Making Prelube Pay

When you get right down to it there is only one reason to put a prelube pump on an engine, and that is to save money. In that way it really is like an investment. You buy the system up front with the expectation that it will pay you back and also pay you a return on your investment. Just like any investment there are risks and benefits. Let’s have a look at each of these separately.

What you risk by putting in a prelube system is that the money that you spend on the system doesn’t return a profit. There are basically two ways that can happen. Firsts it could happen if the extension of engine life gained by prelube is not sufficient to cover the cost of the prelube pump. Calculations need to be made beforehand to be sure prelube makes sense for what you are doing. We’ll get to that in a second. The other way you risk not making a profit is if a catastrophic event happens to the engine before it reaches it “expected life”. For instance, the engine is not maintained or the ship the engine drives sinks. In this case only your insurance man can help you.

The benefit you stand to gain by installing a prelube system is clear cut. By using a prelube pump you make sure there is oil on the engines critical moving parts from the moment they start to move. Oil is the lifeblood of any engine new or old, big or small. Without oil, the life of the engine is literally counted in seconds. The short period of time between the starter beginning to turn the engine and the normal oil pump bringing the oil pressure up to operating levels is the most risky time for the engine. By prelubing it you eliminate this risk all together.

Weighing these two factors, the risk and the benefit, can be involved. The more factors you can bring to the table the more accurately you can predict how profitable prelube may be. I have put together this spreadsheet that can walk you through some of the basic math calculations needed to determine whether prelube is a good investment for a given engine. Put your numbers in and let them speak for them self.

Click here to download the spreadsheet.

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Varna Products Broadens it’s Line of Prelube Pumps with New Offering

The new, low cost EP-4 prelube pump is essentially a scaled down version of Varna’s proven CF-15 prelube pump design. It operates on 12 or 24 volt DC power and shares many of the CF-15’s value adding features such as it’s integrated low pressure-drop check valve, and the quiet running “Whisper-Vane” pump head. After finding that many of the CF installers were using ¾” and smaller hose, Varna built the EP-4 as a more appropriate pump for smaller sizes of hose. It can deliver 60 psi pressure continuously for up to five minutes’ time and includes a built-in pressure gauge to show it. It provides much needed lubrication prior to starting reciprocating engines and compressors by drawing oil directly from the crankcase and delivering it back to the bearings until the main oil pump gets running and takes over. Installation details vary depending on the engine or compressor being lubricated.

Do You Need to Prelube Your Engine Installation?

It is widely understood that the period of time between when the engine begins to turn at startup and the time when fresh oil from the sump reaches moving parts causes up to 90% of the wear an engine sees during its lifetime. A prelube pump puts the oil where it is needed before the engine begins to move, thus reducing this high wear period.

Historically operators of large engines would avoid shutting them down. This was done to reduce startup engine wear in addition to other operational advantages. In colder climates for instance, letting an engine cool all the way down can cause significant problems when trying to restart it. Fuel “gels” and very cold engines can be nearly impossible to start. Until recent years the simplest and most widely used solution to this problem was to just leave the engine running. Large engines might only be shut down for periodic maintenance. Fuel was inexpensive and environmental concerns were not considered. As the price of fuel climbs ever higher and idle emissions are no longer acceptable, operators are shutting down engines more than ever before.

Fuel costs as well as the EPA and other regulatory agencies are increasingly requiring engines to go into “auto start” mode rather than just idle. In auto start mode the engine starts its self and runes only long enough to warm the fuel, coolant, oil and the engine block back up to operating temperatures. The engine then shut itself back down to save fuel and emissions. As a result the number of times some engines need to be started in their lifetime may go up from only 80 or 100 to as many as 86,000 times. It’s easy to see how wear rates that were considered acceptable with only 80 lifetime starts would have a significant impact on engine life with 86,000 lifetime starts.

In the end the decision as to whether a prelube system is appropriate for a given installation comes down to the cost benefit analysis of three factors. The number of times the engine will need to be started in its lifetime, and the cost of replacing/rebuilding the engine, against the cost of adding the prelube system.

As an example a good prelube system may run in the range of $1500 by the time it is installed. So if the engine is small and only costs $10,000 a prelube may be impractical. As the engine size goes up in the calculation though, a $1500 investment could save many times its price in future repairs and downtime. Likewise if an engine were only going to be shut down every three months for maintenance, the cost of a prelube system might be unjustified but for a system that is restarted multiple times a day it would be a necessity.

Considerations in wiring power to a prelube pump

A prelube pump is operated prior to cranking the engine. Its purpose is to fill the oil passages with oil prior to startup. The power to operate the prelube pump comes from the starting battery or from some other auxiliary power source.

