A good friend of mine works for Chevron back in Texas. He's one of the engineers who works with the "additives" in their different quantities to formulate oils for different applications- in short a sort of oil chef. I picked his brain about oils on a road trip- and it bored my wife to sleep (literally).

Here's what he said, (if my memory serves me correctly)- and please don't flame me on this, I'm just passing on HIS opinion and our conversation as I remember it (and I'm thinking the opinion of an engineer who works in lubrication for industrial apps is usually worth more than...well... the guy in the auto dept at Walmart, but then I could be wrong).

1. ANY oil changed at regular intervals will provide better "lubricity" (whatever that is) than an oil left-in too long.

2. Synthetics are great, but expensive. Old formulations used to cause problems with some gaskets and rubber, and distorted their shape- causing leaks and oil burning in older engines. Newer synthetics do not cause this as much anymore- they've corrected for it.

3. Synthetic blends? Were partially formulated because of #2 above, and no longer provide much benefit over regular dino oil, just cost more.

4. Diesel oil is formulated to reduce "soot" in the oil of a diesel motor- and can be formulated to run for long periods at high temps (like in industrial apps). Because it retains the flow characteristics of regular oil, yet reduces "soot" it helps keep passageways clean. SO- many oil engineers run diesel oil in their gasoline motors. (He obviously is a proponent of Delo 400).

5. Keeping a synthetic oil in a motor for longer periods and changing it less frequently is generally a bad idea, especially if the driving is usually in heavy traffic at high temps. The synthetic "base" (?) and some additives of many synthetics cannot hold up to that sort of use. SO- the longer you leave it in, the less protection you have.

6. Oil works best (whatever type it is), and the additives hold up longer if it flows at higher oil pressure, and is cooled by a car moving/circulating/cooling it's oil at say, highway speeds than moving slowly at low pressure in a hot motor at idle for long periods. So- a driver that is able to run only at highways speeds MAY be able to stretch the oil changes a little bit. The guy in the car that is in stop and go traffic for long periods everyday, with the ac running, and the window down- with his bad (insert repulsive style of choice) music blaring as he screams "Hey Dog!" into his cell phone between drags off his cigarette- which he blows into the open windows of the cars around him, and punctuates by intermittently spitting out the window.... (You know this guy?) Well, his oil SHOULD be changed MORE frequently (regardless of what he's using).... but instead he goes to quickie mart and dumps another 99 cent quart of 30wt in his "ride"- which will steadily increase it's spew of blue smoke as time goes on.

7. Diesel cars should NEVER run on regular dino oil for long. In a pinch- it's better than dirty old diesel oil, but the motor creates "soot" that the reg oil can't handle- which degrades it much more quickly, and can cause increased wear internally, in addition to "deposits."

So- I'm running Delo 400 now in the 190d. He runs it in his Acura. I still use the synth in the wife's Nissan, but I pay much closer attention to the oil change schedule on both cars than I used to. If I could keep the 190 out of the shop- it would be getting close to oil change time too.... -J