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Synthetic Oil

Roger Crawford wrote: Synthetic oil has a better shear capability, better cling, and [better resistance to] thermal breakdown, an issue in a daily driver.

Dan Stern added: Other [advantages] include much lower pour point, much less viscosity change over time, and flat-out better lubricity. All of these are quite advantageous indeed--even in daily drivers. That lower pour point is particularly good--it means that oil gets where it needs to be much more rapidly after a cold start, especially in very cold weather. ... What you refer to as "thermal breakdown" manifests itself as sludge and that tarlike goo that comes out of your crankcase every 3k miles. It happens on daily drivers! If you're not driving in conditions that let you take advantage of the lower pour point of synthetic oil, then you're most likely driving in conditions that let you take advantage of the resistance to thermal breakdown.

True or false?

The additives in oil reduce have a limited life, thus waiting longer between changes has disadvantages because the additives lose their effectiveness
Synthetic by design is less prone to breakdown, and does not need the quantity of additives necessary to make dino juice an "effective" oil. Synthetic is much less prone to coking, and less prone to varnish than conventional oil.

Dan Stern wrote, "Oil additives do not deteriorate over time--only over usage. Some modes of usage are harder on oil than others. Lots of short trips put lots of water and acid, etc. in the oil, and things never get hot enough to boil off these contaminants. That's why you hear to change the oil every x,000 miles or x months--because if you're not driving x,000 miles over a period of x months, you're making this kind of short-trip contamination."

The more you change the oil, the better
General Motors' research indicates that 10,000 mile oil changes may actually be quite safe - if conditions are right. GM is switching from standard intervals to computer monitoring.

I thought that once you used conventional oil over time the seals swell more, when then switching to synthetic oil, the seals reduce in size and leaks can develop
If you have leaks with regular oil, you'll have leaks with synthetic. If you have leaks with synthetic, you'll have leaks with regular oil.

Edgar Atheling wrote:

I had several mechanics tell me that [switching to synthetic on high-mileage vehicles] would ruin the seals and cause (or increase) oil leaks. One mechanic stated that the oil consumption in his personal vehicle increased dramatically (about one quart every 750 miles) after switching to synthetic oil in a high mileage car. I, however, have not experienced any increase in oil consumption in either of my high mileage vehicles.
Oil change intervals

Dan Stern wrote:

16,000 miles surely seems like a long time for an oil change, and it is, and it goes against my previously firm belief in the 3,000 mile interval. But I dropped in the Mobil-1 10w-30 and the XHD oil filter. I kept checking the oil and seeing a crankcase full of mighty clean engine oil which didn't smell or feel any different from the stuff that came right out of the bottle. It grew slightly dark--think "soy sauce" if new oil is "honey"--but no darker. It never got sticky or gritty or began to smell gasoliny or carbonacious. It was down by a pint (half a quart!) at 8,000 miles, so I changed the XHD filter, added a pint, and had my mother keep driving.

When I drained the oil at 16,000, it looked great and smelled and felt fine. So in short, I didn't do this because I read about it, or because somebody told me I should, or to rationalize the higher cost of Mobil-1. I did it based solely on my own executive decision.

We're closing in on our second 16,000 mile interval, and will probably hit it within the year. When the engine was apart for a head gasket, everything looked great. No abnormal wear anywhere, no weird noises, no oil pressure problems, no smoke.

More notes on the 53020311 Severe Duty oil filter: List is around $7 per filter. They fit all four of our cars, so I buy them by the case and pay $4.30/filter. It's built with very good materials and workmanship. I have yet to find a sample--and I have cut several open--with sloppy or incomplete gluing, poor construction, foreign material inside the filter, etc. The antidrainback and overpressure relief valves are more robustly designed than any other filter I've ever examined for this application (and there have been many). The filter element inside is very large.
Paul Ivester added: "You might wish to advise your readers not to break-in a new engine with synthetic oil. The first 5,000 miles at least on mineral oil is still the rule [except where the owner's manual disagrees]. Many people still are unaware of this. Chrome rings are very touchy on this."

Also see our discussion of Consumer Reports' study that shows no difference between any motor oils.

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