The Hidden Life of Oil Pumps: Design and Development at Melling

You probably take oil pumps for granted. Yeah, we all know how important they are, and we understand there are a couple of specs with them that have to be chosen correctly. But outside of that, most of us assume they’re pretty simple — some gears, a housing, and a few passages to channel oil in and out, right?

Well, it turns out the development of oil pumps can be pretty involved, both from a technical standpoint as well as a business perspective. To learn how these vital components come to life, we talked to Tim Foster, Product Development Manager at Melling.

How does Melling decide to offer a particular pump for the aftermarket?

It can start any number of ways. Melling sells to such a wide variety of customers that we receive requests from a number of areas. We sell to small engine builders, retail shops — the AutoZones and all that of the world — and production engine rebuilders (PER). We typically want to have as much pump coverage as possible. That’s what we’ve been doing for 75 years.

We try to focus on starting with large applications, like the LS. That’s a no-brainer because it’s in millions of trucks and cars all over the world. We look at how many vehicles in operation (VIO) are there. Is this going to be something that economically makes sense for us to tool up and produce? Are there known problems with the engine that these things are going to get rebuilt quite often? Maybe the VIOs are smaller, but these engines only last three or four years.

There’s a particular engine, I’m not going to say who produced it because I don’t want to call anyone out, but a few years ago there was a particular engine that the original equipment (OE) manufacturer struggled with and they were constantly getting rebuilt. There was regularly water in the oil so they were getting rebuilt all the time. So, that was a good pump to have available.

A lot of different things can go into it. If a PER comes to us and says, “Hey, we’re going to make 50 of these things a month,” but they’re the only ones in the world doing it, then does it make sense to tool something up?

Also, is the engine still in production? Because the OE’s production price for an oil pump can be relatively low, sometimes we can’t compete with that until it’s out of production and they’re not making millions of them. Then their price goes up and ours will be right in line with that. There are quite a few things that go into making the decision.

I’m not trying to understate the importance of proper oil pump design, but typically for an OE project Melling will receive a statement of requirements, where the OE engineers have calculated the required amount of oil or the gallons per revolution that the engine will need and the operating pressure that they believe they need to see in the engine at hot idle (hot idle is the engine’s highest specific rate of demand for oil). The OE will also supply what we call the environment — the area where the pump is going to be assembled to the engine.

So you know roughly the size that you’ll be able to work with and what the engine is going to require. From there, the design process can begin. Almost all new oil pumps are located on the crankshaft, so there is either going to be a gerotor pump, or a variable-displacement pump (a vane pump). Based off of what the engine demands, you design a rotor set or a vane that will meet those criteria.

The oil pump development process is different for aftermarket and OE designs. But once the early development stages are finished, work typically proceeds to CAD designs for either.

Is there a lot of collaboration with OEs on these projects? 

When Melling is approached for an OE project, the amount of collaboration depends not only on the OE customer but even down to the project. For some OE projects, their engineers have worked diligently and ask us for a quote on their pump design. For other projects, you get what we call a one-pager, and it’s “Okay, this pump needs ‘X’ amount of gallons per minute (GPM) at a set RPM with an operating pressure of such and such PSI, and here’s a basic bolt pattern for the engine block.” I’ve seen it both ways, and everything in between.

Once the oil pump design is finished, the CAD files are used to build prototypes, which will then be used for evaluation and testing.

How does the process of designing an aftermarket pump begin?

In terms of designing a stock replacement aftermarket pump, we’ll take an OE pump, measure the critical components, perform the calculations and say, “Okay this is the GPM required of this oil pump.” We then take other factors into consideration, looking for areas of potential improvement. Are there known issues with the oiling system in this particular engine? We typically design a stock replacement oil pump that will be very similar in outward appearance to the OE pump.

However, at Melling we implement design upgrades to the housing, rotor set, cover, and other components that collectively provide a significant improvement in performance or durability when compared to the OE pump. A case in point is the GM LS family of oil pumps, where the Melling pump consistently outperforms the OE offering.

Are there specific problems with some engines that you have to consider when designing an aftermarket oil pump?

Other engine operating issues can also exist that, while not the fault of the oil pump itself, directly affect the oil pump’s performance or even engine performance. The 3-valve 5.4-liter Ford can be used in this example. The cam phasers are hydraulically actuated on this engine and the oil pump’s output (flow) was designed for optimal bearing clearances. However, once that engine gets some mileage under its belt, or wear into the engine, the clearances naturally begin to grow.

Now is a time to discuss a significant principle that I need to point out regarding oil pumps. Oil pressure is the key measurement that is monitored in automotive applications. However, oil pumps do not create oil pressure. Pumps create a flow of oil that is sent through a set of clearances. The resistance to that flow of oil through those clearances is what creates oil pressure.

