Is it ALWAYS better to go thin at cold start temps?

[427Z06]

Here's a chart to illustrate the point that a 0W isn't always thinner than a 5W at the temp you're starting your engine at:

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Calculated cSt, temps in Centigrade

T(C) Mobil 1 Extended Performance 5w30 * GC 0W30 * Mobil 1 5w20 * Mobil 1 SM 5w30 * Mobil 1 Extended Performance 10w30

-20° 2233 2609 1922 2604 3849

-10° 954 1127 811 1107 1483

0° 460 547 388 531 657

10° 244 292 206 281 326

20° 141 169 119 161 178

30° 87 104 74 99 105

40° 57.3 68.4 48.3 64.8 66.6

50° 39.5 47.0 33.4 44.4 44.5

60° 28.3 33.7 24.0 31.7 31.1

70° 21.1 25.0 17.9 23.5 22.6

80° 16.2 19.1 13.8 18.0 17.1

90° 12.7 15.0 10.9 14.1 13.2

100° 10.3 12.0 8.8 11.3 10.5

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[1sttruck]

It's an article on heavy duty diesels, where they appear to have tested 10w30, 15w40, 10w40 blend, and 5w40 syn. Most heavy duty diesels run 15w40 in 'normal' conditions, and it appears that extending the viscosity range with a better oil worked better than using a thinner oil. It'd be nice to see the ful article.


Modern heavy duty diesel engine cold start wear study ... SAE 10W30 VTC in-house reference; SAE 15W40 – full mineral; SAE 10W40 – part synthetic ...www.emeraldinsight.com/...

Title: Modern heavy duty diesel engine cold start wear study
Author(s): A. Plomer, R. Benda
Journal: Industrial Lubrication and Tribology
ISSN: 0036-8792
Year: Dec 2000 Volume: 52 Issue: 6 Page: 277 - 285
DOI: 10.1108/00368790010352691
Publisher: MCB UP Ltd
Abstract: Increasingly stringent European market requirements for improved heavy duty diesel engine performance, such as fuel economy and durability, continue to highlight the need for higher performance engine lubricants. To meet this need, new additive technology is being used in combination with higher quality base-stocks and has resulted in a growing trend towards the use of oils of lower viscosities than those used in the past. Such a trend has led to some concern over the ability of low viscous oils to maintain adequate engine wear protection, not only during extended service operations but also under the more severe conditions of low temperature engine start-up. This paper describes the results of a recent study to evaluate the effect of base oil composition and viscosity grade on the low temperature performance of a modern Euro II diesel engine with respect to wear, using the technique of Thin Layer Activation. Engine test results showed that the use of full synthetic SAE 5W40 grade oils based on Polyalphaolefin provided enhanced low temperature cylinder liner wear protection.
Keywords: Diesel engine, Heavy duty diesel, Wear
Article Type: Technical paper
Article URL: http://www.emeraldinsight.com/10.1108/00368790010352691

 

[Titan]

Just remember the 0W- part means that the oil will show movement at a very cold temperature. It doesn't mean that a 0W-XX is thinner at freezing than a 5W-XX. It may be. It may not be. What it does mean is that at -35 degrees (or somewhere around there), the 0W-xx will show movement when it is tilted, whereas the 5W-xx won't.

The other end, the top number, is much more straightforward...it describes an oil's thickness (measured in Centistokes) at operating temperatures....somewhere near the boiling point of water.