Ferret Oil Capacities
Ver 3.







Engine lubrication system (dry sump) ... ...

3 gal

3 gal


Engine cooling system ... ... ... ...

4 gal

5 gal


Fuel Tank - total including 3 gal

reserve ... ... ... ... ... ...


21 gal


25 gal



Fluid coupling ... ... ... ...

9 pints

11 pints


Gearbox ... ... ... ... ...

1 gal

1 gal


Transfer box ... ... ... ... ... ...

6 pints

7 pints


Inner tracta joint housings,

including bevel boxes ... ... ... ...


3 pints


3 pints



Outer tracta joint housings,

including road wheel hubs ... ... ...


1 pints


1 pints



Brake fluid supply tank ... ... ... ...

1 pints

1 pints


Air cleaner ... ... ... ... ...

4 pints

5 pints


Steering cross-shaft bevel box

(lower) ... ... ... ... ... ...


1 pints


1 pints



Steering bevel box (upper) ... ... ...

1 pints

1 pints



Regardless, "Straight 30 engine oil" for the engine, try not to use multi-grade as the additives will attack your big end bearing metal. I ended up using 40 weight Diesel engine oil (30 weight is a bit thin for our summer).
Generator - whatever you have in the engine, it is plumbed into the engines' oil feed.
Gearbox - same oil as engine.
Bevel Boxes - I am using 90 weight EP (Extreme Pressure) gear oil, I tried the multi-grade version and it just leaked out all the quicker!
Transfer Box - 90EP gear oil.
The Ferret Drivers Manual is without doubt the worst laid out manual I have ever seen! From what I can glean from it the following is the oil call ups. (Believe it or not, there is no chart or grouped information about the different oil types required, instead the info is scattered through out the manual)


Ferret Oil Types





Not spec.

Air Cleaner


Generator Gearbox


Fluid Flywheel

Not spec. - (Aussies use B.P. Aerohydraulic No 2)

(English use standard auto transmission fluid - the red stuff)



Transfer Box


Inner Tracta Joints


Outer Tracta Joints


Bevel Boxes


Wheel Hubs





OF-20 or OF-24

(Dot 3 Brake Fluid?)


Courtesy of Richard Notton here is the conversion info:  

Hi All,
The very helpful lube guy at the Defence Equipment Research Agency here says:
OMD 30 is 5W/20 and now superseded by

OMD 55 which is 5W/30 to API CC/SD,

this allows vehicles to operate over a greater environmental temperature range without an oil change.

OMD 80 is 10W/30

OMD 80X is 10W/30 to API spec CD/SE

OMD 90 is 10W/30 to API spec SF

These are high detergent diesel lube oils.

OMD 110 is SAE 30 (straight)

Please be careful about OMD 75 (10W/30) which was supposed to replace OMD 110 (SAE 30). OMD 75 is a "1970's" style multi-grade and not like the modern products although it is available here as a "classic" oil - at a price. Pressure fed gearboxes (eg Stalwart) are safer on OMD 110.

Many thanks to Richard (England) for this information.



There has been some controversy over oils in the past, both by type, grade and compatability.

Synthetic and mineral oils. Can they be mixed?

The answer to this is both Yes and No. The reason for this is the base used in the manufacture of synthetic oils. Generally the early synthetic oils were of a hindered polyester base. When these hindered polyester based oils were mixed with mineral oils, they form a viscous gel matter, a bit like a really sticky grease rather than an oil and as such, do not lubricate the required parts causing mass mechanical failure.

However, later synthetic oils use a Poly Alpha Olephin base and these mix readily with mineral oils without any side effects.

It is necessary to check with the oil manufacturer as to which base they use in the manufacture of their synthetic oils, especially when deciding to change the mechanical component from mineral to synthetic.

Engine oils, Monograde or Multigrade?

It has been said that multigrade engine oils produce a metallic ash when burned and that this eats away or corrodes the white metal of the big end and main bearings and also that this metallic ash is detrimental to engines.

Not quite so. This is often confused with the metallic additives in oil and a test proceedure which produces Sulphated ash. The 2 being confused. Here is a response from Stephen at Shell.

"Metallic compounds are present in all automotive engine oils, monograde and multigrade, as detergent additives (to keep engine components clean) and to provide the TBN (Total Base Number - to neutralise acids)".

"I suspect the above comments results from confusion about Sulphated Ash, which is a measure of the metallic compounds in an oil. In this test the oil is burnt and then treated with sulphuric acid (hence Sulphated Ash). It is an oil property that is frequently used out of context".

