5w40 vs 0w40 oil - Page 2 - Alfa Romeo Forum
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Status: 159 2.4 20007 plate 19,500 DPF/EGR by Adie (AHM)
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As my last post: 0W30, 0W40, 5W30 and 5W40 are all equivalent to a 10 grade at 100 degrees C.
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Halfords have a good deal on Castrol Edge at the moment
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Lots of horror stories about castrol, and the offer is only on part synthetic...

also the deal is 37.98....but castrol comes in 4L not 5L (i was in halfords earlier on today) 9.49p/L

normal price for mobil1 is 49.99 for 5L 9.99p/L
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Originally Posted by kandlbarrett View Post
As my last post: 0W30, 0W40, 5W30 and 5W40 are all equivalent to a 10 grade at 100 degrees C.
Well unfortunately that's ********. Firstly 10 grade motor oil doesn't exist. Under SAE J300 standard the SAE grades for motor oil start at 20 grade. Winter grades for motor oil (such as 10W) are measured by different testing methods to determine crankabilty and pumping (Cold Cranking Simulator and the Mini-Rotary Viscometer) only at low temperatures ( in the case 0W the temperature is -35C) and the the SAE grades 20 - 50 are measured for kinematic viscosity at 100C to determine their grade.

In a 5W40, the cold oil has crankabilty (cold start resistance to cranking) value of 5, and when at 100C it has the viscosity of a 40 grade oil. So when you tip 5W40 oil out of the bottle into your car exhibits the properties of 5W and when it heats up to 100C and thins out, it is a 40 grade viscosity not the equivalent at of some non-existent 10 grade.

A multigrade oil with a cold viscosity of 5W which has been tested at 100C and is found to have the viscosity in the range described as SAE 40 it is labled 5W40, one with a thinner viscosity at 100C in the range specified by the SAE as SAE 30, it is labled 5W30. To suggest that xW30 and xW40 are the same at normal operating temperatures is misleading. They are different.

xW30 may provide some small gains in fuel economy and power over xW40 due to reduced windage and pumping losses, but may thin out too much for mechanical protection in high stress and overheat situations. What is IMHO just as important as the grade of oil (making sure it is within the manufactures specification) is the Viscosity Index (VI) as this number gives you an indication of how resistant a particular oil is to viscosity change with temperature, i.e. its resistance to thinning out as the temperature rises. Higher VI is better

Anyway see Viscosity Charts - Bob is the Oil Guy to get a visual on comparative viscosity

Darryl in New Zealand

Last edited by KiwiAlfa156; 04-02-12 at 19:37.
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KiwiAlfa: yes my mistake I have expressed it badly. But all Xw30 grade oils are in the same viscosity band at 100 degrees C (or should be.) All Xw40 grades are within the same viscosity band (but different to Xw30 band) at 100 degrees C.

Personally, I would have the DPF removed and plump for Mobile1 0w40. Being 40 grade it doesn't need to meet the requirement forced on 30 grades for economy and therefore seems to have a better additive pack.

In the UK I wouldn't worry about the difference between a 5w or 0w grade but as you have stated be looking at far more important issue like additive content and viscosity index etc.
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GENERAL MOTORS recommend dexos 2 fully synthetic 5w30 for their models and as the 1.9 jtd is the same engine that is used in the vectra it is perfect for your ALFA. If you can get 4 of your friends to chip in your Vauxhall main agents do a box of 4 x 5 litre cans for about 60 ( 15 per 5 litre ) I checked the spec with my Q8 rep and he says its ideal for the alfa engines ,petrol or diesel..ultimately its all down to your own preferences but if you get a gallon of cheap "supermarket" oil you are asking for trouble. Oils nowadays, especially the long drain ones are of such a high quality that you should have no trouble at all ...if you choose wisely and make sure use the ones that meet or exceed ACEA A3/B4/C3 specs
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There is more to an oil than it's xWxx rating. Check the Oil specifications and you will see a number of different measures. The kinematic Viscosity in (centistokes) at 40 deg and 100 deg and the HTHS which is a shear rate which I don't fully understand! The Kinematic viscosity is how long it takes for a ball bearing to fall through the liquid. It is a good indicator of how thick the oil is at the 2 temperatures. The lower the value in centistokes the thinner the liquid.

If you look at the manufacturers specs, you can see that Shell helix ultra 5W40 is actually thinner than Mobil 1 0W40 at both 40 degrees (cold) and 100 deg (normal operating temperature).

Shell Helix Ultra 5W40
40deg = 74.4 cSt
100deg = 13.1 cSt

Mobil 1 New Life 0W40
40deg = 78.3 cSt
100deg = 14 cSt

Fuchs Titan Supersyn 5W40
40deg = 86 cSt
100deg = 14.2 cSt



Both are definitely thinner than a cheaper 5W40 such as Fuchs Titan Supersyn. Fuchs TITAN SUPERSYN 5W-40 High Performance, Fully Synthetic, Engine Oil

At normal operating temperature they are all fairly similar, but when cold the Shell Helix Ultra is thinner than the Mobil 1 which in turn is thinner than the fuchs.

I do a lot of very short journeys and when i change the oil next month I will be putting Shell helix Ultra 5W40 in my Brera as it's the thinnest 5w40 I have seen. I was going to put in Mobil 1 0w40 as I presumed the 0W would be thinner, until I read the specs.

Last edited by Chuffy; 05-02-12 at 14:41.
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Looking at the Shell PDF from Chuffy's link above, interesting to see that Shell's 5W40 is actually slightly thinner than their 0W40.... the difference being the lower pour point of the 0W40, but not that low for a 0W oil.
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Use BobIsTheOilGuy and do some reading.

In the forum section (scroll halfway down the page to "Oil Analysis Results") there are analysis results for both used and virgin (unused) oil samples. Have a look here and you will get loads of info on most oils:-

Bob Is The Oil Guy - Forums powered by UBB.threads™

Please bare in mind that the used oil results may be affected by what condition the engine is in and how the engine has been used while the oil was in it. That includes things like how hard it has been driven, cruising or stop / start, short or long journeys, has it overheated?

Last edited by kandlbarrett; 07-02-12 at 17:08.
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0w40 , 5w40 , oil

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