Question for automotive experts

[Ed62]

I don't drive much anymore, but I try to keep my car in shape. The oil is typically changed at the 3 month period, but it's not uncommon for me to have driven 1,500 - 2,000 miles since the last change. Probably 75% of my driving is for trips less than 10 miles. 3,000 miles or 3 months between changes is recommended. But what if I only drive half the amount of miles? What happens to the oil to make a recommendation of 3 months maximun between changes? If I drive it for 5 months, and 3,000 miles, is that detrimental?

Ed

[sacherjj]

I'm now driving a good bit over 3k per 3 months. I usually wait until 4k or 5k to change, but use a high mileage synthetic. My 96 Maxima is going great, just flipping to 250k miles. Everything in the engine is original, except one change of the timing chain. If I am on a road trip, I will let it go 6k miles, if those are run up in under two weeks. But, I'm no expert, I've just had cars that I run until they fall apart, well after 300k miles.

If I were driving very short drives to make up those low mileage 3 months, I would go ahead and change the oil. If you don't sufficiently warm up the motor and oil, it can be hard on the motor. I don't drive the truck often, but when I do it is for a decent amount of time. It might go 6 months before 3k miles and don't bother changing the oil until those 6 months.

[LCHIEN]

I'm now driving a good bit over 3k per 3 months. I usually wait until 4k or 5k to change, but use a high mileage synthetic. My 96 Maxima is going great, just flipping to 250k miles. Everything in the engine is original, except one change of the timing chain. If I am on a road trip, I will let it go 6k miles, if those are run up in under two weeks. But, I'm no expert, I've just had cars that I run until they fall apart, well after 300k miles.

If I were driving very short drives to make up those low mileage 3 months, I would go ahead and change the oil. If you don't sufficiently warm up the motor and oil, it can be hard on the motor. I don't drive the truck often, but when I do it is for a decent amount of time. It might go 6 months before 3k miles and don't bother changing the oil until those 6 months.

Most manufacturers now state 7500 miles between changes for normal driving and 3700 for tough driving including towing trailers, idling in heavy traffic a lot etc. like taxi cabs and police cars.

only your oil change centers are telling you 3000 miles between changes.

Myth: Engine oil should be changed every 3,000 miles.

Reality: Although oil companies and quick-lube shops like to promote this idea, it's usually not necessary. Go by the recommended oil-change schedule in your vehicle's owner's manual. Most vehicles driven under normal conditions can go 7,500 miles or more between oil changes. Some models now come with a monitoring system that alerts the driver when the oil needs changing. Depending on driving conditions, these can extend change intervals to 10,000 or 15,000 miles.

Why oil needs changing (my understanding):
2 main reasons -
1) the oil breaks down with temperature and age, it's viscosity is reduced and won't coat the surfaces its supposed to protect
2) the oil gets contaminated with chemical stowaways in gasoline, like sulfur oxides and nitrous oxides, and over time creates acidic content in the oil (sulfuric and nitric acids) with the combustion byproducts (H2O) which is not good for the cyliders, pistons and seals.

I drive about 9-10K miles per year, I try and change my oil every 6 months.
Changing your oil more frequently as Consumer Reports indicated is a waste of time and money. Even if it did make your car's engine last 200K instead of 120K miles, are you going to keep it that long when you only drive 10K or less a year?

[Ed62]

Thanks for the replies. I thought it was just a way to make an extra dollar for the oil change places and the oil manufacturers. Guess I'll be waiting a little longer between changes. I have a '97 LeSabre with 72,500 miles on it. If I can get 200K, that should give me another...let's see.....18 years or so.

Ed

[mpc]

Besides contaminates from the gas, the other big contaminate in engine oil is water vapor. Outside air gets into your engine via the PCV (Positive Crankcase Ventilation) system. Any humidity/moisture in that air can condense into the oil. Short trips that don't fully heat up the engine are the worst for this - the water never evaporates enough to get sucked out of the crankcase via the PCV valve. So lots of short, don't-warm-it-up drives, can contaminate the oil quickly this way...that's where the "3 months" generally comes from. It's more of an issue in humid areas of course. As long as the engine is fully warmed up and driven for a few minutes once a month it won't be a big issue.

One of my cars (the only one I ever bought new) sometimes gets less than 1000 miles a year on it... and it too is a "3 month/3000 mile" change interval from the factory since it's a turbocharged engine. I run Mobil 1 and generally change it once a year - basically when I think "jeez... I can't remember the last time I changed the oil in this thing... wonder how long it's been?" And find out it's been 11-12 months and 700 to 1000 miles. My daily driver gets changed whever the odometer reads a multiple of 5000 miles regardless of time; that generally equates to about twice a year. I don't drive much. At 220K miles, I pulled that engine to rebuild it - it was running fine but I figured "why not" before it threw a rod or anything. It was 20+ years old. The bearing wear was not bad at all and there were no signs of oil related damage anywhere. The daily driver was an east coast car for the first 150K miles of its life too; now it's a SoCal car where humidity isn't an issue. Do you change the oil filter every oil change or every other time - some car makers suggest the latter. I always change my filters with every oil change regardless.

So as long as you use a quality oil... I wouldn't worry too much about the 3 month criteria. Just make an effort to drive the car for 20+ minutes once a month and don't worry about it.

Over the road truckers have been using mail-in centers and recent electronic gizmos to test their oil... just take a sample from the crankcase and have it analyzed. Most find they can go MUCH longer before the oil contamination reaches levels even remotely questionable. Some diesel RV owners are doing this now too. Dad is doing it with his RV; at the "recommended" oil change interval his oil tested at something like only 10% of the "needs to be changed" status - i.e. from brand new to needs to be changed, he was 10% degraded from brand new and had 90% more to go before changing was needed. Wow.

mpc

[parnelli]

Most manufacturers now state 7500 miles between changes for normal driving and 3700 for tough driving including towing trailers, idling in heavy traffic a lot etc. like taxi cabs and police cars.

only your oil change centers are telling you 3000 miles between changes.

Agreed, but if I'm not going to trust the oil refiners, why would I trust the auto manufactuers if they say 7500 or 3700?

They have zero interest in my car living anything past the warranty period.