Interesting Oil Temperature Issue...

Well, I think we found it.

We took the oil cooler off today and the bottom 1/2 (the inflow 1/2) certainly looks plugged...at least partially. It seemed to be "crudded up" with a substance that was eerily similar in color to the varnish that MoGas leaves behind on various part...yes I burn about 75% MoGas.

The passages are so tiny that it's hard to tell for sure though.

IF this is indeed it, I guess I find it surprising that a new oil cooler would plug up in 6 years/625 hours especially since I'm running with an oil filter and not just a screen. Maybe a function of MoGas and those tiny passages....??? :dunno:

It's being cleaned up by a local shop and will be re-installed as soon as the local UPS driver...who's been to my house on countless occasions...removes his head from his butt and remembers where we are again. He couldn't find us yesterday. He has the gaskets...I wish I had them...especially heading into a holiday weekend...
 
BTW...If this is indeed it...I still don't understand why it used to be an intermittent issue that's now become continuous...
 
timwinters said:
BTW...If this is indeed it...I still don't understand why it used to be an intermittent issue that's now become continuous...
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Fluid flow in pipes can be a little non-intuitive with scale build-up on the walls. Oil gets cold, it stops flowing, oil gets warm it starts flowing again right up to the point the effective inside diameter is so small that it prevents flow of even the hot oil.

Maybe that's the explanation...maybe it isn't.
 
Clark...

What it used to to is:

...run high temps/low press right after an oil change.

...stay high for maybe 15 minutes...maybe 2 hours...maybe 2 days...

...the return to normal and remain normal until the next oil change...

...change oil again...

...repeat process...

I used to think that maybe "an air bubble" was developing in the oil cooler when I changed the oil and that it took some time to flush it out. But now that we've had the vernatherm off and back on...and now have the oil cooler off...and I see how everything is piped...there's no way that was the issue...

I'm at a loss on that one really, and so is the mechanic.
 
timwinters said:
Clark...

What it used to to is:

...run high temps/low press right after an oil change.

...stay high for maybe 15 minutes...maybe 2 hours...maybe 2 days...

...the return to normal and remain normal until the next oil change...

...change oil again...

...repeat process...

I used to think that maybe "an air bubble" was developing in the oil cooler when I changed the oil and that it took some time to flush it out. But now that we've had the vernatherm off and back on...and now have the oil cooler off...and I see how everything is piped...there's no way that was the issue...

I'm at a loss on that one really, and so is the mechanic.
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Just discussion points...several things change the base oil viscosity over time, fuel contamination is a large variable which usually reduces viscosity, combustion products usually increase the viscosity, and shearing of the oil by any gears will reduce viscosity.

It could have been that new oil wouldn't flow well through the cooler until it had been diluted or sheared to reduce viscosity. After the viscosity was down oil would flow and cool just fine.

Perhaps now the oil can't get thin enough to flow (too much scale build-up has restricted the ID to the point that not enough oil flows to make a significant contribution to cooling) and so it runs hot all the time.

Another thing to consider is that the scale may be a bit of insulator so the heat flow capacity of the cooler is reduced.
 
Thanks Clark.

Hey, do you know what propane prices might do this winter by chance? :)
 
So, oil cooler was flushed and came back squeaky clean. We re-installed it this morning and went flying.

No change...

Oil temp climbed slowly to 195 (OAT was 70dF @2500') and pressure dropped to 43.

I did a steep turn (60 deg bank) 360 degrees in both directions. By the time I exited the second 360 the oil temp was down to 176 and the pressure up to 52. I find that to be an amazing change for less than 90 seconds of maneuvering.

These readings were confirmed with both my engine monitor and stock gauges so it's not a gauge/sensor issue.

Once back to straight and level the temp slowly climbed back up to 195. It took 4 or 5 minutes to do so.

I'm completely perplexed. Plan to call Continental Monday.

Everything is still well in the green...but the oil's 10 to 15 degrees hotter (and press 10 PSI lower) than this engine has historically run. Something's not right and the steep turn change is really confounding.
 
timwinters said:
So, oil cooler was flushed and came back squeaky clean. We re-installed it this morning and went flying.

No change...

Oil temp climbed slowly to 195 (OAT was 70dF @2500') and pressure dropped to 43.

I did a steep turn (60 deg bank) 360 degrees in both directions. By the time I exited the second 360 the oil temp was down to 176 and the pressure up to 52. I find that to be an amazing change for less than 90 seconds of maneuvering.

