Caterpillar G3520H

2,519 ekW continuous at 45.30 percent electrical efficiency, with hydrogen blends to 25 percent

Caterpillar G3520H is one of 23 gas engines tracked in the SecondWatt catalogue, each with specifications, lead times and indicative secondary-market pricing.

Caterpillar G3520H: 2,519 ekW continuous at 1.0 pf, 45.30 percent electrical efficiency, hydrogen to 25 percent. Specs, pricing and inspection.

The Cat G3520H is a continuous-duty gas generator set published at 2,519 and 2,500 ekW at 1.0 power factor, inside a band of 1,763 to 2,519 kW, with a maximum electrical efficiency of 45.30 percent. On the 50 Hz sheet it is rated 2,485 ekW with pumps (3,106 kVA) and 2,500 ekW without pumps (3,125 kVA) at 0.8 power factor. Caterpillar offers it at both 50 and 60 Hz and lists the United States and Canada among its markets. The engine is a 20-cylinder unit of 170 mm bore by 215 mm stroke and 97.5 L, the long-stroke H-series block. Two builds are published: Humidity/Fuel Tolerant at 11.1 compression and High Efficiency at 12.1. At full load with fan on the 50 Hz sheet the High Efficiency build burns 7,909 Btu/ekW-hr against 8,086 for the tolerant build. Dry weight is 24,800 kg, the heaviest set in the Caterpillar G3500 gas range. Hydrogen capability is the point of difference. Caterpillar publishes hydrogen blends up to 25 percent for this model against 5 percent on the G3516 FAST RESPONSE, which matters to a buyer underwriting a twenty-year asset against a fuel transition. NOx is published at 250 mg/Nm3, or 0.49 to 0.50 g/bhp-hr, and at 500 mg/Nm3, or 0.94 to 0.96 g/bhp-hr.

Why it matters

This is the model that carries Caterpillar's hydrogen story into the megawatt class a data center actually buys. A published 25 percent blend capability plus 45.30 percent electrical efficiency makes it the hedge purchase in the range, and it has more used price evidence behind it than any other current Caterpillar gas model except the G3516.

Who buys it

Continuous-duty buyers in the 2 to 2.5 MW block who want efficiency and a hydrogen pathway in the same machine. Data center developers building multi-unit behind-the-meter plants where N+1 at 2.5 MW granularity beats a single large turbine. Industrial cogeneration and municipal utility operators running high annual hours where heat rate dominates the operating budget.

Role in the data center

Continuous behind-the-meter prime power in multi-unit plants at roughly 2.5 MW per set, where N+1 granularity and part-load heat rate matter more than raw output per unit. The hydrogen blend rating gives this model a role the rest of the range does not have: a twenty-year asset with a published fuel-transition path. Weigh that against the G3520K, which publishes a better full-load heat rate at 7,474 Btu/ekW-hr.

Key specifications

Technical summary

Continuous rating: 2,519 and 2,500 ekW at 1.0 power factor; published band 1,763 to 2,519 kW. Continuous rating, 50 Hz sheet: 2,485 ekW with pumps (3,106 kVA), 2,500 ekW without (3,125 kVA) at 0.8 pf. Maximum electrical efficiency: 45.30 percent. Heat rate at 100 percent load with fan, 50 Hz: 7,909 Btu/ekW-hr High Efficiency; 8,086 tolerant build. Bore and stroke: 170 mm by 215 mm; displacement 97.5 L (5,956 cu in), 20 cylinders. Compression ratio: 11.1 Humidity/Fuel Tolerant or 12.1 High Efficiency. NOx: 250 mg/Nm3 (0.49 to 0.50 g/bhp-hr) or 500 mg/Nm3 (0.94 to 0.96 g/bhp-hr). Dimensions, 50 Hz: 6,940 by 2,173 by 2,473 mm. Dry weight: 24,800 kg (54,675 lb). Fuel: natural gas, hydrogen blend up to 25 percent. Frequency: 50 and 60 Hz, with the United States and Canada listed as markets.

Major variations

Two builds are published: Humidity/Fuel Tolerant at 11.1 compression and High Efficiency at 12.1. The High Efficiency build is roughly 177 Btu/ekW-hr better at full load on the 50 Hz table, and the trade is fuel-quality and ambient tolerance against heat rate. One Caterpillar document inconsistency is worth knowing before purchase. Caterpillar's 60 Hz H-series and K-series sheets list an engine speed of 1,500 rpm, and the CG170 brochure lists 1,500 rpm alongside both 50 and 60 Hz outputs. A 1,500 rpm machine on a synchronous alternator produces 50 Hz on four poles, not 60 Hz. The pattern appears on at least three separate Caterpillar documents, so it is not a single typo. A resale listing describes a 60 Hz G3520H at 1,800 rpm, but a reseller listing is not a substitute for the OEM specification; confirm engine speed on the nameplate.

Configurations and options

Ratings are published with and without engine-driven pumps, a difference of 15 ekW at 50 Hz between 2,485 and 2,500 ekW. Quote which arrangement you mean, because the two figures appear interchangeably in resale listings. Hydrogen blending up to 25 percent is published for this model, against 5 percent on the G3516 FAST RESPONSE. Caterpillar offers the set at both 50 and 60 Hz and lists the United States and Canada among its markets.

