The International Cessna 170 Association

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We gave 98C about 1.6 hours of exercise today. The Weather Channel recently mentioned that Saginaw Bay was frozen over, so we flew up to check it out. Temp was mid to high teens on the ground, and about +10 at 4500 and 5500. When we flew last Saturday in similar temps, I had added about 2 inches of tape to the cowl inlet area blocked off by the winterization plates and got the cruise CHTs on the hottest cylinders up to about 375 and oil temp of about 160, but almost no air through the cabin heater. Today I flew with only the plates and got about 340 CHTs, 150 oil temp, and more cabin heat that I could use, especially southbound into the sun.

I would still like to pursue the addition of front baffle plates as in some early 172 O-300 installations, to get the very front CHTs up a bit. Today I saw only about 200 on #5 and about 185 on #6.

Do you think the tape covered just a bit more area than the baffles resulting in slightly higher engine temps but somehow the difference from the baffles made a significant difference in heater output?

Any thoughts on the heater output change between the two?

This is interesting.

Bruce Fenstermacher wrote:Do you think the tape covered just a bit more area than the baffles resulting in slightly higher engine temps but somehow the difference from the baffles made a significant difference in heater output?

Any thoughts on the heater output change between the two?

This is interesting.

The extra tape blocked the cowl inlet in front of heater inlet (about the middle of the horizontal baffle in front of cylinder #5), and I think it created a low pressure area there. The next time it’s that cold I think I’ll try just adding tape to only the upper upper half of the cowl opening. In retrospect, the engine seemed to be rougher than usual with carb heat applied, which could be a similar issue in front of cylinder #6.