Sign In   Register
  • Page:
  • 1
  • 2


Oil, what is it all about? 10 years 8 months ago #45827

  • PQD44's Avatar Topic Author
  • PQD44
  • Offline
  • Master MGer
  • Master MGer
  • It's only the first 100 years that are difficult
  • Posts: 4386
  • Thanks: 1265
Oil, what is it all about?

Here is your 16 step guide to the ‘liquid engineering’.

Warning: This is long, so leave now if you want a one line answer, if you have a bit more time perhaps look at the titles for each section and choose the ones of interest .. or if you're feeling brave, get a cuupa and then read on. ;)

1) How is oil manufactured; transformed from the black sludge that comes out of the ground, into the nectar-like substance we pour into our cars?

Super simplified, crude oil, which is usually thin, (contrary to popular belief) is distilled into light and heavy fractions, with several intermediate ones.
The lighter fractions, usually more than 90% of the original crude, are converted into petrol and diesel. Some of the heavier oils, (still dark and smelly!) go through several processes to clean them up and remove wax. Out of about a dozen oily products 4 clear, bright amber oils are commonly used to blend modern engine and gear oils. These are roughly equivalent to SAE 10, 20, and 30 engine rating and 140 gear rating. Oil refineries also produce all sorts of gases and chemical compounds which can be used to build up 'tailor made' lubricants: synthetics!

2) What are the most important substances added to the refined base oils? What do they do?

In the Dark Ages, engines used blends of refined mineral oils 'straight', with nothing added. The trouble was the oil didn't last very long, and hence the engines didn't either.

Black sludge and corrosion were the killers, and both were tackled in the 1950s with detergent and antioxidant chemicals. The detergents washed the carbon from fuel combustion off the bores and out of the ring grooves, and at the same time reduced bore and piston ring corrosion.

The antioxidants stopped the oil reacting with oxygen in the air, which cut acid sludge formation which in turn reduced corrosion and oilway blockages. Some antioxidants had the useful side-effect of reducing wear as well. This added up to longer oil and engine life, both improving about three times. (Straight oil had to be changed every 1000miles) OK, I admit there were design and metallurgical improvements, but they needed that vital 'liquid component' to be fully effective.
Later came dispersant compounds which held the carbon as tiny particles in the oil which didn't settle out anywhere, and slipped through the oil filter as if it wasn't there.(Solid bits in well-used modern oil are about 1/1000mm across; the pores in an oil filter are at least 15 times bigger.)
The other big problem with oil used to be cold starting. It was usual to have SAE 20 Winter or 'W' grades, and SAE 30 or 40 Summer grades, and even the so-called Winter types would defeat the starter in serious cold weather. Unfortunately, oil is very thick when it's cold, and very thin when it's hot. To have an oil thick enough to look after a hard working engine, you had to use a grade which was too thick when it was cold.

The answer was (and is) multigrade! What was needed was an oil that behaved like a 20 'W' grade in the cold, but only thinned down to a SAE 40 or 50 when really hot; yes, 20W/50! This can be done by mixing thin oil with thick polymers based on plastics and synthetic rubbers; these don't do much in the cold, but as the oil warms up they unwind and thicken it up to some extent. The oil still thins down, but not as quickly as a polymer-free or monograde type.

Multigrades started to catch on around 1960, but these pioneer types were easily ruined by mechanical shear effects, more so in gearboxes than engines. These days the better quality polymers resist shear even in combined engine/transmissions, so it is essential to use good quality shear-resistant types in a gearbox fed by the engine (such as the traditional mini!), which gives its oil a hard time in both engine and gearbox.

Incidentally, there are large amounts of these additives and polymers in there, it's not just 'a little bit of this, a little bit of that'! A good quality mineral 10W/40 can be 80% base 20% additive chemistry, and guess which is the expensive ingredient!

3) What are the differences, in layman's terms, between mineral, semi-synthetic and fully-synthetic engine oil? (In terms of structure and performance.)

Before we get into details, the first thing to realise that there is no chalk and cheese difference between mineral and synthetic based oils. After all, the chemical compounds which make mineral engine oils so much better are themselves synthetic. Synthetic lubricant bases are stepwise improvements on mineral oil.
To imply that dreadful things will happen if the 1970 V8 is run on anything other than good’ ole mineral oil is ridiculous. It may not need a 2012 synthetic, but it isn't going to come to any harm using it.

