Cowl flaps?

[David White]

It seems in cruise that if I close my cowl flaps all the way my CHT and oil temp start creeping up towards red line. I don't have a real engine monitor, just a single probe CHT and oil temp (and EGT in Celcius, WTF?) So I leave the cowl flaps in trail all the time. The baffling looks good, I'm just not sure if I can trust the gauges. I've got electronic FF and I usually run at either 2500RPM and WOT or 2500RPM and 24" depending on how high I am. I was told to aim for 10gph on FF so I do. I've played around with it and it doesn't seem that changing the FF changes the engine temps any noticeable amount.

Any advice?

Thanks,

Dave (1981 M20J)

[The-sky-captain]

I was told to aim for 10 gph when I was getting training in my plane by an old skool guy as well and had the same issues you are having. Once I started leaning correctly, 100 ROP or 30-50 LOP or so the temps were well within normal. At 7-8k shoot for around 11.5-8 gph ROP or 8.5-9 gph LOP running 2500 RPM, full throttle and see if that helps. I do have an engine monitor which helps a great deal running LOP. I know several guys on here run LOP without the 4 probe monitors so maybe they can chime in as well.

[aaronk25]

10gph wide open at 4000 feet works well in my J. Temps stay cool. If your at 10gph at 6-9k your gonna get the high cht because you'll be somewhere just rich of peak egt.

Sky captain is right on, just wanted to add that. Lean until you feel the power slightly reduce that's peak or lean of peak.....and watch your cht gauge come down.

At 4k rich of peak you'll need to be 12.5 13 to keep it cool.....rich of peak operation waste fuel but some don't care.

[David White]

Awesome advice guys, I'm gonna go do some mooney aviating tomorrow and see if I can figure it out. I do have intentions of installing an engine monitor but I have other costs (see my leaky tank thread) that I want to address before I add one. I'll most likely just wait until SnF and pick one up discounted there.

[OR75]

it would be worth looking at the POH . it details MP, RPM and FF based on altitude

[jetdriven]

either run 100 ROP or richer, or 15-30 LOP with balanced injectors to avoid overheating. You should not see 400+ CHT or redline oil temp with a conforming engine and good baffling.

[mooney389]

Check your oil cooler fins and make sure they are not all flattened. A new oil cooler reduced my temperatures by 20 degrees. Aero Classic makes a replacement for the Stewart Warner. FAA-PMA

[scottfromiowa]

Hi Dave. Something is not right here. I have same engine as your J and at 4500 feet MP at 2500 and RPM at 2500 leaned to 9.5 to 10GPH I am 50LOP. ALL cylinders WELL under 350 on G3. 4000 is low enough that I might not be full throttle at 2500MP. Others are saying 9.5-10GPH is ROP....Not by my gauge.

I think you should get the engine monitor. My number two runs 50 hot on gauge...you need to know what is going on in the engine.

If you pull until rough and then enrichen a tad you should definitely be LOP at 4000.

[scottfromiowa]

it would be worth looking at the POH . it details MP, RPM and FF based on altitude

Yes, but mine doesn't have the MP/RPM/FF combinations that I fly listed.

At 5000 feet and 2500 RPM I have:

MP 25.0 %HP 82 Fuel Flow 11.5

MP 24.0 %HP 77 Fuel Flow 11.0

MP 23.0 %HP 73 Fuel Flow 10.5

MP 22.0 %HP 70 Fuel Flow 10.1

There is no listing for 2500RPM 2500MP and 9.5-10GPH fuel Flow...

[OR75]

There is no listing for 2500RPM 2500MP and 9.5-10GPH fuel Flow...

that was my point . i did not find that combo either.

[jetdriven]

Atmospheric conditions change from day to day and you cannot set a ROP percent of power with a fuel flow number.

[201er]

Atmospheric conditions change from day to day and you cannot set a ROP percent of power with a fuel flow number.

Why?

[DonMuncy]

Because ROP, all the fuel is not being burned (and thus not producing power). There is no way of mesuring the power that is not being produced and thus no way of measuring what part of the fuel is not being burned.

[scottfromiowa]

that was my point . i did not find that combo either.

Sorry, my bad. I thought you were saying check your POH for information on engine operation and there is NOT information there regarding LOP operation.

My point is that my engine monitor is showing LOP at 9.5 to 10.0GPH fuel flow at 4500 feet with ALL cylinders below 350...so if he is setting fuel flow for 10GPH he should be LOP and NOT seeing such high cylinder head reading...and why he would benefit from an updated four probe EGT Cylinder Temp monitor. I look at this like a shoulder harness. IT is MUST HAVE item in 21st century.

[jetdriven]

Why?

mostly because of density altitude. 6,000 feet on the altimeter might be 5,000 density or 10,000'. On a standard atmosphere day those numbers may work out closely. But 95 degrees in Houston is 3,000 density sitting on the ramp. I abhor that "I only lean above 3,000 feet" statement. "I only lean above 3,000 feet density altitude when above 75% power in a climb" is quite appropriate.

Plus, you still have accuracy issues with fuel flow instrumentation, tachometers, and MP guages. Remember the difference between 50 ROP and peak might only be .3 GPH. However your RPM is within 50-75 RPM, the FF is within 5%, and the MP guage is only accurate to half an inch. Setting the MP / RPM / FF numbers printed on your sunvisor is really a cop-out, and is asking for engine damage. Degrees LOP/ROP are far more precise. Then verify with long-term CHT trend.

