I'm confused about the "cold" oil viscosity rating

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I am confused about why, for example, a 30w oil is available when a 10w30 or 5w30 would apparently work just as well when hot and work much better while cold. Would there be a disadvantage to using 0w30 in hot weather instead of SAE 30?
 
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As I understand it, the SAE 30 is more resistant to breaking down in heat (due to the lack of viscosity improvers, which are only good for so long). So, while 5w30 is fine in summer, the ranking is probably
SAE 30>10w30>5w30 (for hot weather). This is why you will see SAE 30 used in lawn mowers. But, practically, there isn't too much difference and 0w30/5w30 can be used year-round.
 
An SAE 30 will have no VII (Viscosity Index Improvers) in it, which would make it immune to mechanical shear. However, generally your premise is correct in that there would be little advantage to using an SAE 30 over any of the grades you've mentioned.

Also, there are oils like Amsoil's 10w-30 that have no VII's in them and can also be labelled an SAE 30, muddying things further.
 
Ive always wondered if you had a situation where a vehicle was run around the clock most of the time, such as vehicles serving police, taxi, or ambulance duty, if you would be better off using a straight 30 weight oil.

How many miles on average before you see viscosity breaking down?
 
Originally Posted By: 5AcresAndAFool
Ive always wondered if you had a situation where a vehicle was run around the clock most of the time, such as vehicles serving police, taxi, or ambulance duty, if you would be better off using a straight 30 weight oil.

How many miles on average before you see viscosity breaking down?


If you look at oils designed for extended drain intervals like M1 0w-40, GC 0w-40...etc which are also a broad split on the visc side, it's easy to conclude that the straight weight may not offer any inherent advantage in that department. Where they do shine are in applications of high shear or where low cost is required, as they are cheap to blend, unlike a synthetic extended drain Euro oil.
 
Originally Posted By: 5AcresAndAFool
How many miles on average before you see viscosity breaking down?

As low as several hundreds of miles of a multigrade in use.
Often times, it stays sheared-thin at the end of OCI of 5-10k.
 
People are afraid of SAE 30 although it's one tough Hombre.
It costs more too since it only comes in quart bottles.
 
Originally Posted By: Avery4
I am confused about why, for example, a 30w oil is available when a 10w30 or 5w30 would apparently work just as well when hot and work much better while cold. Would there be a disadvantage to using 0w30 in hot weather instead of SAE 30?


Generally, the answer to this question is no, there is no disadvantage to using the 0w30 in hot weather versus a 30-grade and yes you could use the 0W-30 year round.
 
Originally Posted By: OhOMG
Originally Posted By: Avery4
I am confused about why, for example, a 30w oil is available when a 10w30 or 5w30 would apparently work just as well when hot and work much better while cold. Would there be a disadvantage to using 0w30 in hot weather instead of SAE 30?


Generally, the answer to this question is no, there is no disadvantage to using the 0w30 in hot weather versus a 30-grade and yes you could use the 0W-30 year round.


No disadvanteages ?
* Higher NOACK
* More VII to shear down in service
* Lower HTHS

a 20W20 would do...
 
Originally Posted By: OhOMG
Originally Posted By: Avery4
I am confused about why, for example, a 30w oil is available when a 10w30 or 5w30 would apparently work just as well when hot and work much better while cold. Would there be a disadvantage to using 0w30 in hot weather instead of SAE 30?


Generally, the answer to this question is no, there is no disadvantage to using the 0w30 in hot weather versus a 30-grade and yes you could use the 0W-30 year round.


According to my handbook, I could use an SAE30 year-round, but I can't get it.

So I use an SAE40 year-round
 
Originally Posted By: Merkava_4

It costs more too since it only comes in quart bottles.


What?!?!?!

Go to a farm or truck supply store....
1 gallon, 5 gallon, 30 gallon, 55 gallon are all READILY available.
 
Originally Posted By: Ducked
Originally Posted By: OhOMG
Originally Posted By: Avery4
I am confused about why, for example, a 30w oil is available when a 10w30 or 5w30 would apparently work just as well when hot and work much better while cold. Would there be a disadvantage to using 0w30 in hot weather instead of SAE 30?


Generally, the answer to this question is no, there is no disadvantage to using the 0w30 in hot weather versus a 30-grade and yes you could use the 0W-30 year round.


According to my handbook, I could use an SAE30 year-round, but I can't get it.

So I use an SAE40 year-round
no 30wt?
 
In the 80's I worked for an airline that had about 50 pieces of ground equipment such as baggage tractors and aircraft servicing trucks. SAE 30 was used in all the vehicles and the oil was never changed. They did however, change engines. Said it was the most cost effective way to operate.
 
Originally Posted By: WobblyElvis
SAE 30 was used in all the vehicles and the oil was never changed. They did however, change engines. Said it was the most cost effective way to operate.


[censored]
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SAE 30 will maintain it's viscosity better because it has no viscosity index improvers which break down with use, this also means less engine deposits as these VII's create sticky deposits when they are destroyed.
In a place with a warm climate, where temperatures never go below freezing, in theory there is no real reason, or need for multigrade oils.
 
Originally Posted By: 5AcresAndAFool
Ive always wondered if you had a situation where a vehicle was run around the clock most of the time, such as vehicles serving police, taxi, or ambulance duty, if you would be better off using a straight 30 weight oil.

In practice, the taxis we ran were "on" almost around the clock, and this was the late 1970s on, using conventional 10w-30 for 10,000 km OCIs. Engines lasted hundreds of thousands of miles. I'm sure an SAE 30 would have done just as well. This was the days before HTHS talk, but my dad seemed to have an instinctual understanding of the concept, and contended that an SAE 30 (that thick expletive, he called it) would provide slightly poorer fuel economy than a 10w-30, which is always something to consider in fleet usage.

For me, in practice, I don't like switching by season, so grab something I know will word fine in the cold, and use it year round. And, as OVERKILL points out, some of the most capable extended drain oils on the market certainly are not monogrades. The real world isn't ideal, and I think when it comes to automakers, it's simpler and safer to specify one grade for year round use, particularly in a country with as diverse a climate as the States, and just let us strange BITOGers obsess about viscosity tweaking.

Merk: Our Walmarts carry SAE 30 in 5 gallon pails, and most oil company distributors do, too, I'd wager.
 
Run 0w30 in you Detroit Diesel and watch it expire. There you difference. Now Why you may ask.

There are Service categories along with grade.

There are compromises with commodity blends to achieve the multigrade required improved gell point and pumpability. Much of that compromise can be drirected to ILSAC GF-X Energy savings and its attendant POOR HTHS rating for specified grades.

More at Light oil and high % VM = sludgemaker.
 
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