Switch to synthetic on high-mileage engine --> leaking?

Messages
263
Location
LA, CA
I have a 1989 BMW 325is with 123K miles that has been running dino 20w50 oil for the past few years. I'm thinking about switching to Mobil 1 15w50 as many others have, but lots of people claim that this switch can lead to oil leaks do to the different composition of synthetic oil. Synthetic oil supposedly undos some of the seals that the thick, old dino oil has formed. What are your experiences or thoughts on this?
 
Messages
47,770
Location
Everson WA - Pacific NW USA
123K miles? The thing maybe is broken in....but certain not "high mileage". If it doesn't leak now, it won't leak with synthetic. If it leaks now, it will leak faster with synthetic. 20W-50 dino? Can I recommend AutoRx before the switch?
 
Messages
7,077
Location
Ontario, Canada
Every engine , but one, that I've switched to synthetic has started leaking. But the leaks stopped after about 500 miles. Even my B&S 3.75hp lawnmower's main seal under the deck seeps oil when I use synthetic (Mobil 1 truck and SUV right now).
 

DaveInLA

Thread starter
Messages
263
Location
LA, CA
quote:
Originally posted by Pablo: 20W-50 dino? Can I recommend AutoRx before the switch?
What's AutoRx? Anyway, I'm thinking about switching to synthetic because I only put 3-4K on the car per year, and want to go longer than a few months between oil changes. Last time I waited about 1500 miles and 4 months, and the oil was pretty dark. Also, I've heard that synthetic oil makes the engine run smoother.
 

GSV

Messages
696
Location
Utah
A quality synthetic will not cause leaking. They just find the existing leak (or gap/mismatch). [Cheers!] [Patriot]
 
Messages
13,132
Location
By Detroit
quote:
Originally posted by TC: Some basic info here on switching to/from synthetic oils: http://www.quakerstate.com/pages/carcare/whattoknow.asp
I was going to run the free Synpower in my wife's Aerostar 3.0 V6 (1992), which has 102,000 miles. Valvoline techs told me not to because of the high mileage it might leak. But this Quaker State sites says it will only leak if it already is leaking. The Aerostar does not drip any oil on the pavement where it parks, but like all engines, I expect there is buildup around the seams. Perhaps those would start to seep more. Anyway, I think I will use the Synpower and see what happens. If it leaks, well, I have a case of Maxlife I can run in it next.
 
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