I have a VDJ V8 70 series and the recommended oil is 5/30 this would be ok for cold climate use but like you Doug we are enjoying the warmer weather up north.
I used to work for Ampol formulating oil for a while and the rating they give relates to the viscosity of the oil at 40 degrees vs 100 degrees. All we did was measure the time it took for 100ml of oil to pass through a capillary at both temperatures then refer to a table that provided an value known as intrinsic viscosity.Good oil had a high value which meant they didn't break down as easily at higher temperatures.
As the oil gets hotter it flows faster so it can be seen that if an oil is still very thick (40W) at 5 degrees it would not do a good job of getting to all the bearings and wear areas, by the same token if it was very thin (5W) at 100 degrees it may not stick to surfaces as well to provide lubrication. Modern synthetic oils have wide ranges like 5/50W that cover all eventualities. So read the range best suited to the temperatures you will spend the most time in.
Don't mix mineral and synthetic.
Change oil and filter if you can at 5k or 10k at the most, all oils break down with use even when they still look new, black oil is not necessary no good it just contains a lot of soot. Sometimes with an older engine it is worth doing a flush every now and again to get rid of some of that gunge that may lead to overheating particularly with oil cooled turbos.
All notes here relate to diesel engines!
Brian

G`day,

Being an old oil company man who specialised in lubricating oils and greases I thought I would post this brief history of oil grades.

Way back in time in the 50s and beyond we only had mono grade oils. The Society of Automotive Engineers ( SAE ) in the USA adopted a system which graded oils into seven categories with their viscosities specified at 210* F. The three lightest of these grades SAE 5w, 10w and 20w were known as Wintergrades . They had to meet specific viscosity requirements at 210*F and 0*F. The other four grades SAE 20, 30, 40 and 50 oils had to meet viscosity requirements only at 210*F. We then had the development of multigrade oils. These are oils that cover in one oil a winter grade and a normal grade specification giving good lubrication at high and low temperatures and are designated by two grade numbers, e.g. 10w/30 and so on. The instrument referred to by Brian is a capillary viscometer and it measures absolute viscosity. Measurements are taken at 40*c and 100*c and are required for calculating " viscosity index ". This is a measure of the relationship between viscosity and temperature. Engine manufacturers and oil companies work together to develop oils to meet manufacturer`s specifications and that's why I believe it is important to choose an oil that meets your manufacturer`s specifications. I hope that this has not been boring.

Cheers,

Jontee.

hi
First beaware of yours and others description of full and part synthetic . Oil companies have different definitions . There has been world wide court battles over this .
Second multi grade oils 5-30 were introduced as fuel economy oils . Maximum economy at the expence of engine wear . This grade of oil is not for every one . Always use an oil that's suitable to your climate and end use.
In nth Qld 10-40 full synthetic even 15-40 in some cases
Beaware that 10-40 is a difficult oil to make reliably that's why you typically see in at least semi syn variant
10/40 in the the days of mineral oil use to break down very quickly ! some semi syn and of course full syn has solved this .

Remember all oils degrade and shear [loose viscosity] some just do it faster than others.

Always break engines in on mineral unless specified

Full synthetic oil in AUST is just another RIPOFF from the big end of town . OZzY 10.oo ltr at least USA 5.oo$/ lt

Carefull if u have a dreaded DPF filter

I've always used Castrol magnatec diesel 15W40 in my Land Rover Td5 with 380,000km on the clock. Never even had the head off and the sump only came off about 50k km ago to change the rear main and to check the notorious oil pump bolt. BUT. The Td5 has two filters - a full flow filter and a centrifugal filter. Oil stays clean between 10k changes but I'm sure it loses at least some of its lubricating capabilities.

I don't think it makes a jot of difference what you use as long it's within manufacturers specs and as long as you adhere to the old adage of "clean oil, clean filters (air, oil and fuel) and clean fuel". 

-- Edited by markf on Saturday 22nd of July 2017 12:24:29 PM

We used to strip engine. Barrel. Flush fluids.

EVERY race day. when 2 str dirt racing.
I had my Maico 400 down to under 1\2 hr.
Head. barrel. Rings, and transm oils.
Ceramic Sleeve every season. Normally.

Those things could bloody go.

Two stroke TMK ??

Big Mal wrote:

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I think Tony Bev that the Fiat Duacto 2.8 lt diesel is the same one we have in the Colorado, a VM Motori engine which also appears in Discovery's and Jeep Cherokee's, basic engine is the same just the bits that hang off like manifolds, turbo's and such are changed to suit engine bays. I doubt you will go wrong with a syn 10W40, if you look at the list of specs for a certain oil you will find most manufacturers are covered, things like Dexos2 etc mean the manufacture has checked and licensed ($$) that oil to show that logo, even though the oil before had the international oil specs that the manufacturer recommended anyway......things like B4 or C3 etc.

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 One thing i'd like to ad to Mal's post is with modern diesels like you've mentioned is a lot of these have DPF's (Diesel Particulate Filters) so when choosing an oil it is important to look at the SAPS (Sulphated Ash, Phosphorous, Sulphur) rating. It should be as low as possible to prevent the premature build up of soot in the filters, thus increasing burn offs (re generation periods)

NB: I've used Mobil 1 ESP 5w-30 in my Grand Cherokee as it has a SAPS of .6%

Hope this helps