Diesel Engine Troubleshooting for Hydrovac Operators: Complete Guide

Everything on your hydrovac depends on one thing: the diesel engine. Vacuum system? Powered by the engine. Water pump? Powered by the engine. Boom hydraulics? Powered by the engine. When that diesel goes down, your entire operation stops.

I've been working on diesel engines for 25 years — from the big Cummins and CAT engines in heavy trucks to the Power Strokes and Duramax engines in pickups. As a certified diesel mechanic, I've seen every failure mode these engines can throw at you.

This guide covers what hydrovac operators need to know about their diesel engine: common problems, warning signs, and when to call for help.

How Your Engine Powers Everything

Before we troubleshoot, let's understand what your engine is doing:

The PTO (Power Take-Off): Your engine's power is transmitted through the PTO to drive:

• The vacuum blower (the heart of hydrovac operation)
• The water pump (on many configurations)
• The hydraulic pump (powers boom, tank lift, outriggers)

The demands: Unlike a truck engine that varies its load constantly, a hydrovac engine runs under sustained heavy load whenever systems are operating. Full RPM, full power, for extended periods. This is harder on the engine than typical trucking.

What this means: Your engine needs to be in good condition. Any weakness gets exposed under sustained load. Small problems become big problems fast.

Common Diesel Engine Problems in Hydrovacs

Problem 1: Loss of Power

What you notice:

• Engine struggles to maintain RPM under load
• Slower boom operation
• Water pressure drops
• Vacuum builds slowly

Common causes:

• Clogged air filter (most common, easiest fix)
• Fuel delivery issues (clogged filter, weak lift pump)
• Turbocharger problems (wastegate, boost leaks)
• Injector problems (poor spray pattern, clogging)
• Exhaust restriction (DPF clogged)

What to check first: Air filter — seriously. A heavily clogged air filter restricts airflow and chokes the engine. Check it, and if there's any doubt, replace it. This costs $30-50 and takes 5 minutes.

Problem 2: Hard Starting

What you notice:

• Extended cranking before start
• Rough running until warmed up
• Worse in cold weather

Common causes:

• Glow plug problems (cold starting essential)
• Fuel system air leaks
• Weak batteries
• Injection timing issues
• Low compression (worn engine)

What to check first: Batteries — hydrovac trucks need strong batteries because they run lots of electrical accessories. Test them, clean connections, and replace if marginal. Cold cranking kills weak batteries.

Problem 3: Excessive Smoke

Black smoke:

• Running rich (too much fuel, not enough air)
• Clogged air filter, turbo problems, injector issues
• Some black smoke under hard load is normal; constant black smoke is not

White smoke:

• Unburned fuel (cold engine, glow plug problems)
• Coolant entering combustion (head gasket, cracked head)
• If it smells sweet, that's coolant — bad news

Blue smoke:

• Burning oil
• Worn rings, valve seals, or turbo seals
• Blue smoke gets worse over time if ignored

Problem 4: Overheating

Overheating is a hydrovac killer because the engine runs under constant load.

Common causes:

• Coolant system problems (low coolant, bad thermostat, failed water pump)
• Blocked radiator (external debris or internal clogging)
• Fan clutch failure (fan not pulling air)
• Head gasket issues

What to check first: Coolant level and radiator condition. Clean the radiator externally (they get packed with debris). Verify the fan engages when the engine is hot.

Problem 5: Rough Idle or Misfires

What you notice:

• Engine shakes at idle
• Uneven running
• Check engine light

Common causes:

• Injector problems (one or more not firing properly)
• Fuel quality issues
• Compression variation between cylinders
• EGR problems

What to check first: Listen for a regular miss pattern. If one cylinder is clearly not firing, that points to injector or compression issues on that cylinder.

Warning Signs Every Operator Should Know

Catch these early and avoid expensive repairs:

Warning signs that need attention:

Immediate Stop:

• Sudden loss of oil pressure
• Engine knocking or metallic rattling
• Steam from under hood
• Coolant temperature in red zone

Needs Prompt Attention:

• Check engine light comes on
• Gradual power loss
• Unusual smoke on startup
• Fuel consumption increase
• Rough idle that's getting worse

Monitor and Schedule Service:

• Minor oil consumption increase
• Slight power reduction over time
• Occasional rough cold start

The Emissions System: DPF, DEF, and EGR

Modern diesel trucks (2007+) have emissions systems that add complexity:

DPF (Diesel Particulate Filter): Traps soot from exhaust. Needs periodic regeneration (burning off accumulated soot).

DPF problems are common in hydrovacs because:

• Short operating cycles prevent regen completion
• Idle time accumulates soot without burning
• Heavy load causes lots of soot production

DEF (Diesel Exhaust Fluid): Required on trucks since 2010. Reduces NOx emissions. Running out causes power reduction and eventually stops the truck.

DEF system failures are increasingly common. Sensors fail, pumps fail, and operators get stranded.

EGR (Exhaust Gas Recirculation): Reduces emissions by recirculating exhaust. Can cause performance problems when clogged or stuck.

The bottom line on emissions systems: They require attention. You can't ignore warning lights. And you need a mechanic who understands these systems — not every diesel shop does.

Fuel System Basics

Diesel fuel systems are precision equipment:

Common fuel problems:

Contaminated fuel:

• Water in fuel (causes injector damage, poor running)
• Algae growth in tanks (clogs filters)
• Dirty fuel from questionable sources

Filter neglect:

• Primary and secondary filters need regular changes
• Clogged filters starve the engine of fuel
• Delayed filter changes cause pump strain

Injection system:

• High-pressure injection systems (common rail) are sensitive to fuel quality
• Injector problems are expensive ($300-800 per injector)
• Prevention (good fuel, clean filters) beats repair

Cold Weather Diesel Issues

Diesels and cold weather have a complicated relationship:

Fuel gelling: Below certain temperatures (varies by fuel formulation), diesel fuel thickens and won't flow. Additives or winter-blend fuel are essential.

Glow plug problems: Cold starts depend on glow plugs. Failed glow plugs = hard starting = excessive cranking = dead batteries.

Battery issues: Diesel engines require more cranking power than gas engines. Cold batteries produce less power. Double whammy.

Block heaters: Use them. A warm engine starts easