Oil type

brialin - The original specs were for 10W wt in the hydraulics, and 30 wt engine oil in the rest of the drivetrain (engine, tranny and final drives). This was Cats idea for keeping oil stocks low and eliminating mixups or confusion about which oil was what, and what went where.

In the 1980's, they changed their recommendations and went back to heavy weight gear oil for the transmission and final drives, because it was reported there were too many early failures in final drives, in particular, because of a lack of EP additives in the engine oils recommended.

Accordingly, the recommendations were changed to 80/90 wt gear oil in the transmission and final drives, for ambient temps between 32°F and 100°F. Below 32°F, 50 wt gear oil is recommended in these compartments.

Engine oil recommendation is still 30 wt (or multi-grade such as 20-50, if you feel the need, or can spare the extra $$'s) .. between 32°F and 100°F .. and the hydraulics are still 10W wt for between 0°F and 100°F.
You can use 30 wt engine oil in the hydraulics, but the hydraulics get a little sluggish, when the ambient temps get down around 40°F or below.

brialin - 15W-40 is a multigrade oil, formulated to cope with a wider range of ambient temperatures. Many people don't like using multigrade oil in older Cats .. they claim it wasn't invented when the Cats were built, and the old Cats don't like it.

One of the greatest arguments regarding multigrade oils is that there is less "oil" in it. To create lubricating oils, chemical engineers take a "base stock" crude oil and add additives to it. In the old days, "base stock" crude oils varied substantially in their purity and undesirable, natural additives. Pennsylvania crude was regarded as the worlds finest and purest crude and made the best oils.

Nowadays, many refineries use "catalytic crackers" to break down the crude to the pure base oil, and then add the necessary additives. By doing this, they end up with a more uniform product, and a product that does not contain any undesirable natural additives.

Additives are added to oil to improve its performance under many adverse conditions. Byproducts of combustion form acids, water, gums and varnishes .. and all these are detrimental to engine bearings, rings, seals, and polished, hardened surfaces. These by-products create oil oxidation, deposit formation and bearing metal corrosion.
There are at least 7 additives added to base crude oil to make the finished product. They are ..

1. Detergents - detergents keep the engine clean by chemically reacting with oxidation products to stop the formation and deposit of insoluble compounds.

2. Oxidation Inhibitors - these help prevent increases in viscosity, the development of organic acids and the formation of carbon deposits.

3. Dispersants - these help prevent sludge formation by dispersing contaminants and keeping them in suspension.

4. Alkalinity Agents - these help neutralize acids formed by combustion processes.

5. Anti-wear Additives - these reduce friction by forming a protective film on metal wearing surfaces.

6. Pour-point Dispersants - these keep the oil fluid at low temperatures by preventing the growth and agglomeration of of wax crystals.

7. Viscosity Improvers - these help prevent the oil becoming too thin at high temperatures.

The last additive is where many arguments against multi-grade oils commence. Viscosity Improvers are synthetic chemical additives comprising what chemists call "long chain polymers". In essence, they are hydrocarbon compounds whose chemical structure comprises long chains of atoms and molecules held together in a repeating structure by covalent bonds. Basically, what we normally refer to, as "plastic" .. however long chain polymers can have a wide range of properties besides just being plastic.

VI's are added to oil because the long chain polymers have the ability, if you can imagine, like a long spring. They are elastic, and stretch out when cold, and tighten up when hot. Thus, they keep the oil viscosity steadier, over a very wide range of temperatures, as compared to just pure oil. As a result, VI's thin the oil when cold, and thicken it when hot, to improve its lubricating abilities.

Some multigrade oils contain up to 30% of VI's by volume. The argument is raised that this means there is 30% less oil to do the lubricating.
In theory, this is correct .. but in practice, what it means, is that the lesser amount of oil can perform better, in doing what it it's supposed to do .. form a protective cushion of oil on bearing surfaces, to prevent wear.

Oil viscosity is absolutely critical to an oils performance. If your oil gets too thick (when cold), it can't flow properly to lube the bearing surfaces .. and if it gets too thin (when hot), the oil film breaks down, and the moving parts suffer from severe wear.

As a result, there is really no problem with using multi-grade oils in older tractors. New oils are constantly being produced with improved additives, and these are usually made "backwards compatible" (i.e. - compatible with older engines and previous oils). However, it always pays to check with your oil manufacturer to ensure that this is the case.