Looking at buying a used STR (most of them on the market with about 50k miles).

If you're unsure if the previous owner used syn or dino oil, would you use synthetic oil going forward?

I understanding that switching to synthetic oil's higher detergents may actually promote leaks in some gaskets (by removing any built up crud) if the engine has only been using non-synthetic oil.

What say you?

 

Stick anything in that meets the spec you like for your area from the handbook. Never heard of any S-Type having grief if you do that.

 

I switched mine around 50K now at 90K and no leaks.
Don't lose sleep over it.

 

Agreed. Run whatever makes you happy. I run conventional Castrol 5W-30 with an oil & filter change every 6,000 miles in both our S-Type (70,600 miles) and XK8 (43,300 miles). Both cars are doing just fine and I don't overspend on synthetic oil....

 

+1 on all the comments above. There's no real benefit in switching to synthetics unless an extended change interval is taken advantage of.

 

Yeah same here put what you feel comfortable with as lOng as you are within the limit of the specs. I have been using comfortably 10w/40 castrol syntec ever since owning my car used.

 

My Triumph Stag did actually start leaking when I switched to synthetic oil after it had a mineral oil only diet from rebuild. The engine had probably done around 20,000 miles at that point.
Different V8, tolerances and technology I know from the Jag V8. But after I had rebuilt my Triumph 2500S (2.5 litre 6 cyl, and much older tech engine than Stag V8) it started on a synthetic only diet and never leaked.
Could have been a multitude of reasons; like brands of oil and conditions etc. But its a curious point you rase and may have some credibility.
In talks I have had with the local Jag dealer, they have only ever used synthetic on my car they tell me.