For the cam phasers to operate correctly in the Ford 5.4, a specific oil pressure is required. Once wear begins to erode the engine’s ability to maintain that pressure, i.e. clearances open up, the oil pressure drops in the engine, and the cam phasers begin to operate erratically. This will lead to improper engine timing and poor engine performance. I mention all of this to simply say that we at Melling take this historical data on the aftermarket side, and ask ourselves, “Okay, if the stock pump is ‘X’ GPM, do we need to create a higher-volume version? And will there be demand for a higher-volume version than the stock version?”

The initial development of an oil pump can move quickly. In many cases, the project goes from specifications to building prototypes in just a few weeks.

How important are the specific materials used in an oil pump?

One of the other major considerations that we take into consideration on the aftermarket side is materials. The OEs prefer to use a stamped steel cover on their oil pumps, or here more recently they’ve been moving to die-cast aluminum covers on pumps. Cost implications when making hundreds of thousands of pumps are the motivating factor for the OE’s regarding material selection.

Melling’s philosophy has been that what is best for the end-user should be used in our oil pumps. Because of that line of thinking, we prefer to use a double-disc-ground cast iron cover on as many of our pumps as possible. The cast iron covers provide dual improvements over other materials including additional lubricity at dry-start and an enhanced pressure tightness because of the rigidity of cast iron.

In order to document the improvement of a cast iron cover versus an aluminum cover, we conducted a performance test of an OE pump with an aluminum cover vs. a Melling aftermarket pump with a cast iron cover on our R&D test stand. Around 2,500 rpm, the OE pump started leaking oil profusely between the pump housing and cover. In the side-by-side video we were able to note that at the same RPM there was no leakage on the cast-iron pump cover. In fact, leakage between the housing and cover didn’t begin until after 5,000 RPM. This results in a more efficient pump when compared directly to the OE pump.

Who decides what basic pump type to use — spur-gear, gerotor, or variable-displacement?

That is typically spelled out by the OE. Most of the OEs are going more and more to the variable-displacement pumps (VDP). Up until a few years ago, it was a relatively new style oil pump. Now that they’ve gotten better at designing them and producing them, the variable displacement seems to be getting more popular. But that’s really up to the OEs. As with any new technology, there are tradeoffs.

For years, oil pumps — whether spur gears or gerotor design — were designed to produce more oil than the engine would demand. It’s a safety factor thing. Again I refer to the hot-idle discussion from earlier. The oil pumps were designed to produce a specific amount of flow over the engine’s requirements at hot idle. This philosophy leads to inefficiencies.

With the variable-displacement pump, the goal is to make a more efficient pump, that’s producing a more accurate flow of oil that the engine needs at a certain RPM, without wasting energy. VDPs do have limitations regarding increased oil flow at higher RPMs. Above certain rotational speed, a variable-displacement pump cannot produce additional oil flow, which becomes an issue in performance applications.

Once prototypes of a new oil pump design are built, the project moves into Melling’s test lab. The test and evaluation process tends to be much longer for OE pumps than for aftermarket designs.

So it’s not using a relief valve the same way as an old-style pump?

Variable-displacement pumps still use a pressure-relief valve (PRV). The relief valve is a safety thing. Even in the vane pump, if something happens and the pump suddenly begins producing 130-plus psi, you don’t want to send that through to the filter. Oil filters are typically rated at around 120 psi. So the PRV is a safety valve to dump oil back into the pan or back into the inlet of the pump. Fixed-displacement pumps (spur-gear or gerotor) provide an increased flow of oil per engine RPM (oil pump displacement is calculated in GPM per RPM). The PRV is designed to regulate the amount of flow into the engine without causing excessive operating pressure or damage.

With variable-displacement oil pumps, no two designs are alike either. For instance, on the GM LS variable-displacement pump that’s on all the 5.3-liter trucks now, there are only two operating ranges. The pump’s output is electronically controlled and the vane goes from higher output to lower output depending on the speed of the crank.

How long does it take to develop a new oil pump?

On the aftermarket side, typically it’s a few weeks for design and prototyping components. We can have a pump design released for production in just a few months after our project start date.

On the OE engineering side, it depends on the amount of information provided by the OE. For instance, the Ford Predator (5.2-liter Mustang GT500) engine, it took a mere few weeks on the design side to create prints and prototype components. However, for product validation, testing, durability testing, and review it covered nearly 18 months to two years from contract award until it was in production.

Melling developed the OE oil pump for the Ford Mustang GT500’s 5.2L supercharged V8.

Is Melling planning on offering an aftermarket pump for the GT500 engine?