Compatibility and dependencies

The G3516 and the 3516B diesel share the Cat 3500 block. Caterpillar publishes 170 mm bore, 190 mm stroke, 69 L and a V16 layout on both. They are not the same engine: the diesel is a 14.0:1 compression-ignition unit with electronic unit injection, while the gas set is spark-ignited with a gas fuel train and a different emissions package. What carries across is parts overlap, shared service tooling and a Cat technician base already fluent in the 3500 platform. What does not carry across is ratings, duty, overhaul intervals or the emissions rule. Diesel sets fall under 40 CFR 60 Subpart IIII for compression ignition; this one falls under Subpart JJJJ for spark ignition.

Pricing and availability

Comparable secondary-market band: 151.9–310.4 $ per kW. Trend: rising Condition in this category is dominated by hours to overhaul, not by model year or cosmetic state. A 40,000-hour engine three years from a major is worth materially less than an older unit fresh out of one, and the resale boards rarely publish hours at all. That is why the used spread is so wide. Ask for hours since major and hours since top-end before any other question, and treat a listing without an hour meter reading as unpriceable. Lead time, new: The only dated model-specific schedule on the public record is the Monarch alliance: announced 28 January 2026 with G3516 deliveries running September 2026 through August 2027, which puts first units at roughly eight months from announcement at 2 GW scale. Global Power Supply publishes 26 to 39 weeks for natural gas gensets of 70 to 500 kW in 2026 and no band at all above 500 kW, which is the range the G3520H occupies. Do not extrapolate it upward.. Lead time, used or refurbished: No published lead time for used G3520H units..

Lifecycle and maintenance

Caterpillar publishes no MTBF and no overhaul interval in hours for the G3520H. The only Cat-published maintenance interval in the gas line is up to 4,000 operating hours on the CG170 series. MWM publishes major overhauls at 48,000 to 80,000 hours and cylinder head inspections at 24,000 to 40,000 hours on the CG-series engines Caterpillar also owns. Those are MWM figures on different engines. The strongest evidence for this model is transactional: a 2019 G3520H with 37,000 hours sold at 520,000 dollars, which is 208.84 dollars per kW and shows the machine holds real value well into its service life.

Thermal and emissions profile

Caterpillar publishes the G3520H at 250 mg/Nm3, equal to 0.49 to 0.50 g/bhp-hr, and at 500 mg/Nm3, equal to 0.94 to 0.96 g/bhp-hr. The upper figure sits directly against the 40 CFR 60 Subpart JJJJ ceiling of 1.0 g/HP-hr, or 82 ppmvd at 15 percent O2, for lean-burn natural gas non-emergency spark-ignition engines at or above 500 HP. A set on the 500 mg/Nm3 tune meets the federal rule natively with almost no margin. The 250 mg/Nm3 option is a different engine-out tune rather than aftertreatment, at a small heat-rate cost. Selective catalytic reduction is a capital line item that appears when a local permit rather than the federal rule governs, which is the usual case in a non-attainment area. No carbon monoxide or formaldehyde figure is published; formaldehyde falls under NESHAP RICE.

Common failure points

• Detonation from low methane number gas — Knock under load, rising exhaust temperature, controller retarding timing
• Spark plugs and ignition coils — Misfire, rough running, rising carbon monoxide, output derate
• Charge-air and aftercooler fouling — Charge air temperature rising and heat rate drifting above the 7,909 Btu/ekW-hr baseline
• Exhaust valve and seat recession — Compression falling on one cylinder, exhaust spread widening, hard starting
• Emissions drift past Subpart JJJJ — Annual stack test returns NOx above 1.0 g/HP-hr or 82 ppmvd at 15 percent O2
• Turbocharger bearing failure — Oil in the charge air, surge, sudden loss of boost and output

Inspection checklist

Hours since major overhaul: the dominant price driver in this category, ahead of model year. Hours since top-end: used G3520 units reaching the open market carry 37,000 to 49,800 hours. Nameplate duty: rated continuous; a continuous rating is not a prime or standby rating. Power factor: 2,519 ekW is quoted at 1.0 pf while the 50 Hz sheet quotes 2,485 ekW at 0.8 pf. Build variant: Humidity/Fuel Tolerant at 11.1 compression or High Efficiency at 12.1. With-pumps or without-pumps rating: 2,485 against 2,500 ekW on the 50 Hz sheet. Frequency and voltage: offered at both 50 and 60 Hz, and the resale channel mixes both. Heat rate verified under load: expect about 7,909 Btu/ekW-hr on a High Efficiency build. NOx tune: 250 mg/Nm3 or 500 mg/Nm3; the 500 setting sits on the federal ceiling. Engine manufacture date: the Subpart JJJJ ceiling binds engines built on or after 1 July 2010.

Procurement channels

New units go through Cat dealers and Cat dealer pages price as Request a Quote. Named dealers holding gas stock include Quinn, Hawthorne, Empire, Western States, Cleveland Brothers, Carter, Stowers, Foley, Holt, Milton, Mustang, Ring Power, Toromont, Wheeler and Boyd CAT. The used channel is quote-driven and deep in Texas and western Canada. DEPCO Power Systems publishes more numbers than anyone else; Industrial Motor Power, Power Generation Enterprises, McKain, Powersafe, Collicutt, Lenmark, NineX, Aaron Equipment and Worldwide Power Products carry inventory but mostly withhold price. Price opacity is the defining feature here.

Regional notes

Caterpillar lists the United States and Canada among the markets for this model and offers both 50 and 60 Hz. The 50 Hz spec sheet is the more complete public document, so confirm which frequency any published figure refers to before quoting it. Caterpillar's own claim for the Cat dealer network is 24/7 service, 99 percent parts availability and a 24-hour response guarantee. That is a Caterpillar claim rather than a measured figure. It is still the commercial argument that matters most in this category, because every large competitor is European or thinner on the ground in North America.