--- title: "Oil temperature of an injection molding machine" url: "https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-temperature/" --- # Oil temperature of an injection molding machine Why injection molding machine oil temperature matters, the typical working range, what makes the oil run too hot or too cold, and how to find the cause. Injection molding machine oil temperature is the temperature of the hydraulic oil in the tank, shown on the tank thermometer and on the controller. Machine manuals typically ask for a working range of roughly **35 to 55 °C**; the exact limits and the alarm settings for your machine are in its manual. Inside that range the oil has the viscosity the pumps and valves are designed for, so movements, pressures and the molding process stay repeatable. Oil that runs too hot thins, leaks internally and ages quickly; oil that is too cold is thick and makes the machine sluggish. The oil cooler, highlighted in the drawing, is what holds the temperature steady. ## Where the heat comes from All the power the pump puts into the oil that does not end up as movement turns into heat: - **Pressure drops** across valves, especially when a [relief valve](https://www.imspares.com/injection-molding-machine-parts/hydraulics/relief-valve/) or a proportional valve throttles flow back to the tank. - **Internal leakage** in the pump, valves and cylinders: oil forced through a small gap at high pressure heats up. - **Friction** in the pump, motors and pipes. A fixed-displacement pump driven at constant speed keeps delivering oil while the machine waits, for example during the cooling time, and that oil has to go somewhere. A [servo pump system](https://www.imspares.com/injection-molding-machine-parts/hydraulics/servo-pump/) slows the pump down when no flow is needed, so it puts less heat into the oil. ## How the oil temperature is controlled - **The [oil cooler](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-cooler/)** on the return line, fed with water from the [cooling water manifold](https://www.imspares.com/injection-molding-machine-parts/hydraulics/cooling-water-manifold/). The water flow is set by a hand valve, a thermostatic valve or a solenoid valve switched by the controller, depending on the machine. - **The temperature sensor** in the tank, which feeds the controller display and the oil temperature alarms. Some machines warn or stop automatic operation when the oil is too hot or too cold. - **The tank** itself, which holds enough oil for the returning oil to settle and lose some heat. See [oil tank](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-tank/). - **Warm-up**: at start-up the oil is warmed by running the pump. Some controllers have a warm-up function for this. ## Signs that the oil is too hot - The temperature on the controller or tank thermometer climbs above its usual value during production. - Injection speed, pressure or cushion become less stable as the shift goes on. - Movements become slower, or the pump becomes noisier. - The oil darkens quickly or smells burnt. - Cylinder and valve seals harden and start to leak. ## Causes of high oil temperature - **Cooling water**: the valve is closed or stuck, the strainer is blocked, the flow is too low, or the water is too warm, for example when a cooling tower cannot keep up in summer. - **A fouled oil cooler**: scale, mud or algae on the water side stop the heat getting through. - **A relief valve** set too close to the working pressure, or stuck partly open, dumping oil to the tank. - **A worn pump** that leaks internally: see the [hydraulic pump types](https://www.imspares.com/injection-molding-machine-parts/hydraulics/hydraulic-pump/). - **Leaking cylinder seals or valves**, which turn pressure into heat. - **A low oil level**, so the same heat goes into less oil. - **The wrong oil grade.** See [hydraulic oil](https://www.imspares.com/injection-molding-machine-parts/hydraulics/hydraulic-oil/). ## Oil that is too cold Cold oil is thick. It passes the suction filter, lines and valves less easily, so the pump can cavitate, movements are sluggish and pressures and speeds differ from their settings until the oil warms up. Parts molded during warm-up may not match the parts made later. Causes are a cold building at start-up and **overcooling**: a water valve stuck open, or full cooling water when little heat is produced. Overcooling can also encourage condensation, which brings water into the oil. Let the machine reach its working range before production, and check that the cooling water is controlled, not just left fully open. ## Finding the cause of a temperature problem 1. **Check the reading.** Compare the controller display with the thermometer on the tank. 2. **Check the oil level and condition** in the sight glass. 3. **Check the cooling water.** Is the valve open, the strainer clean and the supply cool? Measure the water temperature into and out of the cooler. If the oil is hot but the water comes out barely warmer than it went in, the cooler is not passing the heat: it is fouled, or the water is bypassing it. If the water comes out very warm, the flow is too low. 4. **Measure the oil** before and after the cooler. A small difference with the water flowing well points to a fouled cooler. 5. **Find where the heat is made.** With the cooler working, look for components much hotter than the rest with an infrared thermometer: a relief valve and its return line, a valve body, or a pump case. 6. **Check the settings**: the system relief pressure and, on fixed pumps, the unloading during idle times. The [hydraulic oil problems](https://www.imspares.com/blog/hydraulic-oil-problems-injection-molding/) and [hydraulic pressure loss](https://www.imspares.com/blog/troubleshooting-hydraulic-pressure-loss/) articles cover pump and valve tests in more detail. ## Parts that affect oil temperature The cooler is the usual suspect. The [oil cooler / heat exchanger](https://www.imspares.com/parts/o-tc-04/) we supply is a water-cooled shell-and-tube or plate type. To quote a cooler, see what to send on the oil cooler page, and for the rest of the oil circuit the [hydraulic system guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/). ## Questions ### What is the normal oil temperature of an injection molding machine? Machine manuals typically give a working range of roughly 35 to 55 °C for the hydraulic oil, but the limits and alarm settings differ between machines. Follow the range in your machine manual. ### What happens if the hydraulic oil gets too hot? The oil thins, so more of it leaks inside the pump, valves and cylinders. Movements and pressures become less repeatable, the oil oxidizes and darkens faster, and the seals harden and start to leak. ### Why does my machine run slowly when it is cold? Cold oil is thick. It flows less easily through the suction filter, lines and valves, so the pump can cavitate and movements are sluggish until the oil reaches its working temperature. Let the machine warm up before starting production. ### How do I lower the oil temperature of an injection molding machine? Check the cooling water first: that the valve is open, the strainer is clean, the water is cool enough and the cooler is not scaled. If the cooler is working, look for where the heat is made, such as a relief valve dumping oil or a worn pump leaking internally. ## Replacement parts - [O-TC-04 Oil Cooler / Heat Exchanger](https://www.imspares.com/parts/o-tc-04/): Hydraulic oil cooler (heat exchanger) for injection molding machine oil temperature control.