The Cessna 120-140 Association Forum

Can someone enlighten me on the importance of keeping the blast tube that is aimed at the oil temp probe/ oil screen.

I have recently installed an oil filter and de-soldered the oil screen. So the probe will stay in there permanently now without continuous removal.

Never did understand how ramming cool air at sensor would give accurate reading. And as part of winterization I always tape over the tube anyhow.

Just curious...thanks

Chris

All of the oil that goes thru the engine goes thru the oil screen cavity. The blast provides a cooling effect to, therefore, all the oil that is in the engine.
It is proper to block off the blast tube in the winter. Maybe you don't face the 110 degree temperatures we have here. The blast tube helps a lot.
Did you get your engine running again?

8261 wrote: ↑Sun Oct 07, 2018 12:56 pmNever did understand how ramming cool air at sensor would give accurate reading.

This is a common misconception. The blast tube is aimed at the screen housing, not the sensor. The only way you can affect the reading from the sensor is to cool the oil surrounding it. All the oil passes through that housing, so if you're lowering the indication on the gauge you're doing so by lowering the temperature of the oil. All of the oil...

Removing the screen has no effect on the cooling.

Covering the entrance to the blast tube is part of the original winterization kit; the added cooling isn't needed.

Danged internet! My post gets lost in the ozone while Randy beats me to the punch!

I know, John. You and Randy are all of over it, but he's always a tad quicker on the draw!

Roger that on the blast tube. Thankful I don't have to deal with those 110 deg temps...or 80 for that matter!

Randy, I should have the engine fired up tomorrow. Exhaust port on that #3 ended up having a crack as well...no old style cylinders in town. New style cylinders require pushrod tube conversion...yada yada...turned into my last resto project, where one bolt came off and then it turned into a frame off.

Anyhow, better to get it all done before the temps drop and the snow starts falling...man, a hangar sure would be sweet!

FWIW We were told by an old Cessna engineer that the blast tube is there to match the indicated oil temp to the actual oil temp. I had a secondary oil temp probe at the front of the engine and it read consistently 20 degrees higher the the rear case probe.

Bill

The probe in the oil screen is reading the temperature of the oil that is sucked up from the sump. It has had a chance to cool in the sump.