Multigrade Oils
A multigrade oil is simply an engine or gear oil that meets the requirements of more than one SAE viscosity grade classification,and that can be used over a wider temperature range than a single grade oil. To achieve this a multigrade will typically have a thinner base oil, for good cold flow performance, and a VI improver to maintain viscosity at high temperatures.

From the above information, it certainly appears to me that a multigrade oil is far better and gives better lubrication protection than a single or monograde oil.

Will Gear oil, with extreme Pressure additives corrode yellow metal plain bearings and bushes?

The answer to this question is No. Once again, a response from Stephen at Shell.

The API (American Petroleum Institute) devised the GL system in 1969 in order to standardise the numerous equipment manufacturers, government and military automotive transmission oil specifications. Defenitions were written for 6 grades of oil, designated GL-1 to GL-6 which varied according to the severity of operation and type of gear. GL-1 was for the mildest of conditions for use in spiral bevel and worm gears, GL-6 the most severe used in high offset hypoid differentials where there is a significant proportion of sliding as well as rolling friction.

Gear oil formulations contain yellow metal corrosion inhibitors (also called copper passivators) to prevent corrosion of yellow metal components. Gear oil standards will also commonly include copper corrosion tests. It is important, however, when choosing a gear oil to ensure it has an appropriate GL rating and Viscosity grade.

Again, the questions have been answered with thanks to Shell.

Remember, it is important when selecting your oils, to consult the manufacturer and the specific manual for your vehicle in making the best decision as to the viscosity grade and other factors when purchasing your oils and protecting your vehicle.

Remember too, that many of the vehicles we are dealing with are by todays standards, very old and the improvements in oils these days is quite incredible. Your manual may list a monograde oil, although at the time of printing your manual, was possibly the best. Remember however, that may have been 50 years ago and since then , you may well be better off using a multigrade oil.

This article is only to make you more educated about oils and as such more informed about the decisions, you as an individual can make about the type of oil you wish to select.

For more detailed information, I can suggest you contact you local oil supplier and distributor or the API.

Many thanks to David and Stephen at Shells Technical Department for the information and correspondence.

Alex (a former Australian Army tracked vehicle mechanic).


Ferret Specifics revisited:

Again the issue of oils has come up, Alex and I have been debating the subject on the Ferret mailing list.
Here is my decision on what I use in my own vehicle and the reasons why. I will at this time point out that my decision is influenced by my experience with radial engined tanks. In the 1960s - 1980s people were recovering these things and restoring them to various degress. A bad mistake was to use modern oil in a radial, especially a worn one. Radials were designed for large clearances and to use a specific oil from a specific time period. When modern owners used modern detergent oil they caused themselves big problems. Straight away a formerly nice engine turned into a oil burning underpowered liability. Quite simply, the engine had been running on non-detergent oil and had large amounts of carbon build up and was quite happy. In went the modern detergent oil, even worse if it was a physically thinner multi-grade and straight away it cleaned out all the carbon. Essentially the engine became worn out in a couple of hours running. The other benefit of radial specification oil is that it is a really sticky oil and is a great presevation aid for engines that aren't used very often, last I asked, it was still available, I wouldn't however use it in a normal engine - wrong stuff.
Sometimes a modern product can be too good!

Engine - SAE 30 or 40 (due to Broken Hill summer heat), whether it is "straight" (mono) or multi-grade will depend mostly on what is available locally and if I need to buy more oil for my gearbox.

Gearbox - most definetely straight 30 or 40. I will not use multigrade due to the unknown interaction of the additives with the gearbox brake bands.

Transfer Box - Multigrade gear oil sounds like a good idea, but the reality is that I need to keep a 20 litre drum of straight oil for the bevel boxes and wheel hubs, so more than likely it will in reality end up with straight oil in it if I can still buy some. If not, then 85W140 rather than the thinner 80W90.

Bevel Boxes and Wheel Hubs - My experience has been that multigrade gearoil leaks out much quicker than straight grade gear oil. The lower the viscosity range of the oil, the quicker it leaks. I prefer to use a straight grade or a multigrade with the number before the "W" being as close to 90 as possible. I prefer the older technology and thus more limited lubrication ability in order that the oil stays in there.

Lastly, so as to clarify the confusing terminology of civilian oils, here is a chart showing the most common terminology. You will note that SAE engine oil and gearoil has completely different grades for any given temperature.

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