Interesting Oil Temperature Issue...

timwinters

timwinters

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58 C182A
O-470L, 3335 TT, 1217 SMOH. Both engine and cylinders are original, third run.

This engine has always had an interesting oil temperature anomaly. I used to fly a lot of XC for work and on the first XC after an oil change I would notice that the oil temp was about 15dF higher than normal and it might remain elevated 10 minutes, or it might for an hour. And then it'd return to normal and remain normal until the next oil change. It didn't elevate after every oil change but definitely the vast majority of them.

Interestingly, and completely by chance, I figured out that a 360 deg steep turn to the right would correct the temp issue. The cooler is on the right so a 45 deg bank significantly lowers it relative to the engine.

This year, since it's turned warm, the engine is running hot all the time (about 200dF instead of 185dF on an 85dF day). I thought maybe it was the vernatherm so we put a new one in today...no change. Temps were 200dF on the flight home from the mechanic's field, the exact same as they were on the way up. At today's temps aloft they should have been running about 185.

So...

On the way home I did a 360 deg steep turn to the right and temp dropped from 200dF to 187dF in the short time it took to do the turn. But, then it began slowly climbing as soon as i re-entered straight/level...back up to 200dF. A second 360 deg turn produced the same results...as did a third.

Okay engine gurus...

WTF?
 
timwinters said:
Stats:
58 C182A
O-470L, 3335 TT, 1217 SMOH. Both engine and cylinders are original, third run.

This engine has always had an interesting oil temperature anomaly. I used to fly a lot of XC for work and on the first XC after an oil change I would notice that the oil temp was about 15dF higher than normal and it might remain elevated 10 minutes, or it might for an hour. And then it'd return to normal and remain normal until the next oil change. It didn't elevate after every oil change but definitely the vast majority of them.

Interestingly, and completely by chance, I figured out that a 360 deg steep turn to the right would correct the temp issue. The cooler is on the right so a 45 deg bank significantly lowers it relative to the engine.

This year, since it's turned warm, the engine is running hot all the time (about 200dF instead of 185dF on an 85dF day). I thought maybe it was the vernatherm so we put a new one in today...no change. Temps were 200dF on the flight home from the mechanic's field, the exact same as they were on the way up. At today's temps aloft they should have been running about 185.

So...

On the way home I did a 360 deg steep turn to the right and temp dropped from 200dF to 187dF in the short time it took to do the turn. But, then it began slowly climbing as soon as i re-entered straight/level...back up to 200dF. A second 360 deg turn produced the same results...as did a third.

Okay engine gurus...

WTF?
Click to expand...


Air flow through the cooler is getting disturbed???:confused::confused:.......:dunno:
 
Something trapping air in the oil cooler? Sort of a vapor lock phenomenon. Maneuvers move the block out of the way momentarily. Maybe time for an oil cooler flush?

Steve
 
A coordinated turn to the right/left will not change the oil's position.

Your oil temps are not high.......the variation is probably in the indication system.
 
kgruber said:
A coordinated turn to the right/left will not change the oil's position.

Your oil temps are not high.......the variation is probably in the indication system.
Click to expand...

Yes, yes they are.

I have both an EI Engine monitor and the stock gauges. They are completely independent of each other. Both reflect high temps and correspondingly lower pressures.

When the oil temp is 185 the pressures are 50ish.

When the temp is 200, the pressure is 42ish.

Always in the green, either case.
 
Why? My redline is 225. I said the temp was high...not at redline.

And, I certainly have a lot more confidence cruising at 50psi than 42...but both are in the green.

Or maybe your mission is to play games and be pedantic.
 
Weird, thought I just replied to this.

Thinking along the lines of pressure, turn lowers the pump and centrifugal force creates higher pressure making the pump more efficient.

After oil change, you needed the higher pressure to loosen something up.

Guessing.

Indication of failing pump? Or a stable but weak pump? Maybe no problem at all
 
Check your cowl flaps, one is blowing closed.
 
Have you tried a level skidding turn to see if centrifugal forces get the air out of the cooler? I'm assuming that your steep turns were 100% coordinated.

Dan
 
Dan Thomas said:
Have you tried a level skidding turn to see if centrifugal forces get the air out of the cooler? I'm assuming that your steep turns were 100% coordinated.

Dan
Click to expand...

No, worth a try. And yes, my 360s are coordinated...essentially.
 
Do you have the STC'd spin oil filter on this engine ?. If so then my guess is that when it was installed it moved the oil temp probe further back away from the air blast tube that was aimed at it. This causes the temp sender to read hotter or to be exact , to read more accurately since the blast tube cooled it and lowered the temp reading to make it read what Cessna wanted it to. When you are turning the air flow inside the cowling is changing and cooling the probe a little more. When you go straight it goes back up again. Ok its late and I getting sleepy so that is my best guess at this point and I may actually be incapable of rational thought. Goodnight.
 
