Recommended Oil Viscosity for High Mileage Oil Leaks

by David McGuffin
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Any car, especially as it accrues more mileage, is susceptible to oil leaks and consuming oil. However, there are a few tricks and procedures that can be used to help plug up oil leaks and to prevent more from happening. One such trick, includes changing the viscosity of the oil in your engine by draining it and adding a heavier oil. However, it's important to note that you shouldn't exceed the manufacturer's recommendations for an engine's oil viscosity as it could cause permanent engine damage and failure.

Manufacturer Recommendations

As an engine heats up, the oil thins, becoming more susceptible to leaks through faulty gaskets. Draining the oil from your vehicle and replacing it with a thicker weight or synthetic oil can help to prevent oil from leaking through some of the smaller breaks in the gasket seals. Before adding a thicker weight oil to your vehicle, especially if it is still under warranty, consult your owner's manual for the thickest possible weight the engine is designed to handle. As an example, According to VCOA, a TSB (technical service bulletin) was issued for Volvos concerning oil viscosity recommendations, relating that the maximum acceptable viscosity should be 15W-40. However, the TSB also noted that 15W-40 should only be used for extreme duty vehicle uses and high mileage vehicles in hot climates.

Heavier Always Better?

Heavier motor oils cause more friction, which can also lose fuel economy. According to TexLube, about 10 percent of the engine's power is lost due to internal friction, hence, adding a heavier weight oil will cause more power loss. Heavier oil also has the potential to cause extra wear and tear during cold starts and colder weather, as heavier oils don't circulate as much as thinner oil grades.

Reading Oil Labels

If you see a "W" (winter) appear on the oil label, as opposed to "SAE," it means that the oil has been tested at a colder temperature than the standard 100 degrees Celsius. As a result, an oil with "5W-30" on the label is able to perform similar to oil with the SAE 5 rating at the colder temperature, which is specified by the oil manufacturer, while also performing at the same viscosity as the SAE 30 at 100 degrees Celsius. Thus, the engine has a quicker oil flow when it is started cold, which also translates into less engine wear.

Other Options

According to Trust My Mechanic, small seeps from gaskets, such as the valve cover gasket, are normal for cars with 30,000 miles or more. However, as the gasket continues to fail, the seep will turn into a larger leak, indicating that the gasket must eventually be replaced. In the long run, replacing the gasket for whichever component is leaking is the best fix, rather than only adding a heavier weight oil or an additive. Replace the gasket by removing the component, using a plastic scraper to remove the gasket and any chunks left behind in the gasket slot and installing a new gasket. Most parts benefit from using automotive gasket silicone to help seal the new gasket to the other half of the component.

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