[fantom]

.....you still have accuracy issues with fuel flow instrumentation, tachometers, and MP guages. Remember the difference between 50 ROP and peak might only be .3 GPH. However your RPM is within 50-75 RPM, the FF is within 5%, and the MP guage is only accurate to half an inch.....Degrees LOP/ROP are far more precise. Then verify with long-term CHT trend.

Amen...amen...amen!

Don't make engine management harder than it has to be, and don't count on a degree of instrument accuracy that is both unavailable and unnecessary in our planes.

Over the long weekend I flew 100 ROP when in a hurry to get there, 7,000 ft, 2500 RPM, 24 MP, oil 186, ~1370 EGT, ~340 CHT, cowl flaps in trail ~10 degrees, TAS 162.

Coming home last evening not in a hurry, 6,000 ft, 15-20 LOP, about the same engine settings, TAS 154, and a FF of about 1.5 GPH less.

Life is good.

[scottfromiowa]

Amen...amen...amen!

Don't make engine management harder than it has to be, and don't count on a degree of instrument accuracy that is both unavailable and unnecessary in our planes.

Over the long weekend I flew 100 ROP when in a hurry to get there, 7,000 ft, 2500 RPM, 24 MP, oil 186, ~1370 EGT, ~340 CHT, cowl flaps in trail ~10 degrees, TAS 162.

Coming home last evening not in a hurry, 6,000 ft, 15-20 LOP, about the same engine settings, TAS 154, and a FF of about 1.5 GPH less.

Life is good.

What was fuel flow?

[fantom]

See Jim's post about. My Shadin Mini Flow has always read 8 to 12 percent high. Adjusting the K factor screwed things up worse....about 15 years ago....at the Mooney factory! Shadin pointed to Mooney and visa versa. I got a new Shadin out of the deal, but it still reads ~10 percent high....which is better than it reading low. Hopefully when I install a JPI 900 the issue will go away.

Be careful fooling with the K factor, Jim.

My FF was ~ 11.3 on the rich side, and about 9.8 LOP.

[OR75]

ROP or LOP, your choice based on your belief and engine monitoring devices you have ....

But you must be able to close the cowl flaps at flight level cruise.

[Wistarmo]

_{If I understand correctly, the original question had to do with engine temperatures and cowl flaps. It is quite a simple adjustment to have the cowl flaps open 1/4" when in the closed position. I did that a couple of years ago and it has eliminated the issue of temperatures rising with fully closed cowl flaps. It is a big help here in Central Florida. I have seen no adverse impact on cruise speed.}

[Becca]

It seems in cruise that if I close my cowl flaps all the way my CHT and oil temp start creeping up towards red line. I don't have a real engine monitor, just a single probe CHT and oil temp (and EGT in Celcius, WTF?) So I leave the cowl flaps in trail all the time. The baffling looks good, I'm just not sure if I can trust the gauges. I've got electronic FF and I usually run at either 2500RPM and WOT or 2500RPM and 24" depending on how high I am. I was told to aim for 10gph on FF so I do. I've played around with it and it doesn't seem that changing the FF changes the engine temps any noticeable amount.

Any advice?

Thanks,

Dave (1981 M20J)

I think the other people covered cooling options reasonably well. You might rig the cowl flaps so they are slightly open even when in the full closed position too, I think that's a relatively simple thing to do.

My advice is to get a multi-point engine monitor, in the long run it will save you more than it costs you - and I am not talking just LOP/ROP debate, but in terms of monitoring the overall health of your engine and individual cylinders and catching problems before they become expensive or dangerous..

I think you can get a used JPI unit installed for around $4000 all-included which should give you all the data you need, you don't need to get fancy. At least add it to your short-term upgrade list.

(Yes, I'm a zealous convert, I didn't think this was at all important when first bought our plane..)

[David White]

After I owned my 172 for a year I bought a JPI last year at SnF for $1400 with FF, I think I paid $600 to have it installed. I'm getting some avionics work done soon and I'll see if he can order me one.

[KSMooniac]

There seem to be a decent number of used EDM-700s on the market now for $1000-$1500 and that is a bargain IMO for all that it provides. If you got one with FF for $1400, then that was a MAJOR deal. I wouldn't own a plane without a monitor these days...perhaps the best bang-for-the-buck option we can add.

[fantom]

I'll have one available in a couple of months if anyone is interested. Had a complete IRAN software upgrade several years ago. OAT, and oil temp, but no FF. Of course I'll have a Shadin Mini Flow available, that for me anywhay read about 10 percent high. I think it's an installation issue, however, and will have it checked when I pull it out.

Let me know if anyone is interested.

[David White]

I went flying today. Due to wx it was brief but gave me the information I needed. I can't get it to stay cool ROP. It just won't work. I had it doing 12.5gph at 5500' WOT 2500 RPM and it was still getting very close to redline. When I tried doing LOP I got it down to about 9.0 gph and it was quite smooth, using my egt I figured I was about 25-50 degrees LOP. 10 knot speed penalty though, but I could close the cowl flaps! I'm having my avionics guy quote me a price for a new JPI when I get my work done.