Without starting an oil brand/filter brand war here....

My '03 Ranger is basically just a weekend driver and sometimes goes 2 weeks without being driven, sits in the garage a lot. Currently has 61,900 miles on it. I bought it last Sept with 57k miles and even though the oil had been changed at the dealer I bought it from, I switched it over to my favorite Mobil 1 synthetic/motorcraft filter soon after. Thats been in there for about a year and is still relatively clean and looks fine. Wondering if I should just change it yearly (like now) even though it's under mileage or just realize the oil is in a more expensive container (the truck) and it's fine? I'm leaning towards once a year changes since I'm sure moisture can build up in the oil over a year but could be just a waste of money. What do you think? Our Walmart has the 5qt jugs of Mobil 1 for pretty cheap and the Motorcraft filters in stock so once a year is less than $40....no sweat.

 

Keep stable in the gas and check the oil before you drive it. If it looks milky then you got water, otherwise yearly or by mileage it should not matter.

 

Conventional engine oil degrades (loses viscosity) with both time and mileage. You should change it whenever you hit either the mileage or time limit in your car's owners manual.

On the other hand, synthetic engine oil is much more stable and as a result has a longer life. So I see no problem changing synthetic oil only once a year if you don't go over the mileage.

You are correct with regard to moisture buildup if you only drive short distances.