How cool is to cool?

[The-sky-captain]

Two questions/ comments here... With the frigid winter temps here in the midwest my coolest CHT gets down to 290-300 while running LOP. The other 3 are in the 330 range. Other than running ROP I really don't see how this can be changed. Secondly my oil temp doesn't get over the magic 180 degree mark in cruise to burn off the moisture the Lycomings hate so much. It does get over the 180 mark in climb but cools down to 176-178 or so once cruise configuration is reached. Does this make my 3 hour cross country flights as useless for engine longevity as a ground run?

[Jeff_S]

No, because you are only considering the oil temperature at the gauge where you get your readings. These temps are generally somewhat cooler than the oil in the main friction zones, so even if your gauge is showing less than 180 it's a good bet that the oil is still getting hot enough to evaporate the moisture.

 

Plus, in most climates, the air is drier in the winter anyway so moisture and corrosion is less of a problem. I don't think you have anything to worry about.

[Marauder]

Two questions/ comments here... With the frigid winter temps here in the midwest my coolest CHT gets down to 290-300 while running LOP. The other 3 are in the 330 range. Other than running ROP I really don't see how this can be changed. Secondly my oil temp doesn't get over the magic 180 degree mark in cruise to burn off the moisture the Lycomings hate so much. It does get over the 180 mark in climb but cools down to 176-178 or so once cruise configuration is reached. Does this make my 3 hour cross country flights as useless for engine longevity as a ground run?

I just finished a trip on the east coast with my F model. The air temps were in the high 20s and my factory CHT never saw the green. My Insight GEM 602 showed the temps in the 300 to 350 range (mostly on the lower end). My oil temp was barely in the green. I have been flying this way for 22 years with this plane.

If your oil temp doesn't reach temp, I would be more concerned with this number. Running cool CHTs is not a bad thing. Running too cool of oil, is more concerning.

[aviatoreb]

I just finished a trip on the east coast with my F model. The air temps were in the high 20s and my factory CHT never saw the green. My Insight GEM 602 showed the temps in the 300 to 350 range (mostly on the lower end). My oil temp was barely in the green. I have been flying this way for 22 years with this plane.

If your oil temp doesn't reach temp, I would be more concerned with this number. Running cool CHTs is not a bad thing. Running too cool of oil, is more concerning.

 

So what exactly is bad about lower than 180 temps.  Is it the fact that water isn't burned off so the danger is the corrosion after you land while sitting in the hangar, or is it somehow the viscosity is wrong and you are not getting proper lubrication in tight places and so there is wear while running the engine in flight?

[carusoam]

Clearances will be different between hot and cold temps... -a-

[Hank]

Fonzie is cool; Fonzie in a P-51 is too cool; Fonzie jumping a shark is not cool at all. 

 

Do you think your oil temp is accurate at <180? You can test the probe easily, just run an extension cord or use a camp stove, remove the probe, boil some water and drop the probe in it, it should read 212º or a little less if you are high up in the hills or under a really low pressure system. Just don't let the probe touch the pot, use the wire to suspend it in the water.

[Marauder]

I just finished a trip on the east coast with my F model. The air temps were in the high 20s and my factory CHT never saw the green. My Insight GEM 602 showed the temps in the 300 to 350 range (mostly on the lower end). My oil temp was barely in the green. I have been flying this way for 22 years with this plane.

If your oil temp doesn't reach temp, I would be more concerned with this number. Running cool CHTs is not a bad thing. Running too cool of oil, is more concerning.

So what exactly is bad about lower than 180 temps. Is it the fact that water isn't burned off so the danger is the corrosion after you land while sitting in the hangar, or is it somehow the viscosity is wrong and you are not getting proper lubrication in tight places and so there is wear while running the engine in flight?

As Hank points out, your oil reading could be off. On the F I fly, it takes a long time to come off the peg in cold weather. It eventually does and even on the coldest days, the gauge will read on the green, often barely. If your gauge is accurate, the only thing I would be worried about is the engine getting warm enough to burn off any moisture. Even if your oil temp is 180, there is enough heat to disperse the oil.

I take the original engine gauge readings with some reservation. If they still have the original probes and meters, determining how accurate they are is challenging unless you have some way to compare. As I mentioned earlier, my factory CHT was in the non green area but my GEM was showing temps in the 350 range. I have a tendency to believe the newer data.

[The-sky-captain]

The probes are fine. I have the original factory probe as well as an oil temp probe hooked up to my EDM. Believe it or not but the factory probe is still pretty darn accurate. I'll be headed to N. MO tomorrow so I'll try to remember to note the correct OAT and oil temps.