The simplest wiring system consists of a pushbutton switch to operate the prelube pump. The operator pushes the switch for the appropriate length of time and then starts the engine. Most prelube pumps draw too much current for an ordinary pushbutton switch, so an electric relay is usually added to the circuit, as shown in the diagram below.




In automating the engine prelube, there needs to be some measurable condition that indicates that the prelube function is complete. One possibility is to check the oil pressure. This is the fastest way to safely start the engine. If the oil pressure is not zero, then you can start the engine. But, most prelube pumps are too small to significantly raise the oil pressure in an engine of any size, especially if the engine has been run recently and the oil is still hot. While these pumps may fill the passages with oil they cannot raise much pressure within the engine because of the many places the oil must go, such as spraying cooling oil to the underside of the pistons, etc. Therefore, unless a large prelube pump is used, checking oil pressure as a condition to start the engine is problematic.

If an oil pressure switch is used to signal prelube completion, make sure that the prelube circuit is disabled after the engine starts. This is to avoid the situation where the oil pressure gets low enough to restart the prelube pump, such as when a hot, well used engine is running at idle. At this point the prelube pump could cycle endlessly as it adds enough oil to bring the oil pressure up only to be shut down again.

Another measurable condition is time. One could run the prelube for, say 5 seconds, and then start the engine. The actual time would depend upon the pump, its plumbing, and the engine. There are several options here.

1. Prelube for longer than anyone would think is enough. Advantage, for sure the passages have oil in them. Disadvantages, longer time until start, and extra drain on the battery.
2. Find out experimentally how long it takes for the oil passages to have sufficient oil. Prelubing a cold engine will probably cause some pressure increase when the oil passages become full. At that point an oil pressure gauge may indicate a little pressure or the sound of the pump may change a little. It is a reasonable guess that a warm engine with hot oil will take about the same time to fill the passages. Advantage, the time to start is shorter and the drain on the battery from the prelube pump is less. Disadvantages, it is just a guess and certain situations may require longer prelube, such as when the engine oil has been changed.
3. One might also remove an oil port at the furthest point possible from the oil filter and see how long it takes for the oil to start flowing out. Advantages and disadvantages, the same as #2 above.
4. If the engine has a glow plug cycle, the prelube pump circuit can be connected there to provide a prelube cycle the same length as the glow plug cycle. Advantage, easy to do and requires little extra circuitry. Disadvantage, the glow plug duration may not be optimal for prelubing.

The diagram below shows one example for wiring a prelube pump using a timer.



When all is said and done, how accurate does the length prelube cycle need to be? What happens when the prelube cycle is too short? One must realize that any prelube at all is better than none. So, if the prelube time is a bit short, the oil passages will still have gained additional oil. As the engine starts, the passages will fill faster than if the prelube was not done at all. There will always be some benefit.

Prelube - Pressure Verses Flow

To explore this topic let us start by considering the crank bearings of a running engine. The tight clearance in the bearing area between the crank shaft and the crank arms is filled with pressurized oil from the service oil pump. As the engine turns the load rotates around the crank shaft. This rotating load is therefore constantly climbing onto a fresh pillow of oil film substantially preventing wear as there is never any metal to metal contact.

Now let us consider the engine after having sat for some long period of time. The oil has drained back to the tank leaving only the slightest of oil films. The weight of the crank arm has pressed the pillow of oil out of the way and left it sitting in near metal to metal contact. If the engine is started at this point without prelube, wear will occur at a far greater rate than during normal running until oil from the service oil pump reaches these surfaces to reestablish the oil volume needed for the pillow. As the engine wears from this kind of event the bearing clearances get bigger requiring a greater volume of oil to fill them. Thus an engine with more wear will wear more at startup than a new engine. This leads to progressive failure.

The greatest value of the prelube system is that it reduces to near instantaneous the time between when the engine starts to crank and when the pillow of oil is established to prevent metal to metal contact. If the prelube pump has moved enough oil during its cycle to fill the clearance voids around all running surfaces, then as soon at the engine starts to move it immediately rolls onto a thick film of oil and very little wear takes place. For most applications prelube oil flow should be sufficient to extend the starting wear failure mode well beyond other failure modes that would take the engine out of service.

Very little wear however is still wear and that is where pressure comes into play. In order to prevent that last little bit of wear, the engine bearings must be designed in such a way as to cause oil pressure to lift the components out of metal to metal contact. Obviously this is an innate property of the engine and is not under the control of the end user. Having lifted the components out of metal to metal contact during the prelube cycle the parts are temporarily set back onto the oil film if the prelube cycle ends just prior to engine crank. This however is insufficient time for the oil film to dissipate and the components are still protected.

