Originally Posted By: Joe90_guy
First off, is there a typo in your post? Do you mean CF-4? (CF-5 doesn't exist as far as I'm aware). In my experience, the Japanese are pretty much a law unto themselves. They usually do have a good reason for doing the things they do but they don't usually explain themselves well. For reasons I could never fathom, even the most mundane of technical facts are treated as State Secrets!
If I were to guess at what's behind the logic, Nissan might have had concerns about high dispersant treat rates (which have gone up for every new generation of HDDO's). Maybe they felt these were too aggressive to some of the seals used in the engine? Or it might have been they wanted oils based on Group I base stock (the higher iterations of HDDO progressively moved to Group II).
A3/B4 oils are mixed service PCMO's. They can be used on both gasoline and diesel engines. If anything, these days, they are more orientated towards diesel service because the tests are harder to pass and have more impact on the shape of the DI pack.
Hope that helps...
Found this (again) after reading your post a few times
.1,d.dGY]Old Caltex Paper
Quote:
Other design factors influence lubricant suitability for use in Japanese four-cycle diesel engines. Generally the sump capacity
of a Japanese diesel engine is smaller than in equivalent power
North American or European engines. This reduction in lubricant
capacity, and a tendency in the past for Japanese diesel engines
to have lower oil consumption than equivalent North American and
European engines, means that increased thermal stress is placed
on oils used in Japanese diesel engines. Japanese diesel engines
are designed so that piston crown temperatures are lower. This
leads to a reduction in nitrogen oxide emissions, as nitrogen oxide
emissions are a particular concern in Japan. The transfer of this
heat from the piston into the engine oil places even greater thermal
stress on the lubricant.
So an oil used in Japanese diesel engines must have substantially
greater oxidation resistance than North American or European style
oils. The level of oxidation resistance in Japanese diesel engine
manufacturer's "Genuine" diesel engine oils (3) is usually very high
to address the thermal stress placed upon the oil, and additives
used in Japanese "Genuine" oils will usually be of a specific
chemical type to enhance oxidation resistance.
Dispersants, which are used in very high levels in North American style engine oils, are not thermally stable. So the level of dispersant which can be included in a Japanese style diesel engine oil Is limited, and higher dispersancy, low-ash North American style diesel engine oils provide inferior performance in Japanese diesel engines.
Diesel engine oils suitable for use in Japanese diesel engines are formulated with a level of dispersancy carefully balanced to prevent the build up of insulating sooty deposits under the piston crown, which would reduce the transfer of heat to the piston, and at the same time not contribute to oil oxidation.
So an engine oil for use in Japanese heavy-duty four-cycle diesel engines will be highly detergent, typically have a sulfated ash level around 2.0 %, be highly oxidation resistance, and have a carefully balanced level of dispersancy.
Caltex's recommendation for Japanese four-cycle car, truck and bus diesel engines is Delo CXJ Multigrade SAE 15W-40. An appropriate monograde version of Delo CXJ may be used where the manufacturer approves monograde lubricants. Reduced oil drain intervals are recommended when diesel fuel with greater than 0.8 % sulfur content is used.
The ZD30 engine in my Navara, and particularly in the Patrols has a known history of burning down number three piston.
CXJ and it's ilk are long gone in Oz now I think.