Synthetic Oil

We’ve typically changed engine oil every 3,000 miles for many years, but began using synthetic oil (Mobil One) a couple of years ago. Shops still tend to want to change the synthetic oil every 5,000. Is this a reasonable interval, or how often SHOULD it be changed?

We have had many posts on this. Synthetic oil has basically the same additives (that fight rust, sludge, acids) as good regular oil, so for stop and go driving, cold starts, it won’t last much longer than regular oil until the additives are depleted.

Since all oils have improved significantly, the oil change interval can be stretched from what it used to be. Fuel injection and computer combustion control makes engines run much cleaner as well, so less oil contamination.

You did not tell us what your driving pattern is. Toyota now recommends 5000 miles for all types of driving, while others recommend 7500 for mainly highway drivng in good weather, and 3750 for normal city and commuter driving, which most of us do.

In summary, synthetic oil does not lengthen your oil drain interval; it is most effective for very hot, very cold, and heavy load (trailer towing) operation. If you are now using synthetic, like Mobil 1, 5000 miles is OK unless you only do stop and go city driving. In that case I would stick with the 3000 mile interval.

There will be other posters who will recommend longer drain intervals, but I am using the mileage that will give you the longest engine life without having to rebuild the engine before the rest of the car wears out.

You should have the oil changed at the mileage recommended by the maintenance schedule that came with the car. Shops recommend more frequent oil changes because they get paid to do them, not because they are necessary or beneficial.

Regardless of the type oil you use, don’t exceed the manufacturer’s oil change interval, and remember, the schedule probably has a both a mileage and a time limit. Don’t exceed either.

The only authority on on that subject is the manufacturer of your car. They took the time to write the instructions in the owner’s manual. Find that little book and follow the instructions there. Make sure you use oil that meets or exceeds the specifications in the owner’s manual and change the oil at the recommend (lesser of time or miles) specified for your kind of driving.

Engines and oils are far far different than the old days. You don’t need more frequent oil changes. Remember the shops will generally suggest more frequent changes than needed, after all that is where they are making their money.

Might I recommend the following, if you’re insanely curious and want to spend a little money finding out.

Send an oil sample of used oil, after a mileage you feel comfortable with to Blackstone Labs ( They’ll tell you what’s really going on with your oil.

Here’s a sample from my '06 Honda Pilot after approx 6700 miles on the same oil:

Their recommendation is to try 7500 miles. This is fairly conservative of them, however.

My other car, an '03 VW Passat, has these results:

Their recommendation is that I can easily do 10,000 miles.

Since they’re actually a lab, I trust their recommendation over any non-scientific “rule of thumb.” I have a little rig set up for suctioning the 3 or so ounces of oil they need through the dipstick tube, so no need to drain my oil to send a sample.

Cheers to Constantino for the correct answer. The only way to determine the optimum oil change interval for your car, oil, and driving conditions is by used oil analysis. It also can provide early warning on several serious engine problems.

Blackstone is a fine lab, but they are not the only ones so choose as you will.


SYNTHETIC RULES.10k between changes,Honda element city driving.depends on your vehicle as in vw pcv system is horrible,so case by case.

thats it.

A good synthetic oil like Mobil one or Pennzoil Platinum will last a lot longer than regular oil does, BUT that does not mean that you should go longer between oil changes. It all depends on which oil FILTER you’re using with the synthetic oil. If it’s a cheap walmart fram filter then you should change your oil VERY often - regardless of what oil you’re using. However, if you are using a good filter like one from K&N or Mobil One, then you could certainly go a lot longer between oil changes.

I’ve been using Mobil-1 for years. An oil analysis is the best way to tell how much life you have left. Oil won’t last as long in extreme conditions, or in very cold weather, where it may not routinely get warm enough in stop-and-go driving to cook off condensation and other impurities. Plus in cold weather (and depending on the condition of your engine), it will be more contaminated by blow by. If your car uses a little oil, the quart or so you add will extend the life of the oil too.

But basically I just change mine at about 6,000 miles instead of 3,000. My oil probably has some life left in it at that point, but since synthetic costs about twice as much as good dino oil, I figure it works out to the same cost as using dino oil that way.

It all depends on which oil FILTER you’re using with the synthetic oil. If it’s a cheap walmart fram filter

While there seems to be plenty of evidence that Fram filters are cheaply made, I have yet to see any evidence that they fail more often or filter less effectively than other filters.  All this anti-Fram stuff comes from backyard mechanics who hacksaw filters apart and make their judgments from what they see.  I have yet to see any comprehensive study of real life (or even lab) results.  

If you can reference some real, valid, verifiable test to support the anti-Fram club, I would like to see it.  

If anyone feels better about not buying Fram, that is fine.  I agree they look flimsy, but please make sure that everyone understands the bases for your Fram opinion.

If you have any warranty in effect, you can’t go longer than the manufacturer’s stated change interval. If out of warranty, you can either keep to the manufacturer’s interval, or, with the help of the oil analyses described above, go to a reasonably longer interval.