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Discussion Starter #1
Hi all,

Going to do a service on my 159 2.4 (75k)

I did a service on my mums similar car using 0w40 mobil1, and my brother with a 1.9 JTD used the same oil in his stilo.

My question is what are the general views on using 0W40 over the recommended 5W40?0

(both my mums alfa and my brothers stilo run quite nicely with 0W40)

Thanks
 

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Discussion Starter #4 (Edited)
I am going to have my DPF removed, DPF/EGR deleted and remap pretty soon, if that makes any difference (i dont see why it should though)

EDIT: im tempted to use the 0W40 as the viscosity will be more runny when cold than 5w40...so technically, would be better, as it will more willingly get around the engine than 5w40.

5W30 is no good, as the running temp viscosity is too thick (the 30 means its thicker when running than 40) so wouldn't be advisable to use it as the engine is specced to have a viscosity rating when running of 40 (higher may be better tho, although it could be TOO thin)
 

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5W30 is no good, as the running temp viscosity is too thick (the 30 means its thicker when running than 40) so wouldn't be advisable to use it as the engine is specced to have a viscosity rating when running of 40 (higher may be better tho, although it could be TOO thin)
Completely wrong!
5W30 is thinner at operating temperature than 5W40.

As for a 0W40, the main benefit of 0W oils is VERY low pour points, ie -60degC, but all 0W oils loose ability at operating temperature to enable them to get down to the 0W rating.

Given your obvious confusion, your safest option is to stay with the spec that is listed for your engine.
 

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Discussion Starter #7
:lol:

Oh wow, my apologies, that is indeed total crap. totally arse about face...ive been knee deep revising for a Digital communications exam on friday, so wasn't thinking straight.

I think ill go for the 0w40, unless there is a credible source for the degradation of oil performance due to getting it to perform well at low temps? (i couldn't find anything with a brief google)

Specifically, im looking at Mobil1 oil.
 

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Does oilman post on this forum? If not here's a wealth of information on his website opie oils. There's links to technical PDFs explaining pretty much everything.

Engine Oil, Motor Oil, Gear Oil, Car Oil, Motorbike Oil from oilman at Opie Oils

In my opinion there would not be a lot of difference between 0w40 and 5w40 unless you live in the Scottish highlands, which you don't. Brand I'd consider more important, and Mobil 1 often comes recommended.
 

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Completely wrong!
5W30 is thinner at operating temperature than 5W40.
...
I would phrase it like that:

At normal operating temperatures both oils should have the optimal viscosity.

If (through high stress) the engine and oil get hoter than "normal", the 5W40 oil is able to keep the optimal viscosity for higher temperatures while the 5W30 oil will sooner become too thin for save operation.
 

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No.
At normal operating temperature, the 5W30 has a lower viscosity (ie is thinner) than a 5W40.

Fine to use a 5W30 in an engine that is designed for it, but not in one that isn't!
 

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What I wrote was what I remembered from an very detailed report by Castrol about their 0w40 oil. I thought I had understood it and it made sense to me, but if I look at some technical spec sheets now (from Liqui Moly for example), it seems that you're right.
The sad thing is: The more I read these spec sheets the more I have trouble recognizing any concept at all, which isn't helped by the fact that nobody states the viscosity for higher temperatures than 100 °C and that they offer for example different 0w30 oils (standard / for VAG cars / for high economy) with substantially different viscosities.
It's time to get my coat, I guess ....
 

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It is difficult, especially as they are viscosity bands, ie one W40 will be a slightly different viscosity to another. One could be bordering on a W30 and another could be almost a W50.

It isn't always easy to find, but if you can get the HTHS rating for various oils it can be a good way to compare different oils of the same grade.
 

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At normal oil temperature of 212 degrees 0W30, 0W40, 5W30 and 5W40 will all have the same claimed and industry required viscosity between 9.3 and 12.4. Indeed the 40 grades may be lower down the scale than the 40 grades. Do not get too hung up on viscosities when you are using quality semi or fully synthetic oils.

I wouldn't use a 15W graded oil though. That really is too thick when cold.

I guess if you push I would always go with the lowest grade as these are the thinnest when cold so 0W30 or 0W40. Most (90%) of engine wear takes place when your engine is cold so you want that oil to get around the engine as fast as possible. Not only are thicker oils more resistant to flow but ,when cold, due to the higher pressure most of it will go through the pressure relief valve rather than circulate through the engine. Some people don't like thin oils because they think it will run off engine components overnight; modern oils have very good "cling" properties and good quality filters or pumps have non return valves so the oil is held in the oilways.

If you are going 18k between changes make sure it is long life.
 

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The "5W" in 5W30 means the oil is a "5 weight" oil, and the "30" means it will thin as much as a 30 weight oil would at 100°C.

Using oil with higher viscosity, e.g. 10W, may have the adverse effect of oil not reaching tight gap in plain bearings, and also the effect of higher oil pressure. Contrary a lower weight oil, e.g. 0W, may be too thin and also a lower pump pressure.


Just use whatever the manufacturer specified, as the engine is designed.
 
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