Kevin B

I have heard that this can cause oil leaks to occur more easily. Is this true? Any other concerns that I should have? Thanks. My car is a 98' 4.2.

ohbw

I have the rarest kind of mechanic: utterly competent (25 years of tending German iron at a high level, and the go-to guy for people in Boulder, Colorado who have very nice and often heavily modded Porsches, Audis, Benzes, and Beemers) and absolutely honest (he's never failed me nor any of the friends I've sent to him in seven years in (a) doing perfect work, and (b) doing it for a reasonable price). I completely trust him, something I never thought I'd say about a mechanic. He's a prince, I tell you!

Anyway, Randy says if you love your car and want it to last, synthetic oil is worth the tariff. If you're deeply in love, synthetic everything (except A8 ATF, where for reasons mystical and practical you must use the OEM fluid or risk being excommunicated from this forum and having your transmission instantly transformed into a boat anchor).

Good synthetics like Pentosin, according to my guy and, I believe, the weight of recent studies, lubricate and hold up slightly better and longer than the other stuff -- better enough that after 25 years experience, he uses them in all his own vehicles and recommends them to all his customers. He's not the kind of guy at all to recommend something just because it costs more. My unscientific survey says this is pretty much consensus these days among good mechanics. Issues about switching over are largely non-issues and generally only occur in very high mileage cars -- that's my understanding and the opinion of my guy as well.

I would be remiss in my ethical obligations to Randy if I failed to remind you that using synthetics is not an excuse for being tardy about or -- ye gods! -- skipping regular oil and filter changes.

PaulW

Yes, it can cause leaks

ohbw

I switched when I bought my 8 at 63K, now at 67K, dry as a bone

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How many miles do you drive between oil changes?
When do you decide to change your oil? Two factors: miles driven and time between the last change. Usually it's the sooner of the two.

The primary advantage for synthetic is a longer change interval based on mileage. If you always reach the time interval before the mileage interval that is recommended by the manufacturer for your type of driving, synthetic is a waste of your money. Syns will hold up better for higher mileage - but will still need to be changed at the same time interval as a Dino-based oil.

The reason is crankcase contamination from water, which combines with other byproducts of the combustion process to form acids. Synthetic oil is more hydroscopic than dino oil, so it will attract and old more water - hence the need for the same time -interval change.

The most important feature of today's motor oils (besides the weight) is the additive package - NOT the base stock. A good dino oil will hang right with any synthetic oil under nearly all circumstances that most drivers face.

High Performance racing engines driven at max loads and high rpm will benefit from synthetic oil - but the average daily driver doesn't exert enough stress on their engine or their oil to justify paying 3-4 times the price for a synthetic.

Some cars require synthetic oil due to factory-set higher engine running temps for emission controls and the lack of an external oil cooler (1992-1996 LT1 Corvettes for example). Here a synthetic makes perfect sense, and is required by GM for warranty coverage.

Sure, we want the best for our cars, but for most of us, a good Dino oil changed at the recommended interval will work just fine.

100-A8

I typically purchase "slightly" used cars with 50 - 80 K miles on them. The first thing I do is replace all lubricants w/ synthetic ( still haven't found the nerve to try it in the tranny). I have used Amsoil in all of my vehicles for the past 15 years. I have never experienced a situation where an oil leak developed that was from the switch to the synthetic.

One explanation I have read why this might happen, is that most sythetics have a high amount of detergents, and may dissolve some of the "gunk" that is keeping those tired seals from leaking w/ the old oil.

When switching from mineral oil to the synthetic, I always use an engine flush for the first change.

I have driven several vehicles over 175K miles, following the change to synthetic, and the performance seems to stay the same - no evident engine wear!.

I do notice 5 - 10% increase in fuel economy from the reduced friction provided by the synthetics.

I hope you have similar results!

ohbw

Science! The molecules in a synth oil are slightly smaller than in a dino oil, so it can find its way through a tired seal before the dino oil will. My guy says in practical application he doesn't switch to synth if a car has 150K or more on the clock. Before that, no worries, worth the switch for better lube and longer time between changes.