Geico266 said:
Oil is good up to 245F. Don't worry about it.
Click to expand...


Glad to hear that. I just got back from a flight where the oil temp hit 235! Of course, the OAT was 115, so that probably didn't help.

I was asking as little from the engine as possible, and had reduced climb rate to 200 fpm. Still hovered around 235. Leveling out at altitude, it made its way back down to 210-220 or so....
 
dans2992 said:
Glad to hear that. I just got back from a flight where the oil temp hit 235! Of course, the OAT was 115, so that probably didn't help.

I was asking as little from the engine as possible, and had reduced climb rate to 200 fpm. Still hovered around 235. Leveling out at altitude, it made its way back down to 210-220 or so....
Click to expand...

Try the "stair step" climb approach. Normal climb until the oil hits 220 then level off for a while to cool. Repeat. Slow climbs are not good in hot weather, IMHO.
 
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Norman said:
I would suspect air is getting into the cooler at oil change.
Click to expand...

I thought about that too, Norm but...then I thought...wouldn't the cooler (hard mounted to the side it the case immediately adjacent to the prop) drain at every shut down? Why would draining the sump change anything?

Unless...

Changing the oil filter allow the cooler to drain when it otherwise doesn't.

When we changed the vernatherm yesterday (which is right next to the oil cooler on the front of the case), and while cleaning the seat, I noticed that the oil passageway leading to it extended (from what seemed to be) all the way to the rear of the engine...maybe a direct line from the pump? Which is adjacent to the oil filter.

(Aftermarket filter, F&M "pistol grip" design, no external hoses like the Air Wolf)
 
BTW Norm...you'll appreciate this...

I asked this question over on the CPA site too. Pretty much silence thus far. One guy responded thus far and he's wildly shooting from the hip. That place is a ghost town compared to what it was ten years ago. It'll be interesting to see if any constructive input is offered. I won't hold my breath. But if it does come it'll be from the peanut gallery and not anyone from CPA.

Cessna Autopilot Association.
 
Does anyone know of a document that describes the lubrication system of an O-470 both verbally and pictorially?

I have the Operator's Manual, the Overhaul Manual, and the Illustrated Parts Catalog and none show the "system, " rather only the individual components.

I'm trying to wrap my head around how the oil flows through the engine...and specifically if the tube I'm looking at with the vernatherm removed is a supply line or return line.

Also, there are two openings in front of the vernatherm seat. One to the side, going to the cooler. One dropping straight down.

Lastly, from what I've read the vernatherm is open when the oil is cool and this allows oil to bypass the cooler, Then it closes when the oil temp rises forcing the oil to circulate thru the cooler. Looking at the design of the vernatherm, this seems backwards and unintuitive. It is a spring loaded t-stat, just like the one in a car. Not sure how the spring would strengthen as the oil temp rises and force the vernatherm closed.

????
 
timwinters said:
I thought about that too, Norm but...then I thought...wouldn't the cooler (hard mounted to the side it the case immediately adjacent to the prop) drain at every shut down? Why would draining the sump change anything?

Unless...

Changing the oil filter allow the cooler to drain when it otherwise doesn't.

When we changed the vernatherm yesterday (which is right next to the oil cooler on the front of the case), and while cleaning the seat, I noticed that the oil passageway leading to it extended (from what seemed to be) all the way to the rear of the engine...maybe a direct line from the pump? Which is adjacent to the oil filter.

(Aftermarket filter, F&M "pistol grip" design, no external hoses like the Air Wolf)
Click to expand...

My thought is based on a 421 I used to work on. At every oil change, we had to prime the oil pump. It was fine the rest of the time. Had to have a leak somewhere that was letting the oil drain back into the sump.
 
timwinters said:
BTW Norm...you'll appreciate this...

I asked this question over on the CPA site too. Pretty much silence thus far. One guy responded thus far and he's wildly shooting from the hip. That place is a ghost town compared to what it was ten years ago. It'll be interesting to see if any constructive input is offered. I won't hold my breath. But if it does come it'll be from the peanut gallery and not anyone from CPA.

Cessna Autopilot Association.
Click to expand...

I've heard that place has gone downhill. Haven't been there since 2006 and you know why. LOL.
 
Norman said:
My thought is based on a 421 I used to work on. At every oil change, we had to prime the oil pump. It was fine the rest of the time. Had to have a leak somewhere that was letting the oil drain back into the sump.
Click to expand...

But the pressure is fine right after the change, Norm. 75 to 80 psi when cold.

Or, are you inferring that I might should have to "prime" the oil cooler? That possibility is distinct. Have no clue how that would be accomplished though.
 
I didn't read all the posts, it's just an air bubble trapped in a part of the cooler, and as the engine runs, the flow gradually pushes it out.