Locomotives Then and Now

The business of buying and selling railroad locomotives has its roots in the days of steam. Before the early 1900s steam power was high tech. Boiler horsepower was the source of energy for industrial enterprise on land and sea, and the railroads made abundant use of their share of it. Steam locomotives developed over the years to become the mighty iron horses that transported both people and freight overland faster than any other means. Wherever railroads were available, economic expansion flourished. However, since time is of the essence in railroad operation, every railroad had to have its own locomotive shop to maintain and rebuild its locomotives in a timely manner so as to keep the trains running. The gross inefficiency of the steam locomotive's use of energy, 4-6% at best, was technically embarrassing if anyone thought about it, but in those days steam meant power and opportunity. To optimize that, mechanical efficiency was of no economic consequence.

Later, when locomotive builders began thinking seriously about improving efficiency, calculations showed that diesel-electric power stood head and shoulders above steam and everything else. However early attempts to build diesel-electrics were such a departure from steam experience that these early efforts didn't go well. Vibration from the diesel engine and the unfamiliar road action of the running gear caused unanticipated surprises for both the locomotive builders and their railroad customers. General Electric became an early builder of diesel-electrics along with ALCO, and shouldered most of these problems in the process.

This situation was a sitting duck for a disruptive technology if one were to appear. Enter, GM's Charles F. Kettering, who had fostered Detroit Diesel Division's development of a large two-cycle diesel engine for marine applications. He was also an innovative designer of electrical equipment. By combining the two cycle diesel engine with an innovative high rpm traction motor, GM's Electromotive Division produced a diesel electric locomotive from scratch that was presented to the railroads as the successor to steam. The railroads were skeptical and locomotive builders were concerned that General Motors was using its clout as a railroad customer to force the railroads to buy EMD locomotives. But EMD locomotives just ran and ran and ran quite smoothly without serious maintenance and soon the steam locomotive was a thing of the past. EMD 's SD40-2 became the best performing, and most reliable heavy haul locomotive ever produced up to that time.

But the railroads still had their locomotive overhaul shops and EMD was only too happy to show them how to maintain and rebuild their new locomotives. With EMD's system of insignificant part numbers, it maintained an ironclad hold on the supply of spare parts. If the parts list called for a 40077367, there were only two places to go to get one. Either you bought a new one from EMD at a non-competitive price or you swiped one from an existing locomotive that was out of service or scrapped for one reason or another. Nobody else knew what it was and could only guess at how to make one. And EMD would not even talk to you unless you were a railroad locomotive owner. Only railroads and scrap yards were the players in that game.

So EMD could do no wrong. - Until the EPA entered the picture. Diesel locomotives as a group were easy to identify as an atmospheric pollutant. They were owned by a few large corporations vulnerable to government scrutiny, and furthermore they spilled black dirty oil everywhere they went. EMD was too fat and happy to pay attention to storm clouds on the horizon but GE took this as their opportunity to excel.

By introducing a new diesel engine plus upgrades to existing systems, GE was able to not only meet, but exceed the EPA requirements with its new GEVO (Evolution) locomotive series. GE was going "green" for all it was worth - and being successful at it. But GE locomotives were a significantly different breed from EMD locomotives While EMD had designed, built and tested substantially all of the components of its locomotives, GE locomotives were to a considerable extent built from components purchased from suppliers in the open market. GE engineers had to pick and choose from components they were available to buy, while EMD engineers designed and had built what they considered to be right. Like horses and mules, either one could do the required job but their genetic makeup and temperament were different.

There were differences in the railroads' maintenance and overhaul operations as well. Although GE put its own part numbers on the spare parts it sold, their commercial counterparts could also be obtained at more competitive pricing. To combat this, GE decreed that its locomotive warranty would be void for locomotives in which non-GE part numbered parts were installed. The logic for this was that GE purchases its parts in accordance with specific Purchase Specifications that include critical to quality (CTQ) characteristics not always found in the open market. Another difference between the maintenance and overhaul of the two breeds of locomotives is that, understandably, there is more commonality among the components of various EMD models than among the GE locomotive models. Some railroads, CSX for example, maintain two separate overhaul shops, one for each of the two makes of locomotives.

There will never be another SD40-2. But watch out for the next disruptive technology to hit the railroad scene. It will come from China. China has already published its Locomotive Purchase Specification and nobody makes a locomotive quite like it. China can take the opportunity to build its future high speed, heavy-haul railroad infrastructure around new technology while the US and others remain economically and politically tied to the past wherein every new railcar and locomotive must be capable of functioning properly with the oldest equipment still available, and also with the roadbeds, curves and tunnels designed long ago and which is difficult to change.