[jetdriven]

The oil temp (In the J model) is read after the oil cooler. You probably still have the 212 degree oil temp in the bearings. The after oil cooler temp is lower.

 

Beech guys tape off half the oil cooler in winter. Might not be a bad idea.  Some JPI installations put the oil temp sensor in the oil gallery.  What do they read?

[tony]

That is interesting; the oil temperature sensor  in my F model is in the oil cooler adapter (before the oil cooler).  With this variability in the design across the M20 type, how could the oil temp (installed) limits be the same for all?  or are they different?

[aaronk25]

Hey I got some facts.  Skycaptain I have a m20j and have the same issue with mid 170s oil reading in cruise.  Identical to yours on climb out to.  Since I live in MN and it can be really cold up here I did a oil analysis on my last oil change at blackstone and there was "0" moister content to the oil!  

 

Hopefully make you feel better.  The only thing that can be done to get the oil temp up, besides (Jetdrives advise) is to run closer to peak egt, just be careful.  

 

Aaron

[aviatoreb]

So what exactly is bad about lower than 180 temps.  Is it the fact that water isn't burned off so the danger is the corrosion after you land while sitting in the hangar, or is it somehow the viscosity is wrong and you are not getting proper lubrication in tight places and so there is wear while running the engine in flight?

 

No one answered this and I am still curious.

[jetdriven]

i think the primsry risk is water building up.  If you are seeing 180 then the oil temp before the cooler is higher, and the temp in the bearings is higher still.   You want the oil to see 212 F somewhere. 

[aviatoreb]

i think the primsry risk is water building up.  If you are seeing 180 then the oil temp before the cooler is higher, and the temp in the bearings is higher still.   You want the oil to see 212 F somewhere. 

 

So is this correct: that is a corrosion risk?  Not an inflight risk?

[jetdriven]

 I think primarily its an engine longevity issue due to moisture remaining in the oil and causing corrosion. That said,  I wouldnt take off with zero degree oil in the engine, I give it ten minutes to warm up.  Our 1977 owner's manual says do not runup or fly until the oil temp indicates off the white dot, which is 75 degrees F.  But that is after the cooler.  We used to do that but do not anymore. It would take 20 minutes of ground running to get the oil temp up to that.  In the 1982 POH at least, that reference is deleted.

 

On the 201 the oil temp is measured after the cooler and we usually show 180 degrees, which, perhaps is 200 before the cooler, and 212 somewhere in the engine.  Beech guys tape up 1/2 of their oil coolers with aluminum tape to get the oil temp to acceptable numbers in the winter.

 

It is my understanding the JPI probe is mounted in an oil gallery in the front of the engine on some installations. i'd be curious what the JPI is showing for oil temp compared to the factory guage.

[aviatoreb]

 I think primarily its an engine longevity issue due to moisture remaining in the oil and causing corrosion. That said,  I wouldnt take off with zero degree oil in the engine, I give it ten minutes to warm up.  Our 1977 owner's manual says do not runup or fly until the oil temp indicates off the white dot, which is 75 degrees F.  But that is after the cooler.  We used to do that but do not anymore. It would take 20 minutes of ground running to get the oil temp up to that.  In the 1982 POH at least, that reference is deleted.

 

On the 201 the oil temp is measured after the cooler and we usually show 180 degrees, which, perhaps is 200 before the cooler, and 212 somewhere in the engine.  Beech guys tape up 1/2 of their oil coolers with aluminum tape to get the oil temp to acceptable numbers in the winter.

 

It is my understanding the JPI probe is mounted in an oil gallery in the front of the engine on some installations. i'd be curious what the JPI is showing for oil temp compared to the factory guage.

 

Thanks Byron,

 

Yes, that is what I thought.  I have been thinking about taping some of my oil cooler since on cold days (high 20s) I see only high 160s but I am having a hard time deciding how much to tape.  We have been getting such wild temp variations around here in recent years.  If it is 0F (on the ground) like it was last Friday when I flew to middlebury VT, I didn't even get up to 160F during the flight.  But then this weekend coming it will be 50F and I am sure that even without tape I will see 180F. So I am inclined to tape just a little bit for winter ops.  Following this very thread - I am in discussion with my AP about how much to tape.

 

That said, and ...not to open an old debate so please forgive me - if I crack my oil dipstick to allow airflow, and with my "turbo reiff" running full time time in the hangar, and wrapped in a cowl blanket, if I do finish a cold flight where oil temps are not high enough indeed I see a dabble of water on the dipstick - and when I return the next day it is dry as a bone in the crank case as far as I can tell.  To back this up all my blackstone oil analysis always shows 0% measured water in the oil.  Doesn't that alone indicate something good?  I believe the more powerful full system heaters cause an airflow of rising heated air through the crank case that dries it out the oil from the last flight, hopefully faster than the oil drips off the parts - it is protected from corrosion as long as there is recent oil on the parts.  That's my theory and I am sticking with it...for now.