These readings were confirmed with both my engine monitor and stock gauges so it's not a gauge/sensor issue.

Once back to straight and level the temp slowly climbed back up to 195. It took 4 or 5 minutes to do so.

I'm completely perplexed. Plan to call Continental Monday.

Everything is still well in the green...but the oil's 10 to 15 degrees hotter (and press 10 PSI lower) than this engine has historically run. Something's not right and the steep turn change is really confounding.
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Gotta be airflow through the cooler...
 
N801BH said:
Gotta be airflow through the cooler...
Click to expand...

Yeah, but it's not in the back like some nor is it served by ducting or scat, it's right up front at the cowl opening in front of #5 cylinder. And nothing has changed that would affect the airflow.

Maybe an experiment with a "scoop" built around it........

:dunno:
 
timwinters said:
Clark...

What it used to to is:

...run high temps/low press right after an oil change.

...stay high for maybe 15 minutes...maybe 2 hours...maybe 2 days...

...the return to normal and remain normal until the next oil change...

...change oil again...

...repeat process...

I used to think that maybe "an air bubble" was developing in the oil cooler when I changed the oil and that it took some time to flush it out. But now that we've had the vernatherm off and back on...and now have the oil cooler off...and I see how everything is piped...there's no way that was the issue...

I'm at a loss on that one really, and so is the mechanic.
Click to expand...

Have you ever replaced the Vernatherm?
 
From a few posts up:

"These readings were confirmed with both my engine monitor and stock gauges so it's not a gauge/sensor issue."

Besides... as the temp drops the pressure rises (as one would expect it too). This too confirms that it's an actual change and not gauge/sensor issue.
 
timwinters said:
From a few posts up:

"These readings were confirmed with both my engine monitor and stock gauges so it's not a gauge/sensor issue."

Besides... as the temp drops the pressure rises (as one would expect it too). This too confirms that it's an actual change and not gauge/sensor issue.
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You said you have an oil filter kit right? Will changing just the filter reset the cycle? Are you possibly triggering the bypass?
 
Henning said:
You said you have an oil filter kit right? Will changing just the filter reset the cycle? Are you possibly triggering the bypass?
Click to expand...

Don't know...Oil filter and pump are the next targets of investigation. Regrettably...because it involves pulling the engine...

Oh, I should have said...my next target is a call to Continental to see if they have insights.
 
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Tim, I have seen meta-stable fluid flow patterns shifting back and forth with no discernable trigger. Air is a (compressible) fluid. Pretty far fetched but could the manuevering trigger shifts in the air flow pattern through the engine compartment that result in different air pressures at the back side of the cooler? This would change the air flow through the cooler. This would not account for the changes after an oil change. or - if the temperature in the sump isn't totally homogenous, flow pattern shifts in the sump could result in picking up warmer or cooler oil.

Where I've seen this is was in the outlet pipe (hot leg) of a power plant reactor with water at about 2000 psi and 500 plus degrees. The outlet temperature across the top of the core is not constant across about a 12 ft. diameter and had not become totally mixed before reaching the temperature sensor in the hot leg. At steady state conditions, the indicated temperature would shift between two different values as the flow pattern shifted from one meta-stable condition to the other.
 
Henning said:
You said you have an oil filter kit right? Will changing just the filter reset the cycle? Are you possibly triggering the bypass?
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I'm trying to wrap my brain around how the bypass could affect oil pressure...any insights?

I can see how the oil pressure relief valve, if not properly seating, would affect things...and it is, I've confirmed that (I think anyway), but the bypass valve? Not sure exactly how it works, only that it bypasses the filter if it's getting plugged.

(Oh, and to answer your question, check out post #84)
 
timwinters said:
I'm trying to wrap my brain around how the bypass could affect oil pressure...any insights?

I can see how the oil pressure relief valve, if not properly seating, would affect things...and it is, I've confirmed that (I think anyway), but the bypass valve? Not sure exactly how it works, only that it bypasses the filter if it's getting plugged.

(Oh, and to answer your question, check out post #84)
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Sure, oil filter takes up oil pressure and flow (typically the sender is after the filter), open the bypass and both pressure and flow through the cooler increase.
 
