I change the oil in my 1977 Century about every 6 weeks, using Castrol High Mileage 10W30, along with a filter change. Before adding my oil, I add a quart of Rislone into the crankcase. It's a product that helps keep the valves and lifters clean and cuts down on sludge. The Buick's 350 has just passed the 100 000 mile mark and I'm aiming for another 100 000 miles. This is what works for me. I thought about going with synthetic, but the car's been on regular oil since new. Would it really make a difference if I switched?

You must drive LOTS of miles. I usually change my cars when they have anywhere from 2500 to 5000 depending on how they are used. If I am going on an extended trip, and run even 6000 on all interstate highways I do not feel I am hurting my engine. smile.gif

I am not a big believer in synthetics. I believe that if you change your oil on a regular basis to keep it clean, that will be sufficient.

The biggest (and only, IMHO) advantage to synthetics is their ability to withstand severe heat without breaking down. Turbo motors, race motors, Tow Truck motors all tend to push the engine pretty hard and the extra thermal stability of synthetics may be an advantage in some of these applications. However for 97% of us, I consider synthetics to be money not-well-spent.

BTW, 6 weeks may be a bit more often than you need- 3 months/3000 miles is usually often enough.

-Bob Cunningham

I use half synthetic in all my cars, including the '73 and am pleased with it.
I would'nd go full synthetic if I where you
The seals in your engine are not disigned for the full synthetic oils. (so I have been told)

I recently changed to full synthetic on my relatively high (72K miles) mileage Electra on the advice (constant pestering) of a trusted friend. Roadmouse is right, what happens is the synthetics do such a good job cleaning out the gunk that your seals/gaskets will start to weep. I have read a few studies recently on the topic and synthetics do better in the scour tests while synthetic blends don't do any better than conventional oil. I wouldn't waste the money on synthetics or synthetic blends, especially if your changing the oil every 3000 miles. It's better to put the money into a good filter instead!

Even though synthetics do a better job in the scour tests, I regret changing to them because of the mess it's created... I'll be switching back to conventional oils! graemlins/shield.gif

My understanding is that it's not so much a matter of incompatible seal material, but the fact that over the years, the additive package in a certain oil will seep into the seals and make them swell- then when you change oils like that, the additives that are usually in the oil are now quite different and the old additives migrate out of the seals causing the seals to shrink (and hence to leak).

Most oils are very high quality, but differ in the additives that they use. That's the reason why I think the best piece of advice is to choose one particular brand of oil (synthetic or not) and stick with it for the life of the automobile. Or at least the engine.

-Bob Cunningham