Yanmar Marine Overheat Alarm
The YANMAR-OVERHEAT-MARINE (Yanmar) diesel fault code means: Yanmar Marine Overheat Alarm. This is a critical severity code.
- Keep driving?
- No — stop driving
- DIY difficulty
- intermediate
- Estimated cost
- $20-$800
What Are the Symptoms of YANMAR-OVERHEAT-MARINE?
- Buzzer / alarm on helm
- Steam from exhaust
- Coolant temp lamp
What Causes YANMAR-OVERHEAT-MARINE? (Most Likely First)
- Blocked raw water intake (sea grass, plastic bag) Very Likely
- Worn or shredded impeller (annual replacement) Very Likely
- Plugged heat exchanger tubes Likely
- Failed thermostat Possible
Can I Still Drive with YANMAR-OVERHEAT-MARINE?
No — stop driving. YANMAR-OVERHEAT-MARINE is rated critical severity. Continuing to drive in this state risks further damage — get it looked at before your next trip.
Frequently Asked Questions
What is Yanmar code MARINE-OVERHEAT?
Yanmar MARINE-OVERHEAT: Yanmar Marine Overheat Alarm. This code is reported on Yanmar equipment running the described engine family.
Can I keep working with Yanmar code MARINE-OVERHEAT?
Do not continue operating. Risk of engine damage or unsafe shutdown.
How much does Yanmar MARINE-OVERHEAT cost to fix?
Estimated repair cost: $20-$800. Off-road diesel shop labor runs $125-$175/hr in 2026. Dealer diagnostic software (Yanmar SmartAssist / YDT) is usually required.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose YANMAR-OVERHEAT-MARINE?
Shut down immediately -- continued running will destroy impeller and exhaust mixer.
Close seacock, clear strainer basket, inspect through-hull.
Replace impeller; inspect for missing blades (look in heat exchanger inlet if blades shed).
Acid-clean heat exchanger tubes if scaled.
Which Vehicles Commonly Get YANMAR-OVERHEAT-MARINE?
- Hunter / Beneteau / Catalina sailboats with Yanmar 3JH / 4JH
- Trawlers and sport fishing boats with Yanmar 6LY / 6LF series
- Sailboat auxiliaries with Yanmar 2YM / 3YM / 3JH5 diesels
- Commercial fishing vessels with Yanmar 6LY3-UTP
- Yachts with Yanmar 6LY400 / 6LY440 / 8LV common-rail marine diesels
- Workboats with Yanmar 4LV / 4JH series marine propulsion
- Ski boats and express cruisers with Yanmar marine diesels
- Tenders and RIBs with Yanmar 3YM20 / 3YM30 sailboat aux
- Island-hopper ferries with Yanmar 6AYM / 6HYM commercial series
- Tug boats and small workboats with Yanmar 6HAL-HTP / 6HYM
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