You’re not getting it.
15W-40 oil means the oil has a winter weight of 15. This is true at 90 degrees or at 35 degrees. It’s not until the temperature reaches 0 degrees does the oil begin to thicken up.
Tester
I agree that thicker oil should normally help and is worth a try. I need to keep at least two quarts of 15W-40 oil plus the remainder being 10W-30 or 10W-40 in my old VW diesel to keep consumption to less than a quart between oil changes at 3333 miles. Cold starts with thicker oil should certainly present no lubrication problem in warm weather or if a block heater or a radiator hose heater is used due to residual oil on internal engine parts.
In the bad old days with carburetors, there was a notable difference in cold weather starter speed when using 10W-30 or 10W-40 as a practical matter even though both are 10W on the low end of the specification. I live in a northern state just below Canada and have experienced really cold weather.
In very cold weather with no block heater it would be prudent to keep engine revs down until a little warming is done. If the engine starts with 10W-40, it will be ok. You don’t need to use all 10W-40 or 15W-40. It’s ok to mix it with a lighter grade and another brand of oil. I have been doing this for many years with no apparent problem.
By the way Mr. Tester, my diesel has a cold start knob that changes the injection timing to moderately raise the idle speed.
Paragraphs 9 through 12…
So basically what that report says is, if you use the wrong viscocity oil for the application, you’ll wear the component out. Right?
Tester
No, it says viscosity is dependent on temperature and different grades flow at different rates. In Chart #2, you will see difference between 0 grade and 15 grade is not great enough to cause a wear problem in an engine that is already suffering from excessive wear…I agree completely that using the manufacturers recommended grade of motor oil is usually the best idea…But when operating in extreme conditions, heat, cold, or an internal mechanical problem (worn parts) sometimes it’s helpful to adjust oil viscosity to compensate for those conditions…
Let’s see if I can make this simple for you.
When you have a bottle of oil that’s states that it’s 5W-30 oil or a 15W-40 oil, the winter weight of the oil is as thin as it’s going to get. That’s why it has 5W or the 15W rating. So if it’s sitting on the shelf in the bottle or in the engine at any temperature above zero degrees, that’s the weight of the oil at ambient temperature. It’s not until the oil reaches a hot engine component where it converts from the winter weight to operational weight. Or the 30-40 rating
This is why all oils recommended on new vehicles are 5W-20/5W-30 oils. Because they want that 5W oil to get to critcal engine components at a cold start.
Tester
I found this article more interesting:
Great article CS…This paragraph addresses the O.P.'s concern…
“Certainly engines that have experienced significant ring and liner wear benefit from thicker oils. Thicker oil use results in compression increases, performance improvements and reduced oil consumption.”
The OP’s car only has about 70k miles on it so it should not be worn out, unless it was abused in the past. Based on miles, he should not go to a significantly thicker oil, however I would use 10w30 if it were mine, that is the only oil I use now in all my vehicles from new to junk yard. My highest mileage vehicle is the Saturn at just shy of 255k miles.
I was just wondering why tester said that 15w40 would cause excessive wear and I do see his point about flow issues in the cold. The article circuitsmith linked does also raise this issue, but I have to wonder at what temperature this really becomes a concern. Right now I go by the owners manual that shows that 10w30 is OK for the coldest temperatures we experience where I live, so I use it.
I’m not sure I’d recommend 10w30 to someone living in Minnesota in the winter time though. But we don’t know where the OP lives either.
I liked the article in circuitsmith’s link and believe it to be true, but I do not know much about the web site or the organization that sponsored it and when I tried the link to information about the author, there wasn’t any information there so I don’t know his credentials. As so often with internet blogs, they are hard to vet, so you don’t know if the author is an educated, trained and experienced professional in the field or just another opinionated amateur like myself.