Mineral / Semi-Synthetic / Synthetic Oil ..... Viscosity Selection

[penberth3]

No I was not. Jumble Duck prefers the phrase "viscosity of a 15W oil" whereas I preferred the phrase "15W oil viscosity". If you really think that there's a significant difference between those two phrases then my work here is done.

Richard

You started off talking about "15W viscosity", not "15W oil viscosity". You've changed the quote.

 

[RichardS]

You started off talking about "15W viscosity", not "15W oil viscosity". You've changed the quote.

Did you miss my post #29 entirely?

But, of course, when I said "15W", I was not referring to 15W oil but to 15W size ladies undergarments.

Richard

 

[RichardS]

This is wrong. 10W warmed up gets thinner but it's still 10W. 5W warming up also gets thinner - so the two never meet.

OK, I think we really have to ask some serious questions now, the first being whether you understand what the term "viscosity" actually means?

The second is whether you understand what the phrase "albeit at a higher temperature" actually means?

I can't help thinking that your constant interventions on this thread are more likely to be stalling the exchange of ideas than the opposite, but I suppose it's giving us all a little light entertainment.

Richard

 

[JumbleDuck]

A 5W oil is has a lower viscosity at zero degrees (or whatever) than an 10W oil. However, if you start to warm up a 10W oil, it will soon reach the same viscosity of the 5W oil, albeit at a higher temperature, so an engine which is using 10W oil will sometimes be running on an oil which is the same viscosity as a 5W oil but, assuming that the oil meets the manufacturers ambient temperature specification, the reverse is not true.

You cannot use the low-temperature part of the specification to predict high temperature performance. A 5W-40 is less viscous than a 10W-30 at very low temperatures but it's more viscous at typical operating temperatures. At some intermediate temperature, therefore, the engine using 5W oil will indeed be running on an oil which is the same viscosity as a 10W.

 

[RichardS]

You cannot use the low-temperature part of the specification to predict high temperature performance.

Who is using the low-temperature part of the specification to predict high temperature performance?

I'm using the low-temp part of the spec to discuss low temp performance and the normal engine running temp part of the spec to predict normal engine running performance.

Richard

 

[reeac]

I think that the best, most comprehensible way to state the concept is as follows:
Multigrade oils exhibit a lower reduction of viscosity with increasing temperature than do monograde oils. The best way to take advantage of this effect is to select a lower cold viscosity whilst retaining the same working temperature viscosity. By this means you get the advantage of more rapid oil circulation after a cold start whilst retaining the engine designer's specified viscosity at running temperature. For example change from 30 weight mono to 5W30 multi.

 

[RichardS]

I think that the best, most comprehensible way to state the concept is as follows:
Multigrade oils exhibit a lower reduction of viscosity with increasing temperature than do monograde oils. The best way to take advantage of this effect is to select a lower cold viscosity whilst retaining the same working temperature viscosity. By this means you get the advantage of more rapid oil circulation after a cold start whilst retaining the engine designer's specified viscosity at running temperature. For example change from 30 weight mono to 5W30 multi.

That is indeed correct but I was trying to address a somewhat different issue as it's very unusual these days that anyone is ever starting with a monograde oil.

I'm looking at the situation that I've been in many times where I should be using a 10W-30 oil but that one is not in the sale. However, other multigrades with different ranges are on 25% discount so I need to choose between, say, 0W-20, 5W-30, 5W-40, 10W-40 or 15W-40, in extremis.

Please could all the knockers note that this is a fantasy example just to make it more interesting.

Richard

 

[JumbleDuck]

I'm looking at the situation that I've been in many times where I should be using a 10W-30 oil but that one is not in the sale. However, other multigrades with different ranges are on 25% discount so I need to choose between, say, 0W-20, 5W-30, 5W-40, 10W-40 or 15W-40, in extremis.

So which do you think will have the higher viscosity at working temperature, a 10W-30 or a 5W-40? Bear in mind that you have already claimed that an oil which meets the 5W spec can never have the same viscosity as one which meets the 10W spec.

 

[RichardS]

So which do you think will have the higher viscosity at working temperature, a 10W-30 or a 5W-40? Bear in mind that you have already claimed that an oil which meets the 5W spec can never have the same viscosity as one which meets the 10W spec.

