Why carmakers want you to change oil on time and mileage

Why carmakers want you to change oil on time and mileage

Why do carmakers list oil change intervals based on time and mileage?

Motor oil doesn’t degrade in the bottle but it does degrade in your engine

Oil companies say that fresh oil in the bottle has a five year shelf life. It’s not so much that the oil goes bad as much as the fact that during the five year period, oil specs often change and there are better motor oils on the market during that time period. I

However, once you put oil in an engine, the clock does start ticking. Here’s why:

• All engines create blow-by; gasses that escape past the piston rings and enter the crankcase. Blow-by gasses contain fuel, water, exhaust and soot. Those contaminates mix with the oil in the crankcase to form Formic and Nitric acids and sludge.

• As the engine runs, the acids degrade the oils anti-corrosion additives. Heat and oxygen exposure causes the oil and additives to oxidize and degrade. The longer the engine sits with a partially or fully degraded additive package, the more the engine is exposed to corrosion and further oil degradation.

In other words, even if you don’t drive much, once you’ve exposed the oil to heat, acids and oxygen, you automatically start the degradation process. After sitting in the crankcase for six months, your oil has lost a significant portion of its protective additives.

In addition most owners don’t follow the proper mileage change intervals

Most owner follow oil change intervals based on “Normal” driving conditions when they’re actually operating their vehicles under the “Severe” definitions.

What are Normal 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.

Severe driving conditions increase the amounts of fuel, oil, water and soot that’s added to the oil. That contributes to early oil exhaustion and contamination, corrosive acid formation, sludge buildup, viscosity shearing, depletion of the oil’s additive package and oil oxidation.

Most carmakers want you to change your oil every six months regardless of mileage

The whole point of time-based oil changes it to remove the degraded oil and replace it with fresh oil that contains a full additive package.

©, 2020 Rick Muscoplat