Second Chance Garage
All About Car Restoration
Second Chance Garage
All About Car Restoration


Old Cars, New Oil: Is There Something To Worry About?

The old car hobby is replete with discussions about the incompatibility of using modern stuff in old cars. One subject these days concerns the effects of using ethanol fuels in older cars. Some of these effects are real (fuel system gasket failures and a lack of power in very old, low compression engines) but most aren't.

Remember all the talk about valve recession if you use unleaded fuel? The idea was that the tetraethyl lead in pre-1970s era gasoline protected valve seats by depositing a coating of lead, or lead-oxide. Unprotected valve seats eroded away in some engines, a condition known as valve recession, and unleaded gas was blamed.

Frankly, from an engineering point of view it's hard to believe that lead or lead-oxide could coat the valve seats very effectively. Lead is a very low melting point material and could hardly protect steel valve seats in a combustion chamber. Lead-oxide melts at 888 degrees F — higher, but well below combustion chamber temperatures. Oddly enough, the number of valve seat failures in engines using Amoco unleaded gas in the 50s and 60s were no greater than in those using leaded gas, so it logically follows that valve recession was a function of other engine defects and not the type of gasoline used. Most automotive engineers will tell you that valve recession normally occurred as a result of extended high RPM operation or under extreme loads and had little to do with the valve seat material.

Some automotive historians speculate that the valve recession story was mostly hokum pushed by the Tetra-ethyl lead Corporation when they were trying to lobby against the regulations mandating unleaded gas, but you can form your own opinions.

What About Oil?

The newest "crisis" hitting the old car hobby concerns the use of modern oils. The internet is full of anecdotal stories about the effects of using new lubricating oils in old engines. Common problems include premature bearing failure, oil consumption, leaks and sludge. We have attempted to verify this issue and have come up with a number of reasons to believe it is yet another automotive myth, but first let's set the record straight on exactly what is expected of engine oil:

Engine lubricating oil must perform several functions. These are: reduce friction and wear between moving surfaces; remove heat caused by friction; provide a seal against escaping gases; keep the engine clean by holding carbon and sludge-forming material in suspension; provide protection against rusting and attacks by acids. Oils are classified by type, viscosity and operating conditions by the American Petroleum Institute (API).

The API engine service classification system presently includes classes of service for automotive (spark ignition) engines and for diesel (compression ignition) engines. Five of the automotive and two of the diesel service categories are obsolete. Only currently recommended categories are listed in this guide.

These classifications use either an "S" prefix which means gasoline engines or a "C" prefix which means diesel. A second letter designates specific service/performance characteristics. As any newer classification is added it always includes the performance properties of each earlier category. Newer oils have vastly improved oxidation resistance, deposit protection, wear protection and low-temperature performance over their service life, which means that they should perform better than older oils in any engine.

Oils with the following classifications are obsolete and not suitable for engines built after specific years, as follows: SH, SG, SF, -1988. Those with a designation of SE 1979; SD - 1971; SC - 1967; SB - 1951; SA - 1930. Obviously, if your car is a 1955 and you run SA or SB oil you will likely cause harm. These classifications do not, as popularly believed, mean that they must be run in older engines. They mean that any newer oil classification will more than meet the engine's requirements.

Engine lubrication oils have chemical compounds or additives added to them for improved performance. Good quality oils do not necessarily include all of the following additives but most do:

Oil viscosity

Viscosity is the measure of the resistance to flow. It is the body or thickness of the oil. Viscosity is not a measure of oil quality, but each engine is designed to run most efficiently with a specific viscosity range. If your engine was designed to run on 30-weight oil and you use 5W20, for instance, the engine's bearings will not have a sufficient lubricating layer and you will eventually harm the engine.

The "W" (for winter) following a viscosity number indicates that an oil is suitable for cold temperature and must have the indicated viscosity at 0 degrees Fahrenheit. The SAE categories that do not include the "W" are suitable for use at high temperatures and must have the specified viscosity at 212 degrees Fahrenheit.

A multiviscosity oil meets an SAE viscosity requirement at both 0 degrees Fahrenheit (-18 degrees Celsius) and 212 degrees Fahrenheit (100 degrees Celsius). It does not thin out as much when heated or thicken as much when cooled, as does a single-viscosity oil. Thus, a multiviscosity oil stretches the usable temperature range. It provides easier cold-weather starting, more efficient lubrication, reduced engine wear, better fuel economy and adequate protection against excessive oil thinning at operating temperatures.

So Why Do The Engine's Parts Wear?

Crankshafts, rods and camshafts spin on bearing materials lubricated with oil. These materials traditionally were made of Babbit, a soft, white metal which is an alloy of tin, lead, copper and antimony. Old engines used bearings that were filled (poured) with babbit and machined to a specific size. By the 1950s nearly all engines used babbit-plated bearing inserts for ease of production and repair. As bearings evolved the materials changed, and today's bearings use such advanced materials as copper-lead with overlay, aluminum-tin and aluminum-tin-silicon.

Whatever the bearing material — new or old — might be, the reasons it fails are: 1) improper clearance; 2) catastrophic component failure and 3) contamination. Improper clearance can be the result of a poorly built/rebuilt engine in which the bearing clearances are either too large or too small, or the components aren't perfectly round. Catastrophic failures such as broken rods, crankshafts, valves, camshafts, etc., can happen due to material flaws, overstress (racing, for instance) or lack of oil pressure or flow.

By far, the majority of bearing failures occur due to contamination from combustion — in other words, Dirt. In fact, bearing companies' surveys show that dirt causes 45% of all failures. Misassembly and misalignment cause 25% of failures. Age, lack of maintenance, lack of oil flow and high stress account for the remaining 30%.

Hydrocarbon fuels such as gasoline and diesel fuel form byproducts that cause corrosion and engine deposits. For example, each gallon of fuel burned causes about 1 gallon of water to be formed. Most of the water forms as vapor and goes out the exhaust. However, a small amount condenses on the cylinder wall (especially when the engine is cold) and eventually is trapped in the oil reservoir. This can gradually develop into a mild acid that, over time, corrodes the bearing surfaces as the engine sits.

Carbon (or soot) formed by incomplete combustion of fuel is also picked up by the oil and carried into the oil reservoir. In combination with water, the carbon forms sludge which, if allowed to accumulate, may restrict oil passageways and cause insufficient oil flow to engine parts.

Another source of contamination comes from packaged aftermarket additives. Mixing additives with modern engine oil is not recommended. There is the possibility that their use could upset the chemical balance of the engine oil and its original additive system or shorten the engine oil's serviceable life.


We've asked engineers and chemists from the oil companies and engine manufacturers and none have come up with any reasons to believe the problems (anecdotal as they are) that allegedly result from using new oils in older engines. They say that there isn't any science that backs up the claims about newer oils causing failures in older engines. There is nothing in the chemistry of new oils that would have any adverse effect on older bearings or materials and all agree that there are too many other reasons for premature failures in older engines, such that the oil itself is the least likely cause. So, while old oils will certainly hurt new engines, we have to conclude that new oils won't hurt older engines.

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