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All You Need To Know About Motor Oil Cold Flow

Winter (Cold) flow wear factors in your engine

Engineers agree that most engine wear occurs during cold starts. While the exact percentage depends on several factors and is difficult to define, the reasons include the following…

  • A richer air/fuel mixture at startup washes oil from the cylinder walls
  • Condensation forms inside the engine that causes rust and corrosion
  • Cold piston rings and cylinders don’t seal as well, causing combustion gases to “blow by” the rings and contaminate the oil
  • Gravity causes much of the oil to fall back into the oil sump, leaving components unprotected
  • Cold oil doesn’t flow immediately at startup, temporarily starving the engine of oil

While all these factors are important, lack of oil due to poor cold-flow properties is the biggest culprit. Fortunately, there’s something you can do about it.

“Cold” isn’t just for winter

First, it’s important to define a “cold” start. While true that oil thickens more in sub-zero winter weather and causes increased starting difficulty, an engine is considered “cold” after it’s sat long enough to cool to ambient temperature, typically overnight. Even in warm climates, cold-start wear is a problem.

The oil inside your engine cools as it sits overnight. As it cools, its viscosity increases (it thickens). When it’s time to start your vehicle in the morning, the thicker oil doesn’t flow through the engine as readily as it does when it’s at operating temperature. It’s during this time that vital engine parts can operate without lubrication, increasing wear.

The problem is more pronounced the colder it gets, particularly if you’re using conventional motor oil.

Waxes solidify in the cold

Conventional lubricants contain paraffins, or waxes, that solidify when the temperature drops. These waxes cause the oil to thicken. In the comparison shown here, we cooled a conventional oil and AMSOIL Signature Series 5W 30 Synthetic Motor Oil (ASL) to -40ºF. The conventional oil on the left thickened so much it barely flowed from the beaker. If that oil were inside your engine on a cold morning, it could prevent the crankshaft from spinning fast enough to start the engine, leaving you stranded. Even if the engine started, you wouldn’t be out of the woods. Thick, cold oil can fail to flow through the tiny screen openings on the oil pickup tube (see facing page), starving the engine of oil for several vital moments before the oil begins to heat up and flow throughout the engine.

In addition, thick oil can fail to flow through the tiny passages in the crankshaft to lubricate the main bearings. Similar oil passages in the camshaft ensure the engine’s upper end is lubricated (see facing page). The further away from the oil pump these oil passages reside, the longer it takes the oil to reach components at startup, placing your engine at increased risk of wear.

Poor lubricant cold-flow properties can also affect variable valve timing (VVT) systems. Engines equipped with VVT have solenoids with tiny openings through which the oil flows and acts as a hydraulic fluid to actuate VVT components. The solenoid pictured to the right, from a Ford* 3.5L EcoBoost* engine, contains openings .007 inches across – about the thickness of two sheets of paper. Oil that fails to flow through these tiny passages reduces VVT performance and can trigger a check-engine light.

Here’s how to protect your engine

AMSOIL synthetic motor oils provide better cold-flow properties than conventional oils. Our synthetic base oils don’t contain the waxes inherent to conventional oils. As a result, they demonstrate reduced pour points and provide increased fluidity during cold starts. This translates into oil that flows almost immediately through the oil pickup screen and other tiny oil passages when you start your engine, protecting it against wear.

Look at the oil’s pour point to gauge its ability to flow quickly at startup, typically reported on the oil’s data bulletin. Pour point is the coldest point at which an oil will flow. Lower values equal improved cold-flow and maximum wear protection. AMSOIL Signature Series 5W-30 Synthetic Motor Oil, for example, provides a pour point of -50ºF (-58ºC).

Pique prospects’ curiosity

This type of information can help you create curiosity about AMSOIL products and lead someone from not looking for lubricants to looking for AMSOIL products. Ask pointed questions or provide useful information, such as…

  • Most engine wear occurs during cold starts. Do you take steps to guard against start-up wear?
  • Even in warm climates an engine is considered “cold” after it’s sat overnight.
  • Do you ever have trouble starting your truck on cold mornings?

Once they’ve shown interest, offer more technical explanation if required and offer AMSOIL synthetic motor oil as a solution to difficult cold starts and accelerated cold-start wear.

A little known fact

The differences in brands comparing a 5W-30 to the protection of a 10W-30 or 0W-30 can even be critical to the prevention of wear in the 50 to 65 degree F range. So just because you may live in a southern climate doesn’t mean you are in the green with a older specification viscosity.. A more advanced oil brand allows you to take advantage of the tech of the latest (lowest allowable) start-up viscosity year round.

What Motor Oil is Best for Winter? (And Other Cold-Weather Questions)

The Best Winter Motor and Transmission Oil Choice

Synthetic oil is best for winter.

We’re done here.

If only it were that simple. But most people want empirical data to support such claims.

