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Permalink Reply by Bob Simmons on July 28, 2022 at 12:06am

You really should be putting this stuff in the Jabiru engine forum. Most folks with the earlier generation engines used to redesign the baffles and ducts to lower the CHTs. Don't specifically remember any EGT issues, and never heard of any damage. The generation 3 engines were redesigned to improve cooling, and overheating issues mostly went away. The generation 4 engines seem to have eliminated the problem entirely.

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Permalink Reply by Stephen R. Smith on August 1, 2022 at 12:21pm

I can't comment on gen 3&4 engines. For gen 1&2 engines...

1) High CHTs can cause the head bolts to loosen because the head reshapes itself. Loose bolts allow compression leakage. When you then tighten the head bolts, the problem occurs again and again until the cylinder intrudes into the head which changes valve train geometry and increases compression ratio. High CHT can also lead to detonation and broken through bolts.

2) High EGTs can cause accelerated exhaust valve and seat wear. In an extreme case, the head of an exhaust valve will separate from the valve stem resulting in catastrophic engine failure.

3) High oil temps will cause the oil to thin and lose its ability to properly lubricate, especially in high stress areas such as the cam lobe to lifter interface, resulting in failure of the hardness layer which will cause cam/lifter failure. This then causes metal to shed into the oil and destroy all the crankshaft bearings and crankshaft journals. High oil temps will also contribute to piston ring coking which then causes high oil consumption, loss of compression and cylinder damage.

Jabiru engine temperature limits set by the factory are a little too generous. If you want the engine to last, use lower values and stick to them.

Steve

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