A High Zinc Motor Oil For Winter Use?

A reader asks: My daily driver pickup has a Chevy 283 engine with flat tappet cams. I use this truck all winter and it regularly sees sub-zero cold starts. So, I need a high zinc oil that flows fast in the winter. Will AMSOIL Z-Rod 10W-30 work well for winter use?

Our answer: AMSOIL Z-ROD Synthetic 10W-30 does offer very good cold weather properties. But we have another option that will offer better winter start-up performance.

AMSOIL Series 3000 Heavy Duty 5W-30 Diesel Oil has very high zinc and phosphorus. It is also designed for gasoline engines. This 5W-30 has 1379 ppm of zinc and 1266 ppm of phosphorus. These amounts are more than adequate for flat tappet cam protection.

Series 3000 5W-30 has a cold-pour-point of -47°C (-51°F). Therefore, it will flow very well on those cold mornings, while delivering exceptional flat tappet cam wear control.

What About Z-ROD 10W-30 Winter Performance?

First off, AMSOIL Z-ROD Synthetic 10W-30 offers 1440 ppm of zinc and 1320 ppm of phosphorus. So, its flat tappet cam credentials are ideal.

Z-ROD 10W-30 has a cold-pour-point of -46°C/-51°F. On the surface, it looks like the winter performance between Series 3000 5W-30 and Z-ROD 10W-30 is identical. The cold-pour-points of the two oils are within 1°C.

The cold-pour-point is the temperature threshold where a motor oil stops flowing.

But there is more to the story.

Comparing “Cold Cranking Simulator” Values

An important indicator of a motor oil’s ability to perform in extreme cold is the “cold cranking simulator” (CCS) test. This is a widely recognized industry lab test. In the CCS test, a motor oil is cooled down to a specific temperature. Then a crankshaft is rotated in the chilled oil. The viscosity of the motor oil is measured in “centipoise”. (cP)

A lower viscosity number scored in this test means better oil flow in extreme cold.

Industry standards dictate that 5W-30 motor oils are measured at -30°C and 10W-30 oils are measured at -25°C.

Therefore, the CCS numbers for these two products are not measured on exactly the same scale. But we can extrapolate.

• Series 3000 5W-30- CCS @ -30C is 5286 cP
• Z-ROD 10W-30- CCS @ -25C is 5138 cP

Remember, the lower the score in this test, the better an oil performs in cold weather.

If Z-ROD 10W-30’s CCS test was measured at -30°C, it’s cold cranking performance would turn out to be about 15% worse than Series 3000 5W-30.

To sum up, both AMSOIL Series 3000 5W-30 and Z-ROD 10W-30 offer very good winter performance. The 5W-30 has a distinct edge in terms of winter-cold-cranking performance and would be our choice for this scenario.