Going from std oil to synthetic...OK?

[Bltprf502]

I am looking to buy within the next week a 91 318is.  It has been well maintained through the years.  Both previous owners used conventional oil in it.  Would I be doing justice or damege if I switched to Mobil 1 synthetic oil?  My Lexus mechanic says he does not like synthetic oil. The guy who has wrenched the car over the years says regular oil is "fine".  I am leary of switching the oil types.  Any input as to what I should do?  The car has 129k on it.  Is it worth the switch?  Thanks!

[Jimmy Lewis]

Usually the issue that arises is the synthetic has more solvents that may clean oil passages too much. Old seals that have been sludged up by dino oil may start to leak and such. I believe that's the only apparent downside. I have always just run regular oil in mine and just changed it often. I will let others who have more experience with synthetic chime in.

[quinn11m20]

I just recently contacted Castrol and ask them about changing my regular 20W50 High Mileage Conventional to a synthetic 10W40 and they said: " Even with all those miles, (238k) If you have been running 20W50 and switch to 10W40 you will probably see no difference". So, I personally believe in Castrol, and I have switched to 10W40 and have had no problems. I check my oil regularly like I did before, and thats that. Good luck. Tony.

[strad]

I'd say do whatever you want.  You're going to get longer change intervals with synthetic, but it costs more, so I guess it's a wash.  I run 20W50 Castrol Syntec in mine, and it burns about 0.5 quart/1000 miles, maybe a little less (motor has 206.5k miles on it).  I would guess that the p.o. did not spend money on synthetic, judging by the overall condition of the car when I purchased it.  I do not have any leaks (that I'm aware of) after a change to synthetic, so I guess the change didn't make things any worse than they were before.

[roundel318]

I have 266k on the clock and am considering moving to a valvoline full synth, I do have some light oil leakage mid down on the engine, not sure on exact location.
I would probably not be inclined to switch, however I have been running a synth blend  (valvoline max life 10w30) for nearly 100,000 miles.
My hydro valve guide tappets seem a bit noisy at times after the engine has totally warmed up (they hushen when revved back up a little, and are also quiet on cold start) and was thinking of running some BG engine quick clean on the next oil change, keep the synth blend for one more change and then move to the full synth.
Does anyone think it will help quiet it down, I read places that they tend to gunk up a bit sometimes and the lower oil pressure at idle in the M42 can make them noisey.
Or would it be too risky as the leaks I have could get worse?
Input?
THX:)

[JP 91iS]

JLewis is right, the typical problem going from conventional to synthetic is that it can make old leaks worse and initiate new leaks.  The synthetic oil has solvents that can clean out the years-old deposits left by conventional oil.

In my opinion any oil leaks are signs that the engine needs some repair, and if you want to keep the engine alive longer then the leaks should be addressed.  If you plan on keeping the car for a long time and are willing to dedicate time/money to repair the oil leaks then switch to synthetic. Otherwise if you just want to keep it in operable condition without the possible hassle of oil leaks then stick with conventional oil.