08-12-2025, 04:02 PM
The Problem: Excessive Blow-by and Visible Emissions
Older diesel engines like the Yanmar 3TN84TL—commonly found in compact excavators such as the Takeuchi TB035—often develop blow-by as internal wear increases. Blow-by refers to combustion gases leaking past the piston rings into the crankcase, creating pressure that must be vented. In many older machines, this pressure escapes through a breather hose that vents directly to atmosphere. When the engine is worn, this hose can emit visible smoke, oil mist, and strong odors—raising environmental concerns and creating a mess around the machine.
Understanding the Engine Breather System
The breather system is designed to relieve crankcase pressure and prevent oil leaks or gasket failures. In modern engines, this system is often integrated into a Positive Crankcase Ventilation (PCV) setup that routes vapors back into the intake for combustion. However, retrofitting such systems onto older engines requires careful consideration.
Key components of a typical breather system:
While routing the breather hose to the intake (after the air filter) may seem like a clean solution, it introduces several risks:
An operator in Belgium faced this exact issue with his TB035. The engine emitted visible smoke from the breather, and he considered routing it into the intake to reduce emissions. However, the machine was lightly used, and a full rebuild wasn’t economically viable. After consulting with mechanics, he learned that while the modification might work temporarily, it could accelerate wear or cause unpredictable behavior.
Recommended Solutions and Modifications
Managing crankcase vapors on aging diesel engines like the Yanmar 3TN84TL requires a blend of practicality and caution. While routing the breather to the intake may reduce visible emissions, it can introduce new risks—especially if the engine is already compromised. For lightly used machines, simple solutions like slobber cans or filtered vents offer cleaner operation without major modifications. And for those running older equipment in demanding environments, understanding the breather system is key to keeping engines clean, safe, and under control.
Older diesel engines like the Yanmar 3TN84TL—commonly found in compact excavators such as the Takeuchi TB035—often develop blow-by as internal wear increases. Blow-by refers to combustion gases leaking past the piston rings into the crankcase, creating pressure that must be vented. In many older machines, this pressure escapes through a breather hose that vents directly to atmosphere. When the engine is worn, this hose can emit visible smoke, oil mist, and strong odors—raising environmental concerns and creating a mess around the machine.
Understanding the Engine Breather System
The breather system is designed to relieve crankcase pressure and prevent oil leaks or gasket failures. In modern engines, this system is often integrated into a Positive Crankcase Ventilation (PCV) setup that routes vapors back into the intake for combustion. However, retrofitting such systems onto older engines requires careful consideration.
Key components of a typical breather system:
- Breather hose: Connects the valve cover or crankcase to a vent or intake
- Slobber can (oil separator): Captures oil mist before vapors are routed elsewhere
- PCV valve (in modern systems): Regulates flow and prevents backpressure
- Intake connection: Allows vapors to be reburned in the combustion chamber
- Blow-by: Combustion gases leaking into the crankcase due to worn piston rings or cylinder walls
- Wet stacking: Accumulation of unburned fuel and oil in the exhaust system, often due to light loading or poor combustion
- Engine runaway: A dangerous condition where the engine consumes crankcase oil as fuel, accelerating uncontrollably
- Slobber can: A simple oil separator that condenses mist and returns liquid oil to the crankcase
While routing the breather hose to the intake (after the air filter) may seem like a clean solution, it introduces several risks:
- Oil mist can foul the intake manifold and valves
- Excessive vapor can cause sticky valves or carbon buildup
- In extreme cases, oil ingestion can lead to engine runaway
- Intake air quality may degrade, affecting combustion efficiency
An operator in Belgium faced this exact issue with his TB035. The engine emitted visible smoke from the breather, and he considered routing it into the intake to reduce emissions. However, the machine was lightly used, and a full rebuild wasn’t economically viable. After consulting with mechanics, he learned that while the modification might work temporarily, it could accelerate wear or cause unpredictable behavior.
Recommended Solutions and Modifications
- Install a Slobber Can
A simple oil separator can be placed between the breather hose and intake. It captures oil droplets and allows vapors to pass through, reducing contamination.
- Use a Filtered Vent System
Instead of routing to the intake, vent the breather through a small filter or catch can that traps oil and reduces odor.
- Monitor Oil Consumption and Blow-by Rate
Excessive blow-by may indicate deeper engine wear. Track oil usage and consider compression testing.
- Avoid Muffler Routing
Some operators have tried venting into the muffler’s rain drain hole. This only relocates the mess and can cause external staining or fire hazards.
- Upgrade to PCV Retrofit (Advanced Option)
For engines in regular use, a full PCV retrofit with a calibrated valve and oil separator may be worthwhile. This requires careful tuning to avoid intake flooding.
- Crankcase pressure: Should remain below 1 psi under normal operation
- Oil mist concentration: High levels indicate ring or valve guide wear
- Intake vacuum: Ensure breather routing does not disrupt airflow
- Exhaust temperature: Wet stacking often correlates with low exhaust temps due to light loading
- Change oil regularly with high-detergent diesel-rated oils
- Use high-quality filters to reduce particulate contamination
- Load the engine periodically to burn off deposits and prevent wet stacking
- Inspect breather hose for cracks or blockages
Managing crankcase vapors on aging diesel engines like the Yanmar 3TN84TL requires a blend of practicality and caution. While routing the breather to the intake may reduce visible emissions, it can introduce new risks—especially if the engine is already compromised. For lightly used machines, simple solutions like slobber cans or filtered vents offer cleaner operation without major modifications. And for those running older equipment in demanding environments, understanding the breather system is key to keeping engines clean, safe, and under control.