Henning said:
Sure, oil filter takes up oil pressure and flow (typically the sender is after the filter), open the bypass and both pressure and flow through the cooler increase.
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The pressure on the cooler inlet will increase slightly and the outlet will decrease slightly when the bypass closes. The net pressure on the cooler does not increase with bypass opening or closing. The cooler is always connected to the oil pressure system. Always. The only way to get more pressure on a cooler is for the relief to stick shut or the oil to be very cold. The relief valve on some engines is at the end of the oil gallery system, meaning that the drag of the whole gallery is on that cold, stiff oil and the upstream end will see higher pressures. The oil cooler guys sometimes see bulged cooler channels due to that.

fig9.jpg


See that oilo cooler bypass valve? it's open when the oil is cold and lets the oil scoot across between the cooler inlet and outlet connections, effectively bypassing the cooler. When the vernatherm pushes into that spot, the oil has to pass through the cooler. But the pressure is always on the cooler simply because it's always connected to the pressure system. It's never actually shut right off.

Dan
 
Dan Thomas said:
The pressure on the cooler inlet will increase slightly and the outlet will decrease slightly when the bypass closes. The net pressure on the cooler does not increase with bypass opening or closing. The cooler is always connected to the oil pressure system. Always. The only way to get more pressure on a cooler is for the relief to stick shut or the oil to be very cold. The relief valve on some engines is at the end of the oil gallery system, meaning that the drag of the whole gallery is on that cold, stiff oil and the upstream end will see higher pressures. The oil cooler guys sometimes see bulged cooler channels due to that.

fig9.jpg


See that oilo cooler bypass valve? it's open when the oil is cold and lets the oil scoot across between the cooler inlet and outlet connections, effectively bypassing the cooler. When the vernatherm pushes into that spot, the oil has to pass through the cooler. But the pressure is always on the cooler simply because it's always connected to the pressure system. It's never actually shut right off.

Dan
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Where is the STC'd filter in that drawing? It will be after the cooler where the pressure screen is. When the filter is bypassed, flow will increase through the cooler, and increase the pressure at the sender which is post filter.
 
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Henning said:
Where is the STC'd filter in that drawing? It will be after the cooler where the pressure screen is. When the filter is bypassed, flow will increase through the cooler, and increase the pressure at the sender which is post filter.
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Why would the filter be bypassed? Filters only bypass when they're plugged up with crud. Dirty oil is better than no oil. If the filter's bypass opens it doesn't increase downstream pressure. The bypass opens easily, taking a timy bit more pressure tha it takes to push the oil through the filter media.

Screens have no bypass function. Spin-ons have it built in.

Dan
 
Tim,

How much oil do you add after an oil change? It may be worthwhile to fill it with 12 and see if your condition changes.
 
I typically add 10 + a pint of camguard. That allows two quarts for makeup oil over 30 hours or so between changes and that's typically all it needs, so a case of oil is "perfect" for my engine's cycles.

But...earlier in the thread someone (maybe you?) suggested topping off so I did. No change.

:(
 
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Re: Interesting Oil Temperature Issue...the plot thickens...

...or the oil does...

Interesting new finding today (at least I think so):

I went flying late morning, low and slow up the Mississippi to my hometown like I enjoy doing. Never getting over about 300' AGL.

Oil temps ran about 195dF and pressure about 41 psi (OAT was 70dF). In the green but not the "cool" readings I typically saw before the oil temps started acting up.

Then, on my return trip I decided to climb to a higher altitude just to see if that made a difference. So, since I was eastbound, I climbed up to 5,500'...and climbed purposely aggressively to see how hot things would get (climbed at 1,200 to 1500 FPM). Oil temp got up to 210*F and pressure down to 39 PSI. Still in the green but definitely not readings that give me a warm and fuzzy when WOT.

So, I leveled off and set the engine up at 22"/2300 and leaned aggressively. The oil settled back down to 200dF & 41 PSI (OAT 60dF). I ran about ten minutes back towards Cape, checking readings, scrolling thru the engine monitor, etc. Everything is normal...except the oil temp/press...which had gradually lowered to 196dF. Then I notice that I'd lost about 400' of altitude so I yank back on the yoke, without changing any engine settings, and aggressively climb back up to 5,500' (20* + nose up). In the 15 seconds or so that it took to climb 400', the oil temps dropped from 196 to 185. Then after I re-established straight and level it continued to fall.

It fell to 170dF and the pressure climbed to 53psi (OAT was 60dF). And it STAYED THERE for the 20 minutes I remained at altitude returning to Cape.

hmmmm.....