The most basic type of synthetic is really a special mineral oil. Known as 'hydrocracked' bases, these are made in oil refineries by putting certain types of mineral fraction through special processing, so they cost more than the usual mineral types but not much more. They are useful because they resist evaporation at high temperatures. Although used for years for genuine technical reasons, they are now popular with marketing men because the magic sexy word 'synthetic' can legitimately be printed on the label without spending much on the oil inside the can!

Yes, all low-cost 'synthetics' contain anything from a few percent to 20 percent (i.e. 'semi-synthetic') of special mineral oil. Using fairly simple chemical compounds or gases from oil refineries or other sources, it is possible to 'synthesise' or build up tailor-made lubricant molecules which have very desirable characteristics, such as great resistance to cold, heat, evaporation losses or excessive thinning as they get hot. These are the true synthetics, and the two that are used in engine oils are PAOs (poly ***** olefins) and esters.

Neither is cheap! PAOs are related to mineral oils, and are the ideal carriers for all the chemical compounds used in mineral oils. Because they do not gel at very low temperatures, all genuine 0W-something oils have to be based on PAOs to pass the 0W test at a sub-arctic -35C.

Esters were originally made for jet engine lubricants, and to this day all jet oils are ester-based. Although similar in performance to PAOs, they have a valuable extra trick: they are good lubricants and help to protect metal surfaces. Esters help with transmission and valve train lubrication. 100% fully synthetic oils are actually quite rare, probably because they are very expensive to make, and even more expensive to buy.
Even so, an ester/PAO with a very shear stable multigrade polymer is the ultimate oil for high output engines that are worked hard, which means racing.

4) How does oil work? What gives it its lubricating properties? How does it 'cling on' to surfaces?

A plain bearing such as a main or big end, when spinning fast is 'floating' on a relatively thick film of oil. The metal surfaces literally do not touch. The high velocity drives a wedge of oil between the two surfaces, and the oil film supports the load, just like a water skier skimming over that very thin lubricant, water. But, when the engine slows down and stops the bearing shells drop through the film and touch the crankpins, just as the skier sinks in up to his neck when he lets go of the rope.

It is where there is metal to metal contact that lubrication, that is, something to reduce wear and seizure, is needed. On gear teeth, valve components, and piston rings at top or bottom dead centre, there is no high speed rotation to generate 'wedge' support, so the oil films are very thin, and some metal contact is inevitable. Some fluids, even if they look thick and oily, are completely hopeless! Very pure mineral oils, and some synthetics fall into this group. They depend entirely on chemical load-carrying compounds which react with metal at high pressures and temperatures to provide very thin protective films which prevent micro-welds where metal surfaces come into contact.

Detergent and antioxidant chemicals often double up as anti-wear agents. The odd ones out are esters. These are attracted to metal by electrostatic forces and cling on when surfaces are forced into contact.

5) What are (or can be) the main differences between oils of the same type, i.e. what's the difference between a 'good' and a 'bad' oil?

It all comes down to honesty beware! A good oil is what it claims to be on the can. 10W/40? Does it really pass the cold test at -25C? There is usually an API spec quoted, such as API SH or SL. These are car-based, and a good basic quality guide. If absent, leave it on the shelf, and avoid lawyer-speak: 'meets the requirements of....' or 'recommended (by whom?) for use in....'.

Then there is the 'synthetic' minefield. Generally you get what you pay for. The best performance oils are made in the more developed European countries, but low price buys the cheap 'modified mineral' synthetic and not much of it, with a poor multigrade polymer. As is so often the case, quality follows cost.

6) What are the likely consequences of using poor-quality oil?

Usually, these are fairly long term, except in racing. Think of the oil as a liquid component, and poor oil as a cheap pattern spare. In a road car long-term reliability and performance retention (i.e. acceleration figures below new spec., fuel and oil consumption above) are the casualties. Particularly in a high performance or racing car, the effects can be more immediate and catastrophic.

7) Some oil companies have run advertising campaigns that imply their products have special, unique qualities. Can these adverts be taken seriously?

Yes and no! Generally adverts with marketing-speak terms such as ‘Magnatec’ and ‘Electrosyntec’ are really being used as code words for esters, which are particularly beneficial in performance engine oils. No manufacturer has any unique ‘secret’, so it’s all down to providing the best possible blend for the job at the right price, and making it clear that you get what you pay for. I personally think that the importance of shear stability or ‘stay in grade’ is not stressed enough when quality is talked about.

What is dodgy though is claiming that a mineral based oil with a few percent of modified mineral (‘hydrocracked’) synthetic is the DB’s and suitable for racing, etc. when it clearly isn’t.

