Oil aeration can cause serious issues in high-revving race engines, leading to pressure loss, cavitation in the oil pump, and even long-term engine damage. But what exactly is aeration, and how can it be minimized? Understanding how air enters the oil system, the various types of aeration, and the potential damage it can cause is essential for protecting your engine. In this blog, we’ll break down the basics of oil aeration, its effects on engine performance, and offer some practical tips on how to prevent or reduce aeration to protect your engine from its harmful consequences.

Aeration can cause a range of issues, from oil oxidation and thermal breakdown to oil degradation and compression issues.

Aeration, otherwise known as air contamination, happens when air makes its way into your engine oil. It can show up in four different ways; entrained air, foam, dissolved air and air pockets.

The most common form is called entrainment, where tiny air bubbles become trapped in the oil as it circulates through the lubrication system. There are lots of chances for entrainment to occur, especially in race applications; faster engine speeds create more bubbles, leading to more air in the system. Other factors, like churning from the crankshaft, suction through the oil pump, and reduced resting time in the oil pan, can all contribute to air binding to the oil.

Entrained air consists of bubbles suspended beneath the fluid’s surface, forming trapped air pockets, while foam develops when these bubbles rise and settle on the fluid’s surface.

Foam on the oil’s surface can disperse throughout the lubrication system, interfering with the oil’s role in cooling and protecting critical engine parts

Entrained air will eventually rise to the surface of the oil and try to escape. Depending on the oil’s viscosity and the engine’s temperature, the vibrations and movement from a running engine can whip those surface bubbles into foam. As the foam forms a layer on top of the oil, it can spread throughout the lubrication system, hindering the oil's ability to lubricate and cool vital engine components.

Another form of air contamination is called dissolved air. When air in the system becomes pressurized, it transforms into dissolved air. This form of aeration is particularly deceptive, as it mixes with the oil at a molecular level, so it’s basically invisible. The oil will not appear to be aerated, and there won’t be any visible bubbles, but it can still cause significant damage over time.

Air pockets, otherwise known as free air present another common risk of air contamination, often forming during maintenance services when the lubrication system is unsealed. These pockets can become trapped during oil changes, system flushes, or when seals and lines are replaced. If not quickly addressed and purged, these air pockets can prevent proper oil flow to internal components, leading to potential oil starvation.

Aeration, whether through entrainment, foam, dissolved air, or air pockets, can cause severe engine damage. Oxygen exposure accelerates oil oxidation, resulting in viscosity changes and the creation of harmful sludge, sediment, and varnish. These contaminants clog filters and create blockages, restricting oil flow and affecting performance. Aerated oil can also reduce the effectiveness of the oil wedge in the engine bearings, effectively lowering the pressure at the bearings and increasing the likelihood of metal-to-metal contact.

When air gets into oil—whether from foam, dissolved air, or trapped pockets—it can lead to oxidation, sludge, and blocked filters, all putting extra strain on engine performance.

The IAG Stage 2 CNC Ported EJ25 11mm Oil Pump design allows for increased flow volume and pressure, ensuring that the bearings have a sufficient oil film under all power levels and driving conditions.

Preventing oil aeration is entirely possible with the right precautions. Sealing leaks is crucial, but care should be taken not to introduce air pockets during the process. Once air pockets are detected, they can be purged to maintain proper oil flow. A consistent oil pathway into and out of the pump is essential for reducing air mixing with the oil. High performance oil pumps like IAG’s Stage 2 Oil Pump can be a real game-changer when it comes to prevention. With its precision-machined inlet and outlet passages, the Stage 2 ensures smoother transitions, minimizing entrainment and reducing the risk of cavitation.

To further prevent aeration, it’s important to control oil splash, as this is another opportunity for air to mix in with the oil, increasing the chance of entrainment. The IAG Performance Windage Tray is designed to address this by directing oil from the upper crankcase to the lower crankcase and oil pan. Its precision-formed louvers guide the oil downward, preventing it from splashing up into the path of the crankshaft and connecting rods, reducing aeration and promoting smoother engine operation.

Designed to minimize aeration, the IAG Performance Windage Tray acts as a barrier that effectively manages oil movement within the engine.

Another effective solution is the IAG Performance EJ Street and Comp Series Oil Pans, which incorporate an internally integrated stainless steel baffle designed to minimize oil splashing and reduce the risk of cavitation and oil starvation. The Comp Series Oil Pans also feature one-way baffles to further prevent the oil pickup from being uncovered due to slosh. The pans’ larger capacities also allow more time for air to dissipate from the oil, a process known as detrainment, which enables trapped air to safely rise out before it affects engine performance.