So, I landed, and took back off.

Again, climbed aggressively to 5,500' and went thru the same routine. The oil temps were similar or the same as what is outlined above. The only difference, the first aggressive 500' climb at altitude didn't change anything. The second one, however, did and the oil temps again REMAINED cool for about 15 minutes as I returned to Cape at 5,500'.

So...

That would explain why steep turns lowered the temps. It wasn't the bank that was doing it (since we all agree that the oil doesn't know the plane is banking in a coordinated turn)...it was the (airplane's perceived) climb during the turns...throwing the oil towards the back of the engine...that was doing it.

So, what is getting primed by the oil getting tossed towards the back of the engine?

I think I'm more confused than ever...easy to do...

Still plan to call Continental in the A.M.
 
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Cracked oil suction tube, getting covered by oil in a steep climb. Drop the sump and check it out. Not sure on your engine but you may be able to do this with the engine in the aircarft. How does the oil look immediately after shutdown ?. Is it getting aerated ??. Somewhat milky looking?.
 
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Vaflier said:
Cracked oil suction tube, getting covered by oil in a steep climb. Drop the sump and check it out. Not sure on your engine but you may be able to do this with the engine in the aircarft. How does the oil look immediately after shutdown ?. Is it getting aerated ??. Somewhat milky looking?.
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That's one of the suspects but...

Why would the temps remain low for 20 minutes of straight and level?
 
timwinters said:
That's one of the suspects but...

Why would the temps remain low for 20 minutes of straight and level?
Click to expand...

Well as I am sure you know this is just speculation and thinking out loud but my hunch would be the oil is getting some air mixed into it on startup and then when in flight he climbs steeply the oil shifts in the sump and covers a small crack in the pickup tube cutting off the air. Then the oil acts as a seal in the crack until it is allowed to settle back into ghe sump such as very low power settings or engine shutdown. As I said purely speculation. But if he is lucky this can be checked without engine removal for the cost of a sump gasket and an hour or two of time. If the oil becomes aerated it will not cool as effectively causing a rise in oil temp and a pressure drop.
 
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Dan Thomas said:
Why would the filter be bypassed? Filters only bypass when they're plugged up with crud. Dirty oil is better than no oil. If the filter's bypass opens it doesn't increase downstream pressure. The bypass opens easily, taking a timy bit more pressure tha it takes to push the oil through the filter media.

Screens have no bypass function. Spin-ons have it built in.

Dan
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It depends on the adapter, some have their own bypass valve.
 
Called Continental this morning...they are just as perplexed as my mechanic and I are. He kept saying it sounded just like a vernatherm problem. I told him that's what we thought too and that's why the vernatherm was the first thing we replaced. I also told him that the one we removed had a nice shiny 360* ring on the seat indicating that it had been fully seating...and that I dropped it in boiling water and got a little over 1/4" extension. "That's good," he said, "usually you get about 3/16 or a bit over."

We discussed removing the vernatherm and installing a plug as a test.

He dismissed the "cracked pick-up tube" theory as highly unlikely.

He also dismissed the pump or bearings being the issue (because the filters are always clean when cut and oil analysis reports excellent).

One suggestion he had was to call Champion and discuss the filter by-pass with them. So I did. Summary of that conversation: Even when the filter is in bypass, it's no different than what the engine experienced when a screen was installed and should not negatively affect press/temp.

I "might" change the filter just to see if, somehow, I got a bad one...the last oil change preceded the issue since it wasn't hot yet.

I "might" take the entire F&M oil filter adapter off and re-install the screen (I'm pretty sure I have it laying around here somewhere) as a test.

Leave it to me to have a true "stump the chump" issue......

Again, the only saving grace is that everything is still well in the green...it's just not where I know it should be...
 
The filter bypass opening would not negatively affect it, it would positively affect it back to what the screen gives. When you pull the adaptor, check to see if it has any restrictions that could cause the filter to bypass early.
 
Vaflier said:
Cracked oil suction tube, getting covered by oil in a steep climb. Drop the sump and check it out. Not sure on your engine but you may be able to do this with the engine in the aircarft. How does the oil look immediately after shutdown ?. Is it getting aerated ??. Somewhat milky looking?.
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Is the oil pickup toward the front or rear of the engine?

A ground run up long enough to check the aeration theory may help.

Never heard of this on a piston engine, though. wouldnt some of the air accumulate in the cooler?
 
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