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There have been a number of articles and we have heard comments from various “expert” commentators regarding the more recent API specifications and their impact on older petrol engined vehicles.  Unfortunately there is a lot of mis-information out there and also contradictory information as to what can and cannot be used in older vehicles.

 

The focus has been on zinc, or more correctly, ZDTP (zinc di-thiophosphate).  For many years this has been the anti wear additive of choice as it is the most cost effective (and one of the most effective) chemistry to use.  Also incorrectly described as an extreme pressure additive, its primary role is to prevent wear in the rings and in the valve train (cams, tappets, valve stems etc) of the engine.

 

When you add ZDTP you also add phosphorus.  This is a catalyst poison and there have been limits on it since the days of API SH (1994) when a 0.12% limit was imposed.  Prior to that, in the days of API SG (1989) many manufacturers already had put a 0.10% limit on phosphorus.  So, “low” phosphorus has been with us for quite some time.

 

In effect, an engine oil that contains about 0.1% phosphorus or higher, will easily provide the required anti wear properties for older engines and in fact ones at around 0.07% will do the job very nicely.  As a rule of thumb, zinc content is about 10% higher than the phosphorus content but there are some variances occasioanally.

 

Within these changes was the incorporation of friction modifiers.  The early ones were very active and did cause oil consumption in older engines.  These days, technology is well advanced and this no longer is the case. 

 

Now we have API SM – for the first time, the limit on phosphorus is from 0.06-0.08%.  There are industry concerns about the applicability of these oils in older engines.  However, the limit only applies to 0W-20, 0W-30, 5W-20, 5W-30 and 10W-30 oils (so called “ILSAC” grades, GF-4).  Any other grades are exempt from this. In the US though the same additive tends to get used all the way from 0W-20 to 20W-50 as as a result, the new low phosphorus SM/GF-4 packs find their way into older engines.  This is why many of the "beware of no zinc" papers and articles are coming from the US.

 

There is one other factor with non-ILSAC oil grades.  If they also have the European ACEA A2/A3 with B2/B3 or B4 performance levels, phosphorus levels will also be at 0.10 % to 0.12% as their tests have been more severe than the API for some time.  Hence an oil that is SL (SM)/CF/A3/B3 also well exceeds the anti-wear requirements for older engines.

 

The irony is that API SF and SG oils formulated in recent years usually have phosphorus contents of around 0.08% (usually 0.1% maximum) anyway due to other advances in technology, unless the blender chooses to add extra additive.

 

This brings us to diesel oils. 

 

Currently, they have no phosphorus limits – as such many people recommend them for older cars, even though many others say that the detergent levels are too high and the engine will use oil.  Well, you cannot have it both ways.  This one originated from the USA and hence did not take into account European ACEA standard petrol engine oils, which are easy to find in Australia, NZ and Europe, but a lot harder to find in North America.

 

Yes, it may use oil, but only until the cleaning period is complete – unless you are unlucky enough to move a deposit that is stopping oil leaks that is.  However, an engine in good internal condition will run quite happily on diesel oils as long as the SAE viscosity is correct.

 

Be warned though, some diesel oils already have chemical limits.

 

This leaves Synthetic oils.  Many people say they are too “slippery” for older cars, and can cause wear and oil consumption.  Well, wear protection has little to do with the base oil type and everything to do with the additive (all else being equal).  If the wrong anti wear additive is used (and this did inflict a brand of synthetic oil not that long ago) then it does not matter how good the rest of the oil is, wear will occur.  Hence, a synthetic oil is quite OK in an older car, but unless it is fully reconditioned and then correctly run in, then there is no real benefit to the end user.  It is true that synthetic oils (especially the PAO type) have lower friction, as their chemical structure allows the molecules to slide over one another more easily than a mineral oil, but if the correct additives are used, then this becomes a benefit, not a detriment.

 

The choice of the correct oil for older cars comes down to various factors such as:

 

·         Original Viscosity Specified

·         Condition of engine (leaks, sludge)

·         How often the engine is run

·         How the vehicle is to be used

·         Oil consumption

·         Current oil used

 

Blanket statements are not useful to anyone, be it the vehicle owner or the oil industry.  If you have any doubt as to what oil you should use, contact your preferred supplier – preferably Penrite of course.  On our web pages (www.penriteoil.com) are listings for both post 1970 vehicles and also another section for pre 1970.  In both cases, we have chosen the correct oil in our range that would suit the vehicle shown, basis the condition we would expect the vehicle to be in and how we expect it to be operated.

 

Penrite HPR 15, Classic HPR, Classic 20W-50, Shelsely and Heritage oils all contain zinc.