cold weather oil temp's

[zero.one.victor]

Hang onto your hats-- I'm with George on this one! (I think). The blast tubes are blowing on the oil screen housing of the accessory case. They are cooling the oil there. All the oil goes thru there, so all the oil is getting cooled, however slightly. Just because that's where the temp bulb is doesn't mean anything. If the bulb was downstream of the cooled area, it'd still read the same.If it was upstream of the cooled area, it'd read higher. Just like a temp sensor upstream or downstream of a conventional radiator-style oil cooler would read higher or lower. Miles makes a good point that you can't cool the bulb without cooling the oil surrounding it.
I run 20-50 Phillips year-round. I cover the oil-sump opening in the nosebowl in the winter. I also cover the inlets of the blast tubes inside the engine cowl, with little alum patches held on by one of the blast tube mounting bolts. They stay in place year-round, and are pivoted over or away from the inlet opening as the season dictates.
Doesn't make a big difference, but every little bit helps. If I was in colder climes, I'd probably make some cowl inlet covers too. 419A's are not real pretty,but they are effective,adjustable, and affordable. Function triumphs over form every time!

Eric

[cessna170bdriver]

Miles I think the oil at the sensor is cooler but it doesn't accurately reflect the temperature of ALL the oil. An yes by it's nature the blast tube would cool the oil but not significantly.

We may be getting into semantics here, but we really don't need to know the temperature of ALL of the oil, just that which is about to be fed to the moving parts of the engine. Within the accuracy of the particular gauge we are using, that is what the sensor in it's standard location is giving us. If the gauge indicates a lower temperature then cooler oil is actually being fed to the engine. In other words, I don't think you can lower the temperature of the sensor without actually lowering the temperature of the oil.

FWIW, as George says, the TCDS for the engine specifies an oil INLET temperature. But the 170B IPC shows the "oil temperature adapter" (figure 50, item 25) installed in the pressure screen (oil pump OUTLET). When I overhauled my engine in 1990, I replaced the pressure screen with the Cessna oil filter adapter, and had to move the oil temp sensor to the inlet screen . My indicated oil temp dropped about 20 degrees (using the same gauge), but I attribute this mostly to the presence of the filter, and to the fact that the engine was in better shape overall; not a real indication of a difference between inlet and outlet temps.

Since the temperature readings we use in other seasons has the blast tube cooling that spot how would you compare a reading of 180 degrees i the summer with the blast tube against 180 degrees in the winter without the blast tube. In other words your changing the calibration of the measuring system. IMHO.

A valid test would be to check oil temp with and without the blast tubes being blocked under the same conditions, for example: on about a 30 degree day, go fly with the blast tubes open, let the oil temperature stabilize, then land, block the tubes, go flying again, and let the oil temp stabilize under the same flight conditions, and note the difference, if any, in oil temperature. (CMA: As there seems to be no "approved data" supporting the blocking of the blast tubes, perform this test at your own risk. As usual, be careful to remain within all published limits!)

My point all along is that I have not found it necessary to block the blast tubes to raise my oil temperature to 180 degrees at an OAT of 20F.

That's true for your airplane at +20F, but I sure wish I had thought to give it a try on the day I took off at +7F and cruised at -20, and couldn't get the oil temp above about 125.

[GAHorn]

In regards to oil temps, I think we sometimes get a little distracted by the name we call it. The oil temperature limit.... is not a warning by Continental that we are going to "hurt" our oil. They could care less about the effects upon the oil. (Modern oil grades are more durable anyway.)
The oil circulating thru our engines carry away significant amounts of heat from the engine parts. If that oil's temp is so high it cannot readily absorb additional heat, then the engine's parts will suffer. So, TCM wants limit the maximum oil inlet temperature.
From the engine type certificate data sheet: Maximum oil inlet temperature limit is 240°F, when using Spec. MHS-24 oil SAE No. 50 above 40°F ambient and SAE No. 30 or 10W30 below 40°F ambient.

(Notice that the grades of oil permissible do not include 20W50, or 15W50, for the increased limit.)

Miles is correct as we all know, that the screen where the probe is originally located is the pressure screen. It is immediately downstream of the oil pump. I apologize for the brain-pharrt in my previous post.
By design that is the inlet to the pressure-oil lubricating system, and therefore why the oil temp is measured at that point.

