All Morgan Plus 8s and Triumph engines have flat tappets that require ZDDP

1. In General

2. Watchpoint

3. Victim Comment

4. How Much and How Long Does It Last?

Castrol Classic Oil With ZDDP Anti-Wear Additive

Castrol Logo from 1946Established in 1899, originally as C.C. Wakefield, Castrol launched their first lubricant for cars in 1906 and have been at the leading edge of lubrication technology ever since. With the introduction of low viscosity engine oils and changes to anti-wear additives in modern oils in recent years, owners of veteran, vintage and classics are asking whether modern oils are suitable for their cars.

Choosing the correct lubricant for your veteran, vintage or classic vehicle is essential to ensure peak running and maximum wear protection. The technology of older vehicle engines is very different from today's modern cars, so to assist owners, Castrol reintroduced their older brands with their ‘Classic Range’ in the early 1990s. These Classic oils are produced to original viscosities and importantly have retained the necessary levels of additives including anti-wear additive ZDDP (zinc dialkyldithiophosphate) appropriate for the technology of the engines they are designed for and to provide overall protection. The ZDDP levels are appropriate for engines that are in use or running-in, including those fitted with new or reconditioned components, where care should always be taken to follow the manufacturers’ recommendations when breaking in new components such as camshafts. 

ZDDP additive provides a high level of anti-wear protection, but its phosphorus content, the most important lubricant element in the blend, is harmful to catalytic converters ..makes you womder why people call it "Zinc". (This assumes your car has cats and only then if they are NOT stainless steel) and other emission equipment fitted to many modern vehicles...but not vintage cars.  It has therefore been reduced in the latest specification oils or completly replaced, designed for engines using the latest surface hardening technology and meeting the latest emission requirements for modern vehicles. These requirements also necessitate the use of other new emission equipment friendly additives not designed for use in veteran, vintage and classic car engines, primarily for new cam/lifter start-ups, (but why take a risk?)

WATCHPOINT: The explanation here is diplomatic written but hopefully helpful nonetheless. 
1. The truth is that the US government passed a law requiring a minimum lifetime for catalytic converters. It was found they rot out faster (8 years) with the traditional ZDDP oil additive rather than the 10 year average they wanted manufacturers to assure them of.
2. The additive is needed with only "flat tappet" engines..used with most cars up and through the 1970s. I believe the Land Rover V8 (1963-2004) was last mainstream engine still using flat tappets. But older Morgan fare will have them as well.
3. The damage caused are with new camshafts. Older engines that have been seasoned are unlikely to be effected unless a new camshaft is installed.
However, since the engines effected are often VERY costly and no longer produced, and they do their best on conventional oils which are cheap, it is a wise precaution to play it safe, check your ZDDP level in the motor oil you are using and/or use a ZDDP additive. Also be aware that ZDDP levels can be reduced or eliminated without the name of the oil being changed! Find recent spec sheets and check them regularly.

Oil formulations required for today’s modern vehicles are very different from formulations needed for older vehicles, having thinner viscosity and alternative additive technology as stated earlier, making them generally unsuitable for use in older engines. This has been done in conjunction with new vehicle manufacturers who have increased the surface hardening of engine components to receive maximum protection from the new additives. Oils for modern engines comply with the latest API ratings and are designed for modern engine technology with tight tolerances and compatibility with catalytic converters. A car engine of old design has very different characteristics, with cork, graphite or rope seals, low pressure cog driven oil pumps, wider oil-ways with greater dependence on ‘splash’ and ‘cling’ lubrication, lower revving with lesser machine tolerances. Such widely different specifications demand totally different lubricants of thicker viscosity with appropriate additives specially included for the work they have to do. Oils even of the same viscosity, supplied by different oil companies can have radically different formulations and thus have significantly different performance characteristics. Oil classifications are designated ‘S’ (for spark ignition petrol engines) and ‘C’ (for compression ignition diesel engines). Oil classifications for older petrol vehicles range from SA for vehicles from the turn of the last century to SH, to the late 1980s and early ‘90s.

For older vehicles; veteran, vintage and classic, use an oil of the correct viscosity as recommended by the vehicle manufacturer and shown in your vehicle’s handbook. Where your vehicle requires a specific viscosity such as 30, 40, 50 and 20w-50, avoid using inappropriate low viscosity engine lubricants designed for modern vehicles such as 0w, 5w, 10w, 15w.

Castrol’s vehicle lubrication records date back beyond the turn of the last century, detailing lubricant specifications for engine oils, gear oils and greases right through to today's classics, so to find out which Castrol grade is right for a vehicle, owners can simply refer to their vehicle handbook and select that grade from Castrol’s Classic range. Castrol’s Classic engine oils XL30, XXL40, GP50 and XL20w-50 are formulated to the original viscosities and contain the necessary levels of ZDDP anti-wear additive to provide appropriate protection for veteran, vintage and classic engines. The range is available throughout the UK via leading car specialists. For further information either telephone the Castrol Classic help desk on 01954 231668 or visit

updated 2020

I recently came  across an article written by a mechanic review a Rover V8 he had rebuilt. The rebuild failed fairly quickly, with the new composite valley gasket in pieces and blocking oil passages and the new camshaft noticeably damaged. The cam mirrors reports we have had from mechanics fitting flat tappet cars with new camshafts and using a new low zddp oil additive.

Firstly, I cannot be sure what happened to the valley gasket. I have used them with originally-tin gasket cars with never a problem. I wondering how he installed it..

But more importantly he used Shell Helix HX7 (10W40), a oil NOT recommended for the pre-1996 Rover V8s and with reduced ZDDP additives.  Be warned.

The greatest harm caused by the American governments reduction of ZDDP has been:

1. The original refusal of motor oil companies, worldwide, to inform their customers of the elimination or reduction of this additive while selling their oils under the same names. That has been cured to a large degree after the original vintage market uproar. Consult the oil your using specification sheet.

2. The buffet of ridiculous and erroneous advice it had engendered on car forums. :(  Aside from start-up before the new camshaft and lifters are "seasoned" a bit, 800 ppm is more than enough. Dome of the expensive kickapoo joy juice being unwittingly pushed on consumers is inane.

ZDDP How Much? How Long Does It Last?

A percentage of 1300+ ppm at new cam start up is considered adequate.  If you use too much, it will be vented...without damage unless you use a ton more than necessary continually which will prejudice your cats more quickly. However, ZDDP only lasts 2500 miles..which is about the oil change interval for a Morgan TR or Plus 8.