First, lets go over the automakers recommendations for drain intervals. Back in 1968 the recommendation was to change your engines oil every 3,000 miles or three months, whichever came first. That didnt change much until the 1980s. Today, the 3,000-mile/three-month mantra is officially dead, except for those who believe that it is cheap insurance for their engines. Its hard to argue with that position.

There are essentially two classes of service for passenger cars and light trucks – normal and severe. Some OEMs call these duty cycles or Schedule 1 and Schedule 2. Of course, oil life monitoring (OLM) systems are now in many of the vehicles on the road. More than half (54 percent) of the vehicles seen at fast-lubes last year had these systems, according to a survey by National Oil & Lube News. At any rate, severe-service drain intervals for most vehicles, even those with OLMs, are around half as long as normal-service intervals.

The numbers range from a high of 10,000 miles for normal service down to as low as 3,750 miles for severe service. The most common recommendation for normal service is 7,500 miles, which seems to be the choice for Asian OEMs. General Motors advises an oil change within 600 miles of the time the change engine oil light comes on. The Europeans are more courageous and go with 10,000 miles. For those with an OLM system – found now on U.S., Asian and European cars alike – the recommendation is to not exceed one year, even if the light doesnt come on.

As Ive mentioned before, the dashboard light on my GM pickup with OLM seems to consistently come on at about 4,500 to 5,000 miles. I dont put a lot of miles on my truck so the appropriate driving cycle for me is severe. GM says the new Dexos1 specification has triggered a reanalysis of its OLM algorithm, and likely will increase its oil drain intervals. But thats only for the newest vehicles in their line.

Remember, the OLM compares crankshaft revolutions with oil temperature range to determine what type of driving is being done. That leaves those who use synthetic oils in quite a quandary since there is no direct allowance for differing or premium oil types.

Synthetics have been a major mover in the oil change marketplace. In fact, there is an ongoing conversation about whether or not a synthetic should be preferred if one changes his or her oil regularly. On the yes side are the synthetic oil marketers who are making aggressive claims of up to no drains at all and much better performance, due to the synthetic molecule versus conventional mineral oils. On the no side are those saying 3,000 miles and/or three months is cheap insurance; it doesnt put your warranty in jeopardy; plus conventional oil is all that is necessary, and its cheaper.

A subset of this discussion is still stuck on what truly constitutes a synthetic. About 20 years ago debate raged in the industry over synthetics built up by a specific molecular process, such as polyalphaolefins (PAO), versus synthetics made by extreme refining of petroleum waxes (what later became API Group III base stocks). In the end Group III was defined as one type of synthetic, and PAO became Group IV, another type. Other synthesized products such as esters went into the catchall Group V category.

There is general agreement that synthesized base stocks have performance properties that are not commonly found in conventionally refined petroleum base stocks; they include such things as improved oxidative stability and less viscosity change with temperature (high viscosity index). On the minus side, synthesized hydrocarbons such as PAO are not very good solvents so engine oil formulations based on PAO usually contain an ester as a co-solubilization agent, which keeps the additive system in solution. There are purists out there marketing engine oils that are formulated with PAO plus enough ester material to provide the needed solubility and seal conditioning characteristics for engines.

Meanwhile, there is a great deal of misinformation about synthetics and how well they perform. Boasts of 5 percent to 7 percent gains in fuel economy are common, as well as 25,000-mile oil drains. In addition, synthetics are said to keep engines cleaner and reduce wear. Of course, the additive system is an integral part of any engine oil and it is possible that some synthetics have been formulated with additives that can provide some of the claims made.

As earlier columns have said, good solid field-test data as well as engine test results are the best measures of the performance of any engine oil. Testimonial data, while often used for advertising purposes, do not really demonstrate anything other than a single vehicles experience or the bias of anyone reporting on performance. If youre going to make a claim, at least let it fall within the boundaries of the laws of physics!

The type of driving you do defines the optimum oil change interval you should follow, as does the type of engine in your vehicle. Additive company Lubrizol, on its new www.pceo.com website, goes to some length to point out the many ins and outs about when to change your oil. There are a few simple guidelines that can help you determine the optimum engine oil change interval which will allow you to protect your investment in your vehicle, provide reliable transportation and not waste your money by over servicing, says an article from the website.

The article goes on to advise:

For those with a new vehicle or one still covered by the factory warranty, its best to follow the OEM recommended oil drain interval as defined in the vehicle owners manual. This is important to maintain the warranty coverage. For normal driving regimes, its around 7,500 miles for new vehicles; for older but still relatively newer vehicles, around 5,000 miles.

Have an oil change monitor? The article reminds that these devices do not monitor the actual condition of the engine oil but rather use the vehicles computer to estimate the severity of the driving style and how it impacts oil life. The onboard computer calculates the number of cold starts, idle time, outside temperature, load, mileage and time between oil changes. The monitor cannot do things like detect the oil level, foreign contamination, water, antifreeze, or fuel dilution of the oil. For that, drivers need to pull the dip stick and check!

Have an older vehicles with over 75,000 miles, and wondering if the oil recommendation still applies? As the Lubrizol site explains, Engines tend to build up deposits of sludge and varnish over time. If these deposits are kept under control they do little or no damage to your engine. However excessive deposits can increase emissions, rob your engine of power, and degrade fuel economy. Some engine wear is inevitable, but proper maintenance can minimize wear on critical engine parts and help extend the life of your vehicle. Of oils specially formulated for high-mileage vehicles, it adds, High-mileage oils can help reduce oil burning, condition engine seals, and help control or reduce deposits.

For vehicles driven in severe service – which actually covers most of them – the website again urges a look at the owners manual and to faithfully follow the OEM recommendation, which likely will be for more frequent changes. Whats considered severe? Lubrizol summarizes it as trips of less than five miles in summer temperatures; trips of less than 10 miles in freezing temperatures; driving for long distances at speeds of less than 50 mph, or at high speeds; dusty, muddy or salted roads; long periods of idling, pulling a trailer; carrying heavy loads, and – everyones favorite – stop-and-go or city driving. Most of these will make your oil life monitor flash its warning light sooner.

And lest you think that the OLM is the fail-safe criterion for determining oil change intervals, GM has this word to share with you. It was sent out to 2009 Chevy Traverse owners:

This notice is sent to inform you that General Motors is conducting a Customer Satisfaction Program that affects your 2009 model year Chevrolet Traverse vehicle, equipped with a V6 engine.

Your vehicle was designed and built to meet GMs high standards for quality and reliability. However, we have determined that under certain driving conditions, and with your vehicles original oil change intervals, the timing chain could wear prematurely and cause the illumination of the Service Engine Soon light. Timing chain wear can be affected by the age of the engine oil and driving conditions.

The letter went on to advise that, to ensure owners of the affected vehicles did not experience premature timing chain wear, your Chevrolet dealer will change the calibration of the engine control module, including the engine oil life monitor, which in most cases will recommend more frequent oil changes. This calibration change will be performed for you at no charge until October 31, 2012.

The letter, which was detailed in a 2010 article in LubesnGreases, urged Chevy Transverse owners to come in to have the calibration done as soon as possible, to assure they get the most benefit from more frequent drain intervals. Failure to complete this repair by October 31, 2012, it added, may affect your eligibility for future repair coverage for the timing chain.

Thats the latest on the great oil change interval caper. No doubt there will be more to come and Ill be back riding this pony for all its worth. This could be a Triple Crown winner!