Of course this thread is mostly concerned with getting oil temps up during winter ops. The age-old problem I keep observing is the wild variance among gauge accuracy from plane to plane. Heck, the early gauges (green arc/redline) weren't particularly concerned with the exact temp of the oil at all, except the red line itself. TCM did not specify a minimum oil temp in the TCDS, but commonly accepted practices among aviators is to try to keep the oil temp up to drive out water. I doubt the "un-official" 180 degrees is really necessary. Water evaporates all the way down to the freezing point. (It's called sublimation when it's already frozen.) Any water in the oil is likely the result of the previous flight's shut-down. Because an operating engine is making water vapor, and because some of it ends up in the sump during shutdown/cooldown, it's necessary to get that water heated back up to get it to a state it can be driven out of the sump by the succeeding ring-blow-by. If succeeding engine ops don't get the oil temp up, then ever-increasing amounts of water may be left in the sump. But, If the oil temps are above 100-125 then water will be driven out of the oil, given sufficient flight time, IMHO. If the airplane isn't flown at least an hour each flight with oil temps at/above 125, then perhaps the oil should be changed more regularly. (The foregoing having been derived from extensive laboratory testing, of course.)

[bodine]

That's all good stuff i like it. ill just have to start playing around and find my combo. my 170 seems to run cooler all the time anyhow. Bruce we should try to get a gathering at sentimentle that's one of the best little fly inn's around...

[jrenwick]

Covering up the blast tubes that duct air to the oil screen does not really raise your oil temp. It only increases the indicated temp by raising the temp at the sensor in the screen.

Oil in the engine has a different temperature at different points in the engine. The bearings and cylinders heat it up. The oil pan cools it. You have to measure it at some point where all the oil flows through, and in a straight O-300, the only such place is the lower accessory case near the pump. So if you're blowing cool air on the engine at that point, are you really cooling the oil?

Now we're splitting hairs. Some are saying that there is a temperature gradient from the exterior of the case to the bulb to the oil itself, and the bulb might actually be cooler than the oil it's immersed in, especially if a blast tube is blowing cool air on the case exterior. Maybe so, but how do you prove that?

Here's a "thought experiment." Imagine an apparatus that pipes all the engine oil out of the case, right where the temperature bulb is, and feeds it to an external temperature sensor before sending it back to the engine. If you block off the blast tube and the oil temp at the external sensor goes up, doesn't that mean the blast tube was actually cooling the oil? To put it another way: if you block off the blast tube and the internal bulb registers a higher temperature, wouldn't you expect the external sensor to register a higher temperature as well?

Best Regards,

John

[GAHorn]

It doesn't matter. The mfr specifies that the oil temp is determined at the location provided, in the manner provided for. All the rest is interesting, but unimportant.
It's sort of like the doctor taking your temperature orally or rectally. The reading is a compensated reading.

[Bruce Fenstermacher]

Ok some real numbers from my early cowled 170 A model with an internal cooling box. The Pennsylvania air measured 32F on my OAT with the engine turning 2600 RPM turning a semi cruise prop at about 110 mph and about 23 inches of manifold pressure. Engine slightly leaned. 100w oil (yes I need to go to a thinner oil)

A round inspection cover effectively blocking the oil sump hole. Duct tape blocking the entire top opening and the 3rd from the top opening as well equalling roughly half of the inlet blocked. Oil temperature settled at what I'd call 215 degrees on my gage after about 10 minutes of flight and remained there for the next 20 minutes which was the duration of the flight.

On the return trip with the same conditions except I completely removed the duct tape on the 3rd opening from the top of the cowl effectively only blocking the top quarter of the cowl opening. The oil temperature cooled down and maintained 190 degrees.

[Dave Clark]

My Lycoming is a lot different having a vernatherm (thermostat) that regulates oil going to the external oil cooler. FWIW I have a probe for my UBG on the extra boss on the oil sump. The analog gauge when warm locks on 170 degrees and the oil in the pan stabilizes at about 140. Pretty interesting. For warmup purposes I'll look for 80 degrees in the pan before takeoff.

A friend with a 205 has his probe located between the venatherm and oil cooler so he can see when the oil is warm enough for the vernatherm to start passing oil to the cooler. At that point he'll takeoff. I might change mine to that system.

[zero.one.victor]

I agree with George again (amazing!), it's all academic. Bruce cites empiratical data from his test flight. Different oil temps in same climatic and flying conditions, due to different aircraft cooling configurations.
Bruce, are you postulating (been waiting for years to use that word!) that the lower oil temps are due to more air going into the cowl and therefore into the blast tubes & onto the oil screen housing? Or that the lower oil temps are due to the engine itself running cooler, due to more airflow over the cylinders? Id opt for the latter. The oil temp just mirrors what the rest of the engines doing- after all, the engine gets the oil hot, not the other way around. That's why a lot of airplanes don't have CHT gauges, you must use the oil temp indications to monitor overall engine temp.

