Which engine was standard in the Jeanneau Sun Odyssey 36i, and what weaknesses should I check?

The Jeanneau Sun Odyssey 36i was normally supplied with a Yanmar 3YM30, a three-cylinder diesel rated at about 29hp, driving a conventional propeller shaft. Check the engine identification plate and service history first, then inspect the cooling and exhaust systems, shaft alignment, keel area for grounding damage, rudder bearings and deck leaks.

Confirm engine model and history

The original 3YM30 is naturally aspirated and mechanically injected, with freshwater cooling through a seawater heat exchanger. The installation is straightforward and generally dependable. There is no turbocharger to inspect and, with the usual shaft drive, no saildrive diaphragm.

A replacement engine may have been fitted, so identify it from its plate rather than the sales particulars. The later 3YM30AE is a different version. Order parts against the engine's actual model and serial number.

Ask for invoices covering oil and filters, coolant, seawater impeller, belts and gearbox oil. A low hour reading carries weight only with records to support it. Prolonged inactivity, neglected coolant and saltwater corrosion can matter more than total hours.

• Insist on a cold start; feel the engine before it is started.
• Check for prompt starting, an even idle and working oil-pressure, temperature and charging warnings.
• Look beneath the engine for oil, salt deposits, rusty water tracks and recently cleaned areas that need explaining.
• Check for persistent smoke once the engine is warm. Blue smoke suggests oil burning; persistent white smoke calls for investigation into incomplete combustion or water ingress.

Inspect cooling, exhaust and shaft

Pay particular attention to the wet-exhaust mixing elbow. Carbon and internal corrosion can restrict the exhaust or cooling-water passage while leaving little visible evidence outside. Ask when the elbow was last removed for inspection or replaced. An external glance cannot establish its condition.

Follow the seawater circuit from the inlet seacock through the strainer, pump and heat exchanger to the elbow. Look for leaking pump seals, scored pump covers, hardened hoses and salt crust around connections. If an impeller has lost blades, establish whether the fragments were recovered downstream.

Keep hands, clothing and tools clear of belts and the rotating shaft while the engine is running.

During the sea trial, warm the engine thoroughly and run it under sustained load. The original 3YM30 is rated at approximately 3,600rpm. With a clean hull and correctly matched propeller, it should approach its specified full-load speed. If it cannot, possible causes include fouling, excessive propeller pitch or restricted fuel or exhaust flow. It does not necessarily mean the engine is worn out.

Check for overheating, persistent black smoke and vibration in both ahead and astern. Inspect the engine mounts, coupling, shaft seal and cutless bearing. Failed mounts or poor alignment can cause vibration and accelerate seal and bearing wear. A new bearing alone will not fix the underlying fault.