Did I fill in the wrong engine oil?

[Dieter H. Marschall]

Hello everybody,

accidentally my mechanic filled in synthetic oil Castrol Edge Formula RS 10W60, which I keep in my garage to be used in my TR6 with a recently rebuilt, leadfree engine.

In the Stag I usedmineral oil20W50 so far.

In the meantime I drove a couple of kilometres and could not see any oil leaks or other negative effects. Do I need to worry or is the 10W60 oil perhaps the better choice even?

I was always told not to use synthetic oil in an engine, which had run on mineral oil for a while before. The Stag engine was reconditioned some time ago though.I do not know what sort of work was done on the engine though.

Kind regards, Dieter from Germany.

[Giles]

imported post

I would say that it istoo thin- using a synthetic is OK but it should be a 20/50. If it was mine I would change it to be on the safe side - see what others think first though?

[Guest]

imported post

Hiya Dieter, if you use anything thinner than 20 /50, it will drain down from the camshafts and valve gearwhen you're parked overnight, leaving you with a dry start, not good ! Cheers, Martin.

[Andy Rundell]

imported post

Hi Dieter,

The 10W60 you have used is thinner when cold (the 10W) and thicker when hot (the 60)

I use a regular mineral 20/50 - to be perfectly honest i doubt you will be doing much harm, the only comment may be that, because it is thinner when cold you may get less protection at start-up (if it is so thin it has not clung to bearing journals as well as a 20W ) - which is strictly true.

keep an eye on your pressure and levels - if it seems ok i'd probably leave it until the next oil change and revert to a 20/50.

Your question is likely to generate lots of different opinions - the subject of oil usually does


cheers..............Andy

[mjheathcote]

imported post

I've run Castrol RS before they changed it to Castrol Edge for over 15 years with no problems, although apart from the initial running in oil it has always been synthetic.

I don't get the comments about the oil being too thin it will run off the valve gear etc....well how exactly does a 'modern' engine design cope this this 'problem' then?! they don't run in a submerged bath of oil that never drains away!!!

A lower value (0, 5 or 10) can have advantages in winter of course allowing the oil to easily run through the oil galleries when a higher (20) viscosity is thicker initially until the oil warms up.

When the engine has warmed up, the lower end viscosity is then irrelevant of course.

[mjheathcote]

imported post

This explains it better, by 'oilman':

"I read on many forums about 0w and 5w oils being too thin. I will try to explain it without getting over technical and we'll go from there.

0w-40, 5w-40, 10w-40 and 15w-40 are all the same thickness (14cst) at 100degC.

Centistokes (cst) is the measure of a fluid's resistance to flow (viscosity). It is calculated in terms of the time required for a standard quantity of fluid at a certain temperature to flow through a standard orifice. The higher the value, the more viscous the fluid.

As viscosity varies with temperature, the value is meaningless unless accompanied by the temperature at which it is measured. In the case of oils, viscosity is generally reported in centistokes (cst) and usually measured at 40degC and 100degC.

So, all oils that end in 40 (sae 40) are around 14cst thickness at 100degC.

This applies to all oils that end in the same number, all oils that end in 50 (sae 50) are around 18.5cst at 100degC and all oils that end in 60 (sae 60) are around 24cst at 100degC.

With me so far?

Great!

Now, ALL oils are thicker when cold. Confused? It's true and here is a table to illustrate this.

SAE 40 (straight 40)

Temp degC.........................Viscosity (thickness)


0..........................................2579cst
20..........................................473cst
40..........................................135cst
60..........................................52.2cs t
100........................................ 14cst
120.........................................8.8cst

As you will see, there is penty of viscosity at 0degC, in fact many times more than at 100degC and this is the problem especially in cold weather, can the oil flow quick enough to protect vital engine parts at start up. Not really!

So, given that an sae 40 is 14cst at 100degC which is adequate viscosity to protect the engine, and much thicker when cold, how can a 0w oil be too thin?

Well, it can't is the truth.

The clever part (thanks to synthetics) is that thin base oils can be used so that start up viscosity (on say a 5w-40 at 0degC) is reduced to around 800cst and this obviously gives much better flow than a monograde sae 40 (2579cst as quoted above).

So, how does this happen, well as explained at the beginning, it's all about temperature, yes a thin base oil is still thicker when cold than at 100degC but the clever stuff (due to synthetics again) is that the chemists are able to build these oils out of molecules that do not thin to less than 14cst at 100degC!

What are the parameters for our recommendations?

Well, we always talk about good cold start protection, by this we mean flow so a 5w will flow better than a 10w and so on. This is why we recommend 5w or 10w as the thickest you want to use except in exceptional circumstances. Flow is critical to protect the engine from wear!

We also talk about oil temps, mods and what the car is used for. This is related to the second number xw-(XX) as there may be issues with oil temperatures causing the oil to be too thin and therefore the possibility of metal to metal contact.

This is difficult to explain but, if for example your oil temp does not exceed 120degC at any time then a good "shear stable" sae 40 is perfectly capable of giving protection.

"Shear stability" is important here because if the oil shears it thins and that's not good!

However, if you are seeing temperatures in excess of 120degC due to mods and track use etc then there is a strong argument to using an sae 50 as it will have more viscosity at these excessive temperatures.

