There is no quantitive data at all to change your oil at two or three years old based on time in the box.
The only real worry is the additives coming out of solution but if the car is driven every summer that will not happen.
The oil blenders suggest a shelf life of 5 years for oil. There is no data been published to back this figure up just a good rule of thumb to quote when the question of how long will the oil last is asked.
With regards to mileage the quantative data suggest that the diff is worse for iron in parts per million followed by the gearbox.
From those used oil analysis of gearboxes I have read the ppm of iron is getting to 100 ppm after say 20,000 or 30,000 miles. I have seen diffs at 400 ppm by tht time.
I'm just about to get our Jeep, Impreza and MX5 gearbox oils analysied and it will be interesting to see tha results.
30,000 miles for a gearbox seems a good number to me at the moment to keep this near 100 ppm but to be honest I know of cars with 100,000 miles and no gearbox or diff oil change.
eddie
Last edited by Eddie Cairns; 30/12/14 04:36 PM.
