Synthetic vs Conventional
 

From researching past posts it seems that detergent containing synthetics such as Mobil 1 may be harmful. Because the detergents would loosen good resins adhering to crucial components keeping the engine tight within factory specs. It seems intuitive to have some amount of "protecting" gunk on all parts of the engine exposed to frictional wear. Therefore, could it be more wise to stay with a non detergent containing oil and just change the oil at shorter intervals?

I think all modern Oil's have detergents in them. The thing with sythetics is they are designed to be more liquidy at greater temperature extremes. They also have special chemicals tossed in to help clean out the engine, lubricate more, not cake on bearings when the car is shut off, etc. But all those things come from the same basic idea - sythetics need to flow better.

Well, any diesel grade oil (15W-40), is a detergent oil. It has to be to keep the soot suspended and keep everything clean. Just about everyone here uses one brand of 15W-40.

Protecting gunk in the engine is pure garbage!!! Do not fall for it, a clean engine is a happy engine. You may experience small leaks getting worse as the synthetics flow in small gaps better but that is precisely why you use it in the first place. If you do get leaks that get substantially worse repair them.

Please bear in mind that any gunk in the engine is NOT supposed to be in there and it will not help keep anything tight or in tolerance. There is no such thing as a "good resin".

IF you use a synthetic and want to extend your drain intervals you need to; #1 change the filter at normal intervals and #2 get an analysis of the oil at normal drain intervals to make sure it is still good. Analysis is the only way to make sure your oil is still doing what it is supposed to do. Please let me know if you need help in sampling your oil or want more info on what it entails.

I bought a "parts car" '79 300SD and it runs so good I am still driving 3 1/2 years later. I have no idea what kind of oil was used for the first 160,000 miles, but I started to use Castrol Syntec 5W50 40,000 miles ago. The leaks it had stopped and it now uses about 1 quart of oil in 10,000 miles instead of the 3 quarts it used when I first got it. I also use a small amount of PTFE so all the improvement may not be to the synthetic oil.

P E H