I have a 93 850 GLT with 155K miles on it. I've been doing alot of driving lately (400-500 miles/week) and was wondering if it would be a bad idea (leaks) to switch to synthetic oil. The engine has always had a natural (Castrol GTX) for as long as i can remember.

I changed to Syntec recently. It being a hybrid (synthetic and carbon-based fluid) some 'synth purists' don't care for it. Seems OK, and may have actually cut down slightly on oil consumption. Will keep you posted.

As a lubricant, older engines may benefit from better heat capacity and viscosity stability of the Synthetics. Try it. If you like it, keep it. If not, you've just had a date with your sister. Not really a big problem.

because of work and sunny days ive been doing A LOT of driving lately. about 3000m last two weeks. just hit 388000m. anywho about two years ago i bought some syn oil at a garage sale for a buck a bottle. too cheap to try it before plus these rumors about leaks scared me. sure enough after the change i started getting some leaks or should i say the leaks got worse. really worse. was it the syn or was it the fact that it was 5w30. who knows. later i switched to 15w40 and that has worked much better. i even top up with 20w50. less leaks and the motor seems quieter. well, off to algonquin park another 300m today.

I have changed a number of Volvo's to Mobil 1 over the years with no problem, including a 94 850 with 167K on the clock. Some folks argue against it, so it appears to be a matter of personal choice. I just like the idea of a superior lubricant in the engine.

dick

Some people say the fully synth oil will start leaking past the seals, though it's a case of suck it and see. Any decent brand oil of the right grade, changed regularly, should be ok...if you are doing more miles, then just do more oil changes pro-rata