Not just another engine oil question... OK, maybe it is

[gearhead]

Why do engine manufacturers recommend changing the oil every 3 months? How does the length of time that oil remains in an engine change the protective quality of that oil? I understand how quantitative hours ran on an engine can effect the overall quality of oil by consuming or contaminating the protective additives within, but does it really matter how long oil remains in an engine without it exceeding the recommended duty cycle? Unlike milk, there is not an expiration date on the container of oil purchased from the store, so why does the clock suddenly start to run when poured into the crankcase? Are not the total hours an engine runs more important than some seemingly arbitrary clock?

 

[FitZ6R]

I haven't seen a 3 month recommendation from a vehicle manufacturer.. 6 is typical. That said, "miles or months" intervals are based on the assumption that the vehicle is used periodically, and the fact that frequent, short trips are rougher on oil than prolonged running.

If a vehicle sits completely unused for those 6 months, I would agree that the oil is still good, but I might change it anyway for warranty purposes.

 

[dart1963]

Do some quick searches on "oil breakdown", it happens more when the oil is heated/cooled through normal use, but does happen just "sitting" around as well. Not sure of the 3 month reason, but whatever is recommended should be followed.
Also remember when you do change your oil, you never get 100% of the old oil out, so the nasty acid is reduced when you change it, but not eliminated.
Synthetics are better, they don't break down as fast, but it comes at the price premium.

 

[99vengeur]

Yes, the reason is oil decay or breakdown. I think if you look closely enough to a bottle of oil, you will find an "expiration" date, at least on some brands. I know when I changed my oil last, there was a "use by" or "expiration" date stamped on the bottle.

 

[JSP]

Thats one of the reasons you should do a fresh oil change right before storing your bike for the winter if you cant ride it for a couple months. Oil that has been used in the crank case will break down and start to sludge and start to pit the metal if it just sits there.

 

[vitrox]

just another reason to get good oil that doesn't build up the acidity as fast. amsoil is what I run in my race bike, and I won't run anything else. unfortunately it gets changed quite often and its 60 bucks every oil change (+ filter).