Why is my Yanmar diesel engine overheating?

Yanmar diesel engine overheating may be caused by a clogged seawater filter, damaged impeller, faulty thermostat, blocked heat exchanger, or a failing circulation pump. Start diagnosis by checking the cooling system from the simplest components first.

How do I identify which impeller the pump on my Yanmar GM/YEU engine uses?

Older 2GM and 3GM raw-water-cooled engines typically use impeller 09-806B or 104211-42071 with a 58 mm lid. Freshwater-cooled models use a 70 mm lid, while post-1997 YEU or E-prefix engines generally use impeller 09-810B with a 76 mm lid and O-ring seal.

How do I maintain and clean a Yanmar oil cooler or heat exchanger?

The oil cooler or heat exchanger should be cleaned every 100 to 200 hours or once per season. Remove the unit, inspect for scale, corrosion, and marine growth, clean the tubes with a brush, rinse with water, and use descaling chemicals if necessary.

When should I check, maintain, or replace my Yanmar circulation pump?

A Yanmar circulation pump should be inspected if it shows dripping from the mechanical seal, shaft wobbling, bearing wear, or causes engine heat spikes.

How often should I replace my Yanmar thermostat?

Replace the thermostat every 2 to 3 years in saltwater use and every 4 to 5 years in freshwater use, or sooner if overheating or temperature regulation issues occur.

Is it easy to repair my Yanmar water pump?

Small Yanmar water pumps with shafts up to 16 mm are generally easy to repair. Larger and more complex pumps may require specialized tools, workshop manuals, and advanced mechanical knowledge.

Cooling system Yanmar - Spare parts for the cooling system of Yanmar Marine Diesel

The cooling system of a Yanmar marine diesel engine is one of the most crucial subsystems of the engine, which can lead to serious mechanical failures if left unserviced. The engine can be raw-water cooled or freshwater cooled; the first variant means that the seawater directly cools the engine, while the other option indirectly cools a cooling fluid through the use of a heat exchanger.

A raw water-cooled engine is much simpler in terms of components and cheaper to maintain. However, an indirect cooling system (freshwater-cooled) may turn out more effective in the long run. The majority of the modern Yanmar marine diesel engines are sold with a heat exchanger. Additionally, there are plug-and-play kits to retrofit older engines with a more modern cooling system. The typical layout of a raw water-cooled system includes a seawater pump, a thermostat, and an exhaust elbow. Such an engine will suffer from corrosion and scale buildup issues.

The freshwater option of such an engine would additionally include a circulation pump and a radiator. The thermostat usually opens on a higher temperature range, and the impeller water pump is designed to move larger quantities of water. These indirect cooling systems feature counterflow tubular systems; on the one side of the system, seawater flows. The other tube circulates a cooling fluid, which is not in contact with the seawater; hence, the reason they are also called indirect cooling systems. The greatest advantage of this layout is that, if you maintain it properly, you will minimize the corrosion.

Taking into account all the above, you are expected to find the following components in the cooling system of Yanmar marine diesel engines: raw water pumps and circulation pumps, hoses, heat exchanger units, thermostats, exhaust elbows, and expansion tanks. Poseidon Marine has been offering raw water pump and circulation pump components since our foundation. One of our principles has always been to offer the best possible materials in terms of quality in order to ensure your repair lasts over time. For that reason, we supply premium bearing brands, like SKF, INA, KOYO, NACHI, and other members of the World Bearing Association. Our water pump seals are always marine-grade, and our impellers are of the highest quality. Lately, we have developed our own line of water pump shafts, offering you the chance to overhaul your water pumps, using quality parts, at an affordable price. If Poseidon Marine had to pick a few new products, these would be:

PoseidonMarine® Yanmar 6LP water pump shaft kit 119773-42500 10-24493-01
PoseidonMarine® Water pump shaft kit Yanmar 3JH 4JH 129670-42513 129670-42560
PoseidonMarine® Water pump shaft kit Yanmar 2GM 3GM pump 128270-42000
PoseidonMarine® Water pump shaft kit Yanmar 1GM 1GM10 pump 128170-42200
Recmar® circulation water pump Yanmar 2YM15 3YM20 119540-42000 119540-42001

Besides these new releases, Poseidon Marine offers the following popular seawater pump repair kits:

PoseidonMarine® Water pump repair kit Yanmar 1GM 1GM10 pump 128170-42200
PoseidonMarine® Water pump repair kit Yanmar 6LP 119773-42600 119773-42500
PoseidonMarine® Water pump repair kit Yanmar -YEU 2YM 3YM X03431748 X03431760 128990-42200
PoseidonMarine® Water pump repair kit Yanmar 3JH 4JH 129670-42513 129670-42560
PoseidonMarine® Water pump repair kit Yanmar 2GM 3GM 104211-42070 128270-42000
PoseidonMarine® Water pump repair kit Yanmar 2GMF 3GMF pump 124223-42092 121575-42000
PoseidonMarine® Water pump repair kit Yanmar 4LHA 10-24535 119175-42500 127610-42200
PoseidonMarine® Water pump repair kit Yanmar 6LY2 119574-42500 10-13170 119574-42552

Poseidon Marine has been offering these parts to every corner of the world. From Auckland, New Zealand, to Togiak and Anchorage in Alaska, we manage to deliver the highest quality water pump parts at the right price.

