Oil temperature is a good indicator of overall engine temperature. The cooling fans help keep engine oil cooler by about 10 – 15°C.
Test bike: 2010 Harley Davidson Road King with Screamin’ Eagle Stage IV kit, fitted with Jagg 10-row oil cooler. If you don’t have an oil cooler, the oil temp on your bike could be higher than these test results.
Oil temperature measured by K-type sensor in oil sump.
Test 1: about 26°C ambient temperature
Run 1: Engine thoroughly warmed up. Starting oil temperature 100°C. Ambient temp about 26°C. Cooling fans off.
Ride around Sydney CBD for about half an hour.
Maximum oil temp: 126.7°C
Run 2: Starting oil temperature 105°C. Ambient temp about 26°C. Cooling fans on.
Ride around Sydney CBD for about half an hour – same route and riding style as run 1.
Maximum oil temp: 116.8°C
10°C cooler – that’s a good thing
(Harley states normal operating oil temperature is 110°C – see oil temp gauge fitment guide)
Test 2: about 22°C ambient temperature
Run 1: Cooling fans off. Ride from Parramatta to Sydney City in morning peak traffic. Oil temperature sits at over 120°C for the last part of the journey, peaking at 123.4°C. (On a warmer day and without an oil cooler this could have easily have been over 130°C.) The Engine Idle Temperature Management System (EITMS) kicked in frequently, at just about every red light.
Run 2: Cooling fans on. Ride from Parramatta to Sydney City in morning peak traffic. Oil temperature sits between 105°C and 110°C during the last part of the journey, peaking at 110.8°C. EITMS did not activate at all.
Preventing oil temperature going over 120°C – that’s important.
Info about engine oil temperature
- Add 10% to the oil tank reading to get a better indication of engine temperature.
- Oil oxidation rate increases explosively above 250°F (121°C) for fossil oil like that recommended by Harley. At 270°F (132°C), a mere 20 degrees above the 250 degree limit, the oxidation rate doubles, thereby reducing the life of the oil by half. Sustained riding at over 300°F (149°C) reduces oil life by 80 percent. (maybe that’s why many Harley dealers offer oil changes at twice recommended frequency – at 4000km intervals)
- If the operating viscosity of the oil goes below 10mm2/s, then the oil is too thin to lubricate all components within the engine adequately. At 120°C many oils fall below this viscosity level.
- Once the oil temperature goes over 125ºC the oil is so thin that it starts to bypass the rings and gets burned in the combustion process. The oil is in a very low concentration compared to the fuel and generally is not visible as combustion smoke. In a situation such as this, oil consumption will increase