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#1585030 - 08/31/09 09:09 PM Oil change interval: time vs. mileage, low mileage
Lightsilver Offline

Registered: 04/15/08
Posts: 36
Loc: Midwest, USA
The conventional wisdom is to change the oil every six months normally, and up to a year on a high quality synthetic.

I'm curious: why the change interval at six months?

The reason I ask is that my elderly mother only drives her 1999 Olds Cutlass, (with 52K on it), less than 100 miles a week, the past few years.

The dealership had her convinced to change the oil every 3 months, so she was changing the oil with less than 1200 miles on it.

I told her to change it at 3000 miles. Depending on how much she drives, she could easily exceed 6 months.

I figured that while her car is sitting in her garage, (which it does, several days every week) the oil isn't breaking down...or is it?

I do have her 'trained' to take her car out on the freeway, and drive it for about 5 to 7 miles, rather than just driving the 1 mile to church, or the library, etc., and back. So, she's not doing too much 'short trip' driving. She really doesn't understand why, but she does it.

I check her oil, and it is still quite 'clean' looking, on the dipstick, and on a white paper towel, at around 3000 miles.

I do not know what brand of oil the dealership is using; I'm sure it's dino oil.

So what's the 'conventional' wisdom for dino oil: change at less than 3000 miles, if the time exceeds 6 months?


#1585046 - 08/31/09 09:21 PM Re: Oil change interval: time vs. mileage, low mileage [Re: Lightsilver]
Gary Allan Offline

Registered: 09/28/02
Posts: 39806
Loc: Pottstown, PA
Time (years) will destroy that car before anything else. Most of the OEM recommendations are for daily drivers. I wouldn't go to the trouble of doing the highway thing. It's just spending money on gas.

I really don't see a reason why 2500/6months would be too long.

#1585058 - 08/31/09 09:28 PM Re: Oil change interval: time vs. mileage, low mileage [Re: Lightsilver]
Corvette Owner Offline

Registered: 01/22/03
Posts: 1676
Loc: Waldorf, Maryland
The 1 mile drive is the worst scenario for oil. Short drives, where the oil temperature does not get high enough to "burn off" moisture will wear down oil (through acids), dilute it, and increase engine wear.

It would be interesting to do a TBN (and used oil analysis) on your mother's car's oil. That is really the only way of knowing what condition the oil is in.

Generally, it is accepted that dino oil is good for 6 months and 5,000 miles. Synthetic oil is good for 1 year and 7,500 miles. That is conservative, you can add 2,500 miles to those figures for "good oil".
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#1585130 - 08/31/09 10:14 PM Re: Oil change interval: time vs. mileage, low mileage [Re: Corvette Owner]
daves87rs Offline

Registered: 02/23/09
Posts: 14938
Loc: Michigan
When I've parked my other Cav for weather's sake (it was a nasty winter), I maybe drove it 100 miles in nearly three months. When the weather was decent, I took it for long drives to warm it up good.

I plan on driving it more this winter (weather permitting), and keeping the Napa syn in there until early spring. (about 10 months) It might change if I drive it more....
“Never argue with an idiot. They bring you down to their level and beat you with experience.”