Oil Type You Guys Use?

[Graham Thomson]

For my 1989 110 CSW V8 Roooaaaaarer!

Thanks in advance

[disco_al]

my lubricant book says 10w/40 semi synthetic for the V8's, although i have been using 15/40 mineral in my 91 disco v8

[firemannotsam]

Hi I use 10/40 mineral oil in my 3.9 Disco have used 10/40 Part synthetic too, any of the oils mentioned in the handbook are fine depending on the temp range its used in - just remember change the oil in a V8 regular as clockwork at no more than 6000miles intervals.

my disco is LPG'd and the oil looks mint after 6000miles but still gets changed.

It's the best way to look after the engine.

firemannotsam

[Godlykepower]

15W/40 semi-synthetic isnt it?

[Hybrid_From_Hell]

Er

NO to all the above

The Rover V8 is an old design engine with its roots back in the 50s Buick era.

As such stay well away from semi and full synthetics. What is required is a QUALITY 20/50 mineral oil, and by qulaity not some cheap Comma / Planet / Halfords 'special' type of sh*te. The BEST 20/50 for a V8 by far is Valvoline 20/50 Racing Oil, you'll have to hunt to find it - but it is the very best, and from recomendation for JED thats what I use and mates use who know more than I'll prob ever forget

Next down - and cheaper Duckhams Classic 20/50

Also for a V8 Oil changes are hugely important I would say equal to the oil and use a decent new filter each time.

I have even managed to upgrade and convince Mr Bull Bar Cowboy of Valvoline over his beloved Magnatec, ....which is good, ....but a tad thin and not as good as V20/50 Racing oil

This is valid for all Rover V8s, from humble carbed motors 3.9 4.6 EFIs and up to and inc exotics such as the earlier JEDs V8 DEV etc

Nige

[Guest otchie1]

A lot of oils are made by Morris Oils anyway whatever it says on the tin. So long as you buy a new oil that is correctly spec'ed you really can't buy a bad oil.

Just change it regularly and you'll be fine.

As far as I know proper 'race oil' is designed to last just as long as the engine it's in which is just longer than one race and would be pants in a road going vehicle - anything designed to perform best only in a red hot engine at full load with no expectation of survival isn't best suited to swilling around inside a 50 year old lump for 6 months in all weathers.

[Hybrid_From_Hell]

As far as I know proper 'race oil' is designed to last just as long as the engine it's in which is just longer than one race and would be pants in a road going vehicle - anything designed to perform best only in a red hot engine at full load with no expectation of survival isn't best suited to swilling around inside a 50 year old lump for 6 months in all weathers.

Heres the spec

VR1 Racing® Motor Oil

Extra performance for racing conditions

With over 100 years of motor racing innovation and experience, VR1 Racing lubricants are the leading-edge of racing oil technology.

Formulated to increase horsepower and protect high performance engines under race conditions, it provides the competitive advantage pro-racers and enthusiasts seek. VR1 Racing, the right choice for road or track.

VR1 Engine Oils:

Maximum performance and protection at high RPM and high temperatures

Superior friction reduction boosts horsepower output

Extra anti-wear additives (ZDDP) provide ultimate wear protection

Excellent oil film strength to improve oil pressure

Enhanced additives protect against deposits and fuel contamination

API SL

VR1 Racing 5W-50, 10W-60, 20W-50

VR1_Techspec_Racing_oils___Syn_and_Mineral.pdf

This isn't Castrol R or similar FFS

[rick]

Er

NO to all the above

The Rover V8 is an old design engine with its roots back in the 50s Buick era.

As such stay well away from semi and full synthetics. What is required is a QUALITY 20/50 mineral oil,

<snip>

Nige

geez Nige, that reasoning is totally flawed. So what if it's roots go back to the '50's ? They were built up till recently, with modern metallurgy, finishes, etc.

Please tell me what a 'synthetic' oil wont do (and also please define 'synthetic oil') and what a supposedly 'mineral' oil will ?

Personally I'd use an HDEO (mixed fleet diesel spec) either 5/10/15W-40, only as they will have better anti-wear characteristics than a lot of modern petrol spec oils for the cam and lifters ands don't sweat the base oil unless you are going for extended drains or need to run the engine in ultra low or extremely high temps where you need the benefits of a synthetic oil. ie. flow at cold temps, better retained viscosity at extremely high oil temps (better viscosity index) better oxidation protection, etc.

