Glasair Engine Cooling


These mods have been documented in the past but mainly on Sportsmans and GlaStars. I want to add that the Glasair with its tight cowling has always had issues with high cylinder head temps especially on climb-out.

In an effort to minimize CHTs in my Glasair, I incorporated the following modifications into the cowling and baffling system, especially since I installed an Aerosport IO-375 195hp engine in the Glasair with a dual PMAG electronic ignition system. The PMAGs increase combustion efficiency, which is a good thing, but as a result, the engine will run hotter than a standard mag engine.


Ted Setzer incorporated most of these mods in his Sportsman. I’ll just highlight them and give you the results on a Glasair.

  • Pay special attention to baffles making sure you have a tight seal all around your upper cowl.
  • Add aluminum baffles around rear cylinder heads and seal to improve airflow around cylinder head fins.
  • Build in or install louvers on each side of the lower cowling-this increases airflow exiting the cowl by increasing the free area and negative pressure under your cowl.
  • Do not provide an opening off right rear baffle to use to feed your oil cooler.
  • Add a separate NACA scoop on the side of your lower cowl for the oil cooler.
  • Add an air valve to control oil temp—this will allow you to adjust your oil temperature as much as 25ºF.
  • Cut in to face of front baffles 1”x 2” openings—this enhances airflow around the front fins of cylinders #1 and #2.

Glasair Super II mod results

I performed all of the mods above prior to my first flight with the exception of the 1”x 2” windows on the front baffles on the front of #1 and #2 cylinders.

On my first 5 hours of engine break-in where I was running at greater than 75% power to break in the engine the highest cylinder head temperature I saw was 405ºF.

Once the cylinders were broke in, still at 75% power, the maximum cylinder head temperature was 380ºF.

Around 50 hours in to the break-in, I performed the last mod (the 1”x 2” windows) which resulted in an additional reduction of 10ºF to my front cylinder head temperatures.