There are trade offs here. Thicker oils cause more friction and therefore more heat and they waste power and affect fuel consumption so it's always best to use the thinnest oil (i.e. second number) that you can get away with and still maintain oil pressure.

There is more but this post is too long already so lets keep it to basics.

Cheers
Guy
---------

Thats great and informative info and explains the second number brilliantly, but a bit more about the first number would be interesting too. I get it that for the main use my car gets, that i need to be using a xW 40 oil, but what first number should i use? I usually stick with the stock recommendation of 10w 40 but i don't know why?

-------

Mark,

The best way to illustrate this is by putting up some more numbers but before I do that, remember that at 0degC, 10degC and 40degC the oil is thicker than at 100degC.

The "w" number actually stands for "winter" and it's the "cold crank viscosity" of the oil.

The thickness of the oil varies dependent on viscosity but, here are some examples.

0w-20..at.......... 0degC = 328......at 10degC = 181......at 100degC = 9
5w-40..at ........................811....................... .421..........................14
10w-50.at.......................1039.................. ......539.........................18.5
15w-50.at.......................1376.................. ......675.........................18.5
20w-50.at.......................2305.................. .....1015........................18.5

Obviously the thinner the oil the better the flow at 0degC and 10degC.

If you understand my two posts then you will now be getting the picture of what's best. You need an oil that flows quickly at cold start protecting the engine from wear (5w and 0w do this best) and an oil that will protect your engine when hot depending oil oil temps.

A very good grade for both top and bottom protection is 5w-40 which is very suited to European climates and is more shear stable than 0w-40.

Hope this helps"

[V Mad]

imported post

Thats it in a nutshell (albeit a vary big nutshell)

But there have been reports thatmodern oils may lack an ingredient (it may be zinc)that old oils have which protects components on older design cars such as non-roller cam followersthat run under high pressure. This has been said to cause failures.

[flying farmer]

imported post

I read an article in Practical Performance Car today that modern oils have reduced levels of an anti-wear compound called ZDDP (zinc dialkyldithiophosphate). Apparently it is very hard on catalytic converters so the powers that be have reduced permitted levels. Where this leaves us with classic type oils is anyones guess:?

Neil

[singapore stag]

imported post

Some off road racing vehicles use high zinc oils. High zinc oils are permissible only in this scenario,.... Same article also noted that the Valvoline VR1 had a higher zinc content then its counterparts.

Sukh.

[Guest]

imported post

mjheathcote wrote:

I don't get the comments about the oil being too thin it will run off the valve gear etc....well how exactly does a 'modern' engine design cope this this 'problem' then?! they don't run in a submerged bath of oil that never drains away!!!

If that encyclopedic artical is the source of your information then you've completely missed the point. I must say, if you understand all of it I'm filled with admiration, it reads like something out of Lord of The Rings to me.With the engine off, oil pools around the followers ready to do it's stuff on start up, take a cam cover off and you can see it, if too thin IT DOES DRAIN BACK INTO THE SUMP ! Modern engines are built to much finer tolerances than the Stag, andbenefit from quicker pressure build up with oils that are thinner when cold.:? Martin.

[singapore stag]

imported post

Martin I must confess, you sure have a way with words...

[mike h]

imported post

mike h

new member to the forum but have been a member of the SOC for 9 years.

the oil I use is valvoline racing VR1 20W-50you can get it from Mill Autos.

Cost is approx. £26.00 but it will give you good oil pressure for your stag engine

hope this helps you.

mike h

[Guest]

imported post

singapore stag wrote:

Martin I must confess, you sure have a way with words...

If only I was the same with Ladies and money ! Martin.

[Guest]

imported post

Hiya Mike, welcome to the forum, how have you resisted it for so long ? Martin.

[marshman]

imported post

Martin Stevenson wrote:

mjheathcote wrote:

I don't get the comments about the oil being too thin it will run off the valve gear etc....well how exactly does a 'modern' engine design cope this this 'problem' then?! they don't run in a submerged bath of oil that never drains away!!!

if too thin IT DOES DRAIN BACK INTO THE SUMP ! Modern engines are built to much finer tolerances than the Stag, andbenefit from quicker pressure build up with oils that are thinner when cold.:? Martin.

Sorry but I can't resist adding my 2p to this. If you look at the figuresoil is many times thicker when cold - or put another way its a lot thinner when hot. If thin oil really was a big problem then even your 20w50 would drain away past the cam buckets when hot. As we all know Stag engines are not the coolest (temperature) engines in the world and also seem to suffer from heatsoak. So when you switch off after a blast down the road, your nice 20w50 is like water anyway! and it stays this way for some considerable time. In Dieters case he has gone for a 10W60. As I understand itthis will be slightly thinner than 20W50 when cold and slightly thicker when hot - so in my book he does not havea problem. I think the real difficulties occur when you try using the 0W30 oils that are significantly thinner when hot, this may give you problems with reduced oil pressure due thinner oil and the increased clearances on your old engine.

One last thought - Oils like Castrol Magnatec are supposed to cling to all metal parts when the engine is turned off. I beleive this to be true of a lot of modern oils - I assumeprocess is throughmolecular attraction. This is what you really want to protect the moving parts on a cold start.

Having said all of that - I am a firm believer in a nice 20W50 Mineral oil in older "classic" car engines - it just seems right

Roger