Q: I fly a Cessna 182S registered HP1401. It has a Lycoming IO-540-AB1A5, 3 blade prop. Sea level OAT is 90°F or so year round.
It had a single probe analog CHT display connected to cylinder #1, which always remained around 320°F.
I then installed a digital engine monitor, which showed the rest of the cylinders easily getting into the 400°F range. So I started flying lean of peak with GAMI injectors and cowl flaps fully open all the time and got the CHTs into the 360°F range.
The original engine reached its 19th birthday and some 1,900 hours, so I decided to replace it with a factory rebuilt.
The test data sheet from Lycoming shows all temps completely normal at the factory.
I just flew the first two hours with the new engine, and it’s running much hotter than the old engine, particularly cylinder #2. In order to keep the temp at 400°F or below, I have to keep cowl flaps full open and keep the mixture around 19 gallons per hour.
- At 19 gph CHT1 reads 303, CHT2 reads 402, other CHTs around 375;
- At 18 gph CHT1 reads 311, CHT2 reads 408, other CHTs around 384;
- At 17 gph CHT1 reads 316, CHT2 reads 412, other CHTs around 390.
I’ve read all the Lycoming literature I could find, which boils down to: Baffles, mag timing, induction leaks, exhaust leaks, and obstructed injectors. All of these look good, so I sent Savvy Aviation the EDM download, but they didn’t find anything really wrong.
I then called Lycoming and they told me to check baffling again and to play with mixture and power and continue break in, avoiding continuous flight above 435°F CHT.
A friend who is an A&P as well as a mechanical engineer recommended I reduce the spark advance from 23° which is specified, closer to 20°.
Would you have any recommendations for me? Should I continue breaking in? Should I lean further as long as CHTs stay below 435°? Should I try reducing the spark advance?
A: Henry, welcome to 2018. Your question is a good way to start the new year.
After reading and digesting your situation, I first want to point out the fact that any engine recently rebuilt or overhauled will typically show higher cylinder head temperatures as a result of the tighter tolerances compared to your previous engine with 1,900 hours.
The most important thing I can tell you is all of the temperatures you provided are well within the specific limits for your engine. I would not alter the specific engine timing under any circumstances!
One thing to remember is that the airframe manufacturer decides which is typically the hottest cylinder following their cooling climb tests during the certification process. Cessna has chosen the #1 cylinder for a single probe system location because their tests confirmed that was the hottest running cylinder in this specific installation.
If this engine were installed in a different aircraft with a different cowling design, the hottest cylinder may turn out to be #5.
My suggestion for you would be to continue to break the engine in as recommended in the Cessna Pilots Operators Manual or the Lycoming Service Instruction 1427C.
I agree with the Lycoming guys recommendations and wouldn’t recommend additional leaning. Remember: The two least expensive things you can put in your engine are gas and oil.
Also, running with the cowl flaps open causes drag, which in turn means consuming more fuel, so continue to keep the cylinder head temperatures below that 435° point and keep the cowl flaps closed if possible.
If I were to do anything else in your situation, it would be to really take a close look at the engine baffling again. I feel you may be able to make some improvements in that area.
We know the engine baffling lives in a very hostile environment, so in many cases where an engine is replaced, it makes sense to replace a good part, if not all, of the baffling so that it fits much better than some of the high time baffles that have taken a set over time and may not seal as they did when new.