Yes, some engine designs tend to do better on different oils, but it's usually not the base oil that's the difference, it pretty much always comes down to the additive package.

just my 0.02c.

[Hybrid_From_Hell]

FYI - The reason s are :

The engine is designed with 'Skew Oil' pump drive gears in an aluminium housing

Pressures of around 35 psi @ 2400 rpm otimum - rpm over 5000+ rpm can see alarming wear in gears in pump

which is one key reason to use the correct viscosity for the design and not modern synthetics and low w rated oils

You can get uprated gears made in EN36B (mine) but the oil remains 20/50 or different for pure racing

Most of the pump gears are similar with variances a la SDI MGBGT V8 but most a varination on a theme

Rover V8s do not like modern oils / lightweight / synthetic because the way these are pumped are different

to say a 20/50 high grade mineral, even with these thin oils pressure would show as ok, but internally the sytem

is basically high volume not just high pressure. additionally the position of the oil pump on a v8 can also cause issues on oil

drawn to the system as they are non self priming and excessive wear can result from too thin oils if used.

In essence the V8 does not like modern lightweights oils, the oil cannot be pumped in volume around

the engine internals as it can with the heavier 20/50 type w oils.

On a well used V8 the wear in the gears and base plate can be 0.006 upwards to 0.19+ (new is 0.002 / rebuilt new gears and faced base plare maybe 0.004ish)),

and pressure drops will affect the system accordingly, a 20/50 will to some degree allow continued use and more acceptable pressure

For PURE racing then something a la SAE40 is the answer but not for a rioad motor or for the best for racing Motul V300

With hydraulic lifters the same aplies, often tappetty noises are a clue to too thin an oil, or the wrong type, with bleed down lifters and a tuned engine worse still

Additionally V8s esp tunned have heat disappation isues, too thin an oil makes this worse, a qulaity 20/50 will aid cooling as will a

cooler on top andmany will also up the oil pressure to a max of 50-55 psi.

I am no "Oil Guru" but I know people that are - I only have a basic superfical knowledge on Oils / Grading Ratings and differences, more around the V8,

but there are people who live and breathe Oil and its properties, conversations with them, and expert builders have only confirmed 20/50 Quality oil for V8s

up to and debatable around serpentine V8s which are then another slightly different situation Rover V8s have 2 achilles hells (other than water on dizzys ) Oil / pump / wear / grade and heat - cooling = both water and Oil type capacity etc. They do tend to be outside the norm for oils n engines

Personally I'd use an HDEO (mixed fleet diesel spec) either 5/10/15W-40

Well, there you go, - thats the stuff to use in a V8 apparently - what do I know ?

Nige

[ebdesignDEFENDER]

and what is better for 300Tdi engine-? I heard theat Castrol is the best choose..

[Hybrid_From_Hell]

No idea

I 'don't do' DFFs

Nige

[GBMUD]

So, anyone know why LR would specify the wrong oil?

Chris

[rick]

Well thats brilliant of you to share you vast knowledge with us all,

I wil be sure to explain this to John Eales next time we meet up, neither of us, and others who have huge knowledge of the Rover V8s knew this.

<snip>

Well, there you go, - thats the stuff to use in a V8 apparently - what do I know ?

nige

Boy, get put of bed on the wrong side this morning ?

Mate, I'm not arguing on viscosity, although I always advocate if in doubt, stick to the viscosities recommended by the manufacturer, and if that's XW-40, so be it. I haven't said use NEO 0W-5, I'm calling you on.....

"The Rover V8 is an old design engine with its roots back in the 50s Buick era.

As such stay well away from semi and full synthetics. "

Saying something like that is just wrong.

I come back to what I asked originally.

Why ?

All the reasons you gave above relate to viscosity, not oil base type.

With your reasoning above, and staying with at least an SAE 50 at 100*C, 5W-50 Mobil 1, Castrol Edge 10W-60, Redline 15W-50 and 20W-50, Motul 300V 15W-50, etc would be fine. Any xW-50 engine oil has to fall between 16.3 centiStokes (cSt) and 21.9 cSt @ 100*C, regardless of base type.

