As a follow-up to the previous oil question. Is it advisable to change to oil from conventional to synthetic on a car with 251k? even though synthetic may be better in a turbo? I have recently aquired an 89 745 Tic and the P.O. used Castrol GTX, and I was thinking of changing to Mobil 1, but we discussed that it may not be advisable to change an oil that has worked so well for so many years, any thoughts. What about changing from a fram to Mann filter with same oil. Thanks -

I changed my 700 turbo over to synthetic only to have it develop oil seepages at several places -- gaskets and seals I assume, although it was almost impossible to actually find the sources of the leaks. About 3 weeks later they mostly cleared up except for some minor seepage from the area of the oil return line from the turbo. As the weather gets warmer I'll start replacing seals, which are probably about due anyway, at about 160K miles.

I was pretty annoyed at myself when the oil leaks started, but I believe the extra life I (hope to) get out of the turbo makes synthetic worthwhile.


--
244, 855, 765t

I switched my 1st 740ti SE over right after buying it to Castrol Syntec (75K mi) in 1997. Around 85K mi I switched to Mobile One Synthetic and used that until it was totaled in 2000 (114K mi). It started to develop leaks 'everywhere' around 110K mi.

Switched my Blazer over when I bought it in 2001 (34K). It's had Mobile One synthetic & filter every 5000mi to 7500mi, no leaks or issues as of yet. Just hit 134K mi last week. I'm VERY surprised it hasn't leaked, especially being an American vehicle. I guess I switched early enough for it not to be an issue.

I still haven't decided if I'm going to do it with the 744ti SE I have now. I'm not sure when I'll get around to 'building the engine' I want, it could be in a few months or it could be in 4 years. When I do it, it'll get nothing but Mobile One Synthetic. Until then, I'll probably stick with the regular stuff for now. No need for leaks, and with gas prices the way they are I won't be racing for a while.

Rule of thumb I've heard is never switch after 50K miles (low) / 75K miles (high), if at all possible. At 251K miles, you're just asking for leaks galore if you switch over.

As far as the filter...if you switch to Mobile One synthetic oil, then buy the Mobile One synthetic filter. Anything is better than Fram though, but for synthetic you should use a filter designed for it.
--
MD ( 91 744ti SE w/M46 - 99K | 98 Chevy Blazer LT - 134K )

Synthetics handle the extra heat your turbos produces much better. Your turbocharger will thank you fo it.
--
Paul NW Indiana '89 740 Turbo 110,000

Definately change to the Mann filter. In your case, if you don't "race" your car, I would keep using dino based oil. Just make sure you change it regularly and never use heavy (40-50 weight) oils.

Klaus
--
98 V70Rawd(101Kmi), 95 854T(85K mi), 75 164E(173K mi)