Cold Weather CHT's (J Model)

[Slick Nick]

This is my first winter with my 1991 J Model. I'm trying to determine if I've got an issue with my CHT, either the gauge or probe. I live in western Canada, this time of year can get pretty chilly, especially at altitude. I can never seem to get the CHT's up very much above 200*F as shown on my stock gauge. It's that time of year where I blocked half the oil cooler off with tin tape (common Mooney practice in these parts) to keep the oil temps warm. I know cool cylinders mean a long lasting engine, I just want to make sure they aren't too cool, or that I have an issue with the gauge or probe.

My baffles are TIGHT and seal extremely well.

The other day, I did a 3.5 hour flight at 16,000' where the OAT was about -34*C as shown on my ship's gauge. (Jives with upper wind forecast temps.) With my half-blocked oil cooler, oil temps were stable at 170*F, but the CHT was barely touching 225*F on the gauge. Seems cool to me, even on a cold day? That was 7.1 GPH just lean of peak EGT. WOT, 2400 RPM. At that altitude, worked out to about 16" MP.

As an experiment, I took the plane up for a quick flight a few days later. OAT was -6*C. I went full power, 2600 RPM, leaned to peak EGT, kept the cowl flaps closed, and pulled the nose up to 70 knots for an extended climb. I wanted to get it as hot as I could. Oil temp went all the way up to 230*F, but the CHT topped out at 325*F. Seems to me, even though it was a chilly day, it should have been hotter than that? So, are these temps realistic? Or should I suspect an issue with the indication system?

Don't get me wrong, I know a cool running engine is a blessing. Living in western Canada, we get some absolutely incredible winter flying weather, very cold and crisp days. I just want to make sure I can take advantage of those while still being able to get my engine hot enough not to damage it, and make sure my CHT gauge is working properly. Plane is stored in a heated hangar year round. Thanks for any help that you can provide!

Edited November 20, 2024 by Slick Nick

[Will.iam]

Is that the original ship’s gauge that only measures one cylinder? If so i would highly recommend an engine monitor as you could have another cylinder that is running too hot and not know you are damaging it until it fails and you feel the roughness. This would also allow you to check that one probe is not failing or giving you a bad indication as you could compare it to other probes or past engine data logs you have from previous flights as just about all engine monitors these days has storage capabilities. Mike busch recommends cylinder head temperatures to be no lower than 250 degrees to help facilitate lead scavenging. If running cooler than that you could be at risk of lead buildup on the exhaust valve guide leading to morning sickness due from the start of valve sticking.  At that cold of temp i would be running at peak egt so as to get more heat from the combustion. LOP the cylinder heads run cooler than peak egt and you are wanting the cylinder heads to be at least up above 250. 

[Slick Nick]

8 minutes ago, Will.iam said:

Is that the original ship’s gauge that only measures one cylinder? If so i would highly recommend an engine monitor as you could have another cylinder that is running too hot and not know you are damaging it until it fails and you feel the roughness. This would also allow you to check that one probe is not failing or giving you a bad indication as you could compare it to other probes or past engine data logs you have from previous flights as just about all engine monitors these days has storage capabilities. Mike busch recommends cylinder head temperatures to be no lower than 250 degrees to help facilitate lead scavenging. If running cooler than that you could be at risk of lead buildup on the exhaust valve guide leading to morning sickness due from the start of valve sticking.  At that cold of temp i would be running at peak egt so as to get more heat from the combustion. LOP the cylinder heads run cooler than peak egt and you are wanting the cylinder heads to be at least up above 250. 

Correct. The stock probe goes deep into the well on cylinder #3. I have removed it, cleaned it, and reinstalled. Connections appear solid. No engine monitor (yet, it's in the works) so this is on the ship's gauge. Exactly my thoughts as well on making sure the cylinders are hot enough, which is why I'm asking. I don't suppose there is any sort of a "winter kit" like the Cessna's have for those of us who live in colder climates?

Edited November 20, 2024 by Slick Nick

[Will.iam]

10 minutes ago, Slick Nick said:

Correct. The stock probe goes deep into the well on cylinder #3. I have removed it, cleaned it, and reinstalled. Connections appear solid. No engine monitor (yet, it's in the works) so this is on the ship's gauge. Exactly my thoughts as well on making sure the cylinders are hot enough, which is why I'm asking. I don't suppose there is any sort of a "winter kit" like the Cessna's have for those of us who live in colder climates?

