Manufacturers will have different recommended intervals if they have free service packages. I believe that there can be variations depending on various factors, but the range between manufacturers is pretty crazy.
For example, BMW claims that their differential oil and fuel filters are "lifetime" and never need changing, which is ridiculous. Their oil intervals are 15k, which is way too long for my liking, and we do it at 7.5k instead.
I like my engines running forever, so I've always done 3k oil changes for normal oil. 5k-6k for synthetic
I got it for 15,796 OTD. Thanks guys.
Pics to come, need to get home and get the horse head.
I have a hard time believing your mother drove a car to 80k without changing the oil because this is what happens (not for the squeamish..):
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Congrats man!
And Serra is right. No way it runs for 80k on the same four quarts of oil. I was an ASE certified machinist, and those video are accurate, that's what it looks like when people try to do that lol.