Yanmar inboard/stern engines are known for their quality, durability, and reliability. However, like all engines, they are susceptible to overheating. Overheating, inboards causes many problems including engine damage, loss of power, and decreased fuel efficiency.
Heat exchanger problems are the most common cause of overheating in Yanmar inboard diesel engines. Overtime build-up of debris and scale in the heat exchanger can restrict cooling water flow and cause the engine to overheat.
To prevent overheating, it is important to have your Yanmar dealer regularly service your heat exchanger. Additionally, leaking coolants, low coolant levels, and old/contaminated coolants can also cause the engine to overheat. Make sure to regularly check your coolant levels and condition, and have any leaks repaired as soon as possible.
Most of these inboards are fitted with overheat alarm sensors. If your engine is overheating, the alarm will sound and an error code will be displayed on the instrument panel.
Shutting down the engine immediately and checking the coolant levels is the best course of action when this happens. Once the engine has cooled, you can check for any leaks in the cooling system and repair them as necessary. Let us now look into other factors that can cause overheating.
Bad Thermostat
A thermostat helps to regulate the engine’s operating temperature by opening and closing the cooling system circuit. A stuck-open thermostat will cause the engine to overheat because it doesn’t allow the coolant to circulate properly. Conversely, a stuck-closed thermostat can also cause overheating as it doesn’t allow the engine to reach its optimal operating temperature.
A bad thermostat quite often causes intermittent overheating issues because it gets stuck in one position and then suddenly switches to the other. This can damage the engine over time, so it’s important to have a thermostat failure diagnosed and repaired as soon as possible.
Changing the thermostat is quite simple and can be done by anyone with basic mechanical skills. However, it’s always best to have a professional do it to avoid any further damage to the engine.
Damaged Raw Water Pump
The raw water pump is responsible for circulating cooling water through the engine. If the raw water pump fails, the engine will overheat very quickly. Check your Yanmar’s raw water pump if the inboard is over heating frequently.
A damaged raw water pump can be caused by a number of things including debris in the cooling system. Since these pumps intake raw water directly from the body of water the boat is in, any debris can quickly damage the impeller.
It’s important to have your raw water pump checked regularly by a professional to ensure it’s in good working condition.
Heat Exchanger Problems
Heat exchangers are responsible for transferring heat from the engine coolant to the raw water circulating through the cooling system. Over time, the build-up of debris and scale can restrict cooling water flow and cause the engine to overheat.
To clean your heat exchanger, you’ll need to remove it from the engine. This is a fairly simple process that can be done by anyone with basic mechanical skills. Once the heat exchanger is removed, you can use a brush and some cleaning solution to remove any debris and scale.
A damaged heat exchanger needs to be replaced as soon as possible. Replacing a heat exchanger is a fairly simple process, but it’s always best to have a professional do it to avoid damaging the engine.
Exhaust Elbow or Manifold Problems
A cracked exhaust elbow or manifold can cause the Yanmar inboard engine to overheat. This is because exhaust gases are able to leak into the cooling system, raising the coolant temperature.
In some cases, you might be able to hear a hissing sound coming from the engine when this happens. If you notice any cracks in your exhaust components, have them repaired or replaced as soon as possible.
Strainer Blockages
The raw water strainer is responsible for filtering out any debris before it enters the raw water pump. If the strainer becomes clogged, it can restrict cooling water flow and cause the engine to overheat.
It’s important to clean your raw water strainer on a regular basis to prevent any blockages. The strainer can be removed by anyone with basic mechanical skills. Once it’s removed, you can use a brush and some cleaning solution to remove any debris.
Periodic checks and cleanings of the raw water strainer will help to prevent any overheating issues.
False Over Heating Alarms
Quite often, an overheating alarm will go off even when the engine isn’t actually overheating. This is usually due to a faulty sensor or loose wiring. Keeping a temperature infra thermometer onboard can help to verify if the alarm is accurate.
If you suspect that your overheating alarm is falsely triggering, have it diagnosed and repaired by a professional as soon as possible.
Blown Head Gasket
One of the most common causes of overheating is a blown head gasket. The head gasket is responsible for sealing the engine block and cylinder head. If the head gasket blows, coolant can leak into the combustion chamber and cause the engine to overheat.
A blown head gasket can be caused by a number of different things, such as an overheated engine, a cooling system leak, or a faulty thermostat. If you suspect that your head gasket has blown, we recommend taking your Yanmar inboard to a professional mechanic for diagnosis and repair.
Water in the Oil
If you notice water in the oil, it’s a sign that the engine is overheating. This can happen for a number of reasons including a head gasket failure or a cracked cylinder head.
When water gets into the oil, it causes the oil to break down and creates a foamy mixture. This mixture can’t lubricate the engine properly and will cause the engine to overheat. If you notice water in the oil, have your Yanmar inboard looked at by a professional as soon as possible.
Coolant Leaks
Leaking coolant is another common cause of overheating in Yanmar inboard engines. Coolant leaks can be caused by a number of things including damaged hoses, loose clamps, and cracked cylinders.
To prevent coolant leaks, it’s important to regularly inspect your cooling system for any signs of damage. If you notice any leaks, have them repaired as soon as possible.
Preventing Overheating Issues on Your Yanmar Inboards
There are a few things you can do to help prevent overheating issues with your Yanmar inboard engine. First, make sure to regularly check the coolant level and top it off as needed.
It’s also important to keep an eye on the condition of your cooling system components. If you notice any cracks or damage, have them repaired or replaced as soon as possible. Finally, be sure to clean your raw water strainer on a regular basis to prevent any blockages.
Overloading your boat is one of the leading causes of engine overheating. Make sure not to exceed the maximum weight capacity for your boat. If you’re unsure of how much weight your boat can safely carry, consult the owner’s manual.
Driving at full throttle for extended periods of time can also cause the engine to overheat. If you need to travel at high speeds, take breaks often to allow the engine to cool down.
If you notice any signs of overheating, such as an illuminated check engine light or steam coming from under the hood, pull over and shut off the engine as soon as possible. Once the engine has cooled down, check the coolant level and add coolant as needed. If the problem persists, have your Yanmar inboard looked at by a professional mechanic.
Conclude
Overheating can be a major issue for Yanmar inboard engines, but it’s often caused by simple problems that can be easily diagnosed and repaired. By knowing what to look for, you can troubleshoot and fix most overheating issues on your own. If you’re not comfortable doing the repairs yourself, we recommend consulting with a professional mechanic. Keeping a regular maintenance schedule will also help to prevent any future overheating issues.
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Clifford Slater’s impressive credentials and dedication to his craft make him a trusted authority in the world of boats and fishing. His commitment to staying up to date with the latest developments in the industry, combined with his deep knowledge and understanding of the subject matter, ensures that his writing is always informative and valuable. For those seeking to improve their skills or simply enjoy the beauty of the sea, Clifford’s writing is a must-read.