If an oil is selected on the 'right' viscosity, and I'll take your word for it on the 20W-50 thing, but to my mind an xw-40 should be more than acceptable unless racing, is that the base blend mostly doesn't matter, it's the additive package that counts if the viscosity is right, then base type comes into play if extremely cold or high temps are to be experienced or oxidation and oil breakdown may become an issue, then by all means consider a semi or full synthetic.

[rick]

So, anyone know why LR would specify the wrong oil?

Chris

they probably don't, they would go off the manufacturers recommended oil viscosity.

[rick]

and what is better for 300Tdi engine-? I heard theat Castrol is the best choose..

an 5/10/15W-40 diesel or mixed fleet oil with the best specs that you can afford.

Any reputable name brand is good, and I would aim for at least an API CH-4 or better (CI-4, CI-4+ are current, not counting the latest low ash CJ-4 for low emissions US diesels) or at least an ACEA A3/B3 or A3/B4 for petrol/diesel specs, or E4 diesel (E6 and E7 are the latest specs relating to low emission Euro heavy duty diesels)

If very cold winters are experienced, (eg. below -10*C start up) consider a 10 or 5w-40, and I would take a 15w-40 pretty easy at -10 when starting.

[Bull Bar Cowboy]

Gday rick ……………………………..Good to see you in this thread………..

IIRC you are an ‘oil engineer’ with regard to the chemistry behind modern oils……………… I guess we probably need to clarify a few facts that helped our oil decisions………….

I (and I guess Nige does as well) religiously change our oils at 3000mile intervals, sometimes its sooner………………….this probably is of more benefit to the engine internal than the actual oil used………

After the previous before last rebuild (yes I build a few engines), I spent a long time on the phone to the ‘oil engineers’ at Castrol……………… they reached a conclusion that the best suited oil was 15 – 40 Magnatec, which as you know is a semi synthetic. This oil served me well for a few years but did have drawbacks………

Under sustained high (ish) revs with engine load (i.e. give it some beans up the motorway) the oil temperature would rise steeply and suddenly ………….. and yes, the engine does have a temperature controlled oil cooler of large proportions………..

The above condition would also show a noticeable drop in oil pressure (but not enough to worry about) …………….. I am guessing that the oil was probably beginning to foam ………… one of the biggest issues that I used to have with my race engines in the late 60’s / early 70’s…………..

The Valvoline VR1 option was suggested by a well respected and long standing Rover V8 race engine builder ………………..

TBH this oil does exactly what is says on the tin…………..it seems stable at high rpm, the temperature stays Ok at 80C ………….. and the pressure is fine, once above 1800 – 2000 rpm it sits at relief vale pressure, maybe a little above at 5000 – 6000 rpm………

I think we perhaps need to look at this thread in reality and relate to the folk that will be reading it ……………… most (probably well over 90%) of the rover V8’s will have 100K plus on them ……………. the oil change history and general maintenance will determine the general engine wear, however, the V8 is very good at hiding its wear and a totally f’ked engine will sound quite sweet …………

In these circumstances it would be foolish to use a modern 5 – 40 or 10 – 40 as it is likely to suffer piston ‘blow by’ and get burnt…………. Also the pump on the pre serpentine engines will have difficulty in providing the required volume………. …. these pumps are not renowned for their longevity as the gears and cover plate wear very badly indeed.

Although you suggestion of a mild detergent oil is excellent, I am not so sure it would be a good idea on the pre 94 RV8’s …………..these engines had the 3 row head bolts and it is well documented that the head tips enough to allow gases into the valley……….. this causes a high carbon build up in the camshaft and valley areas ………. I don’t know that I would want to clean this out with a detergent oil and have all those microscopic bits of carbon floating around the already worn bearings, lifters and cam.

I guess the major other issue is that modern oils do not have the required Zinc content to protect flat tappet cams …………… this is well documented by the cam manufacturers and applies mainly to older USA designed engines such as the RV8.

Another area we need to consider is the marginal oiling of the standard pre suffix B engines ………… by the time the oil has reached the cam lobes and lifters of cylinder 7 & 8 it is becoming marginal in both pressure and volume……………

All of these issues can be addressed with a good rebuild………….. my latest rebuild is documented here http://forums.lr4x4.com/index.php?showtopi...l=whats+the+bhp ………….. in fact you get a mention from me in post # 60

I guess in conclusion we should look at the user requirement……….