 

Warm enough oil for take off is another discussion entirely and thanks for bringing it up.  I personally want to see 110F before I roll, and 100F before I will begin my mag check rpms, at the hold short line.  Fortunately with the turbo reiff I will see 90+F on the oil before I even start up even if it is in the 20s and 30s F outside and even 80+F on the oil if it is 0F out.  (Generally I don't like to fly if it is below 0F since 1) an off field landing if necessary becomes dangerous even if you are not injured, and 2) my nose and fingers get too cold in the preflight!  Usually those temps can be avoided if I fly in the middle of the day - most days - but not always - in which case negative farenheit is grounds to cancel, in my own personal comfort book).

[pinerunner]

I think the issue is that water can actually settle out and accumulate in the bottom. Solubility of water in oil is very low so it will separate out. To make it worse used oil can contain organic acids that would enhance the corrosive power of any water in the oil. Dry winter air won't save you since we make water in our engines. Therefore getting our oil hot enough to boil off water is important for engine health.

[aaronk25]

My jpi shows 162-165 in the winter in cruise. My oil analysis shows. ZERO water. I call BS on not evaporating the water out of the oil at temps below 180 in cruise. Water evaporates regardless of oil temp, but I agree it evaporates faster at higher temps. I tapped off 1/2 my cooler and my oil temp indicated 200-208 in cruise and oil consumption went up to 1 qt in 5 hours instead of 1 qt in 7hours running Phillips 20w-50w.

[Alan Fox]

Now that is cool ........

[N201MKTurbo]

Two things

If the water settles to the bottom of the sump, it will be sucked up by the oil pump and emulsified as soon as the engine is started.

Taping the oil cooler seems like a bad idea. The vernatherm should regulate the oil temperature. Cold weather is not the problem, hot weather where full flow through the cooler is not good enough is the problem.

No matter what your oil temp is, the best thing you can do to keep your engine from rusting is to fly it regularly.

[Cruiser]

 I think primarily its an engine longevity issue due to moisture remaining in the oil and causing corrosion. That said,  I wouldnt take off with zero degree oil in the engine, I give it ten minutes to warm up.  Our 1977 owner's manual says do not runup or fly until the oil temp indicates off the white dot, which is 75 degrees F.  But that is after the cooler.  We used to do that but do not anymore. It would take 20 minutes of ground running to get the oil temp up to that.  In the 1982 POH at least, that reference is deleted.

 

On the 201 the oil temp is measured after the cooler and we usually show 180 degrees, which, perhaps is 200 before the cooler, and 212 somewhere in the engine.  Beech guys tape up 1/2 of their oil coolers with aluminum tape to get the oil temp to acceptable numbers in the winter.

 

It is my understanding the JPI probe is mounted in an oil gallery in the front of the engine on some installations. i'd be curious what the JPI is showing for oil temp compared to the factory guage.

 

On the IO550 it is only a couple of degrees at most. I just checked the JPI data compared to a photo of the instrument panel on a flight I made last May. The factory guage was 196 and the JPI was 203

[carusoam]

That's only cool on BT, Alan...

Best regards,

-a-

[pinerunner]

Jon Deakins hs an interesting article

 

Pelican's Perch #84: Don't Set Mixture with CHT 

 

I think it applys here, at least somewhat. His point in short is not to set one number in stone as your target just based on what he and Busch (not mentioned by name) say. In PP#84 Deakins mentions the changes seen when operating the same plane in winter and problems if you try to get the CHT up to 380 as you had it in summer. I think this article makes a good counter to Busch's reccomendation to use CHT's rather than EGT's.  I also think that they're not really disagreeing, but emphasizing things in a different way.

 

I think you need to expect lower CHT's in the winter. I think there is a lower temperature limit where the lead scavengering  compounds in the fuel don't work as well but I don't know where this is. Perhaps check your spark plugs and if no deposits you're OK.

 

I do the the big pull and then set the fuel flow to a value I determined earlier in the year using EGT's to find peak and then get all cylinders LOP with the richest at  30 LOP.  So I'm not routinely goiing into the red box, hunting for peak. I routinely note the CHT's to make sure not too hot. I think I'll redo the EGT check in the winter to get realistic expectations for CHT when its colder.  I also think we should rethink our upper CHT limits in the winter. Getting briefly to 400 on a hot day may just be cause to drop the nose to improve cooling and  back off a little on the power. In the winter, if it manages to get that hot even with the much denser and colder air then somethings likely wrong.