Eric

[GAHorn]

Uhhh...Eric... Ummmn.... I guess as much as you and I would like to agree from time to time (or perhaps the word is "agrrrrrree"
...I don't thnk that's the reason some airplanes don't have a CHT.
The reasons most airplanes don't have a CHT is because they don't have cowl flaps. There's no method available for the pilot to regulate the airflow.
And that's also the reason that using duct tape in lieu of the approved winterization kit is technically not legal. Duct tape carries the problem of haphazard, undocumented placement issues. You can create unwanted "hot spots" by placing tape whereever you "think" it needs to be.
As an example, I'd never block the upper areas of the cowl inlets where the tops of the cylinders might stand in stagnant air. As the air moves upward and over the top of the front cylinders, the area around the upper spark plug base will be in a stagnant area. Lower cylinder surfaces avoid stagnant areas with intercylinder baffles.
Engine cooling airflow isn't as simple as it may first appear. It's not usually the inlet amount of air that is best regulated....it's the outlet air that best regulates overall engine temps. (And anyway, I'd rather perform more frequent oil changes than cylinder changes.)

[cessna170bdriver]

The reasons most airplanes don't have a CHT is because they don't have cowl flaps. There's no method available for the pilot to regulate the airflow.

CHT may not be required on the 170, and there are a lot of us that have gotten along fairly well without it. That said, Eric is right that the oil is the LAST thing to heat up, and I think I'd get a lot of peace of mind in a long climb on a hot day knowing what the CHT's are. You CAN regulate the airflow in that case by leveling off and speeding up. And on the cold days, if you DO decide to use the winterization kit (or duplicate it in duct tape) you'll have some idea of where you are.

Miles

[Bruce Fenstermacher]

..... There's no method available for the pilot to regulate the airflow.
And that's also the reason that using duct tape in lieu of the approved winterization kit is technically not legal.

What? Duct Tape technically NOT legal because I can't regulate the airflow. Is that what you meant to say George?

Why I CAN regulate the temperature. If the engine is to hot I land and take some off. If it's to cold I land and put some more on.

Duct tape carries the problem of haphazard, undocumented placement issues.

Got that covered. First I put it on real straight between the grill openings. So much for haphazard placement and I just documented where I put the duct tape in my earlier post.

The more I read your post George the better I feel. Prior to reading it I thought using duct tape was probably illegal. Know I find out it's only TECHNICALLY illegal. I feel better.

[Bruce Fenstermacher]

Hey just funning in the last post. George has some valid points. I use duck tape at my own risk.

I don't try to duplicate the winterization kit because that plate or the replica in duct tape would cover the heater and carb heat scat inlet scoops at the grill. I need all the heat I can get.

The reason I cover every other slot is to reduce the air intake evenlyover the grill area. I don't feel covering the top slot will restrict any air over any of the cylinders. I have NO data to back that up. It's just my eyeball engineering.

Eric I believe the reduced air over the cylinders does the most to allow higher oil temperatures. Of course there would be less air to blow over the temperature probe as well.

[zero.one.victor]

.............................
...I don't thnk that's the reason some airplanes don't have a CHT.
The reasons most airplanes don't have a CHT is because they don't have cowl flaps. There's no method available for the pilot to regulate the airflow. .........................................

I think the reason more airplanes (like the 170) don't have CHT gauges is cuz the factroy saved money that way. True, I don't have cowl flaps to regulate CHT, I also don't have a means to regulate oil temps-- but an oil temp gauge is still installed, and is mandatory per the FAR's. I've seen airplanes that had MP gauges, even though they had fixed-pitch props. Just cuz you can't control it doesn't mean you may not want to monitor it.
And actually, yes you can regulate CHT even with no cowl flaps. Just the same way you regulate oil temps- when they're too hot, put the nose down and/or pull the power back and/or richen the mixture.
I knew this agrrrrreement business was too good to be true, George!

Eric

[CraigH]

And actually, yes you can regulate CHT even with no cowl flaps. Just the same way you regulate oil temps- when they're too hot, put the nose down and/or pull the power back and/or richen the mixture.

Actually the mixture has a surprising amount of impact on CHTs. While doing some test flights with winterization plates installed, I was able to get between a 50-75F CHT drop just by running full rich as opposed to leaned out.