If an engine has got moon mileage on it, then use nothing less than a good quality 15 – 40 or 20 – 50…………………. If the engine has been rebuilt as stock then I guess you would get away with a 10 – 40 fully synthetic, but don’t expect longevity fore the engine due to the marginal oiling mentioned above……….personally I am using the Valvoline as it is a proven solution from a well respected engine builder who has been in the business a long, long time.

It should also be said that the RV8 seems to benefit from more than regular oil changes……….. every 3K miles………… both oil & filter……….

With the pre 94 RV8 at 80K (even with factory recommended servicing) you can safely say the cam & lifters will be badly worn, the rockers and rocker shafts will be way past their best, the timing chain will have stretched significantly (enough to seriously alter the valve timing) , and the oil pump gears, cover and relief valve will require significant attention. ……………………….all of these issues can be rectified by a careful rebuild using components of choice…………….Rhoads lifters, quality cam, pre-stretched cloyes roller chain and gears, molychrome rocker shafts, and a modified oil pump……..

I guess the don't use synthetics debate came from the early days of Mobil 1 ................ the supposedly wonder oil ............... a lot of folk used it and suddenly their beloved Rover was using oil in copious quantities, and the lifters rattled ....................

Well thats my 10p worth.............

Ian

[Hybrid_From_Hell]

Boy, get put of bed on the wrong side this morning ?

Ok.............

Erm

Yes I did

....and decided to go back and modify me post as it was OTT and uncalled for - but you beat me to it with the "quote Reply" ...and I am guilty as charged.

I have picked me teddy up and apologise for the above ...

( It was something to do with me have a cr*p day so far - and then getting Sikaflex 299 in my ear - don't ask )

From what I have been told (by the experts in Oil and Race V8s etc who do know their stuff) Synthetics "Behave" differently to say a Mineral oil.

The viscosity is key for a V8, and (correct me here if neded) Full synthetics don't have a 20/50w viscosity, the very nature of synthetic is the protection it offers adn less internal drag the "Stickyness" that they are known for means you can get a more modern engine with closer tolerances protected with Synth or semi Synthetic. In fact as I understand it shoving 20/50 into a engine thats wants say Mobil 1 will potetntailly get you in a 'serious mess'

The key here is the 20/50 bit - viscousity, and also LR do state a number of different oils and options dependant on what you can get and what the outside temps are, here in the UK we have a narrower band of "Heat". Oddly enough I have a old "Owners Manual" for A RR and a Haynes book of lies for the early V8 Carb, both are saying 20/50 Duckhams as the recomended oil, the later engines prob co-incided with techology of more modern oils, and hence the options.

However, for many on this forum we will be talking about V8s that are either

1 - Not eaxctly in 1st flush of youth with heavy mileages

2 - Tuned V8s (such as per mine) with all the added strains that can bring

Point 1 would maybe where many are now, and a engine with higher internal tolerances than maybe new would benefit from a thicker oil rather than a thinner oil ?....and 20/50 does this, and it will be mineral to get 20/50, I know that oil as it heats up behaves differently in thickness / thinning between Synthetic and Mineral, but this is where the Gurus have said go 20/50 rather than synthetic as the 20/50 viscosityis more crucial to the engine design / needs, and this mineral 20/50w was an "Original Specification" oil, so on the options available its the thickest viscosity wise which will help vs a high qulalty but "Thinner" Semi or Synthetic

Point 2 - and where I am coming from often is having spent a pigging Fortune rebuilding it (a set of rings was more than some sh engines change hands for ) I wanted the very best "Protection" I could give it, a discussion or 3 with 2 top V8 builders - John Eales being one, was again pointing very strongly towards Valvoline VR1 as it "Behaves" in a 'synthetic way' but its a mineral - (its amazingly sticky) and is what many have sworn by over the years of use and knowledge,.... and its 20/50 to boot.

When I tried Magnatec semi 10/40w (I think thats the spec) I saw oil pressure down after a hard thrash about, more tappet noise (esp on starting up until warm), and higher engine temps generally, when switched back to VR1 the difference was absolutely huge.

