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
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Common Symptoms
- Buzzer / alarm on helm
- Steam from exhaust
- Coolant temp lamp
Probable Causes (Ranked by Likelihood)
- 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
Step-by-Step Diagnostic Procedure
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.
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?
Typical repair cost: $20-$800. Off-road diesel shop labor runs $125-$175/hr in 2026. Dealer diagnostic software (Yanmar SmartAssist / YDT) is usually required.