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.

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Dan Dudley
Dan Dudley is a mechanical engineer, A&P mechanic, and holds CFI, CFII, MEI, MEII, Seaplane, and ATP ratings. He is also an EAA Technical Counselor and Flight Advisor. His professional services include builder assistance, transition training, first flights, conditional and pre-purchase inspections, and aircraft sales. 608-212-2359