Engine oil

[Kev]

On a recent thread a question was asked about what engine oils to use in the RV8. This was covered in some detail by a guy over on the Cobraclub forum, I hope you don't mind but i've copied it below as I think it's informative.

Mods: please remove if it's inappropriate





People get carried away on the dated notion that thicker oils are better but this is not the case. Thinner oils 10w as opposed to 20w flow much better at start up and therefore provide vital protection when the majority of the wear occurs.

Added to that a 10w-50 is as thick as a 20w-50 when its hot i.e. sae 50.

You need to balance cold start viscosity with high temperature protection. The ideal oil for your cars would be a 10w-50 fully synthetic. Not a hydrocracked oil but a proper PAO/ESTER synthetic that contains no petroleum basestocks. This oil is far more thermally stable than a petroleum based oil because it's designed in a laboratory by chemists and the molecules are of a uniform size as opposed to varying sizes in petroleum based oils.

These special oils are superior in all aspects and more importantly if they contain ester, they are polar which is of great benefit.


Esters



All jet engines are lubricated with synthetic esters, and have been for 50 years, but these expensive fluids only started to appear in petrol engine oils about 20 years ago. Thanks to their aviation origins, the types suitable for lubricants (esters also appear in perfumes; they are different!) work well from –50 degC to 200 degC, and they have a useful extra trick.


Due to their structure, ester molecules are “polar”; they stick to metal surfaces using electrostatic forces. This means that a protective layer is there at all times, even during that crucial start-up period. This helps to protect cams, gears, piston rings and valve train components, where lubrication is “boundary” rather than “hydrodynamic”, i.e. a very thin non-pressure fed film has to hold the surface apart. Even crank bearings benefit at starts, stops or when extreme shock loads upset the “hydrodynamic” film.

It is also important to understand the consequences of using an oil that's either too thin or too thick as they can both be detrimental.

Hopefully this goes some way to explaining:

Surely the thicker the oil the better!



This isn't always true - even when using a petroleum oil. Although it is true that heavier viscosity oils (which are generally thought of as being thicker) will hold up better under heavy loads and high temperatures, this doesn't necessarily make them a better choice for all applications.

On many newer vehicles only 0w-40, 5w40 or 10w40 engine oils are recommended by the manufacturer.

If you choose to use a higher viscosity oil than what is recommended, at the very least you are likely to reduce performance of the engine. Fuel economy will likely go down and engine performance will drop.

In the winter months it is highly recommended that you not use a heavier grade oil than what is recommended by the manufacturer. In cold start conditions you could very well be causing more engine wear than when using a lighter viscosity oil. In the summer months, going to a heavier grade is less of an issue, but there are still some things to be aware of.


Moving one grade up from the recommended viscosity is not likely to cause any problems (say from a 10w40 to a 10w50 oil). The differences in pumping and flow resitance will be slight. Although, efficiency of the engine will decrease, the oil will likely still flow adequately through the engine to maintain proper protection. However, it will not likely protect any better than the lighter weight oil recommended by the manufacturer.


Moving two grades up from the recommended viscosity (say 10w40 to 10w-60) is a little more extreme and could cause long term engine damage if not short term. Although the oil will still probably flow ok through the engine, it is a heavier visocosity oil. As such it will be more difficult to pump the oil through the engine.

More friction will be present than with a lighter viscosity oil. More friction means more heat. In other words, by going to a thicker oil in the summer months, you may actually be causing more heat build-up within the engine. You'll still be providing adequate protection from metal to metal contact in the engine by going with a high viscosity, but the higher viscosity will raise engine temperatures.

In the short run, this is no big deal. However, over the long term, when engine components are run at higher temperatures, they WILL wear out more quickly.

As such, if you intend on keeping the vehicle for awhile, keep this in mind if you're considering using a heavier weight oil than the manufacturer recommends.

Hope this helps,

Cheers
Guy

[Kev]

Another tome.





SYNTHETICS vs MINERALS

Oil is the lifeblood of your vehicle's engine. For decades conventional petroleum

oils have been providing adequateprotection for all of our vehicles.

The key word here is adequate. Petroleum oils, for the most part, have done an adequate job of protecting our engines from break down. If you change it often enough, you can be relatively sure that your car will last 100,000 to 150,000 miles without a serious engine problem - maybe even longer.

The real question is, why settle for adequate when something better has been available for

about 30 years?

Today's engines are built for better performance, and, although petroleum oils are designed for better protection and performance today than they were 10 or 20 years ago, there is only so much that can be done. Today's engines need high performance lubricants, and the only true ones available are synthetics.

Conventional petroleum oils are insufficient for use in today's vehicles primarily because they are manufactured from a refined substance, contain paraffins (wax), sulfur, nitrogen, oxygen, water, salts and certain metals. All of these contaminants must be refined out of the basestock in order for it to be useful for use within a lubricant.

Unfortunately, no refining process is perfect. Impurities will always remain when any refining process is done. It simply isn't economical to continue to refine the oil again and again to remove more impurities. If this was done, petroleum oils would cost as much as synthetic oils do.



