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Is it harmful to mix synthetic and natural motor oil?

(2003 BMW 530i)
in North Reading, MA on January 19, 2012
Have both 530i and 323ix. "fULL SERVE" attendant put 2 quarts of 10-30 natural in the 323 without asking. Will oit do any damage to the engine?
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Popular Answer
on January 20, 2012
NO, BUT If it was that low, you've likely exceeded the time factor or miles for the oil and it needs changed anyway. Unless you have a significant leak, I can't imagine being 2 qts low. If it were mine, I'd change it ASAP. I used syn-oil in my 1999 323i and it never leaked, but would use < 1 qt. by the time I changed at 10k miles intervals. KIA at 235k miles and still running great. My now newer 530xi does not loose a drop up to 8k miles between changes on BMW approved Syn-Oil with 68K miles on the odometer.
on January 20, 2012
Thx. Yes, it was due for a change --to synthetic, about 10K between changes -- 125K on the odo. Doesn't burn, but it uses oil. Similar situation with 160 hp aircraft engines I fly -- oil is really the lowest type of insurance. Thx.
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