Wouldn't an 0W30, a 5w30, and a 10w30 all perform the same at engine operating temp? The w number only applies to the cold engine, right? I realize that 30 weight is a range and some of these could be higher or lower in the range, but let's assume the three in question are the same 30 weight. I can only figure that the lower the w number, the greater the spread and the more polymers in the oil and that that would maybe affect the hot performance, possibly making the 0w30 run thinner than the 10w30 at operating temp.

 

With new oil, it is indeed the same at 100C or 210F. Do you know your actual running oil temperature, I don't. If you look at flash points from the data sheets, you will generally see that the higher the "W" number, the higher the flash point. From that I conclude that high temperature performance in areas like oxidation an evaporation are better for thicker base oils. Adding polymers to thin oil only enhance the viscosity and nothing else.

If you really need 0W for arctic conditions, then use synthetics. That is where they have a real advantage.

Jim

 

At operating temp the #W30 should all perform similarly. The big difference is at cold temps. If you get to sub freezing temps the lower vis oil should flow easier thus making starting easier, getting oil to critical components faster etc.

Interestingly, I read a side benefit of thin oils is that the starter, battery, alternator will last longer since they don't have to work as hard.

I DO NOT recommend 0W## weight for anywhere that does not get say below 0F. I have used Mobil1 0W30 in 20 to 30 degree weather and my engine makes noticably more noise at cold startup with it than the 5W30 Mobil 1.

Oils with a wide spread in the viscosities have more polymers in them so they used to be more prone to "burning" or coking up the engine. I am not sure if that is still true for modern oils, but it was a hot topic just a few years back. This is not supposed to be a problem with syns.

From reading, the W number is how thick the oil will act when cold and the other number is how thin it will get when hot. So even though syn is usually pretty thin feeling at room temp it will not thicken when cold or thin when hot as much as a straight dino would without vis improvers. The dino needs more vis improvers and that used to be the problem with it.

The old rule of thumb was that oils with a 30 point spread had too much VI added, so it was recommended to keep the spread as small as fit your temp ranges. So 10W40 was the boogey man in the 90s. 20W50 had the same spread but since it started with thicker oil it didn't seem to have a problem. Now with modern dino oil, I don't know if this rule still applies.

Best bet as always is to follow the engine maker recommendations or check an oil website. For most of the us 5W30 to 10W40 is enough. In Alaska you might go 0W30 and in Texas summer you could go 20W50.

Just my opinions.

Jim Henderson

 

Thanks for the info. Been running 5w30 semi-synthetic in all my vehicles year round for several years. I realize the 5 is pretty thick on startup compared to the 30 when hot, and so thought there might be a better way. Since I installed an oil pressure gauge I notice that the pressure is pretty high until warmed up (which takes much longer than for the coolant temp to warm up). That my pressure drops to about 36 when good and hot (F150, 300 I6) may lead me to a 10w40 for summer use. It will be interesting later this year when the temps are consistently below 40 F and I start using my oil pan heater to see what the oil pressure reads on cold start with hot oil. Right not I get 55 cold dropping to 36 hot. The winter scenario with heated oil, I suspect will go something like 45 on start, moving up to 50 and then dropping to about 40. I expect the initial increase because the cold block invariably cools that oil down a bit before the block warms (I checked once by putting my hand on the upper forward part of the sump and could feel the cooler oil draining back down). Checking without the heater the filter would not feel warm for several minutes or so, but with the heater the filter instantly has warm oil. Got to help reduce wear even if I can't plug in at work. Actually, running the heater for a couple hours even on summer mornings probably would be beneficial, but likely not significantly so.

Do you think I need to join OOA (Oil Obsessives Anonymous)?