I think in my 'clumsy' unknowledgable way what I said originally was "Stay away from full / Semi synthetics" - what I think I was getting at in a roundabout way was that these semis and full synths are not of the 'thickness' viscosity wise that a old fashion mineral 20/50 is, and that the differences between say a cheap 20/50 motor factor "Special" and VR1 Racing is another huge step due to additives and the rating / quality of the product. You'll get the qulaity via a semi or ful synth but not the extra 20/50 viscosity which is what I have been advised to use if you can afford it - and VR1 vs a Full Snth actually seems a Billy Bargain when buying this way via VR1 you get the best of both worlds.

Does that make more sense ?

Apologies again, not so far one of my best days all round

Nige

[Bull Bar Cowboy]

For my 1989 110 CSW V8 Roooaaaaarer!

Thanks in advance

Graham,

I guess we should really be asking you the following,

Whats the mileage ?

Is the servicing history known ?

What do you use the vehicle for ? i.e. off road, Mways, etc, etc,

Ian

[Graham Thomson]

Graham,

I guess we should really be asking you the following,

Whats the mileage ?

Is the servicing history known ?

What do you use the vehicle for ? i.e. off road, Mways, etc, etc,

Ian

Mileage is 124500

A very little service history, although I had it serviced when I bought it at my local man

Motorways and A-roads, the nearest it's been to off-road is bumping on a kerb (I must build up the courage to drive on the wet grass!!!)

[Bull Bar Cowboy]

Ah Ok ............... at that mileage with a relatively unknown history I would be inclined to suggest a reasonable quality 20 -50 oil..............

You can get some idea of the engine condition by looking in the rocker cover thriugh the oil filler .............. if its black in there then its not good news, it should be a sort of golden colour................

As you are running LPG the actual oil colour will not tell you a lot ....................... it tends to stay straw colored...........

Ian

[Guest otchie1]

Heres the spec

VR1 Racing® Motor Oil

Extra performance for racing conditions

With over 100 years of motor racing innovation and experience, VR1 Racing lubricants are the leading-edge of racing oil technology.

Formulated to increase horsepower and protect high performance engines under race conditions, it provides the competitive advantage pro-racers and enthusiasts seek. VR1 Racing, the right choice for road or track.

VR1 Engine Oils:

Maximum performance and protection at high RPM and high temperatures

Superior friction reduction boosts horsepower output

Extra anti-wear additives (ZDDP) provide ultimate wear protection

Excellent oil film strength to improve oil pressure

Enhanced additives protect against deposits and fuel contamination

API SL

VR1 Racing 5W-50, 10W-60, 20W-50

VR1_Techspec_Racing_oils___Syn_and_Mineral.pdf

This isn't Castrol R or similar FFS

Ahh, you have trouble differentiating engineering specifications from sales blurb, my bad.

Wanna buy some STP?

:lol:

[JimAttrill]

If you want to run a synthetic maybe you should try Redline who make a 20/50 for older engines and anything up to a 70 for racing stuff like drag racers.

We use their 10w40 in Rover 3.9s and their 15w40 diesel in diesels. Expensive, though.

[q-rover]

From what I have been told (by the experts in Oil and Race V8s etc who do know their stuff) Synthetics "Behave" differently to say a Mineral oil.

The viscosity is key for a V8, and (correct me here if neded) Full synthetics don't have a 20/50w viscosity, the very nature of synthetic is the protection it offers adn less internal drag the "Stickyness" that they are known for means you can get a more modern engine with closer tolerances protected with Synth or semi Synthetic. In fact as I understand it shoving 20/50 into a engine thats wants say Mobil 1 will potetntailly get you in a 'serious mess'

Yes there is.

In fact I have run 5W/ 15W/ 20W-50 fully synthetics in all my V8 engines (2)

I used to use Mobil1 5W-50 (also comes in 15W-50) but at 5000Km change intervals it got

expensive. I now use cheaper 5W-50 and can buy 10L for the same price as 4L but the specs are

similar. Mobil1 slightly better.

And as someone correctly stated a 20W-50 is a 20W-50 regardless if it is mineral, semi, or synthetic.

They all come from the remains of dead dinosaurs.

[Doctor Who ?]

Yes there is.

In fact I have run 5W/ 15W/ 20W-50 fully synthetics in all my V8 engines (2)

I used to use Mobil1 5W-50 (also comes in 15W-50) but at 5000Km change intervals it got

expensive. I now use cheaper 5W-50 and can buy 10L for the same price as 4L but the specs are

similar. Mobil1 slightly better.

