Switching oil viscosities


I have a 2000 Toyota Tacoma truck. The oil filler cap calls for 5W-30, but the owners manual shows that 10W-30 is okay for use in temperatures above 0 degrees. Here in NC it only drops below 0 degrees in Jan/Feb so I typically run 5W-30 only during the coldest winter months and 10W-30 the rest of the time.

Is there any harm in switching viscosities like this, from winter to summer? Just really curious if I should stay with the same viscosity year around. Thanks.


5W30 will give all the protection your engine needs, promote quicker oil flow at cold-start, and perhaps slightly increase fuel mileage. Why do you think you need a “thicker” oil?


I would switch and there is no harm in doing that. You can even mix viscosities. A higher viscosity oil to a point will provide more engine protection in warm weather and I can guess that it gets pretty warm where you live. Oil can have too high a viscosity but not 10W-30. 20W-50 is too thick for for almost anything but some motorcycles.


No harm at all to switch. Your plan is quite acceptable for your NC climate.


Go with the thicker oil in the heat. You won’t be sorry.


5W30 and 10W30 have identical viscosity in hot conditions. Where they differ is in their viscosity in cold weather.

The “W” and the number preceding the “W” indicates the oil’s viscosity in winter-like temperatures, and the final number indicates the oil’s viscosity when operating in summer-like temperatures. Thus, they have the same viscosity in the warmer months.

In other words, 10W30 does not provide any additional “protection” during the summer. Car manufacturers do extensive testing in order to determine what grade of oil is best all around, and that takes gas mileage into consideration, as well as engine protection. If I were you, I would stick with 5W30 year-round. But, if you wish to switch viscosities, it will not harm the engine.


The only down side to the 5W30 is the fact that there are more addatives than the 10w30 which means less oil. In the old days this was a bit of a problem, but modern formulas have greatly reduced this issue. Synthetic 5w30 oils are superior in all ways to standard 10W30’a


Thank you, VDCdriver, for pointing this out. There is NO DIFFERENCE between 5W30 and 10W30 in hot weather.


I?m not sure that?s actually the case. Few oils get thicker as they get hot. My understanding was that the first number is the viscosity and the second number the protection. In other words, 5W-30 is a 5-weight motor oil that provides the same protection as standard 30-weight motor oil.

So 5W-30 and 10W-30 provide the same protection as 30-weight oil but the 5W is a thinner or lower viscosity.

I could certainly be wrong here, but there does seem to be a noticeable difference in the thickness of the two even to the naked eye.


I agree with MOST of what you said. One point that I’d like to make is that 10w-30 has less additives then 5w-30. Oil is a far better lubricant then the additives are.


You’re right. 5 weight and 10 weight oils are different base weights.

www.carbibles.com has a good primer on oils. I recommend a visit.


That may be true when oil is new but as oil is subject to shear during use, the warm viscosity decreases. I’d still feel more comfortable with the 10W30.