Join Date: Feb 2018
Location: Portland, Texas
Generally speaking, sticking with the Manufacture’s recommendations will assist in ensuring longevity of your machine. However, the 5W-40 shouldn’t be a problem. Don't worry about the oil being too thick, as the 40 portion of the 5W-40 designation refers to the oil film thickness (viscosity) at high temperatures.
At ambient temperature, the 5W-40 should be slightly thinner than the 10W-30, but will maintain its viscosity up to the point at which a straight 40 weight oil would begin to thin from exposure to high temperature.
See Quote below from Total's website:
“Viscosity is notated with the common "XW-XX." The number preceding the "W" rates the oil's flow at 0 degrees Fahrenheit (-17.8 degrees Celsius). The "W" stands for winter, not weight as many people think. The lower the number here, the less it thickens in the cold. So 5W-30 viscosity engine oil thickens less in the cold than a 10W-30, but more than a 0W-30. An engine in a colder climate, where motor oil tends to thicken because of lower temperatures, would benefit from 0W or 5W viscosity. A car in Death Valley would need a higher number to keep the oil from thinning out too much.
The second number after the "W" indicates the oil's viscosity measured at 212 degrees Fahrenheit (100 degrees Celsius). This number represents the oil's resistance to thinning at high temperatures. For example, 10W-30 oil will thin out at higher temperatures faster than 10W-40 will.
Monograde oils such as SAE 30, 40 or 50 are no longer used in latest automotive engines, but may be required for use in some vintage and antique engines. Straight SAE 30 oil is often specified for small air-cooled engines in lawnmowers, garden tractors, portable generators and gas-powered chain saws.”
When in doubt,
Ride it out.