And as someone correctly stated a 20W-50 is a 20W-50 regardless if it is mineral, semi, or synthetic.

They all come from the remains of dead dinosaurs.

...... and sadly getting much dearer by the Day ...

[rick]

G'day fella's,

No worries Nige, we all have days like that..

( It was something to do with me have a cr*p day so far - and then getting Sikaflex 299 in my ear rofl.gif - don't ask sad.gif )

must resist asking, must resist asking

No Ian, not an oil engineer (Tribologist is what they go by ), just an end use like everyone here who has developed an unhealthy obsession with the slippery stuff dating back to my racing days dyno testing various oils.

I talk to the blokes that actually do the blending, as well as the analysts that test the used product and some very savvy end users in the trucking industry here who work hand in hand with the big oil companies.

What you are describing with the Rover V8 is a viscosity and more importantly additive issue regarding your skew gears and just as importantly, lifters and cam. BTW, foaming is usually a lack of silicon compounds in the oil. Racing oils have higher levels of these as scavenge stages in dry sump pumps can make a milk shake out of an oil in short order.

Regardless of your base oil, if the additive package doesn't have enough extreme pressure compounds, (and generally this is zinc dithiphosphate, ZDDP, as it is extremely effective, both in performance and cost for the blender) you will have wear issues in high load areas of the engine.

Unfortunately the levels of ZDDP have been steadily dropping in the last decade to satisfy environmental concerns, it tends to poison the catalytic converter in high levels in the oil. As a consequence, some oils that used to protect OK in the older style engines, don't anymore, although they work fine in OHC and roller lifter OHV engines.

Boron esters are probably even more effective than ZDDP, but they are much more expensive and so are in limited oils. (usually high end synthetic diesel oils like Delvac 1, my current favourite oil)

One issue I think worth mentioning is that we started having lifter/cam problems on Formula Ford engines about twelve years ago and everyone was blaming the oils we were all using. One engine builder was having cam and bore wear issues, so he made all his customers use the then Castrol GP 50 25W-50 ! (thankyou, you just knocked four more HP off our opposition )

The problem was that the lifters coming through were sub standard. The market had started to shrink, QC dropped and the radius on the lifter face wasn't always correct. (nor was the taper on the cam lobe )

We took to individually inspecting each one and would run them in on a special cam rig we made (old engine block hooked up to an electric motor ) just to ensure they bedded in to the cam properly. We could then run the engine in without having to run it for half an hour at 1500-2000RPM bedding in the cam first.

I've talked to a few Chev/Ford V8 people in the last few years and they also believe that a lot of the current flat tappet cam problems that are being laid at the bottle of engine oil are actually lifter radius problems.

My reason for suggesting the HDEO mixed fleet oil is that they still use very high levels of EP and anti-wear additives for the big diesels, in fact the whole additive package is much more sophisticated and robust than the average petrol engine oil, including the premium ones.

You shouldn't have problems with detergents displacing chunks of sludge, they generally soften it slowly as there is only so much a blender can fit in one litre of oil, and while the detergents will remove garbage, they also have dispersant additives that keep it in suspension and wont let it clump. The additives used aren't like the horrible solvent flushes that line the walls of the local spare parts shop.

The only downside with diesel oils in race motors is that the high metallic ash additives used in the detergent/AW/dispersant package may cause detonation problems over time as they will build up in the chamber. this is the reason that Redline's pure race oils don't have any added detergents, although the base polyolester oil's natural detegency is high, so they aren't totally devoid of detergnecy.

Some engine oils like the UK spec VR1, (It's a 10w-40 claimed syn here ) and Oz Castrol Edge Sport 25w-50 have elevated ZDDP levels and are marketed squarely at high performance V8's, as is the latest version of Mobil 1 15w-50 @ 1200ppmZDDP.

FWIW, I used M1 5w-50 for years in a pretty warm 351 Cleveland successfully, and a very famous engine builder here, Pat Purcell used to use M1 5w-50 almost exclusively in all the race boat and NASCAR Chev's (flat tappet cam) he used to build. (this was over ten years ago) Pat's then business partner Tristan used to do my heads, (and a couple of the top V8 teams here)

Regarding viscosities, if an oil is designated 5w-50 or 20w50, at operating temperature (rated @ 100*C) they are both behaving as an SAE 50 oil, regardless of base oil chemistry. Yes, you can have thick and thin 50's, but only within the SAE 50 range !

