Rick's Free Auto Repair Advice

Motor Oil Viscosity Warning

What happens if you use the wrong oil viscosity in your car

Using the wrong motor oil viscosity can cause serious problems like premature wear, a check engine light, and even camshaft damage. Read this article to find out what motor oil viscosity you should use.

Think it can’t happen to you? Read this post on what causes a P0014 trouble code

P0014 cam phaser trouble code

This article is just one in a series. If you’d like to know more about oil click on the links below.

Choosing the right motor oil

Chrysler’s 3.5-liter engine has oil sludge issues

High mileage oil and oil filters

Oil Viscosity Warning

Synthetic Oil Facts and Myths

Synthetic oil versus conventional oil

What motor oil to use

What oil brand is best

What oil should you use

When to change oil

Best Oil filter

When car makers specify a certain oil viscosity range based on outside temperatures, they MEAN it. Today’s vehicles use oil pressure to operate the timing belt and timing chain tensioners, and variable valve timing devices (VVT). On a gasoline direct injection (GDI) the high pressure fuel pump is operated by a camshaft with a high pitch 3-lobed cam. Using the wrong oil or the wrong viscosity oil affect variable valve timing operation and throw cam timing off, and it can literally destroy the 3-lobed cam and high pressure fuel pump. Think about that: just when you think you know more than the engineers you discover there was a method to their madness.

Oil viscosity and variable valve timing

Variable valve timing alters the camshaft timing by rotating the cam in relation to the cam belt or timing chain. The rotation is executed using pulsed oil pressure. In order to command a cam timing change and then check the results, the PCM assumes you’ve used the proper oil viscosity. Switching to a higher or lower viscosity
oil will change the performance of the camshaft VVT solenoid or phaser, so the computer won’t see the cam timing result it expects. That’ll set a check engine light and trouble code and will affect engine performance. Improper cam timing can result in many different performance issues, from rough idle to lack of power.

In other words, when a car maker recommends a certain type and viscosity, the PCM is programmed to make cam timing changes based on that viscosity. When you use a different oil, you get different results and they’re not what the PCM expects to see.

GDI engines and oil viscosity

Gasoline direct injection engines use a totally different type of fuel injector than older port injected engines. A GDI injector injects fuel directly into the cylinder instead of behind the intake valve. Since it’s inside the cylinder, it must inject fuel at a much higher pressure–as high as 2,000-psi. To obtain that kind of pressure, GDI vehicles have two fuel pumps; one in the gas tank and the other connected to the engine and run off the camshaft. It’s the 2nd fuel pump that is the biggest concern when determine the correct type of oil and it’s viscosity. The 3-lobed cam used to drive the high pressure fuel pump demands the exact oil recommended by the manufacturer. Substituting a different oil can cause catastrophic damage to the camshaft and high pressure pump. Shops are seeing  GDI vehicles where the lobes are completely worn off the cam due to the wrong oil.

Car makers have made it known that they will NOT pay for warranty claims based on improper oil viscosity. Screw with the type of oil or change the viscosity and you can mess up your variable valve time devices, get the wrong tension on your timing belt or timing chain (causing jumped teeth or total engine destruction in an interference engine).

Moving to a higher viscosity oil can cause hydraulic lifters to literally “pump up” and bend push rods on a cold start. Keep in mind that in car talk, a cold engine is one that hasn’t run for three or more hours. You don’t have to live in a cold climate to be affected by these kinds of problems. Oil simply doesn’t flow well when it’s cold. So follow the car makers viscosity recommendations and quit trying to second guess their specifications.

© 2012 Rick Muscoplat

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Posted on by Rick Muscoplat



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