Yanmar 4JH4-TE Rebuild, common faults and everything you need to know
Yanmar's best seller in the 40-50 ft segment during its production run. Direct injection with a Bosch VE mechanical distributor pump. Succeeded by the 4JH-CR common rail around 2014.
The 4JH4-TE has one recurring weak point: the aluminium exhaust manifold. At the bronze end caps, where dissimilar metals meet salt water, it corrodes internally - the signature fault of the entire 4JH series. Threads on Cruisers Forum document identical failure patterns on thousands of examples worldwide, often with up to 30 mm of material that has to be milled out. Otherwise the 4JH4-TE is one of Yanmar's most reliable marine diesels. A robust block, direct injection with a mechanical Bosch VE pump, no electronics to chase. We carry out cylinder head reconditioning, cylinder boring, crankshaft reconditioning, turbo reconditioning and complete engine reconditioning in our own machine shop with 12-month warranty. See also our boat engine rebuild hub page.
The 4JH4-TE at a glance
Sourced from the official Yanmar 4JH4-TE datasheet PDF (yanmar.com) and the Yanmar Technical Review 2016.
The 4JH family generation overview
The whole 4JH series from 1985 has used direct injection. Yanmar's Technical Review describes DI as the JH series' distinct engineering choice against the competitors' IDI. The generations differ in displacement, valve configuration, power and emissions category - not in injection technology.
| Generation | Injection | Fuel pump | Period |
|---|---|---|---|
| 4JH-HTE / 4JH-TE | Direct | Bosch mechanical | 1985-1990 |
| 4JH2-TE | Direct | Bosch mechanical | ~1990-1998 |
| 4JH3-TE | Direct | Bosch VE distributor | ~1998-2005 |
| 4JH4-TE Current | Direct | Bosch VE distributor | 2005-2013 |
| 4JH-CR (4JH45/57/80/110) | Common rail | HPCR (Bosch) | 2014-present |
NOTE: The 4JH4-TE is often incorrectly described as IDI in third-party sources. Yanmar's official datasheet PDF (DS_4JH4-TE_A4_022021_HR.pdf) confirms direct injection. The switch to 4JH-CR happened in 2014 after the introduction of EPA Tier 3.
Common faults on the 4JH4-TE
Cross-verified against Cruisers Forum, Trawler Forum, Patrick Childress sailing videos and Yanmar technical bulletins.
Aluminium exhaust manifold corrodes at the bronze end caps
Signature of the entire 4JH series • Critical- Symptoms
- Salt water dripping from the manifold, sooty exhaust, possibly water in the intake.
- Cause
- Galvanic corrosion between the aluminium manifold and the bronze end caps in a seawater environment. Cruisers Forum reports up to 30 mm of material that has to be milled out to reach sound aluminium. Inspect at every major service.
Mixing elbow / exhaust riser corrodes
500 hours / 2 years • High- Symptoms
- Salt water in the exhaust combined with reduced exhaust pressure, possible risk of hydraulic lock.
- Cause
- Yanmar's manuals recommend replacement every 500 running hours or every two years. HDI Marine sells a stainless SS replacement part that lasts longer.
Heat exchanger deposits
8-12 seasons • Medium- Symptoms
- Reduced thermostat opening, overheating under load, falling top-end rpm.
- Cause
- Scale and salt deposits on the raw-water side of the heat exchanger.
Engine mounts age
10+ years • Medium- Symptoms
- Increased vibration under way, play in the propeller shaft, poor access to the mount bolts.
- Cause
- The rubber-in-steel engine mounts age. The rubber separates from the steel core. The 4JH4-TE sits in a tight installation and access for replacement is time-consuming.
Raw-water pump - damage during service
Service error • Medium- Symptoms
- The pump housing leaks after an impeller change, thread damage, cracks at the screw slots.
- Cause
- The pump housing cover gets damaged by incorrect service - overtightening or prying the cover off with a screwdriver. Use the correct puller.
4JH4-TE rebuild prices
Modern Yanmar 75 hp turbo. Prices based on 4 cylinders, 84 mm. Excl. VAT and parts. All main operations - cylinder boring, crankshaft grinding, cylinder head resurfacing - carried out in our own machine shop.
Cylinder head reconditioning
Bottom end
Full rebuild
Aluminium manifold
Cylinder machining
| Service | Price |
|---|---|
| Cylinder boring 4 cyl (84 mm) | 3 318 kr |
| Plateau honing 4 cyl | 1 050 kr |
| O-ringing block 4 cyl | 2 800 kr |
Cylinder head reconditioning
| Service | Price |
|---|---|
| Resurfacing cast-iron cylinder head 4 cyl | 1 590 kr |
| Pressure testing cylinder head 4 cyl | 1 876 kr |
| Valve seat cutting 8 valves | 910 kr |
| Valve guide replacement 8 pcs | 1 580 kr |
See also
Other Yanmar engines and related services.
Questions and answers about the 4JH4-TE
Is the 4JH4-TE direct injection or IDI?
Direct injection (DI) with a Bosch VE mechanical distributor pump. The whole 4JH family from 1985 has used DI - it is the JH series' signature technology against the competitors' IDI, per Yanmar's Technical Review. Common rail only arrived with the successor 4JH-CR around 2014. Confirmed in Yanmar's official datasheet PDF.
What is the aluminium manifold fault?
The signature fault of the entire 4JH series. The aluminium exhaust manifold corrodes internally at the bronze end caps, where dissimilar metals meet salt water. Cruisers Forum reports up to 30 mm of material that has to be milled out to reach sound aluminium. It must be inspected at every major service.
What does it cost to rebuild a 4JH4-TE?
Cylinder head reconditioning 7,500-9,500 SEK in labour. Complete engine rebuild 32,000-48,000 SEK in labour, plus parts 9,000-18,000 SEK. The aluminium manifold often adds 6,000-14,000 SEK depending on whether it is milled out or replaced.
How long does a 4JH4-TE last?
4,000-7,000 running hours with the right maintenance. A mechanical pump and direct injection give it longer life than its common rail counterparts. The manifold and riser are what typically limit it - not the engine itself.
Is the 4JH4-TE still in production?
No. It was succeeded by the 4JH-CR series (4JH45/57/80/110) around 2014 - driven by EPA Tier 3 regulations. The CR version has common rail injection and more power but needs more servicing and pricier spare parts. Many boat owners prefer the 4JH4-TE for its mechanical simplicity.
How long does a 4JH4-TE rebuild take?
Cylinder head reconditioning: 1-2 weeks. Complete engine rebuild: 3-5 weeks in the workshop. Aluminium manifold replacement or milling out often adds to this.
Have a 4JH4-TE that needs looking at?
Call us or send a quote request. Reply within 24 hours. We service all types of boat engines - see boat engine page. All rebuilds with 12-month warranty.