Try about 30 seconds of inverted flight next time, that'll do it. (j/k)
 
docmirror said:
I didn't read all the posts, it's just an air bubble trapped in a part of the cooler, and as the engine runs, the flow gradually pushes it out.
Click to expand...

That indeed used to be the apparent case. The problem is, the temps typically no longer returning to normal but rather stay high. And, on the rare occasion that the temp does return to normal, the issue returns at the next start-up. Used to be, the issue only came back after an oil change.

I'll likely pull the cooler and see if there's a blockage...but I don't think that's the problem, or the temps wouldn't lower so quickly in a steep turn.

????

Someone over at CPA suggested that I might try topping off the sump to 12 qts. to see if that fixes it. That's a cheap experiment so I'll likely try that first before trying anything else.
 
This happens in Porsches and Lamborghinis all the time but in the water coolant chambers. We have a heck of a time on some older models getting all the entrained air out of the cooling system. On one old car, I got so fed up with the problem, when I had a head off, I located the water jacket at the back of the head, and drilled and tapped a vent hole. I did NOT like drilling into a V12 Lambo engine, but it fixed the problem.
 
Tim,

What oil do you use? Have you switched recently? Have you attempted to run any solvent additives like MMO in the oil? I'd be wondering if the pickup tube in the sump was restricted or compromised.
 
timwinters said:
Lastly, from what I've read the vernatherm is open when the oil is cool and this allows oil to bypass the cooler, Then it closes when the oil temp rises forcing the oil to circulate thru the cooler. Looking at the design of the vernatherm, this seems backwards and unintuitive. It is a spring loaded t-stat, just like the one in a car. Not sure how the spring would strengthen as the oil temp rises and force the vernatherm closed.

????
Click to expand...

The vernatherm gets longer when hot and closes off the bypass channel so that the oil has to flow to the cooler.


Called the "Oil cooler bypass valve" in this picture.



Dan
Edit: Why doesn't my picture show up? tried three times...
 
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723839926_Fu4cW-M.jpg
 
What is the orientation of the ports on the oil cooler? Ideally you want to introduce oil at the bottom and remove it at the top. Is it possible that the hoses were reversed at some point?
 
What type of oil temp and pressure intpstruments are you using?

you indicated that pressure dropped with higher temp. It may be that temp rises with lower pressure. You may be chasing the symptom, not the problem.
 
Another thought. Do you use a 110 filter? And your adaptor has the bypass function? Most big TCM guys I know have had the bypass machined out of the adaptor and switched to 108 filters. Something else to add to the list.
 
timwinters said:
But the pressure is fine right after the change, Norm. 75 to 80 psi when cold.

Or, are you inferring that I might should have to "prime" the oil cooler? That possibility is distinct. Have no clue how that would be accomplished though.
Click to expand...

Discussed it with my former boss at lunch. He, too, seems to think "Airlock" in the cooler.
 
The parts manual shows an eight bolt congealing type cooler.

Oops! It also shows a 12 bolt cooler depending on engine specification.
 
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timwinters said:
Yes, yes they are.

I have both an EI Engine monitor and the stock gauges. They are completely independent of each other. Both reflect high temps and correspondingly lower pressures.

When the oil temp is 185 the pressures are 50ish.

When the temp is 200, the pressure is 42ish.

Always in the green, either case.
Click to expand...

Stewartb said:
What type of oil temp and pressure intpstruments are you using?

you indicated that pressure dropped with higher temp. It may be that temp rises with lower pressure. You may be chasing the symptom, not the problem.
Click to expand...


Oil viscosity decreases with increasing temperature so the lower pressure at higher temps, all else being equal, makes sense just on a viscosity basis. Lower viscosity requires less pressure to achieve the same flow rate. I would have no less confidence at 42 psi than at 50 psi, unless the temps were the same at 42 and 50.

Belaboring the point a bit, but this is why we have oil cooler bypasses in the first place. When the oil is cold its viscosity is very high compared to when it warms up and it would require a very high pump pressure to force that thick stuff through the cooler - and would result in lower flow rates. So we bypass it with the vernatherm.

As far as cooling during the 360 right turn, I'm guessing there is a slight change in airflow due to change in AOA and yaw.

But I doubt this has to do with trapped air -

1) why would a 360 deg coordinated turn even be evident to said bubble any more than it is to the seat of the passengers' pants? The resultant "weight" (normal force) vector doesn't change during a coordinated turn.

2) In any case, even if it did, the inside of the cooler is serpentine so being in a turn wouldn't necessarily help a bubble get "out" - and

3) even if it did help it out why would the temps return to relatively higher values after ceasing the turn supposedly without the bubble? In any case,

4) the viscosity of even hot oil is orders of magnitude higher than the viscosity of air. Air of any significant volume would be moved through the cooler by the oil pretty easily.

The bubble hypothesis is implausible.
 
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