Yanmar 3YM20 Hard to Start After Fuel Filter Change?
If your Yanmar 3YM20 marine engine becomes difficult to start immediately after replacing the fuel filter, don't automatically assume the new filter is defective.
A more likely first check is air trapped in the fuel system.
Opening the fuel system during filter replacement allows air to enter. Yanmar's YM-series operating instructions specifically state that bleeding is required after fuel-system maintenance such as fuel-filter replacement.
For the Yanmar 3YM20, the fuel filter element covered in this guide is:
Yanmar Part Number: 104500-55710
When the engine was starting normally before maintenance but suddenly becomes difficult to start afterward, the timing of the symptom is an important diagnostic clue.
For replacement filters and related components, visit Yanmar Marine Engine Parts.
Yanmar 3YM20 Fuel Filter Part Number
The fuel filter reference discussed in this guide is:
| EngineComponentPart Number | ||
| Yanmar 3YM20 | Fuel Filter Element | 104500-55710 |
The Yanmar 3YM20 parts catalogue identifies 104500-55710 as the fuel element used in the fuel strainer assembly.
The filter helps remove contamination from the fuel before it reaches downstream fuel-system components.
Although 104500-55710 is associated with the 3YM20, it is also used in other Yanmar applications.
For parts supply, always verify:
Engine model + engine serial number + existing part number
Why a Yanmar 3YM20 Can Be Hard to Start After a Filter Change
A diesel engine requires a consistent supply of fuel to the injection system.
When the fuel filter housing is opened, fuel can drain and air can enter the system.
If that air remains trapped after the new filter element is installed, proper fuel delivery can be interrupted.
The result may be:
- Longer cranking than normal
- Engine cranks but does not start
- Engine starts and then stops
- Uneven running immediately after starting
- Engine requires repeated starting attempts
- Fuel supply appears inconsistent
The important diagnostic clue is when the problem started.
If the Yanmar 3YM20 started normally before the fuel-filter service and became difficult to start immediately afterward, begin by checking the areas disturbed during maintenance.
That does not prove trapped air is the cause, but it makes the fuel-filter service and bleeding procedure logical first checks.
Air Enters the Fuel System During Filter Replacement
Air entering the system during fuel-filter service is expected.
Yanmar's YM-series instructions specifically state that manual bleeding must be performed when fuel-system maintenance has been carried out, including replacement of the fuel filter.
The engine incorporates an automatic air-bleeding function during normal operation, but this does not eliminate the requirement to bleed the system after it has been opened for maintenance.
This distinction is important.
Normal operation: automatic air bleeding assists the system.
After fuel-system maintenance: perform the specified manual bleeding procedure.
How the Yanmar 3YM20 Fuel System Is Bled
Always follow the operating manual applicable to your exact engine and installation.
For the YM-series procedure, the basic sequence is:
- Check that sufficient fuel is available in the fuel tank.
- Open the fuel cock.
- Loosen the air-bleed screw at the fuel filter.
- Operate the manual priming lever on the fuel-feed pump.
- Continue until fuel flows without visible air bubbles.
- Tighten the air-bleed screw correctly.
Use an appropriate container to catch diesel fuel and follow the applicable safety precautions.
The key point is not simply to see fuel appear.
The goal is to obtain a solid fuel flow without air bubbles before completing the bleeding procedure.
Why Fuel Without Air Bubbles Matters
Seeing fuel at the bleed point does not necessarily mean all relevant trapped air has been removed.
Initially, the fuel may contain visible air bubbles.
Continue the specified bleeding process until the flow becomes solid and free from bubbles.
Once that condition is achieved, the air-bleed screw can be tightened according to the applicable procedure.
After starting, the engine's automatic air-bleeding system can then assist with purging remaining air during normal operation.
Still Hard to Start After Bleeding? Check the Filter Installation
If the engine remains difficult to start after the system has been properly bled, inspect the work that was just performed.
The 3YM20 fuel-filter assembly includes more than the replaceable element.
The parts arrangement includes components such as the:
- Fuel filter element
- Filter housing/cup
- Retaining ring
- O-ring
- Air-bleed connection
- Associated fuel connections
A sealing problem can allow fuel leakage or potentially allow air to enter the fuel supply.
Check that the filter assembly has been installed correctly and that seals and mating surfaces are in good condition.
Check the O-Ring and Filter Housing
The filter housing needs to seal correctly.
An incorrectly installed, damaged or deteriorated O-ring can create problems even when the correct 104500-55710 fuel filter element has been fitted.
During service:
- Keep the filter housing clean
- Inspect the O-ring
- Check the sealing surfaces
- Make sure the element is correctly positioned
- Reassemble according to the applicable Yanmar procedure
- Bleed the system afterward
The Yanmar 3YM20 parts information identifies the O-ring used in this assembly separately from the filter element, which is another reason not to assume that replacing the element alone addresses every possible sealing issue.
Check for Fuel Leakage After the Engine Starts
Once the engine starts and operates normally, don't immediately consider the maintenance job finished.
