Arburg 400 Alarm: Hydraulic Oil Over-Tempe… — Causes & Fixes
Tensile data verified against MatWeb.com database & manufacturer datasheets · Last updated July 2026
Published: 2026-08-15
Arburg Error 400 is triggered when the hydraulic oil temperature exceeds the maximum safe operating limit, typically 60°C for Arburg ALLROUNDER machines. The hydraulic system powers the clamp, injection unit, ejector, and core pull functions....
Arburg Error 400 is triggered when the hydraulic oil temperature exceeds the maximum safe operating limit, typically 60°C for Arburg ALLROUNDER machines. The hydraulic system powers the clamp, injection unit, ejector, and core pull functions. High oil temperature reduces the viscosity of the hydraulic fluid, which decreases system efficiency, increases wear on pumps and valves, and accelerates oil degradation.
Alarm Details
| Alarm Code | 400 |
|---|---|
| Brand / Machine | Arburg |
| Severity | Medium (Process Warning) |
| Component | Hydraulic System / Oil Cooling Circuit |
| Affected Systems | Selogica Controller / Hydraulics |
Troubleshooting Protocol
For water-cooled systems: check the cooling water flow rate and temperature at the inlet and outlet. The temperature drop across the cooler should be at least 5-10°C. For air-cooled systems: check the fan operation and clean the radiator fins. Verify the cooling water regulating valve is fully open.
Low oil level reduces the system's thermal mass and cooling capacity. Check the oil level sight glass — the level should be at the midpoint when the machine is at operating temperature. Cloudy or discolored oil indicates water contamination or oil degradation.
If the machine is running slow cycles with long cooling times, the hydraulic pump may be running continuously without sufficient load to dissipate heat. Consider using the pump standby function to reduce heat generation.
The hydraulic system pressure may be set higher than necessary, causing excess heat generation from the pressure relief valve. Reducing the system pressure by 5-10 bar can significantly reduce oil temperature.
Common Root Causes
The following root causes are ranked by probability based on field experience with this alarm code:
Low oil level is the single most common cause of hydraulic pressure alarms. The pump draws air when the oil level drops below the pump intake, causing cavitation, pressure fluctuations, and eventual pump damage. Check the oil level with all cylinders retracted (clamp open, injection unit retracted). Use only the specified ISO grade (typically ISO VG 46 for most injection molding machines). Mixing different viscosity grades creates erratic pressure response.
Hydraulic oil contamination causes proportional valves, servo valves, and pump wear. Particle contamination (ISO 4406 > 20/18/15) causes valve spools to stick, leading to erratic pressure control and nuisance alarms. Water contamination (emulsified oil, milky appearance) reduces lubricity and causes pump cavitation. Take an oil sample for analysis — particle count and water content (Karl Fischer test) confirm contamination levels.
Piston pumps and vane pumps develop internal wear over time, allowing oil to bypass the pumping elements. This reduces flow rate and maximum pressure capacity. Measure the pump's case drain flow — a worn pump has significantly higher case drain flow than the OEM specification. A typical axial piston pump should have case drain flow below 5% of rated flow; above 10% indicates the pump needs replacement or overhaul.
A pressure relief valve stuck partially open bleeds hydraulic pressure back to the tank, preventing the system from reaching the commanded pressure. Listen for continuous flow noise at the tank return line when the pump is running but no axes are moving — this indicates the relief valve is passing oil. The proportional valve's solenoid coil should be tested for resistance (check against OEM specification) and the valve spool should be inspected for contamination.
Hydraulic accumulators (bladder or piston type) maintain system pressure during peak demand and absorb pressure shocks. A ruptured bladder results in zero accumulator function, causing pressure drops during simultaneous axis movements and pressure spikes when valves close. Check the nitrogen pre-charge pressure with a charging kit — the pre-charge should be approximately 60-70% of the maximum system pressure. A flat accumulator (zero pre-charge) indicates a ruptured bladder.
Preventive Maintenance
Follow these preventive maintenance measures to reduce the frequency of this alarm:
- Take hydraulic oil samples for analysis every 500 operating hours. Test for ISO 4406 cleanliness code, water content (Karl Fischer), and viscosity. Change the oil when the particle count exceeds 20/18/15 or water content exceeds 500 ppm.
- Replace hydraulic return-line filters every 500 operating hours (or per OEM schedule). Never exceed the filter's rated pressure drop — a clogged filter bypass valve opens and allows unfiltered oil to circulate, accelerating pump and valve wear.
- Test accumulator nitrogen pre-charge pressure monthly. Log the pre-charge pressure in the machine maintenance record. A gradual pressure loss indicates a leaking valve core; a sudden loss indicates a ruptured bladder requiring immediate replacement.
OEM Replacement Parts
| Part Name | OEM Part Number | Est. Price |
|---|---|---|
| Arburg Hydraulic Oil Cooler | AR-400-HOC | $1,200-2,500 |
| Arburg Oil Temperature Sensor | AR-400-OTS | $120-250 |
| Arburg Hydraulic Oil Filter | AR-400-HOF | $60-150 |
Prices are estimated US market ranges. Contact your OEM distributor for exact pricing. {zone} = zone-specific variant.
Same Alarm on Other Machine Brands
If you operate multiple injection molding machine brands, the same fault may appear under different alarm codes:
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| Engel Oil Temp Alarm | |
| KraussMaffei Hydraulic Temp Alarm |
Frequently Asked Questions
What is the ideal operating temperature range for Arburg hydraulic oil?
The ideal operating temperature range is 40-50°C. Below 30°C, the oil viscosity is too high, causing sluggish valve response. Above 55°C, the oil viscosity decreases, reducing system efficiency. The alarm threshold is typically set at 60°C.
Can a faulty hydraulic pump cause Arburg Error 400?
Yes. A worn hydraulic pump with internal leakage generates significantly more heat than a healthy pump. If the oil temperature is consistently high despite normal cooling system operation, perform a pump efficiency test. A pump with less than 85% of rated flow likely needs replacement.
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org