Perkins Generator FAQ: Sizing, Oil Filters, and the Questions I Actually Get Asked

I coordinate emergency power installations for a living. When someone's data center is about to lose backup power, or a hospital calls on a Friday afternoon with a Monday commissioning deadline, I'm the one figuring out how to make it happen.

Over the past decade, I've fielded hundreds of questions about Perkins generators—from which 400 kW unit to spec to whether an oil filter really matters. Here are the ones I actually get asked, with the answers I'd give a client. Consider this your Perkins generator FAQ.

What Is a Perkins Generator?

A Perkins generator is a generator set powered by a Perkins diesel engine. Perkins is a British manufacturer that's been building diesel engines since 1932. Their engines show up in construction equipment, agricultural machinery, marine applications, and a whole lot of generator sets.

When we say "Perkins generator," we usually mean the complete package: the engine, alternator, control panel, cooling system, and enclosure. Perkins-powered sets cover a wide range—I've worked with units from 20 kW up to 1250 kVA. They're common in standby and emergency applications because the engines are dependable and parts are available. In my experience, if you're stuck somewhere with a Perkins engine failure, you can usually find what you need within 24 hours. That's not true for every brand.

What's the Difference Between a 400 kW and a 625 kVA Perkins Diesel Generator?

Short answer: kW is real power, kVA is apparent power. They're related by the power factor. For a typical three-phase generator, kW = kVA × 0.8.

So a 625 kVA Perkins generator at 0.8 power factor delivers about 500 kW. A 400 kW Perkins diesel generator is usually rated around 500 kVA. Wait—so they're not the same size? Correct. They're different ratings for different load scenarios. The 400 kW unit is a common choice for medium-sized commercial buildings. The 625 kVA unit covers heavier loads, like large data centers or industrial plants.

One caution: the 0.8 power factor is a standard assumption, but your actual load may differ. If you have a lot of motors or UPS systems, the power factor can drift lower, and you might need a larger kVA rating than the kW math suggests.

How Do I Choose the Right Size Perkins Generator for My Facility?

The question I hear most. Here's the process I walk clients through:

1. List the loads you need to run simultaneously—including starting surge. Electric motors can draw 3-6 times their running current on startup.
2. Determine your duty cycle. Is this a standby unit that runs a few hours a month, or prime power running 100+ hours a week?
3. Apply the 80% rule. I do not recommend sizing a generator to run continuously above 80% of its rated load. That leaves room for growth and keeps the engine from being overworked.
4. Check the applicable standards. In the U.S., NFPA 110 governs emergency and standby power systems. If your jurisdiction adopts it, the generator has to be up and running within 10 seconds of a power loss.

Real example. In March 2024, a client called at 4:00 PM on a Thursday. They needed a generator installed by Saturday morning for a facility inspection the following week. Their original vendor had spec'd a unit that was undersized—it would have tripped breakers when the HVAC kicked in. We ran the load calculation over the phone, confirmed a 400 kW Perkins diesel generator would cover it with 18% headroom, and had the unit delivered by Friday evening. The inspection passed.

The honest version: not every order wraps up that cleanly. Sizing is a tradeoff between upfront cost, fuel consumption, and future flexibility. An informed customer asks better questions and makes faster decisions. I'd rather spend 20 minutes explaining sizing than deal with a mismatched installation later.

How Do I Find the Right Oil Filter? (Prime Guard Oil Filter Lookup)

This one comes up constantly. The easiest way is the Prime Guard oil filter lookup—a cross-reference system that lets you search by OEM part number, engine model, or equipment brand. You enter what you know, it tells you which filters match.

Why use a cross-reference instead of grabbing any filter? Because "looks about right" doesn't cut it. An incorrect filter can have the wrong thread size, wrong bypass valve pressure, or wrong filter media. I've seen what happens when someone forces a slightly-wrong filter onto a Perkins engine.

We had a client in 2023 who saved $40 on an aftermarket filter that wasn't in the cross-reference. It threaded on, so they assumed it was fine. The anti-drainback valve didn't seat properly, so the oil drained back into the pan while the generator sat idle. At the next start, the engine ran for about 30 seconds with no oil pressure. That $40 savings turned into a $12,000 repair. Net loss: $11,960. I still remember the maintenance supervisor's face when the estimate came in.

The filter itself has the part number printed on it. Verify it against the lookup before installing. It takes two minutes and prevents a very bad day.

Where Is the Oil Filter on a Chevy Equinox?

I did not expect to answer this on a generator site. But it's a surprisingly common question in my inbox—I think people find my filter articles and assume I can help with anything that has a filter. Fair enough.

Honestly, I'm not 100% sure across every model year. The Equinox has had several engine options. What I know: on the 2.4L four-cylinder (roughly 2010-2017 models), the oil filter is mounted at the rear of the engine block, behind the intake manifold. You'll usually need to access it from underneath, or from the passenger side of the engine bay.

On the newer 1.5L and 2.0L turbo engines (2018 and later), I've seen conflicting references—some show the filter housing at the rear of the engine, others suggest it's more accessible from below. My best guess is it varies by the specific model year and drivetrain. Check your owner's manual or an online filter lookup. Put another way: I can tell you how the system works; I can not tell you with certainty which bolt to turn on your specific Equinox from memory.

Here's the thing, though. The reason this question matters to a generator guy: filter location tells you a lot about how hard an engine is to maintain. A filter buried at the back of a transversely-mounted engine is a headache. A filter you can reach with a wrench and a little swearing is a blessing. When I spec a generator, I look at how easy routine maintenance is. If it's a pain to change the filter, it won't get changed on schedule. That's just human nature.

How Does an Oil Filter Work?

Let's keep this practical. The oil pump pushes oil through the filter before it reaches the critical moving parts. The filter media—usually pleated paper or synthetic fiber—traps debris, soot, metal particles, and sludge. Clean oil goes to the bearings, piston rings, and other high-wear surfaces. Dirty oil gets recirculated until the next change.

Two valves matter. The bypass valve opens when oil is cold and thick, or when the filter is clogged. At that point, oil flows around the filter straight into the engine. It's a protective measure—better to have unfiltered oil circulating than no oil at all. But if your filter is clogged enough to trip the bypass valve regularly, you're slowly grinding the engine down.

The anti-drainback valve keeps oil in the filter when the engine is off, so startup gets oil pressure quickly. That's the valve that failed in my $12,000 story. When a cheap filter has a bad anti-drainback valve, you get metal-on-metal contact at startup. Not ideal. Not terrible for one time, but over the life of an engine, it adds up.

What's the One Filter Question Nobody Asks but Everyone Should?

Time-dependent degradation. People assume oil and filters only go bad with use. But oil breaks down from time, heat, and moisture—even if the engine never runs.

A standby generator that runs 20 hours a year still needs its oil and filter changed annually. I've seen generators that "ran fine last time" fail during a real outage because the oil had absorbed moisture or turned to sludge. The filter was the original one from the factory. Put another way: an oil filter is not a fit-and-forget part.

My suggestion: tie the filter change to your annual load bank test. You're already running the generator, so change the oil and filter while you're at it. Less than an hour of work, and it's the cheapest insurance you'll buy for your Perkins generator.