Rising oil temp + falling oil press = uh oh....

[M016576]

So there I was....

at the tail end of a 4 hour trip returning from Idaho.  The entire flight through nevada had proven frustrating: a 25kt headwind, plus light to moderate turbulence the whole way (7500-12500').  The normally 3.1 hour flight took just over 4 hours.... ugh...

and... to add injury to insult...

As I was decending out of 12.5, I noticed that the oil pressure, which is normally stable at 65psi, had fallen to 55psi.  meanwhile, the oil temperature had steadily increased to 205 degrees from the normal 170-180 degree range I was used to seeing.  No need for panic or special action, I was already setting up to land (fortunately), so I just kept it coming.  I noticed that as I transitioned, the oil temperature continued to rise (not unexpected, the temperature at pattern altitude was about 100 degrees F).  As I pulled the throttle back during the pattern, the oil pressure fell to 45psi, then as I pulled the throttle to idle over the numbers, it fell to 35psi (but was stable there).  I quickly taxiied back to the line, all the while my JPI EDM830 was screaming OIL TEMP at me (it was at 230 degrees by this point).  As I got into the line, the oil press was still 35psi (at 1000rpm)... I did a quick experiment: I ran the throttle up to 1800rpm.  As I did, the oil pressure climbed back up to 55psi, and the oil temperature actually dropped 7 degrees.  I shut down quickly after the experiment (not wanting to tempt fate any longer).  The next day I went back to the field to check her out.  I didn't start it up, but I did check the oil-> it didn't smell funny, and seemed pretty clean, with a steady 6qts in the sump (it has been 17 hours since my last oil change, and I launched with 6.5 quarts prior to the 4 hour flight)... anyway, I called up the local A&P and we're going to pull the cowling and check it out entirely tomorrow...

I'm thinking it is one of two things:  A) oil cooler is clogged up a bit (not good... maybe the pump is shedding metal into the system or going bad) or the oil pressure relief has failed, or come out of adjustment somehow (maybe in the bouncy turbulence?)?  Has anyone seen anything like this before, or heard of anything like this happening?  If so, what was the outcome?  I was only airborne for about 10 minutes from when the oil pressure started to drop and when I shut down (the JPI EDM 830 was handy for determining the exact timeline of when the PSI started to drop and temp started to rise.  Turns out the temp started to rise before the PSI started dropping... leading me to the oil cooler... ugh...).  Anyway, I'll post tomorrow after I know more, but hoping that someone out there may be able to comment or has some insight into this... Thanks!

-Job

[carusoam]

From an engineering point of view...

It is expected that viscosity drops when the temperature rises. 

Very hot day will cause an increase in oil temperature, which in turn causes a decrease in viscosity, showing lower pressure.

What weight oil is in the engine?  Might you consider a heavier weight oil.

I like your idea of chasing down the cleanliness of the oil cooler.  You definitely want to make sure it is working properly, not sludge filled and certainly not getting by-passed.  There are tests for this and your A&P will be able to know.

Let the engineering discussions begin....

Best regards,

-a-

[M016576]

Well, I've returned from a few hours with the local A&P...

First off, I printed out the JPI information showing the steady rise in oil temp, followed by oil pressure dropping off.  (quick plug for this info-> what a powerful diagnostic tool, having all this availble).  The fuel flows, egt's and CHT's were all relatively constant during the oil temp increase, so the A&P wanted to see and smell the oil.  We checked the oil (right at 6 qts) and went from there.  The oil didn't smell funny, or have any metal shavings visibly apparent so we fired her up and flew her around the pattern.  Sure enough, as the oil heated up, the oil temp rose up to about 200 (but slowly, like it normally would just to a higher temp), and the oil pressure dropped off in to the low 60's (61ish).  on the roll out, same thing, 55psi or so.  We taxi'ed back to the hangars and dropped the lower cowling, plus took a low oil sample for shop analysis... All the big parts were still there and intact (of course )...

The A&P's thought is that it is the low(6qt) oil state causing the high temps and low PSI, due to the 100+ degree temperature OAT.  We filled her up to 8 quarts and I'm going to take her flying in a day or two to see if that helped.

I've been using aeroshell 100W Plus in the motor, which has served me well up to this point.  The more I think about it, the low oil option seems to be a pretty good one due to the ambient temperatures.  All in all, better safe than sorry, and I'm interested to see what the oil analysis says (hopefully this is all just a case of me needing to top off a qt prior to the flight)!

on a side note- I know 6 qts is the minimum "safe for flight" level of oil in the motor, but has anyone had any experience operating right at 6 qts?  I think I've read somewhere that the motor should still be able to run effectively down to 3-4qts, but I can't seem to find a source for that anywhere now that I'm looking for it... anyone heard anything like this? 

