Correlation between Long OCI and Oil Leaks?

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Aug 30, 2004
Not long ago, I was talking to the BMW repair shop who recently did a PPI for me on an used car. During our conversation, they mentioned to me that most of the late model BMWs have a tendency to need gasket replacements (for repairing oil leaks) as they age. This did not surprise me since it is a stereotype that German cars leak oil. wink The first thought that came to mind is that BMWs (and other German makes) spec long oil change intervals (10-15k). Oil change intervals of that length usually means that any acids will remain in the oil for a long time. From some of the UOAs I've seen, TAN often exceeds TBN at the end of the drain. I wonder if the long length of time that the dirty, possibly acidic oil is in the crankcase contributes to early gasket failure. Or, if there may be other factors that link long oil change intervals with gasket failures. Anyone care to speculate? Just a random thought and would be curious to see what trends others have observed.
Originally Posted By: The Critic
Anyone care to speculate?
I'm thinking if the people are willing to varnish their engines by pushing the oil to 15,000 miles, they're not gonna care about their gaskets either.
I read that some virgin oils are detrimental to gaskets and seriously used up oils are too. So the best is to use an oil that is easy on gaskets when new and not use it for too long. Problem is knowing which oils are easy on gaskets when new.
Ive said it many times before... IMO, acid buffering in oils is like doing a titration in HS chemistry. Remember what happens to the indicator before getting to the equivalence point? First you dump a lot of fluid (Say youre doing an acid titration into a base), and nothing much happens. Youre mixing and youre just putting a lot of liquid into the flask. As you reach the equivalence point, what happens? The rate of neutralization becomes much slower due to mass transfer and available molecules to react. You can see it because all of a sudden, the color of the indicator starts showing up. It is slower and slower to go away when you stop adding fluid. All this time, there is still "active" material, i.e. there are molecules to buffer, it just happens slower. Eventually you hit an equivalence point. So if you are buffering slower, you are getting localized acidic zones which could well effect metals and/or gaskets. Now, is that the mechanism of gaskets going bad? I dont know. My 91 BMW doesnt leak any oil. My 82 MB does a bit, and my 81 MB doesnt leak any. IMO it is age and time at temperature that effect plasticizers, the connections and tightness of the sealing surfaces against the gasket, etc. IMO any 10, 20, 30 year old engine sourced from anywhere will leak somewhat, regardless. There is nothing wrong with going 15k on the right oil, especially if you verify it via UOA. If isnt a recipe for sludge or anything else. But people trying to save $5 and using the wrong oil, for too long, ignoring specs and requirements (including some garages that may do this) may well be a cause. Also, I think that euro cars tend to get a longer lifetime over which people care about them and look after this stuff. Your run of the mill US or Japanese car has one caring owner, a second who uses the car in the interrim of going after something better, then another who runs API SA in the car and wonders why it is "unreliable".
OK so why don't any of my cars leak oil? Nor any customers doing extend OCI's? I'm sure if someone didn't do their maintenance - which btw IS different than an extended OCI it may be hard on the seals. Your question is actually a loaded one because you did not distinguish between the two.
I run straight 5k mile OCIs, and the only time my A6 leaks oil is when the PCV system gets clogged up enough to increase internal pressure and blows out an oil seal(s). Otherwise the engine is dry.
It could be a manufacturer defect. BMW's, for example, are known to have electrical issues. This doesnt mean that every BMW has electrical problems or that the issue is caused from without rather than within. I do yearly OCI and haven't had a leak. I don't own any German cars but I bet these leaks are caused by bad maintenance and/or manufacturer flaws.
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