Free Shipping for Orders over £75.00


About Oils

Modern engine lubricants often do not suit older vehicles since they are designed for fuel efficiency, emissions control and extended change intervals. Older vehicles were designed before the advent of this technology, and therefore they require oils specially blended to match their needs. When considering oil choices, the following factors should be borne in mind.


It is usually imperative to use a high viscosity oil in the lubrication of veteran, vintage and classic cars. This is because a) by modern standards the oil pumps are relatively poor and a low viscosity oil will show noticeably lower oil pressure; b) bevel gears and cross shafts will fling off a low viscosity oil; c) oil seals will be more prone to leak, and d) oil consumption will be noticably higher.

Anti Wear Additives

Historically, the anti-wear additive used in the majority of formulations was a zinc / phosphorous based compound known as ZDDP (Zincdialkyldithiophosphate). Unfortunately ZDDP has a detrimental effect on sensitive exhaust emission systems on modern cars, so it has been phased out by oil companies, while engine designs have been changed to accommodate the removal of ZDDP. These oils, while performing well in modern engines designed for them, can cause substantial and accelerated wear in older engines such as accelerated camshaft / cam follower wear.


Detergents are incorporated into all modern motor oil formulations and have been since the 1940’s. Their function is to maintain engine cleanliness and they are also useful in combatting the effect of acid contamination of the crankcase oil caused by combustion by-products. In cars with restored engines, the use of an engine oil containing some level of detergent will not cause any problems. Non-detergent oils can be used either when an unknown oil is being replaced or where there is a likelihood that sludge has built up and risks damaging the engine if it is circulated. Owners of vehicles without full-flow oil filtration frequently express a preference for non-detergent oils.

Transmission matters

When it comes to Gearbox oils, many older vehicles specified EP80 or EP90 weight oils. Because the viscosity of gearbox and engine oils are measured on different scales, an SAE 80 gearbox oil is roughly equivalent in viscosity to an SAE 20 engine oil. An SAE 90 gearbox oil is roughly the same viscosity as an SAE 50 engine oil. Most manufacturers now offer EP80W/90 oils in place of both EP80 and EP90. In viscosity terms, this is analagous to using a 20W/50 engine oil in the sump, and will do no harm. It is important to look at the classification of all gear oils when used in older vehicles. Some ‘GL5’ EP gear oils contain an additive package which can be harmful to yellow metals (eg phosphor bronze) and should be avoided if in any doubt, and a GL3 or GL4 oil used instead. The definitions of the API (American Petroleum Institute) GL numbers are as follows:

API GL-1, oils for light conditions. They consist of base oils without additives. Sometimes they contain small amounts of antioxidizing additives, corrosion inhibitors, depresants and antifoam additives. API GL-1 oils are designed for spiral-bevel, worm gears and manual transmissions without synchromesh.

API GL-2, oils for moderate conditions. They contain antiwear additives and are designed for worm gears. Recommended for proper lubrication of tractor and farming machine transmissions.

API GL-3, oils for moderate conditions. Contain up to 2.7% antiwear additives. Designed for lubricating bevel and other gears of vintage transmissions. Not recommended for hypoid gears.

API GL-4, oils for various conditions – light to heavy. They contain up to 4.0% effective antiscuffing additives. Designed for bevel and hypoid gears which have small displacement of axes, the gearboxes of trucks, and axle units. These oils are normal for later classic synchromesh gearboxes.

API GL-5, oils for severe conditions. They contain up to 6.5% effective antiscuffing additives. The general application of oils in this class are for hypoid gears having significant displacement of axes. Oils in this class, which have special approval of vehicle manufacturers, can be used in synchronised manual gearboxes only.

API GL-6, oils for very heavy conditions (high speeds of sliding and significant shock loadings). They contain up to 10% high performance antiscuffing additives. They are designed for hypoid gears with significant displacement of axes.

Thicker gear oils are available for non hypoid applications, in SAE140 and SAE250 viscosities. The SAE250 oil replaces a grade which used to be called 600W. Thicker than that and you are into semi-fluid greases, which are used in some gearbox applications.

At Classic Oils, we only stock oils which we believe offer a good combination of price and technical performance for older vehicles. We have tried to set out the website in a way that makes sense for enthusiasts, but if you would prefer to talk to someone to discuss your specific requirements, please call us on 01296-488927 at any time.

Viscosity Index

Viscosity Index (VI) is a measure of how oil viscosity changes with variations in temperature. The lower the VI, the greater the change of viscosity of the oil with temperature, and vice versa.

The VI scale was set up in the 1920’s by the Society of Automotive Engineers (SAE). The temperatures used for reference are 100 and 210F (38 and 99C). The original scale only stretched between VI=0 (lowest VI oil, naphthenic) and VI=100 (the then best oil paraffinic) but since the conception of the scale better oils have been produced, leading to VIs greater than 100.

The viscosity of oil decreases as temperature increases, but each will only be at the ‘optimal’ viscosity for a given application over a certain temperature range. The best oils with the highest VI will remain stable and not vary much in viscosity over a wider temperature range, increasing the window within which optimal lubrication can be achieved. Multigrades will always have higher VI’s than monogrades, which is one reason why monogrades typically need to be changed between winter and summer.


ZDDP (full name Zinc dialkyldithiophosphate) is a compound developed in the 1940s consisting of zinc bound to the anion of dithiophosphoric acid. They are soluble in nonpolar solvents, and the longer chain derivatives easily dissolve in mineral and synthetic lubricating oils.

The main use of ZDDP is as an anti-wear additive to lubricants, but over time their concentrations have been reduced to avoid damaging catalytic converters on modern vehicles. Crankcase oils with reduced ZDDP cause damage to, or failure of, moving parts lacking ‘full film’ lubrication in classic vehicles such as flat tappet camshafts and followers, which undergo very high boundary layer pressures and/or shear forces at their contact faces; and in other areas such as piston rings and gudgeon pins. The same ZDDP compounds serve also as corrosion inhibitors and antioxidants.

ZDDP concentrations deplete with use, and are one factor in determining the change frequency of an engine oil.

Base Oil Group

Base Oil Group describes the nature of the raw oil used in the blending of a lubricant. There are five groups:

Group I base oils are classified as less than 90 percent saturates, greater than 0.03 percent sulphur, and with a viscosity-index range of 80 to 120. Group I base oils are solvent-refined, which is a simpler refining process.

Group II base oils are more than 90 percent saturates, less than 0.03 percent sulphur, and with a viscosity index of 80 to 120. They are often manufactured by hydrocracking, which is a more complex process than that used for Group I base oils. Since all the hydrocarbon molecules of these oils are saturated, Group II base oils have better antioxidation properties. They also have a clearer colour than Group I base oils.

Group III base oils are greater than 90 percent saturates, less than 0.03 percent sulphur, and have a viscosity index above 120. These oils are refined even more than Group II base oils in order to achieve a purer base oil. Although made from crude oil, Group III base oils are sometimes described as synthesised hydrocarbons.

Group IV base oils are polyalphaolefins (PAOs). These synthetic base oils are made through a process called synthesising. They have a much broader temperature range and are suitable for use in extreme temperature conditions.

Group V base oils are classified as all other base oils, including silicone, phosphate ester, polyalkylene glycol (PAG), biolubes etc. These base oils are at times mixed with other base stocks to enhance an oil’s properties. Esters are common Group V base oils, which can take more abuse at higher temperatures and will provide superior detergency compared to a Group IV base oil.

Chemical substances (additives) are added to the base oil in order to produce a lubricant with further improved anti-friction, anti-corrosion and cleaning properties.