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-   -   Oil baffle and oil temps (https://vansairforce.net/community/showthread.php?t=209069)

Saville 08-14-2022 04:44 PM

Oil baffle and oil temps
 
So every Fall I attach an aluminum plate to the backside of my oil cooler to try and keep the oil temps up. It seemed to work ok though the temps were never very high.

I would take it off in the Summer. But once off, the temps rarely got above 180 degrees. Usually more like 160.

This Spring and Summer I kept the baffle on. It's mid August and it's still on. Now the temps are 180-190. 200 if I have to sit at the hold short line for a long time. Temps are int eh green during climbs.

I'm wondering if my Verna-therm is working? I would think that baffle would need to come off in the Summer but so far I can see no need.

Strikes me that something isn't right here.

What do you all think?

Saville 08-14-2022 05:14 PM

P.S. After one flight I ran a temperature check by measuring the oil temp with a thermometer and comparing that to the instrument readout. They coincided.

I thought that maybe the readout was incorrect but that possibility was eliminated.

DanH 08-14-2022 07:11 PM

Quote:

Originally Posted by Saville (Post 1627043)
I'm wondering if my Verna-therm is working?

Those results suggest your vernatherm is working very well.

Saville 08-15-2022 07:00 AM

Quote:

Originally Posted by DanH (Post 1627080)
Those results suggest your vernatherm is working very well.

If the verna-therm was working, why did the oil temps never exceed 160 when the baffle was not installed?

DanH 08-15-2022 08:12 AM

1 Attachment(s)
Quote:

Originally Posted by Saville (Post 1627155)
If the verna-therm was working, why did the oil temps never exceed 160 when the baffle was not installed?

Because there is always some flow through the oil cooler, regardless of vernatherm position.

The vernatherm extends when warmed. It is fully extended at about 185F. When it extends, it blocks a bypass hole. With the bypass blocked, all oil is routed through the cooler.

At 160F, the vernatherm is retracted, and the bypass is open. Oil flows through both the cooler and the bypass.
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WingsOnWheels 08-15-2022 09:34 AM

My oil temps run low during the winter as well. I just installed a set of the cooler shutters, we'll see how they do (haven't flown them yet). My install is not ideal with the shutter on the cooler outlet, but install on the inlet would have required much more baffle rework. Since I am in the south, It isn't as great an issue as many northerners have. Problem here in Texas is that the temps can swing wildly, so just a simple blockoff plate would be a pain.

Saville 08-15-2022 09:46 AM

Well to be clear, my problem is that the oil is too cool in the Summer as well as Winter.

The only way I can get the oil temps at or above 180 degrees in the Summer is to keep the baffle block on.

This doesn't seem right to me.

DanH 08-15-2022 10:43 AM

3 Attachment(s)
Quote:

Originally Posted by Saville (Post 1627207)
Well to be clear, my problem is that the oil is too cool in the Summer as well as Winter.

The only way I can get the oil temps at or above 180 degrees in the Summer is to keep the baffle block on.

This doesn't seem right to me.

"Summer" and "winter" are meaningless in terms of analysis. The conditions of interest are engine type, OAT and power setting. Parallel valve engines without piston squirters require less oil cooling. Heat transfer rate is influenced by DeltaT, oil to air. And LOP operation typically reduces both CHT and oil temperature.

180F is perfect, per Lycoming. If you're there, you're fine. I assume your concern is oil temp in the 150's and 160's when OAT and power are both low. If someone it telling you oil must reach 212F to boil off water, hand him a physics text.

The "always flow in the cooler" design was to accommodate very cold climate operation, and yes, that is rather counter-intuitive given it tends to over cool the oil. The problem was single weight oil in the cooler becoming so viscous in an arctic blast that it would not flow, forming a plug of sorts in the cooler during the initial phase of flight. As oil temp rose, the vernatherm would try to close, but oil couldn't flow through the plugged cooler, and with no flow, it would not warm enough to unplug. That's why a vernatherm has a spring loaded tip (see below). The warming vernatherm will extend to block the bypass, but if the cooler is plugged, the tip will float off the seat at about 15 psi deltaP, allowing continued oil flow to the engine.