I was trying to dig up an SAE viscosity chart, but this this is easier, there's one on JB's site here near the bottom of the page. http://members.shaw.ca/jbarge/MTF.htm

Also remember that a synthetic oil, regardless of synthetic type, will have a higher viscosity index than any predominantly mineral oil. What this means is that the hotter the oil gets, the less it will thin out. In other words, if two oils are an identical viscosity @ 100*C, the mineral based oil will get thinner than the syn once the temp starts to climb past 100*.

Now, lets look at synthetic vs mineral based oils.

First up, most oils these days are blends of one kind or another. There is so much cross blending going on that it's almost impossible to call them one or the other !

Secondly, there are that many types of 'synthetics' it's almost impossible to define what one is. In fact it's probably easier to define what isn't.

Oils are broken up into 'Groups' literally Groups I-V

I did have a list of where the VI cut offs were the for the mineral oil groups, but I can't find it ATM.

Group I are the most basic refined mineral oils. They generally have a low viscosity index (the rate at which an oil thins as temperature increases) and higher levels of impurities like sulphur than higher oils. I don't think anyone uses Group I oils as a base for a fully formulated engine oil, at least in the developed world.

I believe they are used for additive solvency in higher level oils.

Group II are more refined mineral oils and are usually the basis of most engine oils today.

Group II+ is basically a sub group of Group II oils. they are obviously more refined than 'normal' Group II. Chevron/Texaco/Caltex use these extensively.

Group III are severely hydrocracked (Chevron method) or hydro treated (Shell XHVI ) mineral oils. These oils are increasingly being referred to as 'synthetic', although are definitely mineral oil in origin. European manufacturers can refer to them as 'Technosynthese' (Motul) 'Molecularly Converted' (Fuchs) or 'Synthetic' (Shell and Castrol)

They offer lower pour points than Group II and II+ oils and have better oxidation resistance, often coming close to PAO's in performance. They have a higher viscosity index than lower oils.

Group IV oils are PAO's (polyAlfaoleofins)

These are the predominate base oils in oils such as Mobil 1, most of Amsoil's range, Castrol Edge 0W-40, 10W-60, etc.

PAO's are generally derived form ethylene gas, and so while having an organic carbon origin, are genuinely synthetic in nature. PAO's have a lower pour point and higher oxidation level than Group III oils, a high viscosity index, but generally not as good a solvency. Other oil Groups are added to enhance their lubricity and solvency.

Group V covers all other oils such as esters, (di-esters, tri-esters, polyolesters, etc, think here of Silkolene, Fuchs, Neo, Redline, Motul, etc.), PolyAlkylGlycols (PAGS), Alkylated Napthalenes (the other synthetic used in most Mobil 1 engine oils) and others.

Esters are an exceptional group of oils, usually having the highest levels of detergency, lubricity, highest viscosity index and the most fluid at temperature extremes. Some can also be highly corrosive in the presence of moisture, although all used in motor and gear oils are highly stable and/or buffered.

They are also bloody expensive. They can be derived from many different sources, and are usually a naturally occurring fat that is esterised. (acid/alcohol/heat) Crop oils, animal fats, etc are used to create these oils.

Most all ester based oils are just that, usually mixed with PAO's, AN's and the other groups to make a full formulated oil. They are also polar in nature, meaning they tend to have an affinity for other polar materials like metal. This is where Castrol derived its marketing for Magnatec. I have no idea how much ester is actually present in Magnatec.

Some esters have been derived from PAO's, and Castrol has cleverly used these to mimic viscosity index improver's in an number of their oils without the VII's downsides. Versions of their 0W-30 engine oils, as well as some of their synthetic gear oils use this chemistry.

PAGs are generally specialised industrial lubricants these days, although there are PAG gear oils around too. PAGS aren't compatible with any other group of oil to my knowledge.

AN's are generally made by Mobil and they replace esters in a lot of their formulations (although it is believed a high % of esters are still used in Delvac 1 and relatives)

(disclaimer. No references are cited as all this carp was off the top of my head, so E&OE)