Proper Lubrication Reduces Engine Wear
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Wear is the natural result of operating an engine. Rings, cylinders, bearings, camshafts, and all moving parts wear in an engine. Regardless of the oil you use to lubricate that engine, wear will occur.
However, did you know that as much as 80% of all wear occurs at start-up? The first few revolutions of that crankshaft, camshaft, and piston movement have little if any oil on the wearing surfaces to prevent metal-to-metal contact.
And, did you know that fire truck engines experience some of the most severe service of all automotive equipment? These engines are started quickly from periods of extended idleness and are driven hard with little or no warm-up time. That’s why they suffer from a higher rate of wear than engines in other services, either automotive or industrial. The time that it takes for the oil pump to pick up the oil from the sump and pressurize the system is the time when high wear rates occur.
All engines, except for small two-cycle gasoline engines (lawnmowers, outboards, etc.), are lubricated the same way. An oil pump (gear) that is driven from the crankshaft through gearing pressurizes a system of drilled passages and distribution manifolds called oil galleries. These galleries then provide oil to other engine areas. Only the pistons, rings, and liners (cylinders) are not pressure lubricated. Oil is thrown or splashed on them by the crankshaft.
All engine lubrication is internal, except for a turbocharged engine. The turbo is an external component, and in most cases it is lubricated by an external line from the oil pump or sump area. Let’s follow the oil flow at start-up and see how the delay or oil lag can affect various engine components.
Main bearings and rod bearings receive oil quickly. Since they are low on the engine and first in line, the delay, or oil lag, is short. But even so, high wear is occurring on each revolution before the engine starts, and slow cranking speed means even more wear. Remember that the oil pump runs off the crankshaft, so slow crankshaft speed means slow oil pump speed, and little if any oil flow or pressure.
Piston pin bearings are generally next in line for lubrication. Camshafts, lifters, rocker arms, and valve assemblies wait for their oil supply after a few more revolutions. Since the cylinders receive no pressurized lubrication, they must wait until oil is splashed or thrown for their lubrication requirements, and, as you might expect, it takes a few more revolutions for that to occur.
Since many fire trucks today are turbocharged, let’s look at the lubrication requirement of the one external component that requires oil.
As mentioned earlier, the turbocharger presents greater problems from an oil lag standpoint than any internal component that we just discussed. Located high on the engine (at the very top in some cases) the oil supply line to it can be from 12-60 inches long. The distance of the oil supply line from the oil supply sump, combined with oil lag, is a killer of turbos.
Depending on oil viscosity, temperature, and location, the turbo can actually be spinning at thousands of rpms for as long as 20-30 seconds at startup without lubrication. The result is high wear rates, reduced bearing life, and premature turbo failure.
What about shutdown? Shutdown generally does not present a wear or lubrication problem for the internal components of an engine. As long as the engine is rotating, the oil pump is pumping oil and the lubrication requirements are met.
However, in the case of the turbocharger, shutdown presents even more severe problems than did startup. Unlike the engine, the turbo is a free-wheeling, exhaust driven device and will have some spindown. And when the engine stops the oil flow stops, leaving the turbo with virtually no oil supply. When this is coupled with the heat soak back from the turbine (exhaust) side down the shaft and into the bearing area, you will have severe and rapid oil oxidation causing oil coking and restricting the small oil passages. Ultimately, these oil flow restrictions will reduce available lubrication to the turbo bearings and result in turbo failure.
All engine manufacturers have starting and stopping procedures that are designed to minimize wear. This is especially true of turbocharged engines. You can greatly extend the life of your engine and turbo if you idle on start with no revving or engine loading until oil temperatures and pressures are up, and if you idle for five minutes or so before shutdown. However, when an alarm comes in and response time is critical, you cannot waste precious minutes revving up to insure adequate lubrication of your engine or turbocharger. So what can you do?
Pre-lubing the engine before start-up will practically eliminate engine wear. But pre-lubing an engine is not practical. Therefore, your oil selection is critical. The name of the game is oil flow and viscosity. The thinner the oil at start-up, the quicker it will reach all areas requiring lubrication.
Today, these problems are being solved by using multi-viscosity oils, which provide rapid flow to all critical components. Using a thinner oil at start-up than a straight graded oil (15w40 vs. 40) will help save the life of your engine.
Another solution is to have a properly sized block heater to keep the oil warm and increase start-up flow rates. Still another solution is to use synthetic oils that have exceptionally good low temperature flow rates and move quickly around the lubrication system.
Some stand-by generators actually use a pump to constantly circulate oil around the engine. This is also done on larger engines such as railroad and natural gas engines, but, as we mentioned before, this is not practical for automotive applications.
The turbocharger is another matter. It can be preand postlubed quite easily. Oil injection devices that provide oil immediately on start-up and for several minutes on shutdown are available. These prevent turbo bearing wear at start-up and oil coking and wear on shutdown. These oil injection pumps are easily installed and are generally maintenance free. They provide pressurized oil to the turbo before engine oil pressure is reached and continue to provide turbocharger lubrication for several minutes after shutdown. This turbo lubrication and heat removal mean trouble-free operation and longer turbo life.
Here’s a word of caution, however. Be sure the turbo lubricator provides a positive pressurized oil flow both at start-up and shutdown. Some devices cannot do this and are essentially gravity flow. As such, they must be mounted above the turbo and can actually reduce oil flow to the turbo on start-up.
While the fire trucks can’t be started and stopped according to manufacturers’ procedures, engine performance and life can be extended by following a few simple steps:
- Start the engine only when necessary. Remember, most wear occurs at start-up.
- Use multi-viscosity oils whenever possible.
- Consider using synthetic oils, if your budget can afford it.
- If cold temperatures are a factor, use a block heater to keep the oil warm, or else keep the truck in a heated garage. Warm oil circulates faster than cold oil.
- If the engine is turbocharged, equip it with an oil injection device to preand post-lube the turbo.
Engine life depends on many things, but lubrication is the most important one. Take care of your equipment and it will take care of you.
