The International Cessna^® 170 Association

Can anyone share photos of their blast tube placement on both sides?

Mine was altered and my A&P and I are trying to recreate the original design.

Point them at the accy case casting at the large oil screen.

Here's the funny story I heard as to why they are there and pointing where they do.
Notice the blast tubes aim right at the temperature sensor. This is, so the story goes, because this was the only way Cessna could get the airplane certificated, by lowering the temperature reading...not the actual motor temperature, or the oil temperature, but the reading itself.
Not sure if it's true, but it is funny.

That's an old anecdote which is believable since indeed, the temp probe is placed within the large pressure screen housing.
What conflicts with the story is the fact that the air is directed at the side of the housing, and between the probe and the blast tube exit-air is the aluminum screen housing, which contains the screen and quite a volume of the oil passing thru it, all of which surround the probe. No sensing portion of the probe receives any air from the blast tube. In order for the probe to sense reduced temperature from this apparatus, the oil temp in which it is submerged must first be affected.
(The certificate limitations of the engine address "inlet" oiltemp. The screen housing is the "inlet" area for the oil gallery.)

This same engine (and it's little brother C125 using the same screens and probes) in some other installations (for example, the Swift) has the benefit of an updraft cooling system. The oil sump sits in cool air prior to cylinder heating. Therefore no blast tubes are required to deliver cooling air to the oil inlet. Those operators frequently complain of low oil temps.

The story does seem to have some validity and i have to admit I told it a time or to in the early days. But over the years George has repeatedly pounded into my head what he once again just said. The probe itself is not cooled, the oil around the probe is cooled. The blast tubes are just part of an overall cooling design.

I've been traveling around in my GREEEN airplanes way to fast to let that concept sink in. George on the other hand has had time for it to sink in at the speeds he travels.

Of course that statement makes a quandary. Could one be faster while traveling in a slow red airplane? Or more likely engineer Cleo Bickford set George straight early on when George related the blast tube cooling the probe story to him.

Last year, I removed one of the blast tubes in order to cool the generator (35amp).
No change in oil temperature noticed. Still at the top of the green.

Doesn't all the oil travel past the temp probe? There are two passages in the area of the temp probe. One that flows oil to the filter and then the oil passage back to the engine. When the tubes are put in that area seems like it can cool the oil that is passing through the area. The housing is cool for both ways of the oil flow. I put on an F& N filter and didn't move the tubes. The oil temps stayed in the green until I started operating in 100 deg days at low altitude. It started running the oil temp up to redline. When I moved them back to the area of the Temp probe the temps dropped a needle width or two in the 100 degree air. I just recently changed the oil and filter (ran it well past my usual 30 hour change) and the oil did not show any signs of being overheated or being run at too high a temp. I'm really not too worried about the gauge reading. It is just 11 years younger than me and it could be operating in the cranky mode, like I do at times.. :~)

Earlier on when I had the old O-300 cont. fitted , oil temp was a big issue here in Australia in the middle of summer and flying in temperatures 100deg. F Plus . With 4 on board and climbing out the temperature very quickly went through the green band. So a Airwolf spin on oil filter was fitted which helped big time . One of the blast tubes was aimed at this area. Then I was given one of the finned heat sinks that clamped to the oil filter . WOW no more temperature issues and oil temps stayed in the center of green .

"Then I was given one of the finned heat sinks that clamped to the oil filter"

Hey Ghostflyer, do you have a link that explains this a bit more? I've never heard of that.

A heat sink of a number of fins is clamped to the spin on oil filter. A friend of mine gave it to me ,I believe he obtained it from Spruce . See example on page 359 on the spruce book 2013-2014. Spruce call it a chiller

Is it the Airwolf Oil Chiller? And there's enough room in there for the fins?

While this device may help to lower oil temperature, a previous post pointed out that the extra weight of the fins on the filter could possibly result in issues with the oil filter adapter due to the extra weight hanging down on the adapter. Might be something to consider

The real question (in my crooked mind) about fins on the filter is..... is the area in an EXIT area of the cowling where the air is heated because it's downstream of the 250-350-degree cylinders? And....if so..., aren't the fins actually an oil-temperature heater?
To know that answer, one would have to place a temp probe (preferably a digital, quick-reaction type) in the area and measure the ambient air in the vicinity of the filter.

My blast tubes are in their original positions and my 35 A gen has a dedicated cooling tube.

The weight of the Chiller or heat sink is very light and the large hollow bolt assembly that holds the filter assy is more than adequate to support the fitting . My oil temperature dropped big time and suggest that some air flow or tubulance from the exit air and on coming air helped. Due to the very high ambient temperatures it was some times impossible to fly with a load and climb out to a height where the air temperature was bearable in the cabin . It was very tight when the fins were fitted but gentle positioning it can be done .

What are your typical oil temps, with the fins?
Many feel that a minimum of 180 is necessary to avoid excess water buildup.
My FM Enterprises filter, non relocated blast tubes, summer Texas heat....new, calibrated oil temp gauge.....indicates 200 F, even l on blistering days.
In other words, there are a lot of variables and differing causes of high oil temps,.....exhaust leaks, poor baffles, bad gauge, etc