Well, take a look at the video. We cooled a conventional 5W-30 motor oil and AMSOIL Signature Series 5W-30 Synthetic Motor Oil to -40º. As you can see, the conventional oil thickened so much that it barely flowed from the beaker. The AMSOIL product, on the other hand, flows almost immediately.

Buy AMSOIL Signature Series

Why the dramatic performance difference? In answering that question, I’ll also answer the question hoss61761 poses on social media:

Conventional oils contain waxes that solidify when the temperature drops. This severely impairs the oil’s ability to flow when you crank your engine. In some cases, the oil can thicken so much that it prevents the crankshaft from spinning fast enough to start the engine.

Prior to using AMSOIL, I had a Cutlass Ciera that was notorious for refusing to start on our cold Minnesota mornings. The dirt-cheap big-box-retailer oil I used back then thickened so much the engine would barely turn over.

Why synthetics flow better in winter weather

Synthetics, in contrast, don’t contain waxes due to the chemical-reaction process used to construct synthetic base oils. As a result, synthetics demonstrate far better cold-flow properties than conventional oil. Not only will your vehicle start more easily (I’ve yet to have one of my vehicles using AMSOIL fail to start, even with temps pushing -30ºF), the oil will flow more quickly, ensuring oil reaches vital components faster. This, in turn, maximizes wear protection, helping your engine last longer.

Check the oil’s pour point

If you want more data to prove synthetics’ cold-weather superiority, check the oil’s Product Data Sheet. Look for the oil’s pour point. Lower numbers indicate better cold-flow, thus better cold-weather performance.

In the example here, you can see that AMSOIL Signature Series 5W-30, the same oil shown in the video above, has a pour point of -58ºF (-50ºC).

What is cold?

Not to get existential here, but it’s a relevant question. Folks in the south whose idea of winter is putting shoes on for a couple weeks in January may think they’re off the hook. Do they need to waste mental energy on motor oil cold-flow properties?

Good cold-flow is important to Southerners, too. Here’s why.

Engineers agree that most engine wear occurs during cold starts. There are several reasons, but two concern us for this discussion:

  • Gravity causes much of the oil to fall back into the oil sump, leaving components unprotected
  • Cold oil doesn’t flow immediately at startup, temporarily starving the engine of oil

While true that oil thickens more in sub-zero winter weather and causes increased starting difficulty, an engine is considered “cold” after it’s sat long enough to cool to ambient temperature, typically overnight.

The oil inside your engine cools as it sits overnight. As it cools, its viscosity increases (it thickens). When it’s time to start your vehicle in the morning, the thicker oil doesn’t flow through the engine as readily as it does when it’s at operating temperature. It’s during this time that vital engine parts can operate without lubrication, increasing wear. So, even in warm climates, cold-start wear is a problem. Southerners are well-advised to use a good synthetic oil with excellent cold-flow properties, too.

Thick or thin oil in winter?

Motorists sometimes ask if they should use thicker or thinner oil in the winter. Fortunately for them, we wrote a whole post on that topic. Check it out here.

Should I Switch to a Lighter Viscosity Oil in Winter?

To summarize, use the lowest viscosity oil your vehicle manufacturer recommends in the winter. Most automakers recommend a lone viscosity year-round. But some allow you to switch to a lower viscosity in winter, which helps improve cold-flow.

If your owner’s manual says you can switch to a lower viscosity oil in winter, go for it.

Shift to better winter protection

While I have you here, I should talk about transmission fluid, too. Like motor oil, it thickens in cold weather. The cold, thick fluid doesn’t flow readily through the intricate network of passageways in the transmission valve body or through the small solenoid openings. What does that mean to you?

  • Delayed shifts
  • Elongated shifts
  • Hard/harsh shifts
  • Reduced wear protection

Cold, thick transmission fluid doesn’t flow readily through narrow valve-body passages, leading to poor shift quality.

Again, I’ll go to the well of personal experience. After buying a Honda CR-V several years ago, I switched to AMSOIL synthetic motor oil…but I neglected to change the transmission fluid. Fast-forward to winter and one of our trademark -20ºF mornings with a wind chill pushing past -40º. The Honda started, but she shifted slowly and with much wailing and gnashing of teeth. The entire vehicle shuddered as it reluctantly found second gear heading down the road.

Switching to synthetic transmission fluid solved the problem. The fluid flows much more readily in the cold, which translates into smoother shifts. It also means the gears and bearing are receiving vital lubrication, too. Anyone who’s shelled out thousands of dollars for a tranny replacement knows how important that is.

Buy AMSOIL Signature Series ATF

Bottom Line: Synthetic motor oil and drivetrain lubricants perform better in the cold than conventional oils. They flow better for easier starts, smoother shifts and better protection against wear. Upgrade to synthetics to maximize cold-weather protection and performance.

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