A SIMPLE WAY TO FIGHT CYLINDER-LINER CAVITATION

In extreme cases, cylinder-liner cavitation in diesels can allow oil and coolant to mix. Then it’s just a matter of time until engine failure. Here’s what you can do to help ensure that doesn’t happen.

Most diesel engines are designed with replaceable cast-iron cylinder liners that are pressed into the engine block. While this doesn’t apply to turbodiesel pickups, it affects heavy-duty over-the-road trucks and other diesels. The piston moves up and down inside the liner, while a jacket of coolant surrounds the outside of the liner to cool the engine.

How cylinder-liner cavitation occurs

When the engine is running, the pistons move vertically inside their liners several thousand times per minute. Meanwhile, the rotary motion of the crankshaft applies a thrust force through the connecting rods to the piston. These contradictory movements cause the pistons to hammer the liners, causing significant vibration, similar to the effect of ringing a bell. This vibration can cause air bubbles to form in the coolant surrounding the liner.

When the bubbles rupture, they direct a high-pressure stream of coolant at the liner. Like a rushing river carving away a canyon wall, the coolant can erode the liner until cavities form. Left unchecked, these cavities can keeping growing and eventually penetrate the liner, allowing oil and coolant to mix. Once that happens, it’s only a matter of time before the engine fails.

Prevention is the best practice when it comes to cavitation. That task falls on the engine coolant, and there are two ways formulators typically design engine coolant to fight cavitation.

How Cylinder Liner Cavitation Occurs
Imploding bubbles direct high-pressure
coolant toward the cylinder liner, creating
cavities through which the coolant can enter
and mix with oil, damaging the engine.

The old-fashioned way

For years, formulators have added metallic salts, like nitrites and molybdenates, to coolant that attach themselves to the liner and form a sacrificial layer. When the coolant bubbles implode, the metallic salts absorb the pressure and break off from the liner surface rather than the metal itself. Metallic salts naturally deplete over time, meaning motorists must replenish them periodically by adding a supplemental coolant additive (SCA) to the coolant reservoir, typically midway through the service interval. Unfortunately, this is often overlooked.

The better way

The trend in the coolant market – and the strategy we use at AMSOIL – is to eliminate adding an SCA by formulating coolant with organic acid technology (OAT). The chemistry of OAT coolants passivates the liner surface, which coats it in a thin, inert layer that provides protection against cavitation and corrosion. Unlike old-fashioned metallic salts, the additives in OAT coolants last much longer, meaning you don’t have to replenish the system with an SCA. Modern OAT coolants also help fight problems associated with old fashioned “green” coolants, like scaling and additive drop-out (which leads to “slime” in your coolant system) due to incompatibility issues.

Coolant Maintenance is Key – Don’t forget about the most forgotten system

Aside from using an OAT coolant, it’s good practice to check your coolant level periodically. Also, make sure to check the pH and glycol levels annually. Glycol is important to the level of freeze protection and the coolant’s boiling point. Over time, the water can evaporate from the system and increase glycol concentration, throwing off the coolant’s balance. Perform fluid analysis once a year for best performance. We offer that service through Oil Analyzers INC. (www.oaitesting.com). We also offer antifreeze test strips (G1165).

Using AMSOIL Heavy Duty Antifreeze & Coolant (ANTHD) and taking care of your diesel’s cooling system go a long way toward avoiding the financial pain of fixing an engine ruined by cylinder-liner cavitation.

We keep this one in the Omaha store due to requests. If you need more than a case of four we can have it delivered next day or shipped to your home.

Pre-mixed 50/50 with high-purity water.
Fully formulated: DOES NOT require the use of supplemental coolant additives (SCAs) or excenders.
All-organic formulation is further enhanced with anti-scalant, anti-fouling and water-pump lubrication additives.
Phosphate-, nitrate-, nitrite-, silicate-, borate and amine-free.
Boil-over protection up to 265 F (129 °C) with a 15 psi radiator cap.
Freeze protection down to – 34 F (-37 °C)

Engine start-stop technology can increase bearing wear

Use only the best quality oil in these engines as the crankshaft needs to float. Even the “so called synthetics” don’t dampen the metal to metal issues mentioned below nearly as well as AMSOIL and you can tell due to the reduction in vibration or more consistent oil pressure as you rack up miles.

