Engine Oil Life

[SeldomSeen]

This is probably a dumb question but... Oil and filter change intervals are always stated as mileage and a time limit for example: "3000 miles or six months whichever comes first." My MGB oil has been in the car for less than 2000 miles but it's been two years since it was last changed. Does oil have a shelf life once it's in the car? Why the time limit? Should I change the oil or not?

[124JOE]

when in dout

[wikkid]

Oil is pretty much fine, but short runs without letting an engine warm up fully, especially combined with long term sits without running, can allow water vapor to condense in the oil, which can lead to rust, as well as white sploogey oil, where the water and oil mix and emulsify (yuck). So it depends on storage and use habits.

[AndyS]

most car collectors I know change the oil at least once a year even if the car was only driven a few hundred miles. I know of a case where an expensive Alfa Romeo engine sustained bearing damage from leaving very low miles oil in there for several years. A yearly oil change is cheap insurance.

[TX82FIAT]

I think it also depends on how hard you drive it when you drive it. Last weekend I did several hard laps around a tight track in third or fourth gear where the tac was averaging around 6000 RPM's. If you drive her hard then I would replace the engine oil annually at a min. I'm changing my oil this weekend at about 2000 miles because of the track day last weekend.

[SeldomSeen]

Thanks all. I live five miles from Lyons,CO, the nearest town. So each time I take a car out it is at least a ten mile exercise. The other most common ride is a thirty-seven mile round trip uphill to Estes Park. I think the "once every Spring" idea sounds about right.

[131]

Some byproducts of the combustion process are dissolved in the oil, over time the oil can become mildly corrosive. I've stripped engines where the old oil was left in them, the main and big end bearings, despite being coated in oil, had holes etched into them as if they'd been put in acid. My car runs on LPG so it doesn't get the black carbon suspended in it that turns oil black, even after 10,000kms the oil is not far off the honey colour of new oil, but it still requires replacement.

[AndyS]

Some byproducts of the combustion process are dissolved in the oil, over time the oil can become mildly corrosive. I've stripped engines where the old oil was left in them, the main and big end bearings, despite being coated in oil, had holes etched into them as if they'd been put in acid

This is exactly what happened to one of my customer's Alfa Gullia Spider engine. An expensive rebuild had been done on the engine, he put some miles on it, got busy , and stored the car away for some time without changing the oil first. when he started driving it again later, it staring making some scary noises. tear down later showed a lot of corrosive damage.

[Kent124]

This is probably a dumb question but...

From the answers, it seems like an excellent question. Corrosiveness of old oil was not something I was aware of. Thanks for the questions it enlightened me.