The Cessna 120-140 Association Forum

What is the purpose of the blast tube that runs from R-side upper baffle to oil screen on original c-85. It is missing on mine and it runs hot. Correlation? I have spin- on filter if it matters.

Its purpose is to cool the oil as it passes through the oil screen housing. It does work. Part of the winterization process is to block the tube. If you have the spin on filter, the oil screen should be removed by de-soldering it from the fitting.

They do work well.
All of the engine oil passes thru the oil screen housing, therefore blowing cool air on it cools the engine oil. I think Airforms in Alaska is making them now.

I'm pretty sure it's required under the Cessna type certificate.

It appears to depend on model year. According to the parts manual, it was installed on all 46 models but left off of 47 120's (all) and 140's until serial #14,5XX or so. There is no fitting for it on my 47 120. Go figure.

My '46 with C90 has a blast tube which I leave open for warm weather ops. On days of 40 degrees F or less I block the tube, and on days near freezing temps I also block the cooling ports on the nose bowl. I lay no claim to being an expert or even knowledgeable enough on this subject to pass along any advice - just doing what I think works best in view of oil temp gauge readings which I like to keep between 160 and 180 for at least 30 minutes on each flight. I'd be happy for any of you experts out there to correct me if I'm doing it wrong.

6863 wrote: ↑Mon Jul 20, 2020 5:54 pm I'd be happy for any of you experts out there to correct me if I'm doing it wrong.

Can't help. You're doing it right!

Mine also. Made a blast tube. HUGE differance. Also, there is an sump baffle which is usually missing. I know of no approval to leave it off.

Since you mentioned the sump baffle...

When I did the STC to install the 150 exhaust my a&p said that the baffle no longer fit properly with the cross brace for the exhaust (cant remember the exact part number of that brace) and the baffle was removed. Living up here in AK where we have now passed our warmest weather for the year it hasn't proven to be a huge issue. Has anybody else run across this problem?

Thanks. I have the C-150 STC also and did not know about the fit. I was going to get a piece of .032 anealed aluminum, cut and fit then heat treat. Temps dropped real well with blast tube. I will post if the "new" baffle works out.