Not that I’m aware of but seems to me you could just tape a pencil on the inside of the cowling where the baffling meets to allow a gap on either side of the pencil and that would allow air to leak around the baffling instead of going down passed the cylinders and see if that would be enough to raise the cylinder head temps. Might need one pencil per side. Or maybe install the top cowl with the baffling folded back instead of forward? If the pencil worked, you could remove it and drill a hole on the baffling the size of the pencil and when the temperatures started warming up just duck tape over the hole. 

[kortopates]

Probably the vast majority of winterization mods for the oil cooler are fabricated in the field by just covering over the part of the oil cooler with some aluminum after first experimenting with some aluminum tape. But with only the 1 factory CHT probe I wouldn't want to touch that at all. You need proper instrumentation before doing that so I suggest holding off till you get an engine monitor. Given these piston engines are always trying to kill us, I would have done that yesterday!

[1980Mooney]

3 hours ago, Slick Nick said:

The other day, I did a 3.5 hour flight at 16,000' where the OAT was about -34*C as shown on my ship's gauge. (Jives with upper wind forecast temps.) With my half-blocked oil cooler, oil temps were stable at 170*F, but the CHT was barely touching 125*F on the gauge. Seems cool to me, even on a cold day? That was 7.1 GPH just lean of peak EGT. WOT, 2400 RPM. At that altitude, worked out to about 16" MP.

As an experiment, I took the plane up for a quick flight a few days later. OAT was -6*C. I went full power, 2600 RPM, leaned to peak EGT, kept the cowl flaps closed, and pulled the nose up to 70 knots for an extended climb. I wanted to get it as hot as I could. Oil temp went all the way up to 230*F, but the CHT topped out at 325*F. Seems to me, even though it was a chilly day, it should have been hotter than that? So, are these temps realistic? Or should I suspect an issue with the indication system?

Do you recall where your CHT's generally were using this single point gauge during the summer when cruising WOT down lower?  In the 300's?

Your case above was incredibly cold - about 17 deg C below Standard at 16,000 ft.  OAT was about -29 deg F. Corrected Density Altitude was about 14,000 ft.  You were operating at the extreme ends of both the Mooney POH cruise charts and also the Lycoming Fuel Consumption vs. HP charts.  At 7.1 gph LOP you might be making 90 HP. - so the engine is not producing a lot of heat.

[Slick Nick]

56 minutes ago, 1980Mooney said:

Do you recall where your CHT's generally were using this single point gauge during the summer when cruising WOT down lower?  In the 300's?

Your case above was incredibly cold - about 17 deg C below Standard at 16,000 ft.  OAT was about -29 deg F. Corrected Density Altitude was about 14,000 ft.  You were operating at the extreme ends of both the Mooney POH cruise charts and also the Lycoming Fuel Consumption vs. HP charts.  At 7.1 gph LOP you might be making 90 HP. - so the engine is not producing a lot of heat.

Yes it was an abnormally cold day at altitude. A giant low the day before had pushed east and that meant some arctic air being forced down to my latitude on the western side of the low. After I landed, the bottom of the wings had fuel frost on them for over an hour!

I bought the plane in September, so I haven’t had a chance to fly it in “hot” weather at all. Nothing above about 15*C on the ground. Then, my CHT’s were just a hair over 300-325. I don’t know if it’s also worth noting that my home field is at 4000’ ASL. 

[Slick Nick]

Here is a photo I took on the day in question. The CHT gauge isn’t super clear, but it was right around the 200* mark for most of the cruise portion of flight. 
 

 

[AndreiC]

As others have said, the first thing to try would be to run rich of peak in these temps (maybe 75 degrees ROP?), while also covering some part of the oil cooler with aluminum tape. If this is not enough to get your CHTs, I would get a full engine monitor and see if all my cylinders have the same problem, and proceed from there.

[EricJ]

Next time you have the cowl off, make sure that CHT probe is clean and seated properly.   Also check that the connections are good back to the display instrument.

And if it's on your radar, start thinking about a proper engine monitor.   They're a good investment.

 

[Ragsf15e]

1 hour ago, Slick Nick said:

Here is a photo I took on the day in question. The CHT gauge isn’t super clear, but it was right around the 200* mark for most of the cruise portion of flight. 
 