                                                                 -Job

[carusoam]

Job,

As you suspect, the oil is used as a "coolant".  Similar to radiator fluid in the car,  it is best to keep a higher level, thus allowing things to cool before cycling through the engine again.

The hot weather will cause an increase in oil temperature, but it should still stabilize.  If it continues to increase while the engine is running steady (check your JPI data) this would warrent serious concern.

Serious engine damage can be a cause of overheated oil.  Oil analysis should be able to point that out quickly.  Bearings going bad can cause things to heat up.  They will show tell-tale metal signs.

Keep up the vigilence.  Flying with full oil, on a cooler day should give comparable JPI data of previous flights. 

How long does it take to get you oil analysis back?  If its only a few days it may be a good idea to wait for it.

In the POH (my 76 M20C - Owners Manual): Section 1-5 Oil Capacity (6 QTS MIN for flight)....8 QTS

Lycoming 0-360s have been rumored to run on much less.  Things are well as long as oil is reaching the oil pump without picking up air.  Temperature will rise and oil pressure will fall with less oil in the system.  It will run, but it will not run the same. 

Oil's ability to lubricate is directly linked to its viscosity.  As it gets hotter, the viscosity becomes less.  If it is burning, such as in a bad bearing, the viscosity will go away.

If oil burns, I suspect you will smell it when taking a sample.

See what the cost of removing and cleaning the oil cooler would be...

Best regards,

-a-

See previous thread with similar issues:

http://www.mooneyspace.com/index.cfm?mainaction=posts&forumid=2&threadid=1051

[scottfromiowa]

I ALWAYS check oil level before flight and add if below six quarts.  If 5.5 on dipstick I add a whole quart...to 6.5.  If 5 quarts i add a quart to six.  I routinely fly with six quarts of oil.  ( I have NEVER registered below five quarts after a flight.  If I add over this amount the oil is just ejected and a waste of oil...others may argue with this practice, but i routinely monitor oil temps in climb and cruise and my plane has never been out of the green on oil temp.  I had the oil cooler re-built with major overhaul 450 hours ago.  I don't do aggrressive climbs.  I cruise climb full rich and max power and 2700 rpm with airspeed at 120mph.  I am covering ground, improved visibility in climb and cooler oil and cylinder head temps.  We don't get 100 very often in Iowa/Wisconsin where I routinely fly, but we regularly get 80's and high humidity.

[Sven]

We've found that if put in more than 6 qts it eventually gets burned off or spit out. So, we usually keep it to six. Never any problems with temp or pressure.

[ErickR]

We're having the same issue with our m20b... Have been running aeroshell 15-50 between 6-6.5 qrts, if we run it with more it just blows out. We are going to try 100w and see if that makes a difference. Already replaced the oil temp sending unit, the bypass valve and the tempature gage, none of them were the culprit. I guess as a last resort I can try flying with 7-8 qrts and see if that helps (probably should have done this first.)

Good Luck!

[Jeff_S]

I'm fairly new to this engine but in my experience it wants to hang out right around 6 quarts on the dipstick. But I've let it get as low as 5 quarts on occasion and haven't noted any real problems...of course, not flying in 100° heat.

[Stefanovm]

I do not have the problem initially posted with this thread, but have been concerned about oil levels. When I fill to 7 or more, it is down to 6.25 in about 1/4 the time it takes to go from 6.25 to 6. I try to keep it at 6+. I have flown 100+ degree days enroute to AZ, Memorial Day weekend and had no pressure or temperature problems with no mre than 7 at any time.

I am concerned about the quick use, or loss, from 7+ to 6. My O-235 in my C152 would not keep more than 5, 4 minimum, 6 maximum in the engine for more than a 15 minute flight. I got tired of pouring in the top and then washing it off the belly. I may get the same way with the IO-360. It does not appear to be going to the belly of the Mooney, but it is many more square feet, so maybe. Both engines have, or had, close compression figures, none below 76 and average about 77+. The C152 had a Sparrow Hawk conversion with high compression pistons.

[Piloto]

Did you try opening the cowl flaps?. On hot days opening the cowl flaps to the mid position provides plenty of cooling with a minimum speed loss of 2kts. The more oil you have in the engine the cooler it will run. I have the M20 oil separator in my M20J and my oil burn at 8qts is 10hrs/qt, it is constant down to 6qts, engine has 300hrs TT.

José  

[PTK]

If you recall your POH states that for extended flights you need 8 quarts of oil.  Certainly a four hour flight qualifies as an extended flight. Also you may want to consider heavier oil in the heat.  I really like the performance Aeroshell 15W50.  Some people say it's pricey but I disagree.  Oil is not an item I'd want to cut cost in! 

