Oil temperature 17 degrees cooler

Two near identical trips on consecutive days show cooling fans keep engine oil temperature down.

Day 1: Parramatta to Sydney city along Victoria Rd. Start 7am, ambient temp approx 18°. Heavy traffic and slow speeds.Fans turned on 10 minutes into the trip. Maximum oil temperature – 100°

Day 2: Parramatta to Sydney city along Victoria Rd. Start 7am, ambient temp approx 18°. Heavy traffic and slow speeds. Fans not turned on at all. Maximum oil temperature – 117°

17° difference – does it matter? The motor company says oil temperature should reach about 110°, so 117° is on the high side. See cooler engine oil for some info about oil temperatures.

These two trips demonstrate these cooling fans have a definite and beneficial impact on engine temperature, especially in heavy traffic condistions.

I’ll run this test again once the weather warms up more.

Surprised by engine heat

Yesterday I rode down the M2 in Sydney, about 20km at 100km/h.

I took the Pacific Hwy exit and immediately was caught in slow moving traffic. I didn’t turn my cooling fans on – it was a cold day (about 15°C) with light rain. I figured the engine wouldn’t need forced air cooling on a day like this.

After 10-15 minutes of slow moving traffic and trying to find a parking spot, the engine went into ‘parade mode’. The engine heat sensor sent a signal to the engine control unit that the cylinder head was too hot; take action to keep it cooler.

I was mighty surprised given the weather conditions and short time in traffic. It reminded me that I should use my engine cooling fans whenever I’m moving under 60km/h.

Do you need engine cooling fans in winter?

Clearly your Harley’s engine will run cooler in winter than it does in summer, but not as cool as you may think. Most Harley Davidson models run air-cooled engines; cooler air means a cooler engine, all other things being equal.

But the amount of cooling depends on the difference between engine temperature and air temperature (remember that from high school science?)

Some calculations:
Summer: head temp 180°C, air temp 40°C: difference = 140°C.
Winter: head temp 180°C, air temp 20°C: difference = 160°C.

So the cooling effect in winter is only 4-5% better (calculated using the Kelvin temperature scale).

Riders feel a big difference between summer and winter, but your engine won’t. I’ve been using my cooling fans in Sydney traffic even in these cooler months.

Engine cooling fans keep oil temperature within range

Two test runs in near identical conditions demonstrate how Cool My Hog engine cooling fans work to control oil temperature. The forced cooling is directed at the cylinder heads but the entire engine benefits.

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.

(Harley states normal operating oil temperature is 110°C – see oil temp gauge fitment guide)

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.

Read about the importance of controlling engine oil temperature at http://coolmyhog.com.au/cooler-engine-oil/

Where to measure Harley engine temperature – oil or cylinder head?

The best place to measure your Harley Davidson’s engine temperature is at the cylinder head. That’s where the Harley design engineers placed the Engine Temperature Sensor – in the fins behind the front cylinder head. If they wanted to monitor engine oil temperature they could easily have done that. But they choose to monitor head temperature.

A surprising thing happened as I got caught in traffic on Pennant Hills Rd after riding down the M1. I was monitoring oil temperature (with a sensor fitted in the oil sump), and had my engine cooling fans off. I was wondering how hot the oil would get with the fans off.

But surprisingly the Engine Idle Temperature Management System (EITMS) kicked in when the oil temperature was only 105°C. (EITMS shuts down the rear cylinder when the engine gets too hot.) So why was the engine too hot while the oil was OK.

Finally I got it! (perhaps I’m a bit slow). Engine temperature and oil temperature are not exactly the same thing. The engine – the cylinder head – can be too hot while the oil is not. That’s why the Harley engineers placed the sensor where they did, and that’s why they’ve built in some corrective action when the engine runs too hot.

I quickly flicked on my cooling fans and the EITMS turned off in under a minute.

Harley engine’s are air cooled, not oil cooled. Reading the description of the oiling system confirms this. The oil system is about providing lubrication not cooling, although there is some cooling as a side benefit.

The cylinder head is the hottest part of the engine. It’s the area that needs cooling. The design engineers have played particular attention to the cylinder head area when designing the new M8 engines.

So, cooling fans that blow air directly on the cylinder head drop the temperature in this critical area.

I’ll continue observing engine oil temperature, but won’t be so obsessive any more.