Will you please stop attributing statements to me that I have never said. You keep repeating this silly tactic, presumably to try and "catch me out".

In this case, I have never claimed that "an oil which meets the 5W spec can never have the same viscosity as one which meets the 10W spec". If you reduce the temperature of a 5W oil it will attain the same viscosity as a 10W oil, albeit that the 10W oil will be at a slightly higher temperature and conversely with the 10W oil.

This is why I said in my post #38 "assuming that the oil meets the manufacturers ambient temperature specification" to ensure that we are working within a pre-determined ambient temperature range as that is particularly relevant at the W end of the scale.

Richard

 

[JumbleDuck]

In this case, I have never claimed that "an oil which meets the 5W spec can never have the same viscosity as one which meets the 10W spec".

A 5W oil is has a lower viscosity at zero degrees (or whatever) than an 10W oil. However, if you start to warm up a 10W oil, it will soon reach the same viscosity of the 5W oil, albeit at a higher temperature, so an engine which is using 10W oil will sometimes be running on an oil which is the same viscosity as a 5W oil but, assuming that the oil meets the manufacturers ambient temperature specification, the reverse is not true.

If you reduce the temperature of a 5W oil it will attain the same viscosity as a 10W oil, albeit that the 10W oil will be at a slightly higher temperature and conversely with the 10W oil.

And if you heat a 5W-40 oil to 100C it will be more viscous than a 10W-30 at the same temperature. The low temperature part of the spec says far less about the viscosity of the oil than you think.

 

[RichardS]

And if you heat a 5W-40 oil to 100C it will be more viscous than a 10W-30 at the same temperature. The low temperature part of the spec says far less about the viscosity of the oil than you think.

Once again, where have I ever said anything different about the high temperature viscosities?

But you were stating that I had claimed something specific about the 5W and 10W specifications.

If the oil is within the manufacturers ambient temperature specification, let's say that is 0 - 25 degrees, then the coldest the oil will get to is 0 degrees and, at this minimum temperature, the 5W oil will always be thinner that the 10W oil. The only way that the engine with 5W oil will ever see a 10W viscosity is if the ambient temperature goes out of specification.

Once again, the reverse is not true but please note that this is stating your emboldened quote the other way round.

Rather than simply sniping from the wings, please explain why you disagree with this?

This viscosity chart might help:

Grade	0°C	10°C	40°C	100°C
0w40	665cst	354cst	82cst	14cst
5w40	842cst	430cst	91cst	14cst
10w40	874cst	440cst	91cst	14cst
15w40	1260cst	595cst	107cst	14cst

Richard

 

[JumbleDuck]

Edit: I have absolutely no desire to prolong this silly row, so I'll leave it there.

 

[RichardS]

Edit: I have absolutely no desire to prolong this silly row, so I'll leave it there.

Indeed. It was absolutely nonsensical.

It's crystal clear from my posts that I'm saying that a 40 oil will be more viscous than a 30 oil at the same high temperature.

Richard

 

[RichardS]

This viscosity chart might help:

To complement the above low temperature multigrade viscosity chart, I managed to find some data in the same viscosity units for the 100°C end of the scale, this being chosen as the nominal fully-warm oil operating temperature for engines. I have reproduced both charts together:

Grade	0°C	10°C	40°C	100°C
0w40	665cst	354cst	82cst	14cst
5w40	842cst	430cst	91cst	14cst
10w40	874cst	440cst	91cst	14cst
15w40	1260cst	595cst	107cst	14cst

SAE Hot Grade ..........................................................................100°C Min Viscosity cst....................................100°C Max Viscosity cst.................................. 100°C Typical Viscosity cst

20			5.6	9.3	7
30			9.3	12.3	11
40			12.3	16.3	14
50			16.3	21.9	19
60			21.9	26.1	24

As can be seen, the multigrade used in the first table was a 40 hot grade which reduced to 14 cst at 100°C and that indeed corresponds to the same 14 cst at 100°C in the second table. This gives some confidence that the charts from different sources are reasonably consistent


Hopefully the figures help to illustrate that, in the absence of a manufacturer's spec oil, using an oil which is lower than recommended at the Winter end of the scale, or higher than recommended at the Hot end of the scale is the safest choice.

Richard

 

[reeac]

Very helpful tables. Two points
1. That's a dramatic reduction in viscosity between 0 and 10 C. Makes me wonder what things are like at -10C.
2. It's remarkable that effective lubrication is possible over such a wide range of viscosities ....typically a factor of 60.

