Diesel Engine Cooling System Structure and Maintenance

The function of a diesel engine cooling system is to ensure the engine operates within the optimal temperature range. A closed forced-circulation water cooling system primarily consists of a radiator, water pump, fan, thermostat, water temperature gauge, and other components. Users and maintenance personnel often face challenges due to limited understanding of its structure and principles. This article focuses on the structural characteristics, working principles, and key maintenance practices of diesel engine cooling systems to assist users in proper operation.

1. Key Components of Diesel Engine Water Cooling Systems

(1) Radiator

Composed of upper/lower water chambers and a radiator core. The upper chamber features an inlet pipe (connected to the cylinder water jacket via a hose) and a filler neck sealed by a radiator cap to regulate internal pressure. The lower chamber has an outlet pipe linked to the cylinder block’s lower water pipe.

(2) Air-Vapor Valve

Integrated into the radiator cap, it maintains pressure balance:

When steam pressure exceeds 19.6–37.3 kPa, the vapor valve opens against spring tension, releasing steam through a vent tube to prevent radiator core rupture.

When pressure drops below atmospheric pressure by 0.98–3.92 kPa, the air valve opens, allowing external air in to avoid radiator collapse.

(3)Water Pump

A centrifugal pump circulates coolant. Driven by the crankshaft pulley, it spins to create centrifugal force, pushing water through the outlet pipe into engine water jackets to cool components.

(4)Fan

Enhances airflow velocity and volume through the radiator core to improve heat dissipation. On small diesel engines, the fan is often cast integrally with the flywheel, drawing air axially and expelling it radially to cool the core.

(5) Thermostat

Regulates coolant flow to the radiator via an expandable brass bellows filled with low-boiling-point fluid. Linked to a pushrod and valves (top and side), it adjusts opening based on temperature:

Cold start: Bellows contracts, closing the top valve and opening the side valve to recirculate coolant internally for rapid warm-up.

Operating temperature: Bellows expands, opening the top valve to direct coolant through the radiator.

(6)Water Temperature Gauge

Mounted on the dashboard, it connects to a cylinder head sensor to display real-time coolant temperature.

2. Operation and Maintenance of Water Cooling Systems

(1) Coolant Selection

Use distilled water, tap water, rainwater, or clean river water. Avoid dirty or hard water to prevent scaling and cylinder liner corrosion; hard water must be softened before use.

(2) Water Refilling and Draining

Overheating due to water loss: Do not add cold water immediately. Idle the engine for 10–15 minutes to cool down, then refill to prevent thermal shock cracking of the block or cylinder head.

Opening the radiator cap: Exercise caution to avoid scalding from steam or hot water.

Cold-weather draining: Drain coolant only after the temperature drops to 60°C to prevent thermal stress damage. After draining, open the cap and crank the engine briefly to expel residual water from the pump.

(3) Fan Belt Tension

Maintain proper belt tightness:

Too loose: Reduces pump/generator speed, slowing coolant circulation and causing overheating; may lower battery voltage.

Too tight: Increases wear on the pump, fan, and belt, potentially leading to premature failure.

(4) Cooling System Repairs

Radiator issues: Common faults include leaks (cracks or mechanical damage) and poor heat dissipation.

Leak detection: Use the water-filling method (observe for seepage after filling with hot water) or air-pressure testing to identify cracks.

By adhering to these guidelines, users can ensure efficient cooling system performance and extend diesel engine lifespan.

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