There are many components of petroleum oil basestocks which are completely unnecessary for protecting your engine. They do absolutely nothing to enhance the lubrication properties of the oil. In fact, most of these contaminants are actually harmful to your oil and your engine.

Some of the chemicals in conventional petroleum lubricants break down at temperatures well within the normal operating temperature range of your engine. Others are prone to break down in these relatively mild temperatures only if oxygen is present. But, this is invariably the case anyway, especially since oxygen is one of the contaminants within petroleum basestocks.

These thermally and oxidatively unstable contaminants do absolutely nothing to aid in the lubrication process. They are only present in conventional petroleum oils because removing them would be impossible or excessively expensive.

When thermal or oxidative break down of petroleum oil occurs, it leaves engine components coated with varnish, deposits and sludge. In addition, the lubricant which is left is thick, hard to pump and maintains little heat transfer ability.

In addition, petroleum oils contain paraffins which cause dramatic oil thickening in cold temperatures. Even with the addition of pour point depressant additives, most petroleum oils will begin to thicken at temperatures 10 to 40 degrees warmer than synthetic oils.

As a result, petroleum lubricants will not readily circulate through your engine's oil system during cold weather. This may leave engine parts unprotected for minutes after startup. Obviously, significant wear can occur during this time frame.

Even when all conditions are perfect for conventional oils to do their job, they fall far short of synthetic oils. Part of the problem is that (because of their refined nature) petroleum oils are composed of molecules which vary greatly in size. As the oil flows through your vehicle's lubrication system, the small, light molecules tend to flow in the center of the oil stream while the large, heavy ones adhere to metal surfaces where they create a barrier against heat movement from the component to the oil stream. In effect, the large, heavy molecules work like a blanket around hot components.

There is also another effect of the non-uniformity of petroleum oil molecules which reduces their effectiveness. Uniformly smooth molecules slip over one another with relative ease. This is not the case with molecules of differing size.

Theoretically, it might be somewhat similar to putting one layer of marbles on top of another (if this could easily be done). If the marbles were all of the same size, they would move over one another fairly easily. However, if they were all of differing sizes, the result would be much less efficient.

In the case of petroleum oils this inefficiency leads, ironically, to added friction in the system (the very thing that lubricants are supposed to reduce). Hence, petroleum oils are only marginally capable of controlling heat in your engine. Considering that motor oil does nearly 50% of the cooling of your engine, that's not a good thing. But,

This being said, petroleum oils are “adequate” for the purpose of protecting your engine, if you don't mind a shorter vehicle lifespan, inconvenient oil changes, or decreased engine

performance. Under normal circumstances, most vehicles lubricated with petroleum oil should run satisfactorily for 100,000 to 150,000 miles without serious incidence.

If you like the hassle of changing your oil regularly, and you are only looking for marginal

performance for the next 100,000 miles or so, petroleum oils are definitely the way to go.

Assuming that you don't relish the idea of changing your oil every 2,000 miles or and are looking to keep your “pride and joy” in tip-top condition then these are the main areas where synthetic oils surpass their petroleum counterparts.

Oil drains can be extended

Vehicle life can be extended

Costly repairs can be reduced

Fuel mileage can be improved

Performance can be improved

[ian.stewart]

There used to be a member on the old site who was a lubricants engineer, I wonder if its the same fella, I cant remember his name,
What he says makes basic sense, but, if you are tempted to go the synthetic route, Certainly on earlier engines, DO NOT run the engine in on Synthetic or Semi syn, becaise of its superior lube ability it will not allow the rings to bed in, and cause excessive blow by and fuming,
Whoever I do run my engine on synthetic, I have used Lucas 20/50 for 3 years now, and not had any trouble with it at all,
Ian

[Coops]

i thought you was on the lucas oil ian?

[ian.stewart]

Must stop listening to the wife when trying to type about cars

[Coops]

[JSF55]

I can get my hands on some Q8 synthetic 15/40w would that run ok in the rover? john

[katanaman]

All very sensible stuff, just a shame it didn't go into the consequence of using too thin an oil than recommended as is often the case with the Rover engine. Not because people think they are doing good but more often than not because it's what Halfrods sells.

[katanaman]

I can get my hands on some Q8 synthetic 15/40w would that run ok in the rover? john

LOL you didnt read that lot did you? Read it again, its the 50 part that's important as that's the hot temperature part. 15/50 or anything 50 is ok anything 40 or less is bad.

[JSF55]

Err, i did read it and thought with the extra slippeyness of synthetic going down a grade wouldn't hurt, i've been running 10/40w in mine for ages, better book it in for a rebuild : (

[katanaman]

no I wouldn't say you need a rebuild at all but you will get better oil pressure with 20/50. Its not the quality or slipines or anything like that, that people are on about its the simple fact that the clearances in the rover pump are too great to pump thinner oil properly. The bearings are fine on 10/40, that's proven by the newer serp pump which runs 10/40. Thick oil isnt any better or worse than anything else, it all depends on what the engine was designed to run on.

[JSF55]

Thats confused m even more, i get 45 psi on a run and about 15 at idle !!!
I'm hoping tp pull the sump in a couple of weeks, maybe then i'll actually find out how good a bargain this ebgine was .... complete SD1 £60 !!