We haven’t even sat down to discuss that one in the aftermarket yet, because it’s still in production. Mellng is the OE source for this pump. So, with it still being in production, the OEs typically don’t want us making an aftermarket pump.

At this point, is developing a new oil pump pretty routine?

It depends on the technology. The spur-gear pumps, yeah, that’s tried and true and there aren’t a whole lot of surprises. The gerotor pumps, I’m sure when those started coming around there was a learning curve. But that’s been around long enough now that I don’t think there are too many surprises.

The introduction of the vane pumps or the variable displacement pumps, that’s still relatively new. It’s not complicated technology, it’s just wrapping our heads around it. Working with the OEs gives us the benefit of speeding up the learning curve. We can learn some lessons from them, they can give us some advice and we can provide our lessons-learned to them as well. That’s one of the reasons we like to work with the OEs. It helps us in the long run with our learning of new technologies. At the end of the day, I wouldn’t say that there are too many surprises in the oil pump realm.

With proven technology that’s been in use for decades, spur-gear pumps generally don’t present difficult challenges for engineers at this point.

Do high-performance engines have unique considerations that you look at?

On an OE performance engine, our input can be limited on the pump design. One of the considerations that we have to talk to them about is materials. You don’t want to go with the most cost-effective material that may not hold up that well in a performance application, and you have to justify the cost to them.

That occurred on the Corvette oil pump that we produced for the C7. The oil pump is a two-stage dry sump that uses a gerotor for the scavenge pump section. When the LT4 supercharger was introduced, we pushed very hard to get a stronger material for the gerotors to live up to the supercharged application. But going into it, on the OE side, it would really just be, “What are we doing with this engine? Is it a performance engine? Is it going to be supercharged? Let’s look at the materials.”

On the aftermarket side, it’s more of the same. The engine’s been out in the market, so if it works on the OE side, are there things that we need to improve upon? Are there known issues with the engine or the oil pump that we need to make improvements on in a performance pump? We do some of that automatically on our performance aftermarket pumps.

The C7 Corvette Z06’s supercharged LT4 V8 warranted more robust materials in the oil pump, which was developed by Melling.

One of the Melling norms is that we typically have a higher-volume pump version of the stock pump, just in case there’s remote oil filters or remote oil coolers or any add-ons that would add to the need for higher volume. Some engine builders like larger bearing clearances. That directly affects the amount of pressure in the oiling system. So we recommend a higher-volume pump if you’re running your bearing clearances larger than stock.

For our performance pumps, we hardcoat-anodize all of our die-cast aluminum housings because performance engines typically run in a higher-RPM range and you’ve got a steel PRV shuttling back and forth in aluminum. You’ve got the gerotors in an aluminum housing. So we’ll hardcoat-anodize to protect against wear.

Especially with crank-mounted pumps, you’re constrained with the amount of room between the oil pump and timing cover or timing chain to make major adjustments to the oil pump’s overall footprint. For example, Melling took an extensive amount of time to develop a high-volume pump offering for the Ford 5.4-liter 3-valve engine that increases the oil pump flow while fitting in the original pump’s footprint without any modification.

Do supercharged engines have different requirements for oil pumps?

No, not that we’ve seen. The biggest issue becomes crank deflection. If the end-user tightens the supercharger belt down really tight, and if the crank’s got a long snout on it, you can get some deflection in the crank snout that goes right into the inner oil pump gerotor. And if you’re pushing the inner gerotor into the outer gerotor, that can cause wear issues. I’ve seen rotors just explode because of this issue.

One instance is the 6.2-liter Raptor engine from Ford a few years ago. The root diameter in the outer rotor was very small and at higher RPM the inner rotor is pushed higher into the outer gerotor and the forces inflicted upon the outer gerotor can cause catastrophic damage. So on some of our Melling performance pumps, where it’s known that this issue can occur, we have what we call the BR or Billet Rotor option, where we make the rotor set out of 4140 chromoly steel, instead of powdered metal.

Supercharged engines don’t have unique oil pump needs says Melling, but improper supercharger belt tightening can be catastrophic for the pump’s rotors.

When developing an aftermarket pump, do you design for specific applications — road racing, drag racing, etc.?

We don’t really break it down into different types of racing. We just consider if an engine is popular in the performance hemisphere. Like the LS or the small-block Chevy are insanely popular in the racing world. So we’ll take that into consideration. But we don’t really take the different genres into consideration very much.

How would you sum up the role of an oil pump?

Our slogan is, “The oil pump is the heart of the engine.”

Article Sources

About the author

David Bellm

David Bellm is an award-winning automotive writer, specializing in hot rods, muscle cars, motorsports, automotive history, and the performance aftermarket. His car obsession started early in life, working on his brother’s custom van in 1977.
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