Which oil?

[MikeT]

Steve, in no way did I intend you to get that impression and I apologise if I have offended you - I can never be offended by a healthy debate.
While I appreciate everyone's comments and arguments (perhaps I fail to convey that well enough?), what I naturally tend to do is question everything. Which I guess is what you refer to as "spikey"? Please don't take it personally Steve, I appreciate facts but anyone making statements as fact while lacking supporting evidence needs to be questioned IMHO.

I have made some discoveries about engine oil that I would like to clarify so brought this question to the forum in the hope of learning more detail and sharing information for the good of all.

Please accept my apology? At least, don't refrain from making forum contributions because of any disagreement with another member.

Regards, Mike.

[jeremy]

One of the risks of too thin an oil is that it won't be retained in the bearings.

This was dramatically illustrated to me when many years ago i had a knackered Daimler V8 250. This thing had an oil pressure gauge and when pushing it hard at highish revs the oil pressure would drop.

Why - well apparently the crank was forced to one side of its bearings (probably middle ones). - So light load - crank runs in the centre of its bearings and has a clearance of X thou. Load it - crank moves to one side as it were - gap one side 0 x X - other side - 2 x X - and the oil that stays there when the clearance is X - floods out when its 2X.

The Daimler seemed to run quite happily like this but looking at the oil pressure gauge was rather distressing.

Oil pressure isn't the be-all and end all of a healthy engine - but maintaining a film of the stuff in bearings etc is.

[MikeT]

To all. I think I better make an attempt to clear the waters a little as I seem to have caused a bit of confusion, make of it what you will, all I ask is you keep an open mind. This is what I understand about engines and mineral engine oil, but if I'm wrong, please enlighten me.

Oil thickens when cooled to room temperature.
Oil flow provides lubrication, not pressure.
No mineral oil can offer proper flow and lubrication to an engine when cold. Not even a 0W/xx.
Manufacturers recommend oils which give the correct viscosity (for proper lubrication) at normal engine temperatures. Therefore xW/30 right through to xxW/50 are perfectly suitable for my car at normal engine temperatures.

[steelcityuk]

Hi Mike,

Let's just move on shall we? No need for the apology in light of your explaination.

I put the link up to the oil bible for members to read and make of it what they can. High level chemistry that oils use is way over my head. I don't think I've read the 'bible' for about 2 years or so but it does sound as though it has changed - no mention of bikes when I was there.

I like a bit of experimentation myself, hence the decision to drill out a set of old spheres to see just how much difference it would make. Only went from 0.6 to 1.0mm but it made a vast difference.

Steve.

[XantiaMan]

To all. I think I better make an attempt to clear the waters a little as I seem to have caused a bit of confusion, make of it what you will, all I ask is you keep an open mind. This is what I understand about engines and mineral engine oil, but if I'm wrong, please enlighten me.

Oil thickens when cooled to room temperature.
Oil flow provides lubrication, not pressure.
No mineral oil can offer proper flow and lubrication to an engine when cold. Not even a 0W/xx.
Manufacturers recommend oils which give the correct viscosity (for proper lubrication) at normal engine temperatures. Therefore xW/30 right through to xxW/50 are perfectly suitable for my car at normal engine temperatures.

I think you have still missed the point, its not directly engine (coolant) temperature its ambient temperature that is more relevant. A 0w 30 at 30 C is too thin for your engine, i'm not gonna stress this again as you might as well put cooking oil in the sump instead!

If you operate an engine in lower ambient temperatures it goes without saying that it will not run as warm as an engine in a hotter climate, so if you ran a thick oil the engine will have a harder time to turn over. The opposite is true if you run a thinner oil at warmer temperature, it will be easier to turn over from cold but when hot, the oil will be too thin.

If a mineral oil was that bad at protecting why do engines run for 100's of thousands of miles on it? Semi-synthetics and FS offer better protection for sure, its the longer life that it provides and the ability to reach a higher temperature without breaking down are the key benefits.

I've run out of puff on this thread and tempted to say go buy some 0w 30, waste £40 quid oil it, wait for a hot day and give the engine some serious stick, then come back and ask how much it costs to replace big end and main end bearings plus a crankshaft regrind...

[MikeT]

I think you have still missed the point, its not directly engine (coolant) temperature its ambient temperature that is more relevant.

Sorry, I wasn't being ignorant (I didn't miss anything) I just cannot get my head round what you're saying. Surely it's the cooling system that regulates the oil temperautre, not the ambient air temperature?

A 0w 30 at 30 C is too thin for your engine

Is that a typo? At 30C the oil would be four times too thick at that point, surely?

