gene cooley
Autocrosser
Mike,
You are right about synthetics. The 3000 mile oil change interval was a marketing campaign by Jiffy Lube (the first commercial oil change chain store). See how effective marketing can be? That said, today most auto manufacturers recommend between 7500 and 10,000 mile service intervals on engine oil. Heck, my new Ford Super Duty has an intelligent oil life monitor and has been flagging engine oil changes at 9500 miles. This on a modern diesel pickup that tows a big enclosed car hauler 50% of the time.
Also, I have been using Mobil 1 engine oil in my street cars and race cars for many years. I have been very happy with its performance. I started using Redline back in the early 90s when I was really beginning to learn automotive engineering and was doing lots of experimenting with X1/9 transmissions. It was 1996 that I went to work for a Pro Racing team (as the team engineer) that had Redline as a sponsor. There I learned a lot about their products and spent a lot of time talking with their engineers. I was already sold on MTL but learned a lot about synthetics and Redline's products specifically. I have used lots of others over the years but always went back to Redline for transmissions and differentials.
Synthetics and petroleum oils both can be contaminated by moisture. Engines and transmissions are vented by necessity and as the weather changes moisture naturally condenses out inside the engine and transmission. That moisture settles into the lubricant. It will be boiled off once the oil reaches normal operating temperatures and can stay there long enough for the moisture to be fully expelled. However, long periods of storage and shorter trips promote contamination and don't burn off the moisture. Over time the oil gets contaminated. Synthetics are less likely to varnish than petroleum oils so they last longer but they are still effected.
As noted above, the average collector doesn't daily drive his car. It sees occasional use and that is often a short trip to cars and coffee. Or a saturday run to the store or dinner. That's not an hour of good hard use to really exercise the car and heat the fluids. Change the engine oil annually and the gear oils every 3 to 4 years. Gear oils can go further if the car is used more regularly. This is all out the window if the car is tracked.
Steve, I have been using the oil monitor in our 2010 2.4L Ecotec for oil change intervals since we bought it in 2011. As you say it gives you 10K oil changes. I'm using "conventional" oil, not pure synthetics.
(Mostly Valvoline)