You can gain absolute control of cooler flow rate by removing the vernatherm, then installing a "viscosity valve" spring and plunger assembly in the accessory case, and a 1/4 turn ball valve in one of the cooler lines. The valve can be cockpit controlled. The SI attached below explains how to remove the viscosity valve and replace it with a vernatherm. Just reverse the process.
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rv8ch 08-15-2022 11:36 AM

Quote:

Originally Posted by Saville (Post 1627207)
Well to be clear, my problem is that the oil is too cool in the Summer as well as Winter.

The only way I can get the oil temps at or above 180 degrees in the Summer is to keep the baffle block on.

This doesn't seem right to me.

I have the same "problem", but I'm not really convinced it is a problem. If the only reason for the desired higher oil temperature is getting the combustion water out of the oil, and we all know that much water will go out the breather, and water will evaporate at lower temperatures with lower pressure, and there are plenty of spots in the engine with very high temperatures (like under the piston), do we really need to get the oil up to 180? Is 160 warm enough? If the oil is flowing, lubricating, capturing particles, protecting against corrosion, and cooling the engine, why do we care if the temp is 150 or 200? Are there special additives in the oil that are only activated at a specific temperature?

Saville 08-15-2022 12:02 PM

Quote:

Originally Posted by DanH (Post 1627220)
"Summer" and "winter" are meaningless in terms of analysis. The conditions of interest are engine type, OAT and power setting. Parallel valve engines without piston squirters require less oil cooling. Heat transfer rate is influenced by DeltaT, oil to air. And LOP operation typically reduces both CHT and oil temperature.

180F is perfect, per Lycoming. If you're there, you're fine.

I am NOT there. That's the problem.

I assume your concern is oil temp in the 150's and 160's when OAT and power are both low.

All incorrect assumptions.

All the rest, below, ignored as not relevant to the question. No one said anything about needing 212. No one is talking about a plugged cooler in the summer time.


If someone it telling you oil must reach 212F to boil off water, hand him a physics text.

The "always flow in the cooler" design was to accommodate very cold climate operation, and yes, that is rather counter-intuitive given it tends to over cool the oil. The problem was single weight oil in the cooler becoming so viscous in an arctic blast that it would not flow, forming a plug of sorts in the cooler during the initial phase of flight. As oil temp rose, the vernatherm would try to close, but oil couldn't flow through the plugged cooler, and with no flow, it would not warm enough to unplug. That's why a vernatherm has a spring loaded tip (see below). The warming vernatherm will extend to block the bypass, but if the cooler is plugged, the tip will float off the seat at about 15 psi deltaP, allowing continued oil flow to the engine.

You can gain absolute control of cooler flow rate by removing the vernatherm, then installing a "viscosity valve" spring and plunger assembly in the accessory case, and a 1/4 turn ball valve in one of the cooler lines. The valve can be cockpit controlled. The SI attached below explains how to remove the viscosity valve and replace it with a vernatherm. Just reverse the process.
.


Ok my wondering if the Vernatherm was malfunctioning (or incorrectly set) was based on the possibility that it was letting oil flow to the cooler BEFORE it got to 185. Nothing you've said proves that this isn't happening. But let's not go down that rat hole right now.

So I'll restate the question:

Flying the Northeast, OAT~68, O-360, level at 23 squared, or climbing at 24 squared, no baffle plate on the back side of the oil cooler blocking the air flow, I can't get my oil temps up to 180.

In the Winter, with the baffle plate on, I can't get the oil temps up to 180 in any flight regime.

Oil cooler is at the left hand side of the engine baffle.

This strikes me as unusual. Is it?

Most of the times I see people talking about oil temp problems, they are talking about oil getting too warm - especially in the climb. I've read lots of those.

Is this a common problem (oil temps too low) requiring some alteration the air flow-through in the oil cooler?

I would have thought that given the oil temp sweet spot of 180 , that designs would be such that they would get you in that vicinity. Maybe I'm wrong.

So, flying in the Northeast:

With no baffle on the oil cooler I rarely get my summer flying temps above ~160

With a full plate on the back of the oil cooler I can't get my oil temps up above 160. Usually it's less.

I would have thought that is unusual.


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