Waukesha VGF F18GL

Lean-burn 18-litre inline six rated 230 to 330 kWb, with a published 24,000-hour top end interval

Waukesha VGF F18GL is one of 23 gas engines tracked in the SecondWatt catalogue, each with specifications, lead times and indicative secondary-market pricing.

Waukesha VGF F18GL specs: 310 to 440 BHP and 230 to 330 kWb, 18 litre inline six, 2.00 g/bhp-hr NOx, plus a published 24,000 hour top end interval.

The INNIO Waukesha VGF F18GL is a lean-burn spark-ignited inline six-cylinder stationary gas engine rated 310 to 440 BHP, or 230 to 330 kWb. INNIO publishes 400 BHP or 300 kWb at 1,800 rpm and 335 BHP or 250 kWb at 1,500 rpm. It displaces 1,096 cubic inches or 18 litres on a 5.98 by 6.5 inch bore and stroke, ordered in either low compression at 8.7 to 1 or high compression at 11 to 1. These are engine ratings at the crankshaft. This is the smallest engine in the VGF family and the only current Waukesha gas engine with a published overhaul figure from INNIO. Fitted with the newer GL cylinder head assemblies, INNIO states that the top end overhaul extends to 24,000 hours. The F18 shares its 152 by 165 millimetre bore and stroke with the H24 inline eight and the L36 V12. Same cylinder module, different counts, which is a parts commonality argument a buyer can verify from three separate data sheets rather than take on trust. At 5,300 lb dry it is by a wide margin the lightest engine in the Waukesha gas line, roughly a sixth the mass of the V16 P9394GSI.

Why it matters

It is the only current Waukesha gas engine for which INNIO publishes an overhaul interval, at 24,000 hours to top end with the newer GL heads, which turns a maintenance reserve from guesswork into arithmetic. At 5,300 lb dry it also removes the foundation and rigging problem that dominates the larger VHP engines.

Who buys it

Operators adding continuous gas generation in roughly quarter-megawatt increments, typically landfill gas, digester gas and small distributed cogeneration sites. It also suits buyers who want VGF parts commonality across several sizes without committing to a half-megawatt block. This is continuous and prime duty rather than NFPA 110 standby, which is the line that defines this category.

Role in the data center

A quarter-megawatt continuous increment, useful where capacity is added in small steps or where a landfill or digester gas stream sets the scale rather than the electrical load. At 5,300 lb dry it avoids the rigging and foundation constraints that dominate the multi-megawatt VHP engines, at the cost of needing many more units for the same block.

Key specifications

Technical summary

Output: 310 to 440 BHP (230 to 330 kWb); 400 BHP (300 kWb) at 1,800 rpm; 335 BHP (250 kWb) at 1,500 rpm. Cylinders and displacement: inline 6, 1,096 cu in (18 litres). Bore and stroke: 5.98 x 6.5 in (152 x 165 mm), shared with the VGF H24 and L36. Compression ratio: low compression 8.7:1 or high compression 11:1, selected at order against the site gas. Heat rate: 7,124 Btu/bhp-hr (10,026 kJ/kWh) at 1,800 rpm; 6,920 (9,789) at 1,500 rpm. Brake thermal efficiency: 35.7 percent at 1,800 rpm, computed as 2,545 divided by 7,124. NOx: 2.00 g/bhp-hr (810 mg/Nm3 at 5 percent O2) at 1,800 rpm; 2.4 (982) at 1,500 rpm. Top end overhaul: 24,000 hours with the newer GL cylinder head assemblies, as published by INNIO. Dimensions: 80.5 x 50 x 68 in (2,043 x 1,264 x 1,727 mm). Dry weight: 5,300 lb (2,400 kg), the lightest engine in the Waukesha gas line. VGF packaged genset line: 350 to 1,250 kVA across 6, 8, 12 and 16 cylinder models.

Major variations

Compression ratio is the main ordering variable, between LCR 8.7:1 and HCR 11:1, matched to the site gas. The newer GL cylinder head assemblies are the variant that carries the 24,000-hour top end interval, so head generation matters as much as engine generation on a used unit. Speed selection at 1,800 or 1,500 rpm changes output between 400 and 335 BHP and shifts both heat rate and NOx.

Configurations and options

Lean-burn operation rules out a three-way catalyst, leaving an oxidation catalyst and selective catalytic reduction as the aftertreatment path. INNIO also markets an F18SE variant with improved oil filtration and longer oil change intervals, though no hour figure is published for it. Packaged VGF generator sets are rated in kVA and sold separately from the bare engine.

