Rick's Free Auto Repair Advice

When to Change Oil — time or mileage

When to change oil — time, mileage or the oil life monitor?

Lots of oil “experts” tell you to ignore the carmaker’s oil change intervals because the newer synthetic oils can last up to 15,000 miles. That may be true in some isolated cases, but it’s not true for the vast majority of drivers. When to change oil depends on many factors and mileage is just one of them.

Owners’ manual oil change recommendations are based on ideal conditions

If you’re going to follow the car makers recommendations for oil changes based on ideal conditions, you better make sure you understand exactly what “ideal conditions” means and what is really a more common “severe” condition.”

What are ideal driving conditions?

• You check your oil level regularly and top off when needed
• You do predominately highway driving
• You keep your engine tuned and follow all maintenance schedules.
• You use the recommended oil and install a premium quality oil filter
• You change the air filter according to car maker’s recommendations

Many drivers think that their vehicles operate under ideal conditions, and thus justifying extended service intervals, when in fact they are operating under severe conditions in respect to the oil in the crankcase and need more frequent oil changes. Stop-and-go driving, frequent short trips, very cold
or very hot weather generally fall into the severe category. — Auto Service Professional Publication

Severe driving conditions:

• Driving while low on oil
• Short trips, especially in freezing weather.
• Frequent stop and go situations.
• Dusty or extreme hot weather conditions.
• Turbo-charged engines.
• Flex-fuel operation.
• Towing/heavy-duty operation.
• High mileage engines or engines that are burning oil.

Each of these conditions contributes to early oil exhaustion and contamination due to water, fuel and dirt intrusion, as well as blow-by gasses, corrosive acid formation, sludge buildup, viscosity shearing, depletion of the oil’s additive package and oil oxidation.

Can you trust the oil life monitoring system in your vehicle?

That depends on which type is used in your vehicle. There are four types:

Mileage based oil life monitoring system

This is the least accurate system because it doesn’t take your driving style into account. If you drive short trips in cold weather, tow or don’t check your oil level regularly, this system will give you a false sense of security.

Tracking Conditions oil life monitoring system

This system is software-based and actually tracks your driving conditions. The GM Oil Life System, for example, tracks driving conditions and classifies your driving into four categories; normal flowing highway, high temperature/high load situations, city driving/short trips and cold starts, and extreme short trips.

GM’s oil research teams concluded that oil degrades primarily due to oil temperature and short trips. Short trips result in water accumulation in the oil, which contaminates the oil. The GM system calculates oil life by tracking your driving habits and lets you known when it’s time to change your oil.

Ford uses a similar system. In both the GM and Ford system, a timer is used to notify you to change the oil after one year, regardless of mileage.

The Chrysler/Fiat systems also use software but their systems also monitor the amount of ethanol in the fuel.

Oil temperature monitoring

VW/Audi calculates oil life based on the oil’s “thermal load.” It uses an oil temperature and oil level sensor and combines that data with fuel consumption, mileage, and time since last oil change.

Oil condition monitoring

An oil condition monitoring system actually tests the oil to determine its dielectric properties. These systems can detect the depletion of the oil’s additives by checking the oil’s acidity level and the presence of engine coolant or fuel in the oil.

©, 2020 Rick Muscoplat



Posted on by Rick Muscoplat

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