If you operate an engine in lower ambient temperatures it goes without saying that it will not run as warm as an engine in a hotter climate

Again, this is a big sticking point for me. They way I understand it, the cooling system and thermostat regulate the temperature, not the air temperature.

If a mineral oil was that bad at protecting why do engines run for 100's of thousands of miles on it?

It's at cold-running that mineral oils are inadequate and it's well known that is when most engine wear occurs. The fact they run for 100K's is down to the hot lubrication.

I've run out of puff on this thread and tempted to say go buy some 0w 30, waste £40 quid oil it, wait for a hot day and give the engine some serious stick, then come back and ask how much it costs to replace big end and main end bearings plus a crankshaft regrind...

I did see one oil priced at a scarey £54! Without splitting hairs though, I don't generally thrash the car but I would have thought that the odd blast off the line wouldn't overheat the engine oil as much as you suspect. It would be good if someone could give me some facts on such operating temperatures though.

[myglaren]

[off topic]
I always liked Castrol-R, or at least the smell. Might not be a very good idea in a HDi Turbo
[/o t]

[CitroJim]

[off topic]
I always liked Castrol-R, or at least the smell. Might not be a very good idea in a HDi Turbo
[/o t]

Ahh, the memories Two-stroke oil has the same effect on me as well

No, Castrol-R is a great lubricant but it is not suitable for any except racing engines that are dismantled after each race. It has absolutely none of the additives needed for long life in a road vehicle and decomposes rather rapidly into a sticky, smelly goo. In two-strokes it produces some incredibly hard carbon in the exhaust. We used to use an oxy-acetelyne torch to decoke our Kart silencers, the only effective way of getting Castrol-R carbon out

But it smells nice..

[steelcityuk]

The stinkiest oil I've come across is Total gearbox oil, I guess this could apply to any EP oil.

I really hate the smell of it.

Steve.

[MikeT]

They now market scented 2-stroke oils. It's an ok idea but they say the oil is poor quality.

[MikeT]

I guess this could apply to any EP oil.

I really hate the smell of it.

Steve.

I hear that!! It's nauseating.

[CitroJim]

Gearbox Oil..

Gosh yes, horrid stuff..

Dickie Seat who writes a fun piece in the back of Classics Monthy hates the stuff too and always mentions it in his likes and dislikes column. His editor apparantly said he must stop the references to gearbox oil so they now go in as anagrams.

One great one: "Argie Bollox" who is, according to Dickie Seat, the inventor of the speed hump..

[myglaren]

The stinkiest oil I've come across is Total gearbox oil, I guess this could apply to any EP oil.

I really hate the smell of it.

Steve.

On this theme, the most disgusting gloop I have encountered is the stuff packed into the GS CV joints. God that was 'orrible!

also Steve

[XantiaMan]

some info on oil

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 in magazines are honest, with marketing-speak terms such as ‘Magnatec’ and ‘Electrosyntec’ really being 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 gallon, but it can be pounds per gallon.)

Please can you explain 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. People sometimes say, ‘I drained the oil when the engine was hot and it ran out like water…’ so I say, ‘Good! It’s supposed to be like that!’

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.

Radical race cars use 1300 Suzuki Hyabusas and work them very hard. (Didn’t one take the old Nurburgring absolute record at one point?). They use our high-ester 15W/50, but that’s OK because they see oil temps around 130C! (No problem for the oil or the engine, but they do fit special oil seals.) At 130C the true viscosity is 10cSt, so the engine thinks its on a thin SAE 30, which keeps it happy.

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…..

What are the main differences between 2 and 4-stroke oil? Why does 2-stroke oil have to be mixed with fuel?

2-stroke oil has a very short working life, straight in and out, and it gets burnt. The 2-stroke engine doesn’t have a sump full of oil and the bearings are all rollers, so there’s hardly any oil drag, hence no need for multigrades. Long term stability is obviously not a problem!

But, 2-stroke must burn off without leaving any plug-fouling or detonation-initiating deposits. The detergent and anti-wear additives used in 4-stroke oil leave hard white ash behind when they burn, just what you do not need in a 2-stroke. So 2-stroke oils use low-ash detergents and dispersants, and the better types use ester synthetics to act as anti-wear compounds.

With current environmental concerns, smoke is a sensitive issue, so most ‘road’ 2-stroke oils are now low smoke, which requires yet another type of synthetic base designed to burn off invisibly. For some rather basic but very high-revving air-cooled racing 2-strokes there’s still some sense in using blends with that marvellous anti-seize liquid, castor oil!

