ive used synthetic in all my cars for years, and while engine wear is minimal, all my cars have had oil leaks when i changed them over to synth. my Z i just bought 3 months ago and instead of running synth i just slick 50'd it and i run castrol 10-30. the car doesnt leak a drop. the whole underside of the car is as clean as the day it was built. FWIW, i ran slick 50 on my synth cars too. im a big believer in the stuff.

my moms miata always had valvetrain noise, even w/ synth, put slick 50 in it and it went away. the cars seem to start quicker w/ slick 50 too.

 

i believe you guys are right. synthetic doesn't start leaks. all i run in my atv's is synthetic, however i ran synthetic in them right after they broke in. i am just personally not runnning synthetic in my engines that have not be ran on synthetic before. here is what happened to me. i had a minor oil leak. i ran synthetic through it. the leak was noticably worse after 3000 miles. the car was drove the same as it always was during this 3000 miles. nothing else was changed besides the dino to synthetic. maybe it just started leaking worse due to the fact that the seal was getting older, i don't know. i just thought it was odd that it just started leaking noticably more after i ran synthetic through it. i also agree that synthetic is better for the engine than dino but with my Z28 having 110K on it, the engine is probally not in the best of shape anyways.

 

frmula1
Somehow I knew we were going to end up here. This is an old spec. but is useful as a demo.

Engine Oil Viscosity Classification - SAE J300 revised April 1997(1)

SAE Viscosity Grade Low-Temperature (°C) Cranking Viscosity(2) (cP)
max Low-Temperature (°C) Pumping Viscosity(3) (cP)
max with no yield stress Low-Shear-Rate Kinematic Viscosity(4) (cSt) at 100°C
min Low-Shear-Rate Kinematic Viscosity4 (cSt) at 100°C
max High-Shear-Rate Viscosity(5) (cP)
at 150°C and 106s-1
min
0W 3250 at -30 60,000 at -40 3.8 - -
5W 3500 at -25 60,000 at -35 3.8 - -
10W 3500 at -20 60,000 at -30 4.1 - -
15W 3500 at -15 60,000 at -25 5.6 - -
20W 4500 at -10 60,000 at -20 5.6 - -
25W 6000 at -5 60,000 at -15 9.3 - -
20 - - 5.6 < 9.3 2.6
30 - - 9.3 < 12.5 2.9
40 - - 12.5 < 16.3 2.9
(0W-40, 5W-40 and 10W-40 grades)
40 - - 12.5 < 16.3 3.7
(15W-40, 20W-40, 25W-40, 40 grades)
50 - - 16.3 < 21.9 3.7
60 - - 21.9 < 26.1 3.7
Note: 1 cP = 1 mPa · s and 1 cSt = 1 mm2/s
1 All values are critical specifications as defined by ASTM D3244
2 ASTM D5293
3 ASTM D4684; note that the presence of any yield stress detectable by this method constitutes a failure regardless of viscosity.
4 ASTM D445
5 ASTM D4683, CEC L-36-A-90 (ASTM D4741)

All oil (Syn. and Dino) MUST flow at the same rate at the spec. temp. ie. a 5W must flow at 3500 cP at -25c, if syn. had a higher flow rate it wouldn't be a 5W, it would be a 0W.

 

I wanted to mention an article that Hot Rod wrote up a while back. They took a car with an auto tranny that was running dino oil and put it on the dyno. I t made something around 400 horses. They took out all of the fluids, put in synthetic in everything (crankcase, tranny, rear diff), and gained around 10 horses for that.

 

Replacing old oil with new oil will usually result in better performance. Did the article mention if the dyno oil was new or old?

 

All I use in my engine is Mobil 1, the stuff rocks. I wouldn't recommend it in the tranny though, but I do use it in the rear.

John

 

But take those two same oils and see how they flow at -40 instead, and then the benefits of the synthetic come through. In most cases a 5w30 dino oil will just barely qualify for that flow rating, while the 5w30 synthetic easily qualifies. Another consideration is that the 5w30 dino oil might qualify as the 5w30 when new, but quickly deteriorates so it's cold pumpability factor is a lot worse than the 5w30 synthetic after just a thousand miles or so. Most 5w30 dino turns into 10w20 oil very quickly.

 

Synthetic is just better,we can all pretty much agree. Most LT1's will leak oil anyways, considering that most of our engines are getting up there in age and the fact that LT1's have an ongoing problem of the intake gasket leaking, so it's more than likely going to leak anyway. Is small leaks that we should be fixing not a good reason, not to run synthetic? I really don't think so. Just don't do it on break in of any kind.

 

From Jim Ingle, GM Powertrain Engineer (this question was asked in terms of adding Mobil 1 to a ZR-1 after engine break-in):

"There is probably more misunderstanding of lubricants and "old wive's tales" about them than any other automotive issue. A lot of this appears to be a result of overly conversative writers of owner's manuals, etc. looking for excuses to deny payment for warranty work.

For years, new cars were shipped with non-detergent oil as factory fill...so called "break-in" oil. I've never quite understood the intent of all this, but it was probably some misguided do-gooder's theory that leaving wear products in place in a new engine provided self-lapping mechanisms to promote burnishing of wearing sufraces. In fact, detergent oils primarily are intended to remove and inhibit combustion products from building up on pistons, valves and other moving parts and hold these in suspension until the oil is changed. The break-in of contacting surfaces is primarily accomplished by the wearing off of microscopic "peaks" protruding through the lubricant film and has little to do with the presence or absence of foregin material. Fortunately, we finally have near universal understanding of the process.

As far as use of so-called "synthetic" lubricants goes, their chief claim to fame is a lower rate of change of viscosity versus temperature. They stay more fluid at low temperatures and more viscous at high temperatures. We us Mobil 1 as factory fill for engine oil in ALL Corvettes now, including the ZR-1, so there is no magic mileage at which it can be used. If there were such a thing as "seating of rings" etc., this will have nothing to do with it. The lubricity of "slipperiness" of synthetic lubricants is generally about the same as conventional "mineral-based" lubricants. (The actual definition of all this is a bit perplexing to me since they are all petroleum products!)

We started using Mobil 1 in all Corvettes with the introduction of the LT1 engine as a 1992 model base engine. Management wanted to save weight and money by eliminating the engine oil cooler and decided to use Mobil 1 instead. Mobil made us an "offer we couldn't refuse" on the oil for installing their logo on the car and allowing them to advertise it as factory fill on all Corvettes.

This was disappointing to me because the oil-to-water oil cooler we used on L98s not only cooled the oil, more importantly it HEATED the oil with engine coolant during warmup to help "boil off" the water (a primary combustion product) which is a major oil contaminant and accumulates if the oil temperature doesn't exceed 212 deg. F each time the engine is operated. Of course, the ZR-1 doesn't have an oil-to-water cooler either, so both cars now share the requirement for frequent oil changes when driven mainly on short trips (this is probably not clear in the owner's manual). My own recommendation, which is shared by many in the industry, is to change oil by the calendar rather than by mileage...to simplify, change at the start of each season (4 times a year).

Bottom line: you can put Mobil 1 in your car any time you want to."