[M016576]

Thanks for the insight, everyone! 

I'm going to wait until I get the oil analysis back from the shop (as suggested on the board) prior to taking her for a test run with 8qts.  Like Jose, my oil consumption is a little less than 10hrs per qt, and I haven't been "blowing oil overboard" as some people have described (ie, my consumption is steady, with little oil on the belly).  I went back through the POH after looking at allsmiles comment and sure enough, staring me straight in the face, was the obiquitous "take 8qts for extended flights." 

As such, I'm now adding the following to the old adage: "three things that do you no good: altitude above you, runway behind you and fuel in the truck"...

my new adage:

"Four things that do you no good: altitude above you, runway behind you, fuel in the truck and two quarts of oil sitting in the back seat unopened."

Thanks all!

-Job

[KSMooniac]

I only fill to 6 quarts as well.  I suggest you have a good supply of belly cleaner and shop towels ready after you get back from that flight with 8 quarts...   In the future if you wish to save time, just open a new roll of shop towels, and pour two quarts of oil all over it and then throw it away. 

[scottfromiowa]

Hey Scott...

 

 made me laugh on that one...

[M016576]

Scott from KS-

I've heard some people have problems keeping their oil level at 8 (it blows on their belly, so they keep it at a lower level).  I've never had that problem.  Don't know why, but mine fills all the way up to 8 and burns at a constant rate without "premature oil-ejection."  Perhaps its the environmentals, perhaps its the single weight oil, maybe it's just the motor.  either way, I've filled up to 8 in the past and not had a oil coated belly....  Sounds like some others have motors that hold all 8 quarts, too, though: you might want to have that looked at! (J/K )

                            -Job

[KSMooniac]

Job, yours does sound like a rare Lycoming!  That is great that it won't eject the first couple of quarts.

[Earl]

Quote: Stefanovm

I do not have the problem initially posted with this thread, but have been concerned about oil levels. When I fill to 7 or more, it is down to 6.25 in about 1/4 the time it takes to go from 6.25 to 6. I try to keep it at 6+. I have flown 100+ degree days enroute to AZ, Memorial Day weekend and had no pressure or temperature problems with no mre than 7 at any time.

I am concerned about the quick use, or loss, from 7+ to 6. My O-235 in my C152 would not keep more than 5, 4 minimum, 6 maximum in the engine for more than a 15 minute flight. I got tired of pouring in the top and then washing it off the belly. I may get the same way with the IO-360. It does not appear to be going to the belly of the Mooney, but it is many more square feet, so maybe. Both engines have, or had, close compression figures, none below 76 and average about 77+. The C152 had a Sparrow Hawk conversion with high compression pistons.

[Earl]

Quote: allsmiles

If you recall your POH states that for extended flights you need 8 quarts of oil.  Certainly a four hour flight qualifies as an extended flight. Also you may want to consider heavier oil in the heat.  I really like the performance Aeroshell 15W50.  Some people say it's pricey but I disagree.  Oil is not an item I'd want to cut cost in! 

[M016576]

Aftermath:  Oil analysis came back "clean" (no metal). I took N3891H flying yesterday filled up to 8qts and am happy to report steady oil pressure at 65ish psi, and stable oil temperature at 190 (OAT was just over 100)!  Turns out it was a case of not enough oil in the sump for a hot day, it seems....

                                                -Job

[skyking]

I am with most of you. Anything more than 6.5 quarts in the pan will soon be all over the bottom of my baby.

 

[PTK]

Quote: ehscott

I'm going by the POH.  This is my baseline and bible.  I also think that all you guys who say it will blow out are being presumptuous in saying 1.5 quarts will blow out in an hour.  I'm not sure that is accurate.  It has not been my eperience.  But even if this DOES happen so what ?  Let the engine do it's own determination how much oil it needs and WHEN at WHAT TEMPERATURES AND OPERATING CONDITIONS !!!  I would rather let the engine blow it out than purposefully starve it of oil !

[PTK]

What I'm saynig carries the assumption that your engine is healthy.  Before I deprive it of oil I would be certain its indeed a healthy engine.   So starting with a well functioning healthy engine I will give it 8 quarts for EXTENDED FLIGHT.  Why? Because the BOOK says so. And this is for EXTENDED FLIGHT folks! Lets not confuse extended flight with brief flight.  We can agree I think that a 4 hour leg in the J constitutes an EXTENDED FLIGHT.  And for the gentleman making a joke about towels and drenching them with oil, I do carry a pack of shop towels but I have never had to use them to clean oil from the belly!