When we talk about “Zinc” in motor oils, what we are really talking about is a family of additives called Zinc DiakylDithioPhosphates – better known as ZDDP.
Many different types of ZDDP additives exist – Primary, Secondary, and Ary. These different types of Zinc have different activation thresholds. You see, Zinc is not a lubricant until the ZDDP reacts under heat and load to create a phosphate glass film that protects the metal surface.
This is critical to protection.
Zinc needs heat and load for it to activate and then lubricate the surface. Some types of Zinc activate faster under less heat and less load than other types of Zinc. These “fast burn” Zinc additives provide better protection during engine break-in because they react faster and establish that protective Phosphate glass coating quickly during the critical break-in phase.
All types of ZDDP function in the same manner. Zinc is a polar molecule, so it is attracted to steel surfaces. Under heat and load, the Zinc reacts with the steel surface and creates a phosphate glass film that protects the steel surface by forming a sacrificial film that covers the peaks and fills in the valleys of the steel surface.
There is heaps of information about ZDDP additives on the web. Such info is best gleaned from people who are not selling such a product.
ZDDP is particularly important in engines that have conventional cam followers - such as A, B and O series engines - they comprise of camshaft lobes that bear directly on followers and thus rely totally on lubricant adhesion to their surfaces to avoid rapid wear.
I currently have an A series engine whose cam followers have been reduced to something like lego blocks. I would assume that it has been run on very bad oil for a long time.
Engines that feature double valve springs - like my modified B series engine and my 70's motorcycle, experience even greater loading on these vital wearing surfaces, so some degree of thought is necessary when choosing oils.
There has been a tendency for oil manufacturers to reduce zinc additives as they have been linked to problems with catalytic converters. Boo hiss.
Interestingly enough, Amsoil who were one of the first to market a fully synthetic oil, have done a huge amount of research on such things.
I have placed a detailed study on my website for a short time - you can get it here..
http://www.kilroy.co.nz/Amsoil_Study.pdf
I was very impressed by the fact that they rated Mobil 1 Vee Twin as better than their own oil in several fields - but both oils stand head and shoulders above many others in the study.
Regarding your "old oil" situation, I would get it out of the engine as soon as possible, as old oil tends to contain rather acidic residues that cause deterioration even when not in use.
I would change oil and filter without running the engine at all - Supercheap Auto often special Castrol GTX 20W/50 - I have picked up 14 gallons of it at $20 per 4 litre - perfectly suitable for our engines and my first line product when not using synthetic.
Once the vehicle is in regular use I would give it a second oil and filter change - and would do that warm.
There is absolutely no danger in moving to 20W/50 fully synthetic from mineral oil - but considering the cost of it - I would not bother if I needed to make several changes in quick succession - nor if the engine proved to have a major thirst for oil. I would rather rectify the problems than continue to pour oil through it...
I buy all my Mobil oils from Allied Petroleum. As I am a business they give me a healthy discount. Here in Christchurch they also have some very knowledgeable people behind the counter - and they have been able to answer all my technical questions.
Hope that is of use.
Cheers.
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