Cracked Heads Prompt Continental (Thielert) Diesel AD

TAE 125-02-125 (Continental CD-170)
Image: Continental

The FAA has issued an AD for operators of Continental TAE 125-02-125 (formerly Thielert) diesel engines after “multiple reports of cracks in the cylinder heads, which can cause engine coolant to leak into the combustion chamber.” The AD, copied below, requires immediate inspection and testing of coolant for metal fragments and replacement of the coolant and cylinder heads with serviceable parts.

Russ Niles
Russ Niles
Russ Niles is Editor-in-Chief of AvBrief.com. He has been a pilot for 30 years and an aviation journalist since 2003. He and his wife Marni live in southern British Columbia where they also operate a small winery.

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Paul Brevard
Paul Brevard
3 months ago

Coolant cavitation within a water jacket in liquid cooled diesel engines is not a new problem. Pitting and loss in structural strength of head castings has been dealt with by designing enhanced coolant formulas specific to the material and vibrational characteristics of the engine across a wide variety of automobile, truck, and marine engines. It’s likely Thielert’s Mercedes background is deep enough to understand this which is why flight characteristics and propeller blade signatures may have generated some unanticipated consequences. The kind that beg for a head casting revision.

Stan Fetter
3 months ago

I had that problem, but was years back on an 01-99 series engine – the very first 1.7L conversions. Roughly 700-ish hours of traffic watch service, 3 hour sorties at 60% power so it’s not like we were running them hard. But that was the only time we had to go into that engine, and it lasted 2600+ hours (Theilert wanted them pulled at 1000). I had real good service out of them, in spite of being the first commercial user of those engines in north America.

My suspicion is that the latest problems may also have something to do with pushing the same basic engine a little farther than it likes being pushed. There is a long history of endless cycles of upping compression, fiddling with the FADEC/ECU and everything it does, and then finding out that simply adding cooling isn’t enough. The automotive world has had to learn that lesson again and again.

All that said, the people I worked with at Thielert in Germany during those early days were absolutely brilliant. Hopefully, Continental has been smart enough to keep that engineering team intact and independent – and if that’s the case, I’d expect this to get figured out and dealt with.

We’ll see….

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