I bought my ’68 Cardinal in 2006 with and love it. It had only 50 hours on the engine, over 8 years, so I kept a close eye on the performance, and put money away for a possible top overhaul. At the first annual I had to rebuild the cylinders, not unexpected, but still a shock. I also elected to replace the rubber baffles and install an EDM-700 to keep a closer eye on the engine. Up until this point I was blissfully unaware of the cylinders health due to the lack of engine instrumentation.

On the first flight on the new cylinders, CHT’s were really high, nearing 450 degrees in the climb, not the recommended 380 degrees. The IA with me on the flight told me that it was probably due to the fact that the cylinders weren’t broken in yet. Sure enough, the temps went down significantly, to where they would max out around 425 in climb. That was still not good, but better than they had been on that first flight. Since then I have been working on getting those temps down, especially on cylinder 3, which was always hottest.

I started by first verifying that the baffle and springs were correct, then opening up the gap between cylinder 3 and the metal baffle as recommended on the CFO website. There appeared to be no appreciable difference, which I attributed to other gaps in the baffling. Next I opened up the fixed cowl flap by creating a gap to allow more air out the bottom of the cowl, which produced the greatest improvement to that point. I could now climb at 105 MPH from sea level to 5000 feet on a 90+ degree Florida day and temps on cylinder 3 would only climb to 410 degrees. More work obviously needed to be done, but in the mean time as the temps climbed, I would level out and let them cool before continuing my climb.

I kept looking for gaps to fill and next was around the alternator. At the next annual I had an A&P close that gap, but unfortunately there was only about a 5 degree change in cylinder temps during a 105 MPH climb. However, it did get cylinders 1 and 4 below 380 at all times, and bring down cylinder 2 to around 390 degrees during the climb. Good news!

I continued to search for ways to fill gaps and get more room around cylinder 3 until the 2010 annual inspection. I decided to see if cylinder 3 had too much open space around the cylinder. There was a gap between the cooling fins and the baffle that seemed about right, but at the end of the cylinder near the spark plug holes was also a big gap that I decided might be letting out too much air and not forcing more air through the cooling fins. I made some plugs out of high temp red RTV and inserted them in the gap went for a test flight.

Climbing from 1000 to 5500 feet at 90 miles per hour (15 miles per hour less than my normal climb speed and closer to best angle of climb) cylinder 3 would not top 400 degrees. At 5500 feet, cylinder 3 had a CHT of 398 degrees, and that temp continued to climb at about 1 degree per minute but that rate was slowing. The result was extremely promising, so back to the barn to refine those baffle modifications to make sure that hole was completely plugged.

Getting the engine temps to stay low is a work in progress for many aircraft owners, and I am no exception. I will periodically update this page as information presents itself.