I bought a 91 TA with 80k and no significant oil leak. After I changed the oil to Castrol SynTech, I noticed oil leaks at front seal and valve covers.

What's up?

 

If it was not leaking with the old oil then replace systetic oil with the regular oil. 10 w 30 is little bit thicker than 5 w 30 so it will leak less. I have been using Castrol 5w30 for over 10 years and I see no problems so far.

Syntetics seen to penetrate engine parts, including gaskets, much better than regular oil, plus i would not use it on engines with mileage higher than 80,000 km.

 

Fix the oil leaks and keep using synthetic. I use synthetic on my 130k mile bottom end. The timing cover leaks a bit, but that's because I suck at sealing it.

 

Yeah. fix the leaks and keep using synth.

the synth just brought the problems you already had to your attention.

 

Fix the leaks and use a real synthetic, not that Castrol "me-too" stuff.

 

Well, I think maybe I should switch to syntetic if everyone is recommending it.

 

Give it a couple of oil changes. Synthetic washes away wax deposits from the convential oil which tend to plug leaks. What you are experiencing is the typical weeping older cars get when you make the switch. The swell agent in synthetic takes anywhere from two to five oil changes to react with the seals. Mobil1's new formulation addresses the weeping problem and usually the problem goes away after a month or so. Danno

 

I switched at 92,000 miles from dino jiuce to Mobil 1 15W-50. The logic in switching to thicker oil was to avoid leaks. I plan to move to thinner stuff as I get confident that I haven't caused any problems...