synthetic oils

I changed the oil in my 78 sc a few weeks ago, and used synthetic oil for the first time. Have I made a big mistake? No leaks so far. Why does synthetic oil leak in older cars? Should I get this stuff out of my car immediately, and have I already damaged my oil seals? Help! Can't afford big buck repairs right now

Several years ago we switched to synthetic in our 1987 Turbo and it took about 4 months before any leaks started. The leak was on the crankshaft seal behind the flywheel, but the rubber centered disk failed about that time so we had to drop the engine anyways. The synthetic oil is much more slippery than mineral based oils and old seals and gaskets tend to not be able to hold it back. I feel the advantages of it far outweigh the leaks, if any that may develop,

Well, oil is always a controversial subject. Here is my own personal view, and what I do.

I do believe that as far as lubricating an engine, synthetic oil is superior to dino oil. How much so, I'm not sure. There are apparently lots of 911SCs with over 200,000 miles on them, achieved on dino oil. Many with well over 300,000, according to Bruce Anderson. On the other hand, an engine that goes 300k on dino oil may have gone 500k on synthetic, who knows?

I once tried Mobil 1 in my 914. What was at the time a mild leaker quickly turned into a big time major leaker! There was a huge difference in leakage between. I have since rebuilt the engine, and it does not leak at all using dino oil, but I'm not about to take a chance with synthetic on that car again (I use dino oil, changing the oil every 1500 miles and the oil and filter every 3000 - it only takes 3 quarts at $1.50 each for the 1500 mile change, and it makes me feel good!).

In my 78 SC, I do not use synthetic. My SC does not leak a drop using dino oil, and I just am not willing to take a chance! It is important to me (I am obsessed with it!!) that my cars do not leak oil. Plus, I only drive the car maybe 800 miles per year or so, and just change the oil once per year. Given the volume of oil involved with a 911 oil change, I can't really justify the high cost of synthetic for just 800 miles of use.

I also have a1986 BMW 535i, which is more of a regular, 7500 mile per year daily driver. It has 102,000 miles on it, and I have used Mobil 1 since I bought it many years ago, at 55,000 miles. It does not have any oil leaks, and never has. I am willing to use Mobil 1 in this car because (1) it is not a notorious "leaker" like 911s and 914s, (2) the BMW big 6 is known to have a cam oiling problem, and I want to alleviate this as much as possible.

As an aside, my friend has an 86 Carrera with about 80,000 miles on it. It has used Amsoil synthetic for at least the last 10K miles. At the last service, the mechanic told him it is leaking from the front seal and from an oil line somewhere.

I certainly would not panic about the fact that you put synthetic in your SC, I'm sure LOTS of people run synthetic in the SCs with great results and no leaks at all. I would just keep an eye out for leaks, just in case. If you are not comfortable with it, I'd just change back to dino oil at your next oil change.

FWIW .I use Castrol synthetic blend in my 78 SC with 106,000 miles on it , with the blend my oil stays clear much longer and I have noticed no leaks . Its a little more than regular oil but it is superior and you dont have to change the oil as often. You may actually be doing more harm than good if you change your oil too often it takes 600+ miles for a new filter to work properly.Having owned a carwash/quick lube center I honestly dont feel its neccessary to change your oil 3000 miles under normal conditions .This is hype from the oil manufacturers and quick lube centers in my opinion .

I definately agree that a 911 does not need to have its oil changed every 3000 miles, given that it holds 14 or so quarts! It would seem to me that the more oil a car holds, the longer it would take to contaminate that oil.

Same for most "modern" cars. In my BMW, I go 5 or 6,000 miles.

But, the 914 is a different story. I don't know if its because of looser tolerances, or something else, but 914s seem really hard on their oil. The oil in my 914 was as black and dirty looking at 3000 miles as the BMW was with twice the miles.

Thanks everyone, for all the good info. I think I'll leave the synthetic until my next oil change. and decide then if I want to switch back.

I've got an 83 SC with 170,000 miles
I use and highly recommend Redline Oil
I change it every 7000 miles.No leaks
cool running,great gas milage.
I also use K&N airfilter.