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Oil Change Time Interval

All the discussions of oil change interval focus only on mileage whereas the manuals tend to say 7,500 miles or 7.5 months, whichever comes first. This is what my 1997 Subaru manual says. I live in Houston, which can get very hot in certain months, and I work at home mostly, probably doing more in-city than highway driving. So I don’t use my car that much any more. It has 112,000 miles on it. I calculate that I normally drive about 850 miles in a 3-month period. Even to follow Car Talk’s 5,000 mile average rule for an oil change, I would only be doing it once every 1.5 years! Following the manual, every 26 months. How can I consider these facts in determining how often to change my oil.

Change Your Oil Every 7.5 Months As Directed By The Manufacturer.

You should consult the “severe service” maintenance schedule to see if the conditions under which you drive (or don’t drive) qualify. If so, follow the severe schedule.

Otherwise, I suggest a minimum of one oil change per year. You should never go longer than a year. That’s a MINIMUM. Once every 7.5 months certainly won’t hurt.

I did consult the manual on that and even asked Subaru, but those “severe” conditions are hard to evaluate or quantify. That’s why I mentioned in my original post that Houston has some very hot months (what’s the definition of “hot”?) and that I probably drive more in-city than freeway. Even on the freeway Houston is often stop and go. I always try to put several short errands together to save gas, but I don’t know if that means they don’t count as “short trips,” which are supposed to be bad. No particularly dusty or muddy roads (occasionally of course but not regularly since I’m in a big city) or towing or carrying heavy things on the luggage rack. How do you weigh all those things to come up with a time interval?

Houston has some very hot months Yea, but the engine is cooled to a set temperature even if it is zero or 100, unless it is triggering your car’s temperature warning. No need to worry about that. The short trips might qualify you, but frankly the hot temperatures will nullify the short trip problems by some extent.

I would stick with the 7.5 months and not worry.

“following the manual, every 26 months” - what about the “or 7.5 months, whichever comes first”? So manual would have you do it every 7.5 months. I might stretch it to 12 months, if there were some highway miles to heat things up, but that’s just me.

Let me clarify the first question. I meant that if I use ONLY my mileage to calculate, then I would be doing it only every 26 months. Since my mileage and the time interval are SO far apart, I didn’t know whether the “whichever comes first would apply,” especially since most mechanics, even the ones I trust, recommend every 3,000 miles or 3 months no matter what the manual says. What I am getting from these answers, though, is that 7.5 months would be GREAT and even once a year would be justifiable, given my driving habits and conditions. Am I right? Another website said that operating the car in “very hot” areas (no definition there) or using it for short trips in cold weather (no definition there either) would count as severe conditions. So short trips in hot weather–not a problem? But it is cold here some of the year, occasionally even below freezing–but not many days like that.

My Dallas miles are likely no different than your Houston miles, and I would do it somewhere in the 7.5-12 month range.

These oil change interval questions make me chuckle. What is hard to understand about 7,500 miles or 7.5 months? I just dont get the complexity that so many people have with when to change their oil.Or go with the mechanic you trust 3K or 3 months.

Only because Subaru customer service disagreed with the 7500 or 7.5 months when I told them my driving habits/conditions. And because oil changes are, for me, expensive and time-consuming. I would do them myself, as I used to do on my other cars, but hard as I try, I cannot get the drain plug loose on this car!

The “whichever comes first” applies, especially because they’re so far apart!

As Lion wrote, that is the reason they have that rule Miles or Months which ever is first! Don’t try to out think it, it is just that simple.

In YOUR case, I would change it every 3000 miles or 2 years, whichever happens first. I have several vehicles that accumulate few miles so I change the fairly clean oil every two years. My neighbor uses the oil in his truck, which needs an oil change every 60 days…he never shuts it off…