A friendly subscriber of mine, just today, brought up three questions about intervals regarding synthetic motor oil changes. The questions that were asked left me wondering how anyone can trust any oil company these days because if you aren’t at the top of your game you can easily be conned into buying a product that won’t necessarily deliver what it promises and will leave you with either engine damage, money damage or ego damage, and none of those sound particularly fun.

To end the suspense, here are the questions:

#1 I have heard that changing your oil every 3,000 miles is an old wives’ tale (or an old hubby’s tale?) but how does that pertain to a synthetic motor oil change?

#2 If I haven’t ran my mileage up to the oil’s limit yet then when’s the right time to change my oil?

#3 Will an initial higher TBN number be beneficial if I’m using oil analysis?

Those questions are great and I hope my answers are some help, so here they are:

Back in 1997, when Castrol managed to get the courts to allow group III basestocks to labeled ’synthetic’, the line between synthetic motor oil and conventional motor oil became very ‘gray’. So ultimately, when it comes to the 3,000 mile myth is concerned, it’s extremely difficult to make a clear distinction between the two. However, I can say in good faith that when it comes to synthetic motor oil that the 3,000 mile or 3 month myth are wiped off the board. A quality synthetic oil with a decent additive package will outlast a traditional conventional oil any day of the week.

#2 and #3 have a common issue of TBN. It is important that the detergents and alkalinity (related to TBN) of the oil are provided for an anticipated duration of the oil in the engine. Additive packages vary depending on the motor oil and their recommended drain intervals. Typically the TBN would be higher to make sure the engine environment does not become acidic and corrosive.

Very short drives are hard on oil (like down to the grocery store). City driving is typically considered ’severe’ when it comes to oil change intervals. Most people caught up in the hustle and bustle of the city don’t have the time to let their engine heat up properly and then unburnt fuel and moisture end up diluting the oil and breaking it down.

For that reason it is best to start up and run down the highway for greater than say 15 minutes to really allow the engine to cook the oil “dry”.

Depending on your driving habits, your oil will deplete itself if it isn’t designed for longevity with a higher TBN and more detergents, etc.

The complexity of additive packages in oils is mind boggling. Every additive comes with a benefit but also an associated cost and each additive has to be balanced with the other additives. It takes a lot of testing to get it right.

To determine for yourself, once and for all, what your motor oil is truly doing to and for your engine you’re going to have to run it in your engine and perform your own periodic analysis. As long as the oil additives in your oil are appropriately balanced then the TBN should stay elevated tonger and keep your engine safer to last through extended drain intervals.  You can find the best motor oil review for all the different oils using a google search.

Mobil 1 Synthetic Oil and AMSOIL Synthetic oil are number one in my book. AMSOIL has been my oil of choice for the past 7 years for both of my vehicles and I’ve had no engine problems with either, only changing my oil in both once a year.

On your last note I agree it really is difficult to feel a 2% change in horsepower or detect a small percentage improvement in gas mileage. A brake caliper dragging a little bit or low tire pressure makes that much of a difference. When I hear people say that they felt a difference when they switched their oil or used an additive I have to chuckle inside my head.