Syntetic vs regular oil!?

[cipo28]

...wich one is better for a turbo diesel engine (high mileage=300k), syntetic or regular oil? A mechanic told me that syntetic oil could produce leaks at the engine seals, I really don't know wich is good! Can you guys clear my mind, please?!!

[chrissev]

...wich one is better for a turbo diesel engine (high mileage=300k), syntetic or regular oil? A mechanic told me that syntetic oil could produce leaks at the engine seals, I really don't know wich is good! Can you guys clear my mind, please?!!

I've been running Castrol syntec 5W40 in my jetta (1.6TD) for over a year now and there haven't been any leaks.  Only thing I noticed right away was that the car was more free revving and easier to turn over in cold temperatures.  I think it is a lighter oil than the dino oil, and also not as thick when it is below 0 degrees outside.  I have redline synthetic in my transmission as well and am also very pleased with that.

[zyewdall]

Well, I haven't gotten the rabbit running yet, so I can't talk about it in particular.

But in my subaru with 200k miles on it, I run synthetic (5W-40) all the time.  Much easier to start when it's below zero, and less valve ticking.   I leave it about twice as long as non-synthetic which partly makes up for the higher price.  As for leaking, it does leak a little more than 20W-50 does -- maybe the same at 10W40 non-synthetic (subaru's are a little notorious for leaking oil), but not enough to be a problem if you add a quart every 1000 miles or so.  The easier starting in the cold is reason enough for me to use synthetic.