How Does AMSOil Perform in the Harley-Davidson Milwaukee-Eight?

2016 saw the introduction of Harley’s Milwaukee-Eight V-twin engine increasing power and lowering the heat of the engine—so how does AMSOIL work in the Harley engine?

First, let’s explore some background. Harley interviewed 1,000 riders in seven cities to learn what they were looking for in the new generation of touring Harleys. Two common recommendations became clear: additional power and less heat.

Conventional V-twin engines that are air-cooled, such as those most common in Harleys, often tend to get hot. In fact, many riders have complained about the strong heat that radiates from the engine during rides—especially in the rear cylinder, which gets less airflow than the front cylinder.

Engines Are Impacted by Heat

Intense heat challenges both the comfort of the rider and the engine. Extreme heat, for example, can lead to pistons expanding beyond an acceptable tolerance, resulting in cylinder wall rubbing that causes scuffing.

Heat can also thin some oils and lower the viscosity, causing the engine to lose oil pressure and even sometimes causing the pressure gauge to bottom out.

Riders may also potentially notice an increase in gear and valvetrain noise as parts clang together. The majority of serious riders know you shouldn’t run an engine with no oil pressure, so he or she will shut down the engine until it can cool enough to restore oil pressure.

Air Vs Liquid

So why do air-cooled V-twins reach such a high temperature? How high of a temperature can they reach? The answer lies in physics:

Air-cooled engines use air flow to remove engine heat. Liquid-cooled engines, on the other hand (like most Indian motorcycles have) utilize a mixture of water and coolant to absorb engine heat and carry the heat to the radiator, where it disperses into the atmosphere.

Air is naturally less effective when it comes to removing heat than a coolant/water mixture is, which means the average V-twin that powers Harley will run hotter than a liquid-cooled bike.

AMSOIL’s intense-heat testing discovered that a 2012 Harley Street Bob reached as high as 550°F(288°C) in the rear cylinder. A 2017 Indian Scout test, on the other hand, revealed an average cylinder temperature of 200ºF (93ºC). The comparison is not quite apples-to-apples, as the Scout did not undergo th same test, but the implication remains that liquid-cooled bikes in general run significantly cooler than air-cooled bikes. Buy V-Twin Motorcycle Oil.

Engine Heat is Affected by Riding Conditions

Riding conditions also have a bearing on engine heat. Have you ever visited Sturgis? Riding in a 4th of July parade or other similar peak-summer event can lead to increased engine heat. The slow crawl of bikes in Sturgis on Main Street is beneficial for enjoying the moment and the blazing August sun, but your engine absorbs these radiated rays and doesn’t have proper speed to properly cool the engine with air flow. The lack of cool air across the engine can lead to hazardous temperatures.

If the heat is intense enough, the electronic temperature controls that keep the bike safe from overheating will trigger, which demands the rider to pull over and stop until the engine cools sufficiently. 

Harley’s Milwaukee-Eight Runs Cooler

Even non-marketing experts would agree that being pulled over roadside, waiting for your engine to cool is bad brand strategy. The engineers at Harley have designed the Milwaukee-Eight engine with this in mind.

Harley’s website showcases the Milwaukee-Eight as the “most powerful, coolest-running motor we’ve ever built”—less heat and more power, like Harley’s 1,000 riders wanted.

AMSOIL and the Harley Milwaukee-Eight

We purchased a 2019 Harley Street Bob with a Milwaukee-Eight 107 engine for extreme-heat testing. We wanted to learn how AMSOIL 20W-50 Synthetic V-Twin Motorcycle Oil worked within Harley’s newest engine.

Before testing, we instrumented the bike and rode on the streets to identify the conditions that would most intensely challenge the bike and the motor oil.

As you may guess, the slow pace and stop-and-go traffic increased the heat and gave the most extreme conditions, like the conditions you might see at a bike rally on a hot summer day.

To test performance, our engineers created a 1,000-mile dyno test that was intended to duplicate the very worst possible scenario: slow-moving conditions in intense heat with very little (or none at all) cooling air flowing over the engine. For reference, 1,000 miles is 640 trips down Main St. in Sturgis.

…So How Well Does AMSOIL Perform in the Harley Milwaukee-Eight?

This test created circumstances which kept the oil-sump temperature consistent at a steady 300ºF (149ºC)for 1,000 miles. The rear-cylinder temperature reached a temperature of over 420ºF (216ºC)—much hotter than your bike should ever be.

Heat that intense leads to chemical breakdown of most oils, leading to loss of viscosity and falling out of grade. This can also lead to oxidation, which speeds up deposits that cause rings to stick, leading to loss of compression and power.

After 1,000 miles under extreme heat, AMSOIL 20W-50 Synthetic V-Twin Motorcycle Oil supplied exceptional protection. If you compare, for example, a brand new rear-cylinder piston before the dyno test to one that has undergone 1,000 miles, the post-test piston has minimal deposits, free rings, and is in excellent condition.

A look at chemical analysis after 1,000 miles at 300ºF (149ºC) reveals that the oil held its viscosity and prevented nearly all wear, which begs the question: does the Milwaukee-Eight run cooler than previous Harley V-twin engines?

Before we objectively answer, more testing would be required, but all indications seem to say yes. Rear-cylinder temperature in the 2012 bike capped at 550ºF (288ºC), while the 2019 Harley maxed out at just over 420ºF (216ºC). Keep in mind that the two assessments were not identical, which means we cannot draw a well-founded conclusion. It certainly appears that Harley has accomplished diminishing heat in its Milwaukee-Eight engine, thanks to a series of oil-filled cooling lines that circulate around the cylinder to carry heat to an oil cooler.

Your bike’s oil should never reach this temperature, but if it does, depend on AMSOIL Synthetic V-Twin Motorcycle Oil to keep your Milwaukee-Eight engine running optimally. Buy V-Twin Motorcycle Oil.