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So I'm considering getting some Motul Synthetic for my car. Figure might as well go for the best stuff.

My car is a 1994 Leg Turbo with 420,000km's on it. Would synthetic be a good or bad thing, comparet to dinosaur snot ?

Thanks.

Bad. I've heard that synthetic oils tend to have detergents in them which clean out deposits from dino oil. These deposits tend to seal up old seals . . . take those deposits away and your engine starts leaking.

Of course, if you change all of the seals anyway, then you can disregard what I just told you.

I always use synthetic, no matter the miles. Never had any serious problems. Subaru specific I have three legacy with over 150k miles using mobil 1.

Are you sure you want to spend so much on Motul? Mobil can be had for 4 dollars a quart.

Motul...really? I've heard people running the brake fluid, but it seems most subaru types going with really good synthetics choose either redline or amsoil. I'd go with redline myself, but my car was always run with amsoil by the previous owner, so I kinda think I should stick with it.
Good luck
Micum

I switched over to full synthetic at around 135K miles, have around 165K now. No problems yet.

MK

I don't know about Subarus, but Moto Guzzi's have a bad tendency to leak when you switch from dino to synthetic oil. Not terrible leaks, but seeps that weren't there before. If dino is doing fine, why change? Unless you're changing all the seals and rings, then you're likely to develop leaks. You'll notice lower oil pressure, and your engine will start to use oil. The cons outweigh the pros, IMHO. Of course, YMMV.

Rob

It's not the synthetic part of the switch that's the problem, it's the fact that you're switching brands of oil. Each brand of oil has its own additives. After a few oil changes, those additives build themselves up on the various seals. When you switch brands, the additives in the new oil strip away the old additives and take time to build their own back up...

The fact that synthetic is slightly thinner than dino doesn't exactly help, but that's not the major problem...

Well the thing is, I bought this about a month ago, quite used. So I have no clue what brand of oil was ever put in it.

The reason you can get leaks when you switch from dino to synthetic has no bearing on oil type/brand, etc.

Synthetic oil is an extremely good cleaning agent. Much more so then dino oil. So what happens is if your engine has lots of miles on it, and the seals have gotten slightly bigger, the dino oil has probably sludged up in it to help seal. When you put synthetic in there, it breaks down the sludge, voila, oil leak. Replace seal, and oil leak goes away.

what is the approximate cost to replace the seals ?

iirc something like an hour labor at a mechanic, the seals that usually go are the crank and cam seals, and i don't believe the seals are over $30 for the lot.

MK

Please let us know the address of the ata mechanic I think it would pay me to drive to IL from Denver to have the work done. One thing about syn oils that we found out years ago on Porsche's was that the syn oils were thinner at low temperatures and the oil would leak past the rings and would get into the chamber and burn on start up and the same holds true for the Subie engine. A good oil such as Shell Rotella or other premium oil is probably the best bet for older engines because of the potential problems mentioned above and a few others that are a little lenghthy to go into such as that some deposits will at times form a "seal" in very small areas and the use of a very high dertergent oil can open these.
AL(CO)
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ata was an obvious word combination "at a" ... ..


MK