 

Being from Canada, you probably already know this, but definitely bring some extra survival gear!  I fly on “cold” days down here in Washington, but I’ve only seen -20c before my heater couldn’t keep up (I was already wearing a hat).  If your engine dies and you make a beautiful landing in a field, don’t let the rescuers find your dead frozen body next to the airplane with no gear/fire/mummy bag!  But being from Canada, you already knew this…

 

Edited November 20, 2024 by Ragsf15e

[Slick Nick]

1 hour ago, AndreiC said:

As others have said, the first thing to try would be to run rich of peak in these temps (maybe 75 degrees ROP?), while also covering some part of the oil cooler with aluminum tape. If this is not enough to get your CHTs, I would get a full engine monitor and see if all my cylinders have the same problem, and proceed from there.

Yep, as I said in the original post, the oil cooler is currently about 70% blocked with speed tape. Does a great job. 

34 minutes ago, EricJ said:

Next time you have the cowl off, make sure that CHT probe is clean and seated properly.   Also check that the connections are good back to the display instrument.

And if it's on your radar, start thinking about a proper engine monitor.   They're a good investment.

 

Probe was removed, cleaned, and reinstalled. Also used contact cleaner down into the well where the probe sits. Connections appear good. 
 

Yes, an engine monitor is in the works.

[Slick Nick]

14 minutes ago, Ragsf15e said:

Being from Canada, you probably already know this, but definitely bring some extra survival gear!  I fly on “cold” days down here in Washington, but I’ve only seen -20c before my heater couldn’t keep up (I was already wearing a hat).  If your engine dies and you make a beautiful landing in a field, don’t let the rescuers find your dead frozen body next to the airplane with no gear/fire/mummy bag!  But being from Canada, you already knew this…

 

Believe it or not, even up at that altitude, I wasn’t able to keep my heater knob pulled all the way without getting hot! I just had my heat muff rebuilt and I gotta say it works like a hot damn!

[Bartman]

I cruise LOP as SOP, but the higher the cruise, the closer I lean toward peak EGT or even slightly ROP.   The IO-360 formula of 14.9 x Fuel Flow will give HP while LOP and anything less than 60%, then I would be at peak EGT or slightly ROP.  Down low, I lose around 5 knots and, depending on altitude may be as much as 15-25deg LOP, but enjoy fuel savings of 2-3gal/hr.  That's a good tradeoff.  It has been my experience that at 16,000 ft, the speed penalty would far outweigh any benefit to running LOP and I would be more like 5deg ROP.  My engine runs better there at those higher altitudes.

[Bartman]

In winter, I also adjust my cowl flaps to be flush or nearly so in the closed position.

[Slick Nick]

2 hours ago, Bartman said:

In winter, I also adjust my cowl flaps to be flush or nearly so in the closed position.

Yes, I just had my cowl flaps re-rigged, and all new bushings installed in the linkage. They sit flush when closed, and have zero play in any position. 
 

 

[Slick Nick]

Okay I will try running ROP or at peak next time I go up, and collect some more data points. It’s supposed to be pretty cold through the weekend so will be a good opportunity to do some experimentation. . 

[PT20J]

According to the Lycoming power charts, an IO-360-A running at 16" MAP and 2400 rpm, at a pressure altitude of 16,000' and -34 deg C OAT will only be producing 105 hp at best power mixture. Leaning to slightly LOP will cost you about 10 hp more. So during your cruise condition, the engine was only putting out about 95 hp. It's really less than that because the Lycoming charts are for an engine on a test stand and the engine installed in the airplane is less efficient due to restrictions in the induction and exhaust systems. So, maybe 90 hp. No wonder the CHT (and the airspeed) is low. 

 

[PT20J]

3 hours ago, Bartman said:

In winter, I also adjust my cowl flaps to be flush or nearly so in the closed position.

The early 201s had a flat left cowl flap and you can adjust it to let more (or less) cooling air flow through it when it is in the close position. The later models like the MSE had a left cowl flap that is shaped like the right one with an opening for the exhaust. So, the MSE will flow more cooling air with the flap fully closed than the earlier models.

[Slick Nick]

31 minutes ago, PT20J said:

According to the Lycoming power charts, an IO-360-A running at 16" MAP and 2400 rpm, at a pressure altitude of 16,000' and -34 deg C OAT will only be producing 105 hp at best power mixture. Leaning to slightly LOP will cost you about 10 hp more. So during your cruise condition, the engine was only putting out about 95 hp. It's really less than that because the Lycoming charts are for an engine on a test stand and the engine installed in the airplane is less efficient due to restrictions in the induction and exhaust systems. So, maybe 90 hp. No wonder the CHT (and the airspeed) is low. 

 

Okay that makes a lot of sense. I was absolutely flying in “Econ” mode that day! Worked out to about 135 KTAS.