Compatibility and dependencies

The VGF family shares one cylinder module at 152 by 165 mm across the F18 inline 6, H24 inline 8 and L36 V12, verifiable from three separate data sheets. Compression ratio must be matched to the site gas at order because it cannot be changed in the field, and INNIO publishes no methane number requirement to guide that choice, so a gas analysis is required. The 24,000-hour top end figure applies only to units fitted with the newer GL heads.

Pricing and availability

Comparable secondary-market band: 2000–3150 $ per kW installed project cost. Trend: stable Value in this category steps down at overhaul milestones rather than by calendar year, and on this model the 24,000-hour top end mark is the step that can actually be placed, because it is the one interval INNIO publishes. Lead time, new: No published lead time from INNIO.. Lead time, used or refurbished: Smaller Waukesha gas units appear regularly in dealer stock, including a 150 kW F-18G at S and W Power Systems on 2026-08-31, but no availability dates are published..

Lifecycle and maintenance

INNIO publishes a 24,000-hour top end overhaul for the F18GL fitted with new GL cylinder head assemblies, which is the only overhaul interval INNIO publishes for any current Waukesha gas engine. That single figure lets a buyer size a maintenance reserve rather than guess at one, and it is a reason to prefer this model where the size fits. No major overhaul interval and no oil change interval are published. Value in this category tracks hours since overhaul rather than build year, so the head-hour record rather than the nameplate date sets the price.

Thermal and emissions profile

INNIO publishes NOx at 2.00 g/bhp-hr, equivalently 810 mg/Nm3 at 5 percent O2, at 1,800 rpm and 2.4 g/bhp-hr at 1,500 rpm. Converting the 810 figure gives roughly 147 ppmvd at 15 percent O2. At 310 to 440 BHP this engine falls in the 100 to 500 horsepower band of 40 CFR 60 Subpart JJJJ, where non-emergency spark-ignition natural gas engines built from 1 January 2011 are held to 1.0 g/HP-hr or 82 ppmvd. The engine therefore runs about twice the limit uncontrolled and needs aftertreatment. Lean-burn combustion rules out a three-way catalyst, which requires stoichiometric operation, so an oxidation catalyst plus selective catalytic reduction is the route. No CO or formaldehyde figure is published, and formaldehyde drives NESHAP RICE.

Common failure points

• Cylinder head and valve seat recession — compression loss, exhaust temperature spread widening across the 6 cylinders, output fading below 400 BHP
• Detonation on high compression units — knock under load, piston crown and ring-land damage, controller derate
• Turbocharger and aftercooler wear — slow load acceptance, low boost, rising exhaust temperature
• Ignition system and spark plug fouling — misfire, unstable output, rising CO and unburned hydrocarbons
• Wrong compression ratio for the site gas — persistent knock on an HCR unit, or lost output and poor efficiency on an LCR unit
• Alternator bearing and winding degradation — bearing noise, falling insulation resistance, winding temperature rise

Inspection checklist

Hours since top-end overhaul: against the published 24,000-hour interval, the only overhaul figure INNIO publishes for a Waukesha gas engine. Cylinder head generation: the 24,000-hour figure applies only to units fitted with the newer GL head assemblies. Suffix is GL and not a rich-burn variant: NOx differs by roughly an order of magnitude across the VGF suffixes. Compression ratio as ordered: LCR 8.7:1 or HCR 11:1, because compression ratio is not a field change. Oil analysis trend: at least the last 4 samples, with wear metals plotted rather than read individually. Compression across all 6 cylinders: a spread beyond roughly 10 percent indicates head or ring wear. Turbocharger shaft play and boost pressure: logged against the commissioning baseline at 100 percent load. Aftercooler core and coolant-side fouling: inspected with the turbocharger as 1 system, never separately.

Procurement channels

Smaller VGF units trade through the same North American network that Waukesha's gas compression and landfill gas installed base created. Marketplaces to work are Surplus Record, Machinio, IPS, Depco Power Systems, Genset Services, Worldwide Power Products, Collicutt and Penn Detroit, with eBay and GovPlanet worth checking at this size where they are not for the multi-megawatt engines. Dealers observed holding smaller Waukesha gas units include S and W Power Systems, Kraft Power Corp and Savona Equipment.

Regional notes

North American channel confirmed. INNIO publishes 60 Hz ratings across the packaged VGF line, and the sibling VGF24GL generator set sheet states 390 to 425 kWe continuous at 60 Hz and 1,800 rpm against 325 to 360 kWe continuous at 50 Hz and 1,500 rpm.