Winterization w/ STC'd cowl

[rydfly]

Hi folks,

Ambient temps are firmly in the 30's now in Ohio so I'm looking to winterize my cowl to keep oil temps in the happy range. Problem is, my a/c has been modified by a previous owner via the STC to use the Airborne vacuum pump which protrudes through the cowl and necessitates a change from the original design. Does anyone else running this setup have a tried and true method to winterize? I'm assuming that I need to cover the small hole between the prop and air filter, but what do do about the large (and a-symmetrical) openings for the cylinders?

I'll try to attach a couple pics to illustrate my setup... bear with me!

-Kennet

[GAHorn]

You are not the only one with that set-up. The winterization kit depicted in the IPC may not be adaptable to the altered cowl, and any custom mfr'd kit would probably have approval issues. You may be forced to use only the oil sump cover and accept the lower cylinder temps and perhaps change your oil more often.
What oil temps do you actually experience without the covers?

click to ENLARGE pics

[rydfly]

I haven't flown it much since the weather got so cold, but this past weekend with OAT around +20F at altitude, I don't think my oil temp ever crept much past 100 degrees on the gauge on an hour-long cross-country flight.

[Bruce Fenstermacher]

I wonder what the guys with the later 172 cowls like yours do?

I'm betting your going to have to make something of your own design and hope it looks airworthy enough to not be questioned. Of course the traditional way to do this is by blocking off some of the air inlet but keep in mind you can accomplish the same thing by blocking the air exit. Might be easier and less suspicious coming up with something to block off some of the opening at the bottom of the cowl.

Just thinking out loud.

[alaskan99669]

Do you still have the "Blast Tubes" working that force air from the high pressure area of your cowl to the oil temperature probe area? If so, go to the hardware store and buy a couple rubber plug stoppers that you can wedge in the opening and stop air flow. Try one side first and if not enough improvement add one to the other side.

[GAHorn]

At plus-20 F I'll bet your oil temp gauge is not accurate if all you get is 100-F indicated. (That's the lowest indication on the gauge for most gauges.) Are you certain your gauge is not Centigrade? (100 - C is 210 - F)

[mit]

I put nut-plates around the oil pan inlet and made a couple of different plates to put over it some with holes. Unless your flying at 30 or 40 below that should be good.

[rydfly]

Do you still have the "Blast Tubes" working that force air from the high pressure area of your cowl to the oil temperature probe area?

I believe I do and if so, will try what you suggest.

Are you certain your gauge is not Centigrade?

It's the original (or appears to be at least), reading in F not C. The needle never moved much from its resting spot on the extreme left of the gauge.

I put nut-plates around the oil pan inlet and made a couple of different plates to put over it some with holes.

I'll definitely be doing this at the very least. Thanks!

[Bruce Fenstermacher]

Kennett

It is always important to be sure your gages are accurate but specially when you are considering modifications based on it. The first thing to do is make sure your gage is pretty accurate by removing the bulb from the engine and putting it in a fluid like heated oil or water that is a known temperature.

It is my feeling that blocking the blast tubes might raise your oil temperature READING but not really raise your engine and oil temperature. The blast tubes are simply cooling the area of the temperature gage bulb.

[rydfly]

It is my feeling that blocking the blast tubes might raise your oil temperature READING but not really raise your engine and oil temperature. The blast tubes are simply cooling the area of the temperature gage bulb.

Yes, I thought about that after I posted my earlier reply. If the gauge is calibrated to read oil temperature correctly with the air blasted on it, changing the airflow at the probing point would change its calibration only which wouldn't actually raise the temperature of the oil.

[jrenwick]

I've never understood how people can say the blast tubes aren't actually cooling the oil. They cool the metal around a passage through which all the oil flows, and the oil is in contact with that metal. The probe is immersed in the oil. If the probe registers a change in temperature, isn't that because the oil is cooler? How is it anything else?

The blast tubes are aimed at the one place in the whole engine where spot-cooling of the oil would make the most difference.

[alaskan99669]

Exactly. Thank you John. My probe is further away from the blast tube out on the end of the oil filter adapter and I can definitely see a change in oil temperature by changing the flow thru the blast tubes. We use air movers at the plant I work at to blow cold air over heat sensitive objects and it definitely cools the medium within. This subject has been argued before in these forums.

[Bruce Fenstermacher]

John and Corey I understand your position and in fact was thinking the same thing as I wrote what I did, The oil has to be cooler at the point of the gage bulb in order to change the reading and that cooler oil has to effect the overall temperature of all the oil. So blocking it would raise the oil temperature. But my personal gut feeling is that any cooling or lack of it from the blast tubes is insignificant in the big picture. I think it a much better solution to raise or lower the temperature of the whole engine by restricting or increasing airflow over the whole engine rather than a localized spot.

I have no evidence or proof to support my gut feeling. It would be an interesting question to pose to a Continental or Cessna engineer familiar with our engine and cooling system.

I would also think it interesting if someone with an IR temperature gun would take readings at various places like the side of the oil sump to see what effect blocking just the blast tubes has on the entire engine over running the blast tubes open. I have the IR gun but as you all know I don't have the airplane at the moment.

[jrenwick]

It would be academic to measure oil temperatures around the engine, because the operating temperature range is specified as being measured at the pump inlet, where the temperature probe is. That's the temperature at which the oil enters the lubrication galleys. It will get warmer as it cools the engine, then cooler once it's back in the sump.

[jrenwick]

....It is my feeling that blocking the blast tubes might raise your oil temperature READING but not really raise your engine and oil temperature. The blast tubes are simply cooling the area of the temperature gage bulb.

Then we should be taping over our blast tubes, so that the air lost through them could be used to help cool the engine!