Yet another reason to upgrade to AMSOIL synthetic motor oil.

Matt Erickson | DIRECTOR, TECHNICAL PRODUCT MANAGEMENT

Nearly every technology shaping the auto industry can be traced to one goal: increased fuel economy. Engine start-stop technology is one more tool automakers have in their arsenals to ensure today’s vehicles meet tomorrow’s tightening fuel-economy regulations.

In principle, start-stop technology is simple: the engine automatically shuts off while you’re idling and restarts when you take your foot off the brake. This reduces fuel wasted while idling. Automakers introduced different startstop systems in the late ‘70s and early ‘80s; however, drivers found them awkward and unworthy of the higher vehicle price. Today’s start-stop systems are less obtrusive and are available on vehicle models from most automakers.

Should be called Metal to Metal Contact Engine

That’s not to say they’re without detractors. In fact, some automakers have installed off switches that allow motorists to disable the feature in response to negative driver feedback. But, despite their pitfalls, they’re likely not going anywhere. Consider these statistics:

According to bearing manufacturer MAHLE*, U.S. vehicles burned 3.9 billion gallons of gasoline while idling in 2017.
Buick* reports that engines with start-stop technology increase fuel economy 4-5 percent using the EPA test cycle.

Automakers leap for joy over minuscule fuel-economy gains, so you can bet they’re going to stick with anything that may provide a 4-5 percent boost.

So, what does that have to do with motor oil?

Maybe you’re aware that most engine wear occurs during cold starts. Well, engine wear occurs during warm starts, too, like every time an engine equipped with start-stop technology restarts.

We have to get technical to understand why.

The crankshaft spins thousands of times per minute in a running engine. As it spins, oil flows through tiny openings in the crankshaft journals and fills the spaces between the journals and main bearings. The crankshaft literally floats on an oil film and doesn’t contact the bearings. We call this scenario hydrodynamic lubrication. In this regime, the bearings suffer little wear and last a long time.

Run of the mill oils (95% on the shelf) are not going to provide protection with this condition

Stopping the engine, however, reduces oil film thickness. The crankshaft settles onto the bearing surfaces rather than floats over them. The oil film thickness shrinks to about the same thickness as the surface roughness of the crankshaft. This is called boundary lubrication. Starting the engine allows the microscopic peaks on the metal surfaces to contact and cause wear until the oil film has been reestablished and the crankshaft is once again floating over the bearings. This is where the oil’s additives play a huge role in protection.

Granted, only minimal wear may occur each time the engine is started. It’s not a big concern in a properly maintained traditional engine using a good oil. But what if you greatly increase engine startstop cycles?

Consider another statistic from MAHLE:

Start-stop cycles in equipped engines may triple over the engine’s lifetime compared to traditional engines.

That means three times more engine starts, three times more instances of boundary lubrication and three times more exposure to increased bearing wear.

Bearing wear can snowball out of control, too. Metal particles can break off and populate the oil. The bearing surface becomes rougher, encouraging adhesive wear in which peaks on metal surfaces grab and tear the mating surfaces. Eventually the crank journal and bearing can weld together, ruining the bearing.

This all points to a simple directive: make sure your customers with engines using start-stop technology are using AMSOIL synthetic motor oil to guard against bearing wear. Oil film thickness shrinks when engines start from a dead stop, placing even more importance on oil additives to maintain protection. Since engines equipped with start-stop technology spend so much more time under boundary lubrication, it’s vital to use an oil with superior film strength and additive quality. AMSOIL Signature Series Synthetic Motor Oil delivers. It provides 75% more engine protection against horsepower loss and wear** to help protect today’s advanced engines.

This is especially needed in vehicles calling for 0W-20, 5W-20 and 0W-16.

Category: Tech Articles