Oil Change Intervals, How Long?

"Every 3,000 miles or 3 months, see you again!"  That's the line most people hear from quick lube shops when preparing to leave after an oil change has been done.  The mileage intervals many people hear are 3,000 miles between oil changes, which adds up to approximately 5 oil changes a year based on an average driving distance of 15,000 miles a year.  So is it a good practice or is it a waste of money?  We were asked what's our take on the debate of how often you should change your oil.  While everyone including experts, dealerships, or manufacturers will vary in terms of their stance on the subject, here's our take.

First, here's a little background about the fluid which many take for granted.  Oil can simply be looked at as having the same function of the lungs in a human.  The fresh oil is like fresh oxygen, except oil provides lubrication and protection to the critical moving parts of an engine.  As the oil continues to protect the engine, the additives and detergents will begin to break down from all the contaminants i.e. exhaust blow by, excess fuel, moisture, dirt, etc.  Just as people inhale to take in fresh oxygen to supply organs with oxygen, car owners change the oil to keep their engine protected and running right. 

Back in the old days, oil's lubricating properties were not as advanced as today's oil.  The oil would tend to sludge up and clog vital passages in the engine which necessitated changing out the oil on a regular basis before sludge formation happened.  Sludge is a very thick, gel-like buildup that occurs when oil deteriorates from heat, moisture, or old age (saturation of contaminants).  Since sludge is very thick in viscosity, it can't travel through the galleries of the engine to provide protection to moving parts which wears things out quicker.  To see this effect for yourself without risking your engine, try drinking a thick milkshake with a coffee stirring straw.  Now try drinking water with the very same straw.  Much easier with a thinner fluid right?  =)  Same thing for your engine!

Oil is available in 3 different types:  Conventional, synthetic, and synthetic blend.  The cheapest oil are the conventional oils, and full synthetic oils are the most expensive.  Synthetic oils provide the best protection against thermal breakdown, and lubricate much better than conventional oils.  There is a myth floating about which states you cannot mix synthetic oils with conventional oils, but that's where synthetic blends come from!

Valvoline's VR-1 oil is one of the few oils with adequate amounts of ZDDP for engines requiring the anti-wear additive.  Photo courtesy of Valvoline. 

You can keep up to date on your oil's standard by looking for a seal which has the American Petroleum Institute (API) label on it.  The API seal will tell you what standard the bottle of oil is following.  For most modern cars, the highest standard of oil is SN.  Generally the higher the letter is after the S, the higher the standard of the oil.  However, for older cars, especially those requiring zinc dialkyldithiophosphate (ZDDP), an anti-wear compound found in lower standard oils, using the SN or oils with less than 1,000 parts per million (ppm) of ZDDP oils may damage the engine.  SN oil has less than 600 ppm of ZDDP.  ZDDP may damage the catalytic converter, and thus is being phased out of oil.  Consumers with vehicles requiring ZDDP can buy Valvoline's VR-1 engine oil which still has a higher level of the compound. 

With the improvements made in oil technology, modern oils are better able to resist thermal breakdown, saturation of contaminants and provide more protection to friction between moving parts.  This results in oil change intervals which can safely extend beyond the often said 3,000 miles.  Some oil companies claim the oil can be good for up to 15,000 miles or more.  Sludge formation in engines has been reduced due to the higher quality oil, but it doesn't mean that an owner can neglect changing the oil either.  Some vehicle manufacturers have had to revise their recommended intervals, and some have issued recalls due to engines being affected by extended intervals of oil changes. 


The biggest factor contributing an oil's loss in lubricating and protecting properties is the saturation of contaminants.  When you first start your vehicle in the morning, there will be some condensation that mixes with the oil and it will stay mixed in the oil until the oil reaches operating temperatures.  The moisture mixes to form an acid which over time attacks the engine from the inside.  Usually this isn't a concern since the moisture will evaporate out once the oil reaches operating temperatures.  However, for people with very short commutes, the oil will never reach operating temperatures, thus keeping the moisture in the oil. 

Blow-by is the byproduct of the combustion process as exhaust gases seep past the piston rings, and every engine has some amount of blow-by.  The blow-by will mix with the oil and also dilute the oil's protective properties.  On heavily worn engines, the oil will have a very noticeable stench when it is changed due to the extra contamination of the combustion gases.  It is for these reasons we do not like to keep the same oil in our engine for 15,000 miles or more. 

In our experience, a good quality conventional oil can provide adequate protection around 5,000 miles of normal driving.  We like to keep our oil fresh so we still abide by the 3-4 month rule for the length of time the oil has been in the motor.  Even if the car isn't being driven, condensation can still form, especially if the vehicle is parked outside where the ambient temperatures can fluctuate.  If the car is parked in a well insulated garage, the time can be extended to up to 5-6 months. 

For synthetic oils, we recommend an interval of 7,500-8000 miles between changes.  By then, the oil filter may start to become saturated from filtering, and if the filter media is clogged, the oil will bypass the oil filter completely leaving the dirty oil to cycle through the engine.  Sometimes just changing the oil filter can allow you drive up to 10,000 miles, but for the sake of security, we just recommend doing both a filter and fluid change at the same time. 

Some people may have a different standard by which they change their oil, and it's fine.  These are just our personal intervals we use.  If you race, drive your vehicle hard, or are towing a heavy load, your intervals for changing oil will be shorter.  As always, if you have a question or topic you would like discussed, email us.  Happy motoring and keep on driving!