Synthetic oil



I have a couple of cars that don’t get a lot of use. One’s a sedan (Mazda 1997 626LX 4 cylinder) I drive less than 2000 miles/year and the other’s a Chrysler Town and Country 1983 mini-wagon I drive around 200 miles/year, used for the occasional hauling expedition.

My mechanic tells me I can get by without changing my oil for much longer if I use synthetic oil. Since I never log enough miles to change at 5000 miles, or similar mileage standard, the concern would seem to be that the oil would break down and lose its effectiveness. The theory here is that synthetic oil will retain its effectiveness in a little used vehicle much longer than regular engine oil.

Assuming this is true, how long can I go between oil changes in these cars (driven in mild conditions in coastal California), between oil changes?


Forgot to mention, mileage on these cars is:

Mazda: 19,000
Chrysler: 119,000


Synthetic offers no benefit over mineral oil in vehicles that see little use. Either type of motor oil is VERY stable and can be used as long as, say, 3 years, without any problems. The oil in your gear-boxes is probably mineral oil and in most cases, it’s there for “the life of the vehicle”. It does not “break down”. When it begins to LOOK dirty or discolored, change it.


You should be OK with conventional oil. Our GM car has an oil change countdown calculator that counts engine revolutions and cold starts for more than hot starts. It shakes out to about 6000 miles to change for our driving habits but the owner’s manual says to change once per year in any case.


While you may get some benefits from switching to synthetic, I don’t buy the advice you got. You might be able to extend the mileage between changes, but synthetic does not really help you when the changes are being done based on time.

Maybe you will get 0.08 mpg improvement.


Personally, I wouldn’t go over one year with any type of oil, regardless of mileage, check your owners manual for the recommended time duration for your car. Synthetic is not likely to be cost effective if you change your oil based on time, not mileage. Synthetic is helpful in cold weather starting, if that’s an issue where you live.

BTW, I would also change these other “life of the vehicle” fluids at some reasonable interval (maybe 50K miles). From the vehicle manufacturer’s point of view, “life of the vehicle” really means “life of the warrantee.”


OKAY, let us assume that when you do start these vehicles you run them at least 10 miles or so to heat them up and burn off water etc so you are not creating problems. Based uon my 6 plus years now of less then 3000 miles per year on one vehicle you can go at least a year with synthetics, probably 2 with no problems. I have done analysis on the oil multiple times after annual oil changes and the oil remains fine for continued use. Now, if you lived in Maine and drove that vehicle 3 miles and stopped it then yes, very frequent changes. I have gone 13 months and gradually increasing the time, the oil (contrary to popular opinion here) does not build up contaminants etc if it is heated up and driven properly once it is started. Short trips are killers!


Maybe true, but what’s the point? An oil change costs less than $50, even with synthetic, so we are talking about $.10 per day over a year (probably $.05 if you use conventional oil).


Your mechanic is wrong. There are two reasons to change oil. One is to remove break-down byproducts of the heat accumulated from miles of driving (not your problem, apparently). The other is to replace worn out additives that neutralize acids and moisture (a bigger problem for short-trippers). Synthetic oil contains no more additives than mineral oil. It does resist thermal breakdown a bit better and is a slightly better lubricant in terms of friction.

My personal opinion is to pick one oil weight and one brand and stick with it. Changing the lubricating properties of an oil can affect engine clearances and engine life. Only when an engine is wearing out and beginning to use excessive amounts of oil should you bump up the viscosity a notch.