 

[Birdseye]

I have been advised by Nanni not to use synthetic oil in my Nanni N4.60 engines. The oil must be straight mineral oil.

Not surprised. I once bu66ered a newish Yanmar by gicing it the oil that I thought was best. A fully synthetic. Then we crossed Biscay in a calm so 30 hours motoring. When we got to the UK the engine was going from full on the dipstick to empty in 3 or 4 hours of motoring. Stripping it apart, the bores were like a mirror. They werent "glazed" in the old sense but polished.

Yanmar said "wrong oil". I thought that was a cop out so I spoke to Castrols tech dept . They said that on an old style engine with a cast iron block that had been honed, I should use old type mineral oils because fully synthetic would do just what had happened. Didnt help that as with a boat, it was motoring at much the same revs for 30 hours. In fact Castrol said use the sort of oil that goes into old busses.

For a modern engine with plated bores etc, its a totally different issue.

 

[RichardS]

Very helpful tables. Two points
1. That's a dramatic reduction in viscosity between 0 and 10 C. Makes me wonder what things are like at -10C.
2. It's remarkable that effective lubrication is possible over such a wide range of viscosities ....typically a factor of 60.

If you had asked me beforehand, I would have guessed that a typical multigrade oil at operating temperature is perhaps 1/10th of its viscosity at room temperature. It's actually more like 40 times thinner. It makes you wonder what happens to a monograde oil.

Richard

 

[jdc]

The Nanni advice only to use mineral oils, never synthetic is also that of Beta, who go further to state that one should use CF oils not any of the more modern service grades. But Kubota- who only make the blasted engines so what can they know - have changed advice and now say that one should use their own brand(1) 10W-40 fully synthetic oil, to CJ-4 spec to boot!

And I'm told by what was my local agricultural machinery service people (TNS in Suffolk) that it's what they now use for all the Kubota range, from the 30+ year old small tractors to the most modern huge turbo-charged things.

This change of advice from Kubota does add support to the thesis that a lower viscosity number for the cold end than an engine manufacturer originally recommended is likely to be a good choice nowadays. Oils have changed: the price of synthetic oil is now lower than good quality mineral oils, the diesel fuel has changed from 500ppm Sulphur to less than 10ppm with the introduction of ULSD necessitating changes to the additives, the amount of ash - which is about all bore-glazing correlates with - has fallen dramatically, and, probably not of least significance, the high quality manufacturers no longer make the old spec oils so any one finds will probably come from unbranded sources.

I think any of these, but particularly the change to ULSD, should have prompted a reconsideration of the advice which was first printed about 30 years ago by yacht engine distributors. I wish they took the trouble to do so (I have a slightly embarrassing recollection of trying to find 15W-40 grade CF oil for my Beta when on St Maarten, and being teased about it by the dutch, who asked 'why do you Brits always chase the old c&%p? We just use the most modern oil from Shell').

(1) It's actually made by Total: data sheet

 

[RichardS]

The Nanni advice only to use mineral oils, never synthetic is also that of Beta, who go further to state that one should use CF oils not any of the more modern service grades. But Kubota- who only make the blasted engines so what can they know - have changed advice and now say that one should use their own brand(1) 10W-40 fully synthetic oil, to CJ-4 spec to boot!

That's very interesting and doesn't surprise me.

There were a few issues with early synthetic oils and I was using it from the very start in the 70's. Some issues were imaginary like "synthetic oils are thinner and can leak past shaft seals" and some had a basis in fact like "the softening of some seal materials" and "causing running-in problems". However, modern synthetic oils have addressed all the potential issues and are technically superior in every way to mineral oils.

The only outstanding potential issue, which also applies to many modern classification mineral oils, is that modern oils tend to have a higher detergent loading and therefore if an engine has been badly maintained over many years and has built up a lot of sludge in the sump, then the detergents tend to flush out the sludge and unless the filter is changed frequently, oil starvation problems can occur. However, it's worth bearing in mind that modern mineral oils can also provoke the same issue and that it is usually easy to identify an engine, certainly in cars but possibly less so in boats, which are likely to be afflicted by this problem and steps can be taken to ameliorate the issue before changing to a high-detergent oil.

Richard