Different Oils for different seasons


Hey everyone, I’ve got a question. In my car manual (which I don’t have on me at this moment to refer to), I’ve noticed that the manufacturer had recommended two types of oil which are 5-30 and I believe 10-40 for different temperature bands.

For example it would say something along the lines of:

-30 degrees - 90 degrees 5-30

5 degrees - 105 degrees 10-40

This is a 1999 Kia Sephia with about 103,000 miles on it, located in Buffalo, NY.

I was wondering for my next oil change since it’ll be about a few months before winter hits, if I should change to the engine oil for higher temperature ranges or does this not matter?

I’ll post up more accurate details about the oil weights and the temperatures once I get a hold of the manual again, but is this something common, and is this something that really makes a difference?



Stick with the 5-30 oil all year round. There’s no need to change with the seasons.


For those of us who live in the Southern states, it has always been traditional to switch to a heavier oil for the hottest months. You live in Buffalo so you only need worry about winter. You can stick with 5W-30 year-'round. No problem with using 10W-40 in summer, however. Your choice.


Is Buffalo really expected to have any extended over 90 degree weather? It looks to me like from 30 below to 90 above is pretty much all season coverage.


With today’s oils you normally should not need to switch oils for the season. Back in the 60’s oils were not as good and “all season” oils had problems. Today, assuming you follow the recommendations in the car’s owner’s manual, you should not have any problems or need to use different oils.

For those in extreme conditions (central Alaska, or upper Canada) you may want to adjust a little.  Even those in the southern US don't need a change.


With todays low additive, EPA approved “Cat Safe” motor oils, you might want to investigate using the 15w-40 “diesel” oil in the summer. This high additive, high protection level oil also meets SH, SG, SL gasoline engine requirements. It’s also known as “Universal Fleet Oil” and offers the BEST engine protection under extreme conditions. It’s a little heavy for small engines in the winter months…


stay with the 5w30 YEAR round. Also, oils have improved 100% OR MOrE SINCE THE 1990 car was built. a 5W30 will easily suffice year round


I remember a book by Tom McCahill that came out in the early 1960’s titled “What You Should Know About Cars”. Tom had no use for multi-viscosity oils. He thought that 10W-30 was “a lousy number 10 and a lousy number 30”. He also didn’t like detergent oils. “I prefer soap in my bathtub, not in my crankcase”. You are correct that oils have really improved since the 1960s. Even in this time period, though, I found it a real pain to run 10 weight in the middle of the winter, 20 weight in the spring and fall and 30 weight in the summer, so I switched to 10W-30 at about 120,000 miles and nothing disasterous happened to the engine in my 1954 Buick. I sold the car with 160,000 miles on the car and no major work to the engine and it was still on the streets a couple years later.


You should follow the ranges in the manual with regard to the temperature extremes. Based on your example, I would use a xW40 for temperatures over 90F and a 5Wx for temperatures below 5F.

My old benz has a similar set of oil requirements based on temperature ranges. Fortunately, current synthetic oils cover a wider range of viscosities in a single oil. In the case of my car, a 5W40 synthetic (diesel rated) covers the full range of recommendations in the manual, so I use it year around.

FWIW, the Mobil website recommends various 5W30 oils for your car:



Stick with the 5W-30. Those few months before winter that you’re referring to could easily be scorchers and you don’t want to be driving around with thin oil.


Whoops, I meant the 10W. Stick with the 10W.


In 90 degree temps the 5W30 and 10W30 have the same viscocity. At 10 degrees the 5W should flow slightly better.

really discussing tiny degrees here, todays 5W30 will easily go year round


True, at 100 degrees both 5W-30 and 10W-30 will have the same viscosity as a straight 30 weight oil. However, his owner’s manual recommendation was for 10W-40, not 10W-30. At 100 degrees 5W-30 will have a viscosity equivalent to a 30 weight oil…10W-40 will have the viscosity of a 40 weight oil at 100 degrees.

I have to agree that both would be fine in this case, since we’re talking Buffalo and not Tupalo.

For a good primer on oils I suggest www.cabibles.com to all who are following along.


You are right to rely on the owners manual to guide your decision. Have you found it yet?

The one seasonally-adjusted oil decision I have made here in Duluth-Superior MN-WI is to use Mobil 1 in the winter, for better lubrication upon startup on the occasional well-below-zero days.

Since 5W30 is what the manual suggests for my Civic and the temperatures encountered, I use that grade always.

The Mobil 1 in winter is probably not likely to do anything to improve the car’s longevity overall, but I just feel better using it in extreme cold.


True, at 100 degrees both 5W-30 and 10W-30 will have the same viscosity as a straight 30 weight oil. However, his owner’s manual recommendation was for 10W-40, not 10W-30. At 100 degrees 5W-30 will have a viscosity equivalent to a 30 weight oil…10W-40 will have the viscosity of a 40 weight oil at 100 degrees.

How often do you think it gets ABOVE 100 in Buffalo?? MAYBE 2-3 times every 10 years.


Granted it rarely reaches 100 degrees in buffalo, what I would suspect and I may not be explaining this pretty well but I would suspect that if an oil has a range of lets say 20-100 degrees or whatever I probably would not be most efficient towards the extremes of those temperature ranges, and lets say it is 85 degrees. If you have two choices of motor oils with temperature ranges of 0-90 and 30-120. Even though both motor oils on paper seem to work sufficiently well at the 85 degree day I would suspect that the 30-120 may provide better engine protection since it is not approaching the extremes of the temperature range.

I will post back with the exact information in my car manual when I have the chance, my car was in the shop until yesterday to have the right CV changed and to figure out what was wrong with a possessed brake light. Now that I have it back I’ll post up the information as soon as I get off work.

Maybe I’m getting a little to involved in this temperature range thing and maybe over complicating things and over thinking things but I was just curious what other people’s thoughts are.



This may be a shocker and a bit odd but the temperature ranges given in my manual are:

-30 to 35 degrees F use 5W-30

-15 to 90 degrees F use 10W-30

I guess I have been putting the wrong motor oil in my car the whole time (5W-30) I guess I should be putting 10W-30 year round.



That’s a little strange, I don’t see much downside to using 5W30 all year because 5W30 and 10W30 should act the same at higher temperatures. However, I would still follow the manufacturer’s recommendations.