Also, there is endless semantic manoeuvring and lawyer-speak around The Magic Word ’synthetic’.

For instance, a ‘synthetic’ oil is invariably semi-synthetic (’Ah! We didn’t say it was all synthetic did we?), and, if low priced, invariably the modified mineral type synthetic. It is a sad fact that you get what you pay for, but even so, stick to the reputable UK/European brands, and remember that shipping an oil half way around the world doesn’t automatically make it better than one made in your home town.

As for TV advertising…well, does anybody believe it? Due to its huge cost, a TV advertising campaign can significantly raise the cost of specialist items such as oil. Everybody assumes it’s just a few pence per litre, but it can be pounds per oil change.)

8) What is the grading system? What is meant by the weight of an oil? What does 10W/40 mean for example?

Weight means viscosity, or resistance to flow. Water and paraffin flow very easily, so they are low or light viscosity. Golden syrup or 140 gear oil do not come out of the can so easily, so they are high or heavy viscosity.

Especially with oils, temperature is very, very important. An oil which looks ‘heavy’ at 20C will be very ‘light’ at 100C.
The American Society of Automotive Engineers (SAE) ratings cover cold starts and ‘up and running’ viscosities. There are two sets of standards, the ‘Winter’ (W) ratings, and the 100C standard ratings. (‘W’ does not, repeat not, mean ‘weight’!)

So a 10W/40 oil has to pass a 10W cold viscosity test at -25C, and a SAE 40 test at 100C. In an oil lab there will be a refrigerated viscosity measuring device for the ‘W’ tests and another at 100C for the standard SAE tests. There are 6 ‘W’ ratings from the difficult 0W at -35C to the dead easy 25W at -10C, occasionally used in India for example!

The whole point of these Winter ratings is to assist cold starts, to get the oil circulating quickly, and to avoid power and fuel wasting drag as the engine warms up. Once it is warmed up, the 100C ratings count. There are 5 of these, 20, 30, 40, 50, and 60 although why anybody bothers with 60 in the 21st Century is a mystery to me!

Sorry folks, but I’ve got to get technical. Viscosity is measured in standard units called ‘Centistokes’, names after a Victorian engineer, Sir George Stokes, who used to time ball bearings as they sank through oil. SAE 30 for example is from 9.3 to 12.5 Centistokes, and SAE 40 follows on at 12.5 to 16.3, although most SAE 40 oils are in the middle at about 14.

Now this is something most don’t realise: engines do not know what grade of oil they’re running on. They’re not clever enough! So an engine filled with 10W/40 will be running on a viscosity of 14 at 100C, but with a sump temperature of 90C its seeing a viscosity of 18, so as far as the engine is concerned it’s running on SAE 50. Likewise, at 110C, it’s down to 11 Centistokes so it ‘thinks’ it’s on a SAE 30! (Which is preferable.)

The lesson is, do not use power and fuel-wasting thick oils in cool climates. A decent 10W/40 or even thinner is perfectly OK unless you’re running a classic with wide clearances and a slow oil pump.

9) What is the best type of oil to use in a road car for general use? Is fully synthetic a waste of money?

Personally I’d go for a shear-stable part ester synthetic, SAE 10W/40 or 5W/40. The ‘shear-stable’ bit (ie, a decent quality multigrade polymer) is actually more important than the ‘synthetic’ part!

If strapped, I’d go for a shear-stable mineral based oil rather than a ‘synthetic’ of dubious stability that’s probably based on modified mineral oil anyway. Unless you’re covering a huge annual mileage, genuine 100% synthetics are probably an extravagance. High mileage long-distance fans can use a light full synthetic and save on fuel and oil changes, and cut overhaul costs if things get to that stage, but more later…..

10) How important is it to change oil regularly? What are the implications of failing to do so?

It is only really important to change oil regularly if the engine covers a low annual mileage made up of slow, short runs. This is being cruel to the oil and the engine! The oil, regardless of its quality, gets contaminated by fuel and water vapour, and never gets the chance to evaporate it all off with a long fast run. The consequences are corrosion, ring and bore wear. It is essential to do a change at least once a year, even if the recommended mileage hasn’t been covered. On the other hand, if you eat up the miles on long blasts the engine and its oil will love it, so with a top-quality oil it is OK to cheat a little on oil drain periods.

11) Do some types of oil (i.e. fully-synthetic) ‘wear out’ quicker than others? How important are timely oil changes? Can you rely on the frequency suggested by your User Manual?

