Rick's Free Auto Repair Advice

Heavier weight oil to solve oil consumption problems

Heavier weight oil (higher viscosity) — does it solve oil consumption problems?

I often see people recommend using a heavier weight oil (higher viscosity) to solve an oil consumption problem. The theory behind their advice is that a heavier-weight oil produces a thicker oil film at the piston ring sealing areas. A heavier weight oil does produce a thicker oil film, but that alone may not stop the oil consumption issue and may actually make it worse.

If you are having oil consumption issues, should you use a heavier weight oil?

Probably not. While a heavier weight oil may reduce oil consumption slightly, it causes far more problems than it solves. Here’s why.

• A high-viscosity oil can actually prevent low-tension piston rings from contacting the cylinder wall, which can increase oil consumption.

• A higher than recommended viscosity reduces the oil’s flow rate. A reduced flow rate reduces heat removal from low clearance bearings and turbochargers, causing accelerated wear.

• A higher viscosity oil may actually prevent the oil from reaching the top piston ring and top of the cylinder, resulting in inadequate lubrication and accelerated wear.

• A higher viscosity oil will cause more internal friction, raising the temperature of the oil while reducing its ability to remove heat. The increased internal friction also results in a loss of energy and lower MPG.

Using a heavier weight oil can cause a check engine light on engines equipped with variable valve timing.

Carmakers use pulsed oil pressure to operate variable valve timing mechanisms (VVT). The pulse rate is calculated by the vehicle’s ECM based on the assumption that you’ve used the recommended oil viscosity. The ECM knows the engine temperature and based on the known flow rate of the specified oil, pulses the oil into the VVT mechanism to obtain a predicted camshaft advance or retard motion. It then checks the actual movement. If there’s a discrepancy between the predicted movement and actual movement, the ECM will set a trouble code and turn on the MIL.

The incorrect camshaft timing will cause a drop in fuel efficiency, a loss of power and an increase in vehicle emissions.

What happens if you add a quart of oil of different viscosity to top off your engine?

The answer is pretty simple. If you had 5W-20 in the engine and you add 1 quart of 10W-30, it raises the viscosity of the crankcase oil slightly. One quart won’t change it enough to worry about. It’s the second quart that starts to change the operating characteristics of the oil. So, if you had to add the second quart of different viscosity, you should change the oil shortly after.

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

Heavier weight oil to reduce oil consumption problems

Oil filter filled with sludge


© 2012 Rick Muscoplat



Posted on by Rick Muscoplat

Custom Wordpress Website created by Wizzy Wig Web Design, Minneapolis MN