Due to crankcase induction and compression, the classical 2-stroke obviously cannot have an oil-filled sump, so the only way to keep an oil film on anything was to add oil to the fuel, or inject oil into the crankcase space where it could mix with the fuel vapour. There are now some engines where the fuel and oil are injected separately, but the oil is still burnt.

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 full of 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.

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 type of oil that is likely to give trouble after low mileage is a light viscosity type with poor shear stability, either mineral or modified mineral based. (Such as one of the USA ‘fuel economy’ oils for lazy car engines that pushed the Japanese OEMs to bring in their own oil spec.) The important thing is the shear stability; the much hyped ‘synthetic or mineral’ nonsense is a red herring.

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.) Just the thing for those touring fiends who pack up and set of for the Transylvanian Alps as soon as the clocks go forward!

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.

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 use a good 5W/40 or even a 10W/40, and take it easy for the first couple of miles, especially in very cold weather.

For racing, a really good warm-up is essential, except perhaps with special 0W/20 low-drag race oils. The trouble is, oil pumps are very good at pushing oil out at 60PSI, but unfortunately there is only 14PSI (atmospheric pressure) pushing it in! (Even less in Katmandhu.) So it’s easy for an oil pump to pull voids or pockets of vacuum in the oil if it doesn’t flow fast enough into to uptake. This ‘cavitation’ obviously reduces the amount of oil the pump can deliver.

Also, in high-speed bearings the oil can be too thick to keep up with the high rubbing speeds reached in modern engines so the ‘wedge’ or hydrodynamic’ effect breaks down. I know it goes against common sense (whatever that is) but the faster a bearing is turning the thinner the oil should be. (A 4cm. diameter main bearing is rubbing its shells at 56 MPH at 12,000RPM! To avoid cavitation the oil need to be less 10cSt or less, which is SAE 30 if the oil happens to be at 100C, or SAE 40 if its at 110C.))

What is the difference between road and racing oils?

The days of incense-like ‘R’ oils for racing only are past, except for classics. At least as far as 4-strokes are concerned, the best synthetic types are ideal for both race and road use.

With ultra-precise components, high-pressure pumps and high engine RPM there has been a move to special synthetic low cavitation/low drag oils to release more power with no reliability loss. These can be (and are!) used in road cars, but 0W/20 is not mentioned in the user handbooks, so there is always some warranty risk. Honda is perhaps the only exception!

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.

I have actually seen this extra power output on the dyno! A very experienced operator in Peterborough who does a lot of test work for Lord Emap used his own year-old Honda Blackbird, with the first run on his favourite 15W/50 high-ester synthetic. 128BHP. Then we changed to a 5W40 high ester synthetic. (So it wasn’t an unfair comparison with B & Q 15W/50!) This time we saw 131.6BHP with a corresponding torque increase. Finally we went to a new (at that time) 0W/20 special synthetic and 134.4BHP appeared! Even the boss was impressed! Later trials in different race and road engines showed this level of improvement was no fluke, so it really does work; and, with the right chemistry to look after the engine and transmission internals, there’s no down side of increased wear.

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.

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 we 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. Just don’t mix 2 stroke and 4-stroke oil!

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’.

[CitroJim]

Gareth! Well done

That was a very good essay. Excellent and most absorbing, a post to perhaps just about put this thread to bed..

I quite concur with all of your conclusions but take issue just slightly with the statements concerning the lifespan of oil. Yes, indeed in a lightly used engine for short journeys only I quite agree that frequent changes are needed for the reasons you give but I have always believed the same applies generally for oil used in a hard-worked engine used primarily for long trips. It all centres around shear-stability. My understanding is that most "mainstream" multigrades derive their multigrade status from the addition of long-chain polymer Viscosity Improvers so say in a 15W/40 the cold 15W viscosity is achived by the base oil itself and the hot 40 viscosity is achieved by the long-chain polymer viscosity improvers swelling under heat, effectively (as far as the engine sees it) thickening the oil. I'm led to believe that these viscosity improvers are relatively quickly chopped to bits by things like the gears in the oil pump and cams acting on followers etc. so very soon an oil that began as a 15W/40 effectively becomes a 15W/30 or even a 15W/20. Because of this, you need to change the oil to ensure these worn-out viscosity improvers are replaced. In paying for a better quality mineral you are actually paying for better quality viscosity improvers rather than the base oil being better quality. Expensive semis apparantly can get their multigrade nature without the use of viscosity improvers and thus last much much longer because there are no long-chain polymers to get chopped up.

LHM is funny stuff in that it has an incredibly high Viscosity Index, a measure of how much the viscosity changes with temperature. LHM changes very little from freezing cold to boiling hot. This quality is essential to ensure the suspension works and feels the same in the Arctic or the desert.