The oils that will last the longest are the relatively rare 100% genuine synthetic shear stable types, which will easily stand twice the recommended drain period in a high-mileage high performance engine. (So in the long run they aren’t really so expensive.)

Of course, User Manual drain recommendations are based on a back-covering ‘worst case’ scenario of low annual mileage on poor quality oil, so they can be regarded as a very safe minimum mileage.

In the past, there used to be trouble with heavy carbon deposits and sludge around the engine with early low-detergent oils, but these days almost any oil with a good API specification will keep everything clean for 10 to 15,000 miles, so that’s the least of your worries.

12) Does oil have to be warm to do its job properly? Is it important to warm up your engine before using at speed?

Yes, it does have to be at least warm, and preferably hot. Most people except the sort with white finger syndrome find metal at 60C too hot to touch, yet 60C is too cold for oil in an engine that’s going flat-out. The best approach is to take it easy for the first couple of miles, especially in very cold weather and keep an eye on that oil temp guage.

13) How does a high-performance oil allow the motor to produce more power?

An engine wastes fuel energy in several ways, and most of them are due to the laws of thermodynamics, which is another way of saying you can’t do much about it. But up to 6% of engine output is lost due to oil drag, made up of pumping losses and viscous drag between moving components. The transmission is included in this.

Provided wear and friction are kept down, there are real gains to be made by using a ‘tough’ but low viscosity oil. Surprisingly, frictional losses are low, down at 3% or less even with conventional oils, so there are few gains to be made here.

14) Why do some engines consume oil? Is this a problem?

Large air-cooled engines or classics with wide piston clearances, or very highly stressed liquid-cooled engines which flex under load, or which use ultra-light pistons with the minimum number of rings are likely to be oil users. There is little that can be done about it. Unfortunately, burnt oil tends to leave hard deposits in the combustion chambers which can initiate pre-ignition, so more frequent top overhauls are usually necessary.
Occasionally, touring engines will use oil for no apparent reason. This is often due to the oil level rising in the crankcase due to air retention, leading to oil loss through the breather. The answer is to move to a lighter grade of oil to improve air release.

15) If you need to top up your engine oil, how important is it to use exactly the same brand and type?

Not very important at all. Unfortunately, due to ‘arse covering’ reasons the oil companies cannot print this advice on the can! Although officially all manufacturers advise against mixing different makes and grades, in fact there is very little chance of any harm being done, even if one is a mineral 20W/50 and the other is a 5W/30 synthetic. Obviously, avoid this if you can, but do not panic if there’s no other alternative and you need to top up a small amount. Just don’t mix 2 stroke and 4-stroke oil!

16) There are all sorts of additives available which are supposed to improve ordinary oil and reduce friction, improve power output etc. Are they worth a try?

Oil is already a very advanced and deeply researched fluid which does not need any ‘enhancement’. There is no secret formula out in the backwoods that the mainstream lubricant chemists do not know about; but there are plenty of half-baked ideas and gullible people out there!

These wonder additives are usually 1930s chlorinated paraffins, long obsolete gear oil additives which should have disappeared in the 1950s, but they keep turning up as ‘Xxtrasuperlube ZX3’ with a mark-up of several thousand percent. They actually corrode engine and transmission internals, so they do far more harm than good.

Others depend upon the total myth that PTFE powder coats engine internals and reduces friction. It doesn’t do anything or the sort. It just blocks the oil filter. The AA tested one of these overpriced PTFE concoctions (‘Quick 60’ or something) very thoroughly back in the 80s. They stated: ‘This is an expensive way of coating your oil filter’.
The following user(s) said Thank You: David Aiketgate, bryan young, Leigh Ping

Please Log in to join the conversation.

Re: Oil, what is it all about? 10 years 8 months ago #45829

  • 's Avatar
  • Visitor
  • Visitor
Very informative ....


Please Log in to join the conversation.

Re: Oil, what is it all about? 10 years 8 months ago #45832

  • tui's Avatar
  • tui
  • Offline
  • Qualified MGer
  • Qualified MGer
  • Penelope Pitstop
  • Posts: 798
  • Thanks: 107
Thanks for taking the time to write up such a detailed run down :woohoo: !

-=Visit my Website!=-
The following user(s) said Thank You: bryan young

Please Log in to join the conversation.

Re: Oil, what is it all about? 10 years 8 months ago #45843

Excellent writeup Paul. I've been working in the oil and gas industry for many years, with some of that time in lubricants at Imperial Oil's main lab in Sarnia, Ontario, Canada, and what you wrote reflects what I know as well. The only point I do not agree with is crude, it can be VERY thick, depending when in the world it comes from. Crude usually needs to be heated for it to flow without the use of high HP pumps.
95 MGF
The following user(s) said Thank You: PQD44

Please Log in to join the conversation.

