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Modern Oils in Older Engines

 

 

Neil McTavish – Australian Automotive Technology Manager Castrol

 

In recent times we have been asked by a number of people to comment on using the latest oils in older engines. Questions have come mainly from car clubs but also from some magazines, racers and engine builders. The questions relate to wear performance on flat tappet cams. Please note, all my comments in this article are about flat (sliding) tappets not roller followers, a different story.

 

Firstly let me remind people, this is Australia not the USA. I have read a number of articles where the information clearly comes from the USA but you are left with the impression that it is written about Australia. The internet can be misleading if the source of the information is not clear.

 

I have been in the technical area of lubricants in Australia for more than 30 years. So I am familiar with engine oil formulations since the early 1970’s and have seen a lot of information on oil formulations back into the 1950’s.

 

Although Castrol is sold in more than 100 countries around the world, products and the range of products are not the same in all countries. The oils sold in Australia are not the same as the USA. There a range of reasons for that including different market needs, mix of vehicles and climatic conditions. The range and type of oils we sell in Australia are decided by people in the Australian business not by people in the USA or Europe. The people involved are a combination of Marketing, Sales and Technology. Our Sales and Marketing people are just as keen to have the best products that suit our market as we are in technology and you the customers’ desire for your vehicles.

 

There are two main industry oil qualification systems. These are API/I LSAC from USA and ACEA from Europe. Both of these systems are developed jointly between the oil industry and vehicle manufacturers. The updates reflect the latest requirements for standard vehicles and applications. The biggest influence most recently is the “Tier 2” emission regulations in the USA and Euro 4 in Europe. These regulations do not come into place for petrol engines in Australia until between July 2008 and July 2010.

 

The US petrol classifications have two types, ILSAC grades for GF-3, GF-4 etc. are; SAE 0w-30, 5w-30, 1 0w-30, 0w-20, 5w-20 and the rest, not ILSAC. The ILSAC requirements require improved fuel efficiency and have chemical limits on Phosphorus and Sulphur. API performance qualifications started at SB in the 1930s, currently the highest API petrol engine specification is SM. ACEA specifications are A1/B1, A3/B3, A3/B4 and A5/B5. ACEA C1, C2 and C3 are newer low Phosphorus specifications.

 

The Phosphorus is limited to help maximise the life of catalytic converters for long-term emission reduction. Sulphur mainly effects base oil type so I will not discuss it further here.

 

The main reason Phosphorus is added to engine oil is for cam and tappet wear protection. The most widely used form of Phosphorus in engine oils is in an organometallic molecule. The material is Zinc Dialkyl Dithio Phosphate, ZDDP or ZDTP for short. Useful molecules that include Sulphur and Phosphorus, they perform most of the antiwear protection on steel surfaces. The most recent API SM/ILSAC GF-4 grades have reduced the maximum allowable Phosphorus content to 0.08% (800 PPM, Parts per Million) from 0.10%, 1000 PPM.

 

The 0.10% limit has been in place for approx. 15 years in the USA and since 1986 in Australia. Yes most petrol engine oils for more than 20 years in Australia have been 0.10% Phosphorus maximum. That was as a result of an agreement between the car industry and the oil industry in Australia. That engine oils for petrol engines would be 0.10% Phosphorus maximum. However most oils from the 1950’s and 60’s had lower Phosphorus content than even the latest passenger car engine oils, i.e. it was typically 0.06% which is even lower than the 0.08% limit set by API SM.

 

ZDDP is a multifunctional additive; it has powerful antioxidant effect in addition to the antiwear characteristics. The size and type of the alkyl group attached to the Thio phosphate within the molecule influences the relative antiwear antioxidant balance of ZDDP additive. Over time Castrol have used modified ZDDP’s that are more intended for wear performance and substituted other materials to boost antioxidant performance of our engine oils. So looking at Zinc and/or Phosphorus levels alone does not tell the full story in terms of wear protection.

 

The majority of the Castrol passenger car lubricants sold in Australia are ACEA qualified as well as API qualified. The ACEA requires extra valve train wear, VTW, tests over and above API requirements. In addition most of Castrol ACEA qualified products are 0.10% Phosphorus maximum. The same as we have used for 20 years or more. So that is why some of our ACEA qualified oils only claim API SL even though they pass all API SM engine performance requirements, the Phosphorus content is above the maximum level allowed for ILSAC grades.

 

There has been discussion about using diesel engine oils instead of passenger car engine oils. Some of these do currently contain higher levels of Phosphorus, ZDDP, than passenger car qualified to API SL or SM. They have higher Phosphorus to help minimise soot related wear. Future generations of these oils will also have Phosphorus limits and be lower over time for the same reasons as for passenger car engine oils.

 

The higher level of Phosphorus is not a guarantee of satisfactory wear protection. As I said earlier, wear performance is related to the particular ZDDP being used. Also many of the diesel oils with higher Phosphorus also contain higher levels of detergent and dispersant which compete for surface area with the ZDDP which can reduce its effectiveness. During the development of the current API SM engine tests, a high phosphorus diesel engine oil was run in a flat tappet, push rod engine test and it failed the wear requirements with worse results than most low Phosphorus passenger car oils.

 

In Australia we have many people rebuilding older vehicles and engines. Many of these people choose to put a modified cam into the engine when it is rebuilt. That is often the case even though they do not plan to get involved with Motorsport and the engine spends most of it life at low RPM. Modified cams with higher lift often require stronger or dual valve springs. All of these modifications increase load on the valve train and increase the likelihood of wear on cams and tappets.

 

The first few minutes of operation for new cam and tappets are very important. Run-in is important for good long service life. Castrol have put considerable effort into understanding valve train lubrication. Research has shown one of the highest if not highest wear mode for a cam and tappets is while the engine is at idle. Running an engine at medium speed, say 2,000 to 4,000 rpm generates much less metal-to-metal contact between cam and tappet than at engine idle.

 

Also ZDDP is temperature activated so running the engine at low oil temperature also accelerates cam and tappet wear. Some years ago a race team contacted us after wearing out three camshafts during run-in on a dyno. They ran the oil at approx. 50°C. We recommended take the oil to 85°C, no more cam wear issues.

 

In summary most of the Castrol passenger car engine oils sold in Australia are still formulated to 0.10% Phosphorus maximum, the same as we have had for the last 20 years but higher than was used in the 50’s and 60’s.

 

When running in new cams and tappets avoid idling as much as possible in the first 30 minutes to hour of operation. Make sure the cam and tappets are pre­lubed with Moly grease and oil. Try to keep engine oil temperature above 80°C. Driving the vehicle or running the engine under load achieves that most quickly. The cam and tappets should be run-in by 250 to 500 km. Castrol Edge Sport 25w-50, previously Formula R 25w-50 and before that GP50, is specifically part of our performance range of engine oils for push rod, flat tappet engines.

 

It has demonstrated excellent wear protection on radical cam profiles. Although rated API SG it incorporates the latest detergents and dispersants for good engine cleanliness, contains 0.10% Phosphorus and retains components for strong wear protection. The off-the-shelf product is widely used in competition engines.

 

If a full synthetic engine oil is preferred then our Castrol Edge 0W-40 or Edge Sport 10W-60 is recommended. Again these are formulated to 0.10% Phosphorus maximum and can be used with flat tappet followers with confidence the same as Edge Sport 25W-50.