The ideal xW oil

Nick1994

$50 Site Donor
Messages
13,447
Location
Phoenix, AZ
Now this may be a dumb question, but it's something that has always made me wonder. I get it that the colder environment you're in, the better the idea it is to go down a grade of oil (as in the xW weight). But according to the BITOG Motor Oil University, it says that all oils are too thick at start up, regardless of weight, that the lower the xW of oil you can go, the better. Or that's how at least I interpret it. So using this logic, what's the point of using a, for example, 10w30 oil these days? Wouldn't this logic mean a 5w30 is better on startup, and a 0w20 is more beneficial than a 5w20?Even in a hot environment. So I guess there is a couple factors to consider, either we are trying to avoid shearing of the oil (which I don't know a lot about) or the Motor Oil University here on BITOG is wrong. I understand that this may open a can of worms, but I'd like to understand better. Please share your thoughts, thanks.
 
Messages
12,925
Location
Northern Kentucky
You are basically thinking right. There's not much sense using 10w30 when 5w30 is the same price. When it comes to 20 grade the difference is price. 0w20 requires synthetic base oils to meet the viscosity requirements while a mineral oil can achieve 5w20 designation, but if price is no object the 0w20 is superior over 5w20 if formulated correctly.
 
Messages
40,851
Location
Great Lakes
Originally Posted By: Nick1994
So using this logic, what's the point of using a, for example, 10w30 oil these days?
No point, for the most part. It's an obsolete grade. Back in the day, this narrow spread meant fewer VIIs required, and hence more shear stability. Today, most of even the the 5w-30 oils are fairly shear stable, so it's not much of a concern.
Quote:
Wouldn't this logic mean a 5w30 is better on startup, and a 0w20 is more beneficial than a 5w20?Even in a hot environment.
Kind of, but it's not so clear cut, IMO. For you in Arizona, cold start-up temp might be 100F. But the 10w- or 5w-, or 0w- designations are achieved at very low subfreezing temps, so they don't really tell you how thick or thin the oil will be at 100F. In reality, the difference between them at 100F may not be much. I guess you could look at 40C viscosity of an oil and use that as guidance instead. And you will find that at 40C, an oil such as PP 5w-30 is actually thinner than GC 0w-30.
 
Messages
10,146
Location
Burlington, Ontario, Canada
So to continue that thought, in an AZ climate you want an oil with the lowest KV40 spec' but has a sufficiently high enough HTHSV to avoid bearing wiping when the oil is as hot as it ever gets including an allowance for possible oil shear and fuel dilution. What could be simpler?
 
Messages
43,676
Location
'Stralia
Originally Posted By: CATERHAM
So to continue that thought, in an AZ climate you want an oil with the lowest KV40 spec' but has a sufficiently high enough HTHSV to avoid bearing wiping when the oil is as hot as it ever gets including an allowance for possible oil shear and fuel dilution. What could be simpler?
Agreed entirely...will just add for the duration of the OCI (self evident)...should we all rewrite 101 ?
 
Messages
5,112
Location
Airlie Beach Australia
Originally Posted By: Shannow
Agreed entirely...will just add for the duration of the OCI (self evident)...should we all rewrite 101 ?
I think that the whole "University" thing needs to be re-evaluated - its writer no longer contributes to BITOG
 
Last edited:
Messages
2,011
Location
War Eagle
The oil should flow easily on startup at whatever temp you are in at the time of start up. And it should resist shearing over the long term to protect components. Not to mention fuel dilution, poor filtration, poor air ingestion, many short trips, and on and on. Maybe Mobil 1 in the 0w40 is the best answer
 
Messages
4,257
Location
Central Maryland
Originally Posted By: Nick1994
Now this may be a dumb question, but it's something that has always made me wonder. I get it that the colder environment you're in, the better the idea it is to go down a grade of oil (as in the xW weight). But according to the BITOG Motor Oil University, it says that all oils are too thick at start up, regardless of weight, that the lower the xW of oil you can go, the better. Or that's how at least I interpret it. So using this logic, what's the point of using a, for example, 10w30 oil these days? Wouldn't this logic mean a 5w30 is better on startup, and a 0w20 is more beneficial than a 5w20?Even in a hot environment. So I guess there is a couple factors to consider, either we are trying to avoid shearing of the oil (which I don't know a lot about) or the Motor Oil University here on BITOG is wrong. I understand that this may open a can of worms, but I'd like to understand better. Please share your thoughts, thanks.
Your understanding is correct, all oil is too thick on startup, but in AZ it's less of a problem then further North. The only argument against running a 5w-30 or a 0w-30 is the Noack values tend to be higher, that is, some of the oil will boil off during the Oil Change Interval (OCI). This is usually not a big deal, especially if the engine's cooling system is fully functional, but it another data point that BITOGer's obsess about. As for Viscosity, there's two issues. In the time leading up to when University was written, Viscosity Index Improver additives (VII's) were more heavily used to make a 10W oil into a 10w-30. When the VII additives broke down you had a 10W oil. Nowadays better base stocks are used that have a higher 40C and 100C viscosity than a 10W, and VII's are a smaller part of the big picture. Besides VII breakdown there is also oil shear. This is more dependent on engine design factors like having timing gears and chains, or other mechanical shear devices within the engine. That's why you see comments about certain engines being "easy" or "hard" on oil. Within any factory OCI this is really not an issue. If you have a "hard on oil" engine and want to run an extended OCI, simply switching to a synthetic will take care of that problem.
 