Inspect the areas disturbed during the fuel-filter replacement.
Look around the:
Filter housing + retaining ring + bleed screw + fuel connections + sealing areas
Check for visible fuel leakage.
Even a small leak deserves attention.
Also observe how the engine runs after the service.
If idle remains unstable or starting behavior has changed, investigate further rather than assuming the system will automatically correct itself.
What If the 3YM20 Still Won't Start?
If the engine has been correctly bled and the filter installation is confirmed to be correct, continue the diagnosis systematically.
Possible areas to investigate include:
Fuel tank → fuel shutoff/cock → fuel supply → filter assembly → feed pump → fuel lines → injection system
Check whether clean fuel is actually reaching the filter and whether the manual priming system is functioning correctly.
Also consider whether the starting problem genuinely began because of the maintenance or whether another fault happened at approximately the same time.
Avoid replacing expensive fuel-system components until the basic supply and bleeding checks have been completed.
Don't Immediately Blame the New Fuel Filter
A difficult start after fuel-filter replacement does not automatically mean 104500-55710 is the wrong or defective filter.
Consider the sequence of events.
Before maintenance:
Engine starts normally
Fuel-system work:
Filter housing opened → old element removed → new element installed
After maintenance:
Engine becomes difficult to start
That sequence makes the recently opened fuel system a logical place to begin troubleshooting.
Check:
Correct filter → correct installation → O-ring/seals → fuel supply → trapped air → proper bleeding → leakage
Only after these basics are confirmed should the diagnosis move deeper into the fuel system.
Why a Clogged Fuel Filter Matters
The fuel filter should not only be considered when the engine refuses to start after maintenance.
A contaminated or restricted filter can also interfere with normal fuel flow.
Depending on the severity of the restriction, possible symptoms may include:
- Reduced fuel delivery
- Poor engine response
- Difficulty maintaining RPM
- Reduced output under load
- Unstable operation
The 3YM20 service information calls for periodic inspection of the fuel filter and replacement of the element when required.
This is why filter condition should be considered both during scheduled maintenance and when diagnosing fuel-delivery problems.
Ordering Yanmar 3YM20 Fuel Filter 104500-55710
The fuel-filter reference covered in this article is:
Engine: Yanmar 3YM20 Marine
Component: Fuel Filter Element
Part Number: 104500-55710
Before ordering, provide:
Complete engine model + engine serial number + existing part number
This is particularly useful because 104500-55710 is used across several Yanmar engine applications, and other components in the fuel-filter assembly have their own part numbers.
For Yanmar filters, fuel-system components and other replacement parts, visit Yanmar Marine Engine Parts.
Alfa Marine Spare Parts can assist with identification and supply for Yanmar marine engine maintenance and repair requirements.
Email: request@alfamarinespareparts.com
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Frequently Asked Questions
What is the fuel filter part number for a Yanmar 3YM20?
The fuel filter element covered in this guide is Yanmar 104500-55710.
Is Yanmar 104500-55710 a fuel filter?
Yes. The Yanmar 3YM20 parts catalogue identifies 104500-55710 as the fuel filter element in the fuel strainer assembly.
Why is my Yanmar 3YM20 hard to start after changing the fuel filter?
Air can enter the fuel system when the filter assembly is opened. Yanmar's YM-series instructions require the fuel system to be bled after fuel-system maintenance such as filter replacement.
How do I know when the air has been removed?
During the specified bleeding procedure, operate the manual priming lever until a solid stream of fuel without air bubbles flows from the bleed point.
Does the Yanmar 3YM20 bleed itself automatically?
The YM-series fuel system has an automatic air-bleeding function during normal engine operation. However, Yanmar still specifies manual bleeding after fuel-system maintenance or when the engine does not start after repeated attempts.
What should I check if bleeding doesn't solve the starting problem?
Check the filter installation, O-ring and sealing surfaces, fuel supply, fuel cock, filter housing, feed-pump operation and associated fuel connections before moving deeper into the injection system.
Should I check for leaks after changing the fuel filter?
Yes. Once the engine is running normally, inspect the areas disturbed during maintenance for fuel leakage.
What information should I provide when ordering a Yanmar 3YM20 fuel filter?
Provide the engine model, engine serial number and existing part number. For the filter discussed here, the reference is 104500-55710.
Conclusion
If a Yanmar 3YM20 becomes difficult to start immediately after changing fuel filter 104500-55710, trapped air should be one of the first things checked.
Opening the filter assembly allows air into the fuel system, and Yanmar specifically requires bleeding after fuel-filter replacement.
Follow the correct procedure until fuel flows without air bubbles, then inspect the filter housing, seals and disturbed connections once the engine is running.
The timing of a symptom matters in marine-engine diagnosis.
When an engine starts normally before maintenance but becomes difficult to start immediately afterward, begin with the components and systems that were just disturbed.
Correct filter + correct installation + proper bleeding + leak inspection
For Yanmar 3YM20 filters and other Yanmar Marine Engine Parts, contact Alfa Marine Spare Parts.
Email: request@alfamarinespareparts.com