Among the cooling system components, the service of radiators and heat exchangers made it a necessity to assemble seal kits that would include the most required components to clean a heat exchanger unit. Recmar innovated in this sector and created their custom line of oil cooler, charge air cooler, and heat exchanger seal kits. Here are the most popular of these:

Recmar® Seal kit Yanmar 3GM radiator 121450-13251 128297-44030 128695-44070
Recmar® Seal kit Yanmar 6LP air cooler 119773-18350 119773-18121
Recmar® Seal kit Yanmar 6LP radiator cooler 119773-44080 119773-44071
Recmar® Seal kit for Yanmar 6LP oil cooler 119773-33070 119175-33370
Recmar® Seal kit Yanmar 4JH oil cooler 24321-000750 24321-000800
Recmar® Seal kit Yanmar 3YM radiator cooler 128990-44100 119717-13110
Recmar® Seal kit Yanmar 2GM radiator 128290-13251 128695-44070 24311-000700
Recmar® Seal kit Yanmar 6LY air cooler 119595-18600 119574-18810 119578-18420
Recmar® Seal kit Yanmar 4LH oil cooler 119175-33370 119175-33380
Recmar® Seal kit Yanmar 4JH radiator cooler 129550-13110 129693-44420
Recmar® Seal kit Yanmar 4LH air cooler 119773-18350 119175-18590
Recmar® Seal kit Yanmar 4JH air cooler 129672-18170 129573-18120

One of the most basic components of every cooling system is the thermostat. Poseidon Marine offers a wide range of thermostats for various Yanmar marine diesel engines. These thermostats are made mostly by Recmar and Crom Marine. A good-quality thermostat is not only made to last long but also to operate under the proper operating temperature; opening too early will keep the engine cold, while delaying will make the engine overheat.

Here are some popular thermostats that you will find at Poseidon Marine:

Recmar® thermostat Yanmar 1GM 2GM 3GM 3HM 3QM30 42° 105582-49200 124233-49250
Recmar® thermostat for Yanmar 3JH 4JH 76.5° RO: 129470-49801
Recmar® thermostat for Yanmar 6LPA-DTP -DTZP -STP -STZ 70°C RO: 119773-49550
Recmar® thermostat Yanmar 2GMF 3GMF 3HMF 2GM20F 3GM30F 71°C 121750-49800
Recmar® thermostat for Yanmar 2YM15 3YM20 3YM30 71°C 128990-49800

If we had to call a component “the heart of the cooling system”, that could not be other than the impeller. Poseidon Marine keeps in stock large quantities of impellers for Yanmar marine diesel. These are branded mostly by CEF, Recmar, Poseidon Marine, or Johnson Pump.

These are our most popular impellers for Yanmar marine:

PoseidonMarine® Impeller kit Yanmar 1GM 128170-42090 128176-42090
PoseidonMarine® Impeller kit Yanmar 2GM20F 3GM30F 3HM 3HMF 3HM35 3HM35UF 128296-42070 3GMF
Johnson® 09-810B F4B Johnson Pump Impeller Kit
PoseidonMarine® Impeller kit Yanmar 2GM 3GM 104211-42070 104211-42090 pump 128270-42000
PoseidonMarine® Impeller Yanmar YEU 2YM15 653-0001 653-0001 128990-42200
Johnson® 09-808B F35 Johnson Pump Impeller Kit

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Frequently Asked Questions About Yanmar Cooling System:

Why is my Yanmar diesel engine overheating?

Maintaining the proper operating temperature may be affected by many different components. To identify the cause of overheating, start by checking the entire cooling system from the easiest components first. Begin with the seawater filter to rule out blockages caused by debris, plastic bags, or other materials restricting flow. Next, inspect the impeller, especially if overheating occurs under higher engine load. In raw-water-cooled systems, the thermostat is also a common cause. If the engine has a freshwater cooling system, additional components such as the heat exchanger and circulation pump should also be inspected.
How do I identify which impeller the pump on my Yanmar GM/YEU engine uses?

Yanmar GM series engines such as 2GM and 3GM use several different seawater pumps, which can be difficult to distinguish. Older raw-water-cooled 2GM and 3GM engines generally use the smaller impeller references 09-806B or 104211-42071, with a 58 mm (2-1/4 inch) lid sealed by a gasket. Freshwater-cooled models include an “F” suffix, such as 2GMF, and use a slightly larger 70 mm (2-3/4 inch) pump lid, also gasket sealed. Engines assembled after 1997 in the European Union may include an “E” prefix or “YEU” suffix and use impeller 09-810B. These pumps feature a 76 mm (3 inch) lid and use an O-ring seal with a channeled pump body.
How do I maintain and clean a Yanmar oil cooler or heat exchanger?

Inspect and clean the oil cooler or heat exchanger every 100 to 200 operating hours or once per year at the start of the season. Disconnect and drain the unit, then remove it from its mounting bolts so it can be serviced on a bench. Remove the end caps and inspect for corrosion, scale, barnacle buildup, and other contaminants. Clean each tube individually with a small bottle brush, then rinse thoroughly with water. For heavy marine growth or scale buildup, use a suitable descaling chemical according to the product instructions.
When should I check, maintain, or replace my Yanmar circulation pump?

The first signs that your circulation water pump needs maintenance are slow dripping caused by a worn mechanical seal or wobbling that indicates bearing wear. Sudden heat spikes may also suggest that the circulation pump requires inspection or replacement.
How often should I replace my Yanmar thermostat?

A thermostat operating in saltwater should generally be replaced every 2 to 3 years, while one used in freshwater may last 4 to 5 years. Commercial boats with high engine hours may require more frequent replacement. Common signs that a thermostat needs replacement include overheating or difficulty reaching normal operating temperature.
Is it easy to repair my Yanmar water pump?

Smaller pumps with shafts up to 16 mm are usually easy to repair and may not require a vise if you are experienced with tools. Larger shafts, mechanical seals, and more complex pump systems may require advanced tools, technical knowledge, and access to workshop manuals for precise repair procedures.

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Water pump impeller for Volvo Penta OMC Cobra RO: 3862281 21213660 21951346 09-1027B

~~Regular price €29,90~~