Full synthetic oil advice

I use full synthetic oil (non-name brand) and a Fram filter for synthetic oil.

My car has 109K miles.

At 7K miles, the oil looked pretty dirty, so I had it changed.

How long can I expect that oil to last?

Is Mobile One any better than the no name brands?

They claim 10K miles.

One person said he changes the filter midway.


In terms of odometer mileage or in terms of elapsed time?
If you pile up the miles slowly, with mostly local, short trip driving, you need to change it on the basis of elapsed time, rather than on the basis of odometer mileage. But, in either case the best answer to your question can be provided by the folks who designed and manufactured your mystery vehicle.

Either the Owner’s Manual or perhaps a separate Maintenance Schedule booklet will provide the answer that you need, and you should follow that guidance instead of what the manufacturer of MOBIL-1 has to say on the topic.


The manual only says to use 5w30 oil.

But nothing about synthetics which may not have been available in 2009 for my Mazda cx7.

That’s what you follow.

The manufacturer only cares about using the proper viscosity and changing it at the proper intervals.


Synthetics have been around many, many years.
The question is how long do you want to keep your car.
In the 80s had a 70 Pinto as a beater. Didn’t care about longevity, so put in synthetic and never changed it, did not care if it died. Whereas my ‘good’ car got changed according to the owners manual.

And how long did the Pinto last with no oil changes?

I sold it after three years. Unknown mileage, odometer was broken whenI bought it, 98000 miles. I did add oil as needed. But 30+ years later, I do not remember how often I added oil.
I would not recommend doing what I did. I was never more than a two miles from home with that car.

One other thing, I was in the high desert, humidity rare exceeded 10%, daytime temperatures would run 90-100 degrees, minimizing atmospheric water condensation in the oil.

Changing the engine oil & filter is probably the single best thing you can do for you car. Suggest to follow the manufacturer’s oil specs & change interval independent of whether it is synthetic or conventional. Unless there’s a reason (driving on dirt roads all the time, very dusty area, etc) I wouldn’t bother w/changing the filter separately from the oil. There’s no penalty at all (other than cost) to change the oil and filter more frequently than recommended. More frequent oil and filter changes will only help, never hurt. As for oil brand, choose one, then stick w/the same name-brand oil for the life of the car. For the filter, I’ve always had good luck w/Fram & MotorCraft filters. I’ve used other name brand filters too, with good results, but I’ve never used a no-name or off-brand cheapo filter.


What exactly does your owners manual say, miles and time between changes? I’d follow that using the full synthetic oil in the specified 5w-30.


While synthetic engine oil is not required it is highly recommended for a turbocharged engine.

The Mazda CX-7 maintenance schedule shows 4 months/5000 miles for severe service,
6 months/7500 miles for normal service.


Color isn’t necessarily the best indicator to go by. If you’re really interested in how your oil is holding up. Get oil analysis done. Blackstone Labs is a name that seems to get brought up most often.


Actually color is a very good indicator. While an oil analysis is probably more definitive - I also think it’s too expensive of a process. You can’t just get an analysis done one time…it needs to be done periodically over the life of the vehicle. Engine parameters change and thus oil life changes. It’d be cheaper (and better for the engine) to just change oil according to manufacturers recommendations. When engine is new the manufacturer recommendation may be too soon…but after 100k miles oil analysis you had at 5k miles says you can wait til 10k miles will now more and likely damage engine if left in that long.


Not always. Ever see how quickly oil will turn black in a diesel? Happens within hundreds of miles. On my old Mustang (the supercharged 03). I had analysis done about once a year. The oil I used religiously (Pennzoil Platinum), was according to Blackstone, good for 6000-7000 (total) after my typical OIC of 5000 miles, The oil always looked quite dark when I would send in the sample.

The OP isn’t talking about Diesel. Yes Diesel is different.

And I never spent the money on an oil analysis. I just changed every 5k miles. The standard oil analysis cost is equivalent to 1 oil change. To me it’s just not worth it. I know the 5k oil change interval keeps my vehicles running for hundreds of thousands of miles.

1 Like

You should do what Mazda recommends. Changing oil at 7000 miles is in line with Mazda’s recommendation of 7500 miles, and is fine. Before I had an Oil Life Monitor, I used the manufacturers recommendations, and never had problems. Three cars all had about 175,000 miles when I sold them, and the engines were in great shape. All three had change intervals of about 7500 miles, and I changed closer to 7000. As for oil, you can use mineral oil if Mazda doesn’t recommend synthetic. You can also save a bit by using semisynthetic oil instead of full synthetic. I used mineral oil in the three cars mentioned above.

I cannot agree with anyone or any article that says oil color doesn’t mean anything. It always does mean something. It just doesn’t always mean what you might think it means.

When oil changes color, something has changed within the oil. Only an oil analysis can tell you for sure what has changed, but I agree with those who say it is not worth the cost to the average motorist. If in doubt, change it.

“Looks dirty” is really subjective. Medium brown can be someone’s “very dirty” where another may not consider the oil dirty until it is thick, black and gritty. If you have ever put clean oil in a tin can and held it over a fire, you will see it gradually darken to a deep brown. If you leave it there long enough, you will end up with a black gritty substance.

Heat alone will cause oil to break down, but in a vehicles engine, the oil is not only subjected to a lot of heat, it also gets subjected to a lot of shearing action due to friction. Most modern engines are sealed against external contaminants such as dirt, but some could get in eventually.

Older engines also start getting a bit of “blowby” when the rings start to lose their seal with the cylinder walls and that increases the rate of oil breakdown.

So I go back to my original criteria for an oil change, if in doubt, change it. It will help you sleep better even IF the engine could have gone a few more miles on the existing oil.

1 Like

I agree with you. I am changing my oil about twice per year.

I drive about 12K miles per year with mostly short trips.

It uses one quart of oil for 10K miles.

I don’t feel that is too bad for a car with 109K miles.

I have been using a generic full synthetic, but will switch to Mobil One as I feel it is better quality and not that much of a price increase.


Use the cheapest oil you can find that meets your vehicles specifications.


1 Like