5 Signs Your Backup Generator Will Fail When You Need It

Your generator is probably showing warning signs right now. Most people just aren’t looking.

When backup power fails during an outage, operations halt, costs multiply, and someone has to explain why. Here’s the pattern: Generators sitting on standby develop problems that only surface when power drops. These warning signs appear between scheduled maintenance when nobody’s watching.

Whether you’re running Rehlko (formerly Kohler), Bobcat, Mitsubishi, or John Deere power systems, these warning signs apply across all commercial generator brands. The difference between catching problems early and managing crisis repairs comes down to working with trusted power technicians in your area who can spot these issues before they escalate.

You’re responsible for uptime, but the generator sits out of sight until it’s suddenly critical. Here are the 5 warning signs that predict failure—and what they cost you.

Sign #1: Your Battery Is Over Two Years Old

Generator batteries last 2-3 years. Period. Age kills them, not use.

Here’s what catches people off guard: Your battery tests fine at 30 months, then fails completely at 32 months—right when the power goes out. Chemical degradation doesn’t wait for convenient timing.

Dead battery means the generator won’t start. Your facility stays dark. Your project stops. The emergency service call costs 3x more than planned replacement, and you’re managing a crisis instead of preventing one.

Warning Signs to Track

Three indicators tell you replacement time is coming:

• Slow cranking during weekly tests
• Visible corrosion on battery terminals
• Batteries approaching the 24-36 month mark

Don’t wait for performance issues. Replace based on age. If you’re not tracking battery installation dates, you’re gambling. Mark the date. Set a reminder. Make replacement part of annual planning, not emergency response.

This is the most predictable failure point. Plan for it instead of reacting to it.

Sign #2: You See Leaks (Any Kind)

Generators shouldn’t leave puddles. Walk past your unit and look at the ground. That simple check catches problems early.

• Coolant leaks: Red, orange, green, or blue fluid on the ground
• Fuel leaks: Clear or oily appearance with a strong smell
• Oil leaks: Dark, viscous fluid beneath the unit

All of them get worse under load.

Here’s why this matters: A small coolant leak during testing becomes an overheating shutdown during a 12-hour outage. Fuel leaks create safety hazards. Oil leaks lead to engine damage that turns a $500 repair into a $15,000 overhaul.

Emergency repairs during power outages run 2-3 times the scheduled service rates. Add equipment rental to keep operations running while your generator is down. Add explaining to your supervisor why backup power wasn’t backed up.

Five minutes of monthly visual inspection prevents expensive failures. Look at the ground beneath your generator. That’s it.

Sign #3: Slow Starts or New Sounds

Normal generator startup: 1-2 seconds from power loss to full operation. Smooth engine sound. No drama.

If your generator takes 5+ seconds to start, requires multiple attempts, or makes new sounds, grinding, clicking, rattling—pay attention. These problems accelerate fast.

A generator that takes 3 seconds to start this month might take 10 seconds next month and fail completely the month after. You won’t get a warning during the actual outage. Just silence when you need power most.

What These Sounds Mean

Each abnormal sound points to a specific component failure:

• Clicking: Starter motor failing
• Grinding: Engagement problems in the starting system
• Rattling: Components shaking into bigger damage

All preventable if you address changes when they first appear.

Generator failures trigger contract penalties, operational downtime, and emergency equipment rental—all because you didn’t investigate that weird sound during last week’s test.

Trust your ears. Document what normal sounds like so you recognize when something changes.

Sign #4: Black Smoke or Exhaust Buildup (Diesel Units)

Black ooze around exhaust pipes or heavy black smoke during operation means wet stacking—unburned fuel building up in your diesel generator’s exhaust system.

Diesel generators need to run at 75%+ capacity to reach proper operating temperature. Most backup generators only run at low loads during weekly testing. Extended low-load operation creates incomplete combustion. Unburned fuel and carbon collect in the exhaust instead of burning off.

Wet stacking slowly destroys diesel engines. Fouled injectors reduce power output when you need full capacity. Eventually requires a complete engine overhaul—$20,000-$50,000+ depending on unit size.

Here’s what this costs your project: A generator that can’t deliver full-rated power during an outage forces you to shed loads or rent supplemental equipment. Neither fits your budget nor timeline.

The Fix

Load bank testing annually at 75-80% capacity burns off deposits before damage occurs. Industry standard calls for running diesel generators at a minimum 30% load for 30 minutes monthly. Weekly low-load tests actually contribute to wet stacking if that’s all you do.

Diesel generators need exercise at real loads, not just idle testing.

Sign #5: Generator Runs But Power Doesn’t Transfer

Your generator starts, runs perfectly, and produces full power. Your facility stays dark.

The automatic transfer switch (ATS) failed to move the load from the grid to the generator. This scenario is worse than a generator failure because, at least if the generator won’t start, you know immediately what broke.

ATS failures mean equipment is running, burning fuel, making noise, delivering zero value. You’re troubleshooting why backup power isn’t working while operations are stopped.

• Tripped circuit breakers protecting the ATS
• Corroded control wiring
• Failed solenoid coils inside the switch
• Manual transfer works, but automatic doesn’t
• Longer delays before transfer occurs
• Partial transfer where some circuits get power, but others don’t

Weekly generator tests may not reveal ATS problems. Many test modes start the generator without actually transferring load. The generator runs, and everything looks fine. Then a real outage happens, and you discover the transfer switch won’t engage.

Test the complete system, not just whether the generator starts. Simulate actual power loss. Verify load transfer. Confirm power reaches your equipment.

Early Detection Costs Less Than Emergency Response

Scheduled maintenance when you spot warning signs costs $300-800. Emergency repair during an actual power outage costs $1,500-3,000+. Equipment rental while your generator is down runs $500-2,000 per day. Project delays cost more.

The difference between catching problems early and managing crisis repairs comes down to having factory-certified technicians who know what to look for. Regular preventive maintenance inspections catch warning signs before they become failures.

Contact your trusted power technicians in your area to schedule preventive maintenance or discuss a service plan that keeps your backup power ready when you need it.

Generators that fail during outages are warned weeks earlier. Most people just weren’t looking.