I'm back!

I had an 88 740 GLE normally aspirated b230f and it had 170k I thought it'd be good to run synthetic in it... it dropped my gas mileage 20% AND it burned a quart of oil in 3k miles... never used oil before. I switched back and after the next change all was back to normal.. now I did have a leak on the oil cap gasket where you add oil and there was some blow by on the valve cover... but not a quart and certainly would not have affected gas mileage. Just one persons story however illogical it may appear to an expert. (which I'm not.)

How could synthetic cause that kinda drop in gas mileage? I only run it in turbo cars where I've never had any noticeable change in performance or oil consumption but presumably the turbo will be less prone to oil coking up on the shaft.

It could cause a drop like that due to less effective sealing of the piston rings in an engine with some wear on it.

I'll agree that it's good to run synthetic in turbos.

Gary

This still doesn't completely answer the question as to whether I should run Synth in the '89 16valve. I would like to. I beleive it increased the mileage in the (nearly new) Subaru, and the 0w30 sure made cold weather starts easy.

RF

The only way to know for sure is to try it. Changing to synthetic won't kill the engine, but it may induce some minor leaks. Changing back to regular oil will get rid of most of those (synthetic will wash out crud that's built up around seals; until it builds back up, you'll have some leakage). If you do change to synthetic and want to stay with it, change the filter after 500-700 miles. If you change back, also change the filter.

Gary

It's worth trying if you want, personally I'd just stick with normal oil in anything but a turbo or other high performance engine.