cht isn't really a destructive element below the max.

This is great insight, thank you. I definitely have it on my list to get gami injectors in the new year.

When you mention doing everything you should be in the climb ie running fairly rich, are you leaning a bit in the climb? If so, to what amount gph would you lean in the climb? I know every engine is different but just an approximate. Or are you just leaning by CHT?

[yanknbank]

Personally, I'll take off with about 16gph. If you still have the old fuel pressure gauge, the markings on that do pretty good for takeoff. After 1000 agl, I'll bring the prop back to 2500rpm, and I'll set the mixture for having the leanest cylinder at 100⁰ rich of peak. I'll note the EGT, and lean to keep the same EGT as I climb. This is for my elevation of 5000 feet though. If you were closer to sea level, you may want a bit richer than 100⁰ rop since you'll be putting out more than 70% power on climb. If you run full throttle on climb like I do, sea level and 2500rpm would be more like 200⁰ rop in my book. and you'll need more than 16gph for takeoff at sea level too.

Edit for context: I'm leaning by egt. Just trying to keep out of the "red fin". If cht gets uncomfortable and I can't do anything else about it, I'll give it a little more on the red knob.

Ymmv

[andy]

I have a JPI EDM800 engine monitor. A rich mixture setting on climb can help keep the CHTs lower in hot weather. I've found that I don't need to lean for additional power below 5,000 density altitude. Another thing that can keep the engine cooler is to decrease the RPM on climb. I use 2500 RPM and 25" MP when I'm climbing above obstacles but when I'm clear I use 2400 RPM and 24" MP for extended climbs. The lower RPM has the additional benefit of reducing engine component wear. I try to keep CHTs below 400F.

[TxAgfisher]

Need to put some baffles in front of the front two cylinders to push the air up and over to the rear 2 cylinders. Start with maybe 1/3 to half the way up and you can experiment with foil tape until you see the temps you want and then use aluminum once you have your measurements.

[andy]

Yes, that's why I asked about the baffles being up against the front cylinders, rather than down under them. Sometimes maintenance shops who aren't familiar with Maules incorrectly re-install the bottom cowling with the baffle seals under the front two cylinders. That allows incoming air to push down the baffle seals and flow under the front two cylinders out the bottom cowling without cooling the rear cylinders.