The Yanmar JH series powers many mid-size sailing yachts and small trawlers, in three- and four-cylinder versions, with turbocharged TE and HTE models. Yanmar's own manual is clear about the part it wants replaced on a schedule, and the turbo models add one more thing to check.
The mixing elbow
What Yanmar says. The operation manual for the 3JH4E, 4JH4AE, 4JH4-TE and 4JH4-HTE says to replace the mixing elbow every 500 hours or 2 years, whichever comes first, even if no damage is found. It also lists cleaning dirt and scale out of the elbow's exhaust and seawater passages.
Why it matters. The elbow is where hot exhaust meets seawater, so it corrodes and scales from the inside. A blocked elbow restricts exhaust and cooling water; a corroded one can let water back towards the engine. See exhaust elbow corrosion.
Where to look. Ask for the date and hours of the last elbow replacement, and compare with Yanmar's interval. Check the outside for weeping, salt and rust at the flanges. On TE and HTE engines the elbow is close to the turbo, so look at both together.
The turbo on 4JH TE and HTE engines
What happens. A reader of SAILING Magazine's Boat Doctor had a 4JH2DTE that wouldn't go above 2,400 rpm. Bob Pingel's answer: the turbo comes in at about 2,200 rpm, and a dirty turbo stops the engine making power above that. He recommends Yanmar's turbo wash every 200 hours or so, and if that doesn't help, a look at the injection pump.
Where to look. On the sea trial, check the engine reaches its rated rpm at full throttle, and watch for black smoke under load. Ask for turbo wash and service records.
Hoses
The same manual lists replacing rubber hoses every 2,000 hours or 2 years. Check the coolant and raw water hoses for hardening and cracks; see exhaust hose.
What to check on a Yanmar JH
| Area | What to look for | Source of the concern |
|---|---|---|
| Mixing elbow | Date and hours of last replacement; weeping, salt, rust | Yanmar manual |
| Turbo, TE and HTE | Rated rpm reached; black smoke; turbo wash records | SAILING Magazine |
| Rubber hoses | Age against 2,000 hours or 2 years; cracks, soft spots | Yanmar manual |
| Raw water pump | Leaks and weeping at the shaft seal | Yanmar manual servicing |
Writing it up
"Engine, Yanmar 4JH4-TE: mixing elbow shows rust weeping at the turbo flange. No record of elbow replacement; Yanmar's manual calls for replacement every 500 hours or 2 years. Recommend replacing the mixing elbow and inspecting the turbo outlet before extended use." Note the engine serial number and hours in the particulars.