Re: Oil, what is it all about? 10 years 8 months ago #45845

  • PQD44's Avatar Topic Author
  • PQD44
  • Offline
  • Master MGer
  • Master MGer
  • It's only the first 100 years that are difficult
  • Posts: 4386
  • Thanks: 1265
You are quite correct Mark it really does depend on where in the world the crude is from.

Just so people can get some idea, the density of water is 1000kg/m3

The crude I worked with was from the North Sea, typically with a density of only 835kg/m3 or from the middle east, typically 870kg/m3. This is the reason crude oil floats on water, because it is less dense.

There are much thicker, denser crude oil sources like the Venezuelan oil or the extra heavy Canadian crude which as you say will need a diluent added to help it to flow.

Again the temperature of the crude will greatly alter it's viscosity. I was not trying to get it out of the ground it was already at the refinery in the huge crude oil holding tanks by the time I clapped eyes on it.
As you say to get it out of the ground, if the oil reservoir is not sufficiently pressurised naturally, you often have to send water down to force the crude up or force super heated steam into the reservoir for TEOR. That is a whole story in itself.

After working in the electronic industry I eventually became a Senior Instrumentation Engineer and worked on EPC Oil refinery design and construction supervision. I worked for Snamprogetti, Chiyoda, M W Kellogg, Brown and Root, Statoil and Fluor Daniel at Camberley in Surrey.

So come on then Bryan, it'snormally about now you tell me who you know, who has an MG and worked for Fluor Daniel or some other Riverside Business Park company in Camberley, who just happens to live just up the road from you, who you wnt to primary school with and his wife bakes cakes cakes with an MG logo in she shape of a long lost concept car and they deliver them to you in a 1936 MG ...... :bust:

Please Log in to join the conversation.

Last edit: Post by PQD44.

Re: Oil, what is it all about? 10 years 8 months ago #45904

Enjoyed that read. Thank you Paul :broon:

Please Log in to join the conversation.

Re: Oil, what is it all about? 10 years 8 months ago #45908

Paul, thanks for this info, I was always in the dark about what all the ratings meant and now I have a reference .. :-)

Please Log in to join the conversation.

Re: Oil, what is it all about? 10 years 8 months ago #45968

I think we are on the page on a matter of points such as the fact that the viscosity is irrelevant yet to hear some classic MG owners, you would think the world would end if you didn't use 20W50!

However, I have always understood that true synthetics such as PAOs/Esters have naturally high VIs and don't need VII additives.

Also, I understood that generally in the USA the use of the term synthetic was ok with GpIII base oils but not elsewhere, and that in the rest of the world to call an oil synthetic would mean a GpIv or V base oil.

Generally, though GpIV base oils are poor additive carriers so there is some Ester in the oil to aid the additive solubility and this is highly detergent and is why modern engine oils seldom have depositing problems.

Please Log in to join the conversation.

Re: Oil, what is it all about? 10 years 8 months ago #45970

  • PQD44's Avatar Topic Author
  • PQD44
  • Offline
  • Master MGer
  • Master MGer
  • It's only the first 100 years that are difficult
  • Posts: 4386
  • Thanks: 1265
:yesnod: Thank you Martin that is a very good link you posted, which expands on the topic further.

Please Log in to join the conversation.

Re: Oil, what is it all about? 10 years 8 months ago #45971

I know when i am beaten :shrug:

The Oil was a fab read, i have saved it all, you certanally know your stuff. :coat:

Please Log in to join the conversation.

Re: Oil, what is it all about? 10 years 8 months ago #45988

I dont think this affects many people on here but some older engine designs need higher levels of zinc additives than modern oils aimed at catallyzed cars contain. Specifically this is ZDDP. This area is a bit complicsted but there are "classic" 20/50s that will work here.
Another intersting area is optimum oil and filter change frequency, and its not just more is better.

Please Log in to join the conversation.

Re: Oil, what is it all about? 10 years 8 months ago #45996

I disagree on the ZDDP based on evidence I have seen and monitored. Part of the issue of wear on cam followers is the quality of reproduction parts rather than any issue relating to the oils in use in my opinion.

Please Log in to join the conversation.

  • Page:
  • 1
  • 2
Time to create page: 0.135 seconds
© 2022 All Rights Reserved. Hosted By SEBS IT