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Gas engine overhaul intervals and lifetime cost vs diesel generation

Fuel is where gas projects win, and maintenance is where they can quietly lose. Here is how overhaul intervals are actually set, what shortens them, and how to build a lifetime cost model you would defend in front of a bank.

Two different "overhauls" — do not mix them up

Service	What is done	Typical timing
Top-end / valve service	Valve clearance, cylinder head inspection, valve and seat work, pre-chamber and spark plug service	Platform-dependent; commonly quoted in the tens of thousands of running hours, adjusted for gas quality
Major overhaul	Pistons, liners, bearings, turbocharger overhaul, full inspection of the running gear	Our large-bore gas platforms are specified with an overhaul interval in the region of 60,000 running hours under matched gas quality, load profile and oil management

That 60,000-hour figure is a design basis, not a promise that survives any duty. It is conditional on gas quality, oil management and how the plant is actually operated — which is exactly why the conditions belong in the contract.

What shortens an overhaul interval

Gas quality. H₂S, siloxanes and moisture are the biggest levers. Contaminated gas can turn a planned 60,000-hour interval into a much earlier intervention — see gas treatment before the engine.
Load profile. Engines running at low load for long periods run cold, build up deposits and wear differently from engines at their rated point. A plant sized at 60% of site demand and run at 25% is a maintenance liability dressed as a safety margin.
Oil management. The right specification, the right change interval, and — above all — actually doing the oil analysis. Most expensive failures announce themselves in the oil report first.
Cooling and ambient. Elevated cooling water and intake temperatures accelerate wear across the board.
Start/stop cycling. Frequent start-stop duty costs more maintenance than continuous running, and it needs to be stated in the load profile you give your supplier.
Air and fuel filtration. Dusty sites and untreated gas both find their way into the engine.

The lifetime cost model — four lines, and one of them dominates

Model cost per generated kWh, not purchase price:

Line	What goes in it	Typical share of lifetime cost
Fuel	Fuel price per unit of energy ÷ electrical efficiency	Dominant — often 60–80% for continuous duty
Capital	Installed equipment cost, amortised over the project life	Meaningful but secondary
Maintenance	Planned services, overhauls, consumables, oil	Often 10–15%; the item most often underestimated
Non-fuel OPEX	Operating staff, insurance, monitoring, downtime risk	Site-specific

The formula worth writing down:

cost per kWh = (fuel price per kWh of gas) ÷ (electrical efficiency) + variable maintenance cost per kWh + amortised capital per kWh

Because fuel dominates, two things move the answer more than anything else: the price of your gas, and the efficiency at your operating point — not at a datasheet point. If someone hands you an efficiency number without stating the fuel, the load and the ambient conditions, the number is decoration.

Gas vs diesel: where the comparison actually turns

Factor	Gas engine	Diesel engine
Fuel cost per kWh of electricity	Low where gas is a by-product, waste gas or locally priced; can approach fuel-only cost of a few cents	Follows distillate prices and the cost of moving fuel to site
Fuel logistics	Pipelined or on-site produced — no truck fleet	Trucking, storage, quality control, theft risk
Capital cost	Higher per kW, plus gas treatment where needed	Lower per kW and simpler to install
Maintenance	Planned overhauls on running hours, oil analysis critical	Frequent consumable service, filters and injectors
Best fit	Continuous prime power where gas is available — oilfields, landfills, digesters, industrial plants	Standby, peaking, remote sites with no gas supply

The clear-cut gas cases are the ones where the gas is otherwise flared, vented or a nuisance: associated petroleum gas at oilfields, landfill gas, digester gas at wastewater or agricultural plants, coal mine gas. In those projects the alternative to generating is not "buy diesel" — it is "burn the gas with no return at all". That is why payback periods in this segment are usually driven by gas availability and regulatory pressure, not by the equipment price.

Delivery: the non-obvious advantage

For buyers in a hurry, the engine technology itself is the argument. Reciprocating gas engines are built on industrial production lines and are quoted on industrial lead times. Large heavy-duty gas turbines in the current market are quoted with delivery measured in years. For a plant that has to be producing power this decade — and especially for distributed generation and multi-unit plants that can be built step by step — reciprocating gas generating sets are usually the only realistic route.

What to insist on in the offer

Overhaul interval stated with its conditions — gas quality window, load range, ambient and oil management
Guarantee values for output, electrical efficiency and gas consumption at your operating point, verified at the factory acceptance test
A maintenance plan with hours and part numbers, not a generic list
Spares strategy: which parts you hold on site, lead times for the rest, and who can service the unit locally
Oil analysis and remote monitoring included in the scope, with a reporting routine

FAQ

Can I extend the overhaul interval beyond the design figure?

Yes, sometimes — with clean gas, steady high load, disciplined oil analysis and documented running conditions. It should be a data-driven decision made with the engine supplier, not a cost-cutting assumption made in the budget.

Is a gas plant cheaper than diesel from day one?

Usually not on capital cost. It is normally cheaper on cost per kWh from the first hours of continuous operation, provided the gas is available at a low price relative to distillate — and provided the unit is run near its design point.

How long does the equipment take to deliver?

It depends on model and configuration. Reciprocating gas generating sets sit on industrial lead times, and we state the commitment date in the offer rather than in a brochure. Ask us for a current date for your size and specification.