(For a Technical Review of the Milwaukee Eight motor CLICK HERE)
Since the 2017 Harley models were released last week, most of the questions I’ve gotten about them relate to the motor’s cooling systems. Some models are dual liquid cooled, using both coolant and oil while others are only oil cooled. Both also rely on air flow to assist with cooling. This has created some confusion on the matter.
To clear things up let me explain. Any 2017 factory model with fairing lowers is dual cooled. This includes CVO Street Glides, any Ultra model and Tri-Glide Trike models.
The fairing lowers on these bikes house coolant tanks and radiators. A water pump sits below the voltage regulator at the front of the bike. It pumps coolant through lines that feed into the cylinder heads, around the exhaust valve guides and then back out of the head, returning to the coolant tanks. The system is well hidden and not noticeable unless your looking for it. Harley Dual cooling has been around since 2014 but in 2017 the pump was upgraded and is now a variable speed, electronic pump controlled by the ECM. It does not use a thermostat.
The remaining touring models, Street Glides, Road Glide Customs, Road Kings, and Free Wheeler Trikes, are not dual cooled. They depend on oil and air flow to keep the motor cool. Because these bikes rely so heavily on oil for cooling they have a high output oil pump with larger gears then the water cooled models. Oil is pumped out of the cam compartment, via external lines, towards the top of the motor. From there it enters the cylinder head, is channeled around the exhaust valve guides and then back out of the head and to the return side of the oil pan creating a stand alone oiling system for the heads.
From what I’ve experienced both of these systems allow the bike to operate at a much cooler temperature then earlier Twin Cam model touring bikes. When I demo rode an oil cooled Street Glide I got caught in stop and go traffic and was relieved to find my leg never got hot and the bike never had to shut down the rear cylinder due to over heating.
For the full review of my ride on a 2017 Milwaukee Eight Touring bike CLICK HERE