Messages
595
Location
Murray KY USA
Many good points made in this thread. The older I get the more I understand if I am getting 200K+ miles out of engines that had 100K miles of unknown history when I purchased them then the motor oils used must to have done an OK job. I have been putting oil in vehicles for well over 50 years and many of they were total worn out. Now with turbos and with people wanting to do 15K mile OCI's I agree motor oil is a more complex subject. In our more simple engines if they will wear out the chassis or then machine I call the motor oil "functional". smile It may sound strange but I am more concerned about the motor oil in the 1989 Ford F700 which we are in the process of replacing the wood floor on the 16' flat dump bed or the 1983 John Deere 310B backhoe. Neither get a lot of use but both are special usage machines that I do not want to have to get rid of over engine failures. Now if the 2002 4.3L Blazer 200K+ miles engine blows I might just junk it and go by something with less miles since it has little cash value and thousands of options for a replacement. On the Ford F700 we have got it tired up well, redid the PTO shaft and resealed the dump pump, flushed the hydraulic fluid tank/refilled with 25 gallons of UTF and have it at the shop for the steel flooring. I can find not real proof synthetic oil is functionally better than today's dino but with little price difference between the two today WHY not go with the best since we do not need more than 25 gallons of motor oil a year. I will go a few years before changing these engines that are seldom used.
 
Messages
6,388
Location
Washington St.
Quote:
But according to the BITOG Motor Oil University
Keep in mind that this was written by a cosmetic plastic surgeon, not a mechanical engineer. Not everything he writes is proven, and some might not be provable. Also keep in mind that every product is a compromise. The range of viscosities from the cold W viscosity to the hot viscosity has compromises, and the wider the range, the bigger the compromises. The highest quality base oils have higher viscosity indexes--less relative change from 40°C to 100°C. To get the very cold flow, pour point depressants are added. Good, but a compromise--these chemicals take up space and don't lubricate. Viscosity index improver polymers are important to get from cold to hot, but again, these don't lubricate, less is better, and lower quality ones shear. There are two types of VII shearing--they can stretch out of shape under load, then return to shape and continue to do their job, or they can break and no longer do their job. All that said, hot viscosity is important. Other things remaining equal (which they never do), higher viscosity oil has higher film strength in the bearing than lower vis. So--I trust the mechanical engineers that designed my engine, tested it, and provided the oil viscosity recommendations more than I trust the good doctor Haas.
 
Messages
28,123
Location
Regina, Saskatchewan, Canada
Originally Posted By: Doug Hillary
I think that the whole "University" thing needs to be re-evaluated - its writer no longer contributes to BITOG
The viscosity article on the main page also seems to have an outdated SAE J300 table, with the allowances for the low HTHS mineral 40s.
 
Messages
7,561
Location
North America
Originally Posted By: Nick1994
Now this may be a dumb question, but it's something that has always made me wonder. I get it that the colder environment you're in, the better the idea it is to go down a grade of oil (as in the xW weight). But according to the BITOG Motor Oil University, it says that all oils are too thick at start up, regardless of weight, that the lower the xW of oil you can go, the better.
Not dumb at all. On a cold start it is true, ALL oils are thicker than what the vehicle was designed for. To pick an arbitrary number and vehicle, at 100C(212F) as an oil operating temp, the vehicle was designed to have a 30 weight. When the oil is cold, it is much thicker than a 30 weight would be at the operating temperature. So when a 10w30 is used, it is thinner at the cold temp than the straight 30. 5w30 is thinner at lower temperatures than the 10w30, and 0w30 even more so. So the lower you go on the "first number", the better the oil flows at a lower temperature even though all four oils are the same consistency at operating temperature.
Originally Posted By: Nick1994
Or that's how at least I interpret it. So using this logic, what's the point of using a, for example, 10w30 oil these days? Wouldn't this logic mean a 5w30 is better on startup, and a 0w20 is more beneficial than a 5w20?Even in a hot environment.
If you live in a warm climate (Florida?) where the temps rarely if ever get to freezing, then a 10w30 is fine. I don't have the chemistry background to discuss in detail, but do understand the concept - that in general, the smaller the spread between the numbers the less chemicals are involved to make the oil adjust to both cold and hot temps, and the better the oil will hold up over time. (that said, the difference in durability between 10w30 and 5w30 used to be huge in this respect, but has narrowed a lot since the 90s and may be gone entirely) But if you live in a climate that sees subfreezing temps or even below 0F, then it is best to use a 0wxx or 5wxx appropriate for the climate. A vehicle might very well be able to start at -20F on 10w30, but there will be a lot of parts that are starved of lubrication in the time it takes for the very thick fluid to make it around the engine.
 
Last edited:
Top