Question 1

How long will a generator run on a full tank of diesel?

Accepted Answer

Runtime depends on generator size, load level, and tank capacity. A typical 100 kW diesel generator at 75% load consumes about 5.9 gallons per hour. With a 500-gallon tank (90% usable), that provides approximately 76 hours of runtime. At 50% load, the same generator consumes about 4.2 GPH, extending runtime to approximately 107 hours.

Question 2

How much diesel does a generator use per hour?

Accepted Answer

Diesel consumption varies by generator size and load. As a rule of thumb, generators consume about 0.07 gallons per kW per hour at full load. A 200 kW generator at 75% load uses approximately 11.9 GPH, while a 500 kW generator at 75% load uses about 24.2 GPH. Consumption is not linear — at 50% load, fuel use is approximately 55% of full load, not 50%.

Question 3

Does altitude affect generator fuel consumption?

Accepted Answer

Yes. Above 3,281 feet (1,000 meters), generators lose power due to reduced air density. Per ISO 8528-1, turbocharged engines lose about 3.5% capacity per 500 meters of additional elevation. A generator in Denver (5,280 ft) will consume approximately 5-7% more fuel than the same unit at sea level for equivalent power output.

Question 4

Can bad fuel reduce generator runtime?

Accepted Answer

Absolutely. Contaminated or degraded diesel fuel can reduce combustion efficiency by 10-20%, directly shortening runtime. Water contamination, microbial growth, and oxidation all degrade fuel quality. During the 2003 Northeast blackout, 20% of backup generators failed due to fuel-related problems. Diesel fuel should be tested annually and polished or replaced if stored longer than 12 months.