Effects of Sulfur Reduction in Motor Oils

The reduction of sulfur in diesel fuel, gasoline and motor oil has had measurable effects on fuel injectors and other vital engine parts. Add to that restrictions on additives like ­ZincDialkylDithioPhosphate(ZDDP), and it seems like the whole world of fuels and lubricants has turned upside down at times.

Before you let all this change give you a case of heartburn, remember that knowledge is power, so here is a summary of the changes in gasoline, diesel and motor oils. You can use this knowledge to steer clear of potential pitfalls as we navigate the new chemical landscape.

We’ll start with sulfur reduction. All crude oils contain sulfur. You may have heard of the term “Sweet or Sour” crude. This is in reference to the amount of sulfur in the crude oil. As a ­result, products of refined crude oil like diesel fuel, gasoline and conventional motor oils ­contain sulfur.

Today’s emissions regulations limit the amount of sulfur in all of these products. While this is a benefit for emissions, it does have some consequences. Primarily, sulfur is a natural ­lubricant, so reductions in sulfur reduce the ­natural lubricity of refined products. This has been evidenced in diesel engines since the ­advent of ultra-low sulfur diesel fuel. Problems with injector wear have been attributed to the lack of lubricity in this fuel type.

The sulfur reduction has also impacted both gasoline and motor oil. The lower level of sulfur in modern motor oils does reduce the natural lubricity of the oil. Starting in the mid-1990s, more and more motor oils are being blended from lower sulfur Group II and Group III base oils as opposed to the traditional, higher sulfur Group I base oils. Couple that with the ­reduction in ZDDP, and it is easy to see why premature camshaft and lifter wear has skyrocketed since the mid-’90s.

The effect of reducing sulfur in gasoline is not related to lubricity, but it is related to corrosive wear. You see, sulfur is not just a lubricant, it has an affinity for metal surfaces, which can prevent other chemicals from reacting with those metal surfaces. Couple the reduction in sulfur along with the advent of Ethanol in gasoline, and carburetors suddenly were at risk.

Again, the timing is similar. In the mid-1990s Ethanol began to be added to gasoIine just as the sulfur levels were reduced. By the mid-2000s, the critical point had been reached – there was too much Ethanol in the fuel compared to the level of sulfur and gasoline detergent additives.

The result was widespread corrosion in carburetors, which continues to this day. Ethanol is corrosive towards the aluminum, steel and Zinc alloys used in carbs, fuel pumps and fuel tanks, and now the fuel has less sulfur to protect those components from the Ethanol.

Couple that with lower levels of gasoIine detergents in pump fuel, and it is easy to see why carbureted engines from Big Block Chevys to two-stroke leaf blowers have been struggling in the past decade.

Ethanol Addition
The reduction in sulfur is not the only issue affecting fuel and lubricants. The drive to reduce emissions resulted in other chemical changes besides reducing sulfur.
One change we already mentioned is the addition of Ethanol to gasoline. This is directly related to emissions, and the advent of Ethanol-blended gasoline has been
effective in regards to emissions reduction.

However, the addition to Ethanol in gasoline has had other side effects – primarily corrosion. Ethanol is hygroscopic, which is a fancy way of saying that Ethanol absorbs water. The chemical cocktail of Ethanol and water is very corrosive to aluminum, steel and Zinc.

The presence of water in the fuel also speeds up the oxidation of the fuel – again, a fancy way of saying the breakdown of the fuel. When the fuel oxidizes, it can lead gummy deposits that affect the performance of both fuel injection systems and carburetors.

Because moisture contamination is related to storage time and conditions, daily drivers rarely see any of these issues.

However, vehicles that see long term storage and infrequent use tend to fall victim. Marine applications are the worst case scenario because they feature both high-moisture environments and long periods of storage.

Another area of chemical change is in motor oil. In order to provide better catalytic converter efficiency, the amount and type of additives used in motor oils have changed.
The most recent API SN and ILSAC GF-5 oil standards call for the use of a new type of ZDDP that provides better catalytic converter protection. At this you may be asking,“aren’t all the Zinc additives the same?”

The simple answer is – no. Several different compounds within the ZDDP family exist, and some are better at protecting catalytic converter performance than others.

These new additives are called Phosphorus Retention ZDDPs, and they have replaced the older-style ZDDP in API SN and ILSAC GF-5 motor oil formulas. While this is good news for modern engines and stock valve trains, engine testing has shown these new ZDDPs are not as good for the older style flat tappet valve trains.

Again, knowledge is power. Now that you are aware of these issues, you can easily take steps to avoid these problems.
Diesel engine owners have a variety of fuel additives to choose from that restore lost lubricity to ultra-low sulfur diesel.
Owners of street rods and lawnmowers alike can seek out non-Ethanol gasoline, or choose to treat Ethanol-blended gasoline with a corrosion and deposit-inhibitor additive.

These fuel additive products impart lubricity, corrosion protection and deposit control to readily available fuels and motor oils with boosted levels of ZincDialkylDithioPhosphate to provide the increased anti-wear protection older and high performance
engines need.