Longer engine life, extended time between oil changes, less cold start friction, and the car just runs a lot better, smoother, quieter, quicker. I switched in my 77 and noticed an immediate difference. My has 205K and is using some oil and leaking some so I switched back to the part synthetic for price reasons. I use Castrol 20W-50. I don't know of any cons.
I am an engineer, and I appreciate real testing with measured data to quantify the performance of products
like this that make claims of reduced wear, longer engine life, more performance, etc.
Consumer Reports magazine tested synthetics (and all
the major oil brands) by running them in dozens of
identically rebuilt engines in New York taxi cabs. They
even modified the engines to the older style mechanical
lifters that show faster wear.
Their conclusion: There was NO difference between the different oils, and the synthetics made no difference.
They concluded this by measuring the wear on the parts (which is what oil is supposed to prevent)
There was no measurable difference between the
different oil brands, or the synthetics.
Bottom line: Save your money. Don't buy the synthetics
or Slick 50. Buy a brand that has the ASME certification, and don't worry.
They also tested changing the oil twice as often as
recommended. Once again, no measurable difference.
Enjoy your ride. Skip the snake oil!
Oh yeah, cons: I have heard of synthetics turning minor oil leaks into major ones!
I always thought that the synthetics were an advantage in turbo's because they could withstand the heat of the turbo bearings with a greater resistance to coking (basically cooking the oil crispy). I don't know of any additional wear resistance other than that. I use Mobil 1 in my 83ZXT, it's only a couple of bucks more per quart and if it helps keep the turbo pumpin' that's cheap insurance.
I spent a lot of time researching this issue and came across the same "taxi" test Patrick refers to. I was more curious about the wear results from different oil change intervals. In lab tests the synthetic oils are superior chemically but in the typical street car that is properly maintained, there is little justification for the extra expense. If synthetic had tremendous real world benefit, auto manufacturers would ship it in their crankcases and spec it in the maintenance schedules (and not just as an alternate) - after all they are carrying a warranty liability.
Popular Science had a great article on motor oil and I learned one important thing from it: IF IT IS API RATED SJ USE IT regardless of brand. I use the cheapest oil I can find that meets the SJ spec and change my oil every 5,000 miles. The "taxi" test showed there was no perceptable wear difference even when oil changes were at 7,500 miles but I like to err on the safe side. As far as the additives Slick 50, DuraLube etc. there is a lot of evidence they do nothing and most are simply pfte (teflon) additives. There is a tremendous amount of dialog on the net regarding these products and with the exception of sites promoting/selling a product few find merit in them.
Consumer report schmumer report. I've seen their reports totally inaccurate, especially with cars, but thats a whole hours worth of explaining ..just.. dont always believe what you read. I'll just tell you what I know about synthetics from my experience.
I used to have an poorly maintained 88 maxima with 130,000 mi.. that burnt oil like a school bus. I mean I'd leave after work and just watch the cloud. I took it to the local import rebuild pros and they said junk it/sell it asap, the engine could blow anytime. So I went out and tried to do a quick detail job/get everything hidden so I could sell it for a couple peanuts, and decided to try a little synthetic oil (castrol)... and well it still burnt oil.. but not so that there was a freaking fog following you. The only way you could tell was by getting out of the car and staring at the exaust.
Also, my best bud races his mustang bi-weekly, and uses Red-line synthetics on everything. He freaking swears by them, (you have to to pay $7 a quart for oil..GOD DAM.) I haven't seen any time-slips, but he seems pretty fanatic.
With out natural resources being used up at a higher rate with each newborn human being I think I will stick to the synthetic vice the fossil stuff..... But they better still sell gasoline long after I am gone to power our Z's....
Synthetic motor oil provides better protection to a worn engine (my opinion), Consumer reports should be testing the difference of wear in two similar worn down engines. I have a 80 200sx w/ 165k miles & i noticed an increase of the 3 miles per gallon using mobil 1 & a smoother ride. I don't think there is much difference comparing the oils in new engines.
From what I have heard is that when you use normal oil and then put in synthetic it can break up the old oil in the motor and cause it to leak more where it used to leak alittle. You also can't use synthetic in new motors becuase it is to slick and won't break in the motor properly (why new car makers don't ship it in their car). I use one additive Petron Plus I have done test and it works. lever on a spining metal circle with a replaceable metal to rub against. Most oils wear it the same and stop the motor and the same lbs torque (7-9lb) petron doesn't barely make the motor work hard at 200lb. surprising stuff. Well we used it in my 84 VW Jetta turbo diesel went from 43 to 50mpg. Smother quieter car too. Well I quit using it do to the oil leak I couldn't fix and the expense of the oil $20 a quart. Just one quart for every other oil change works good. Blew a head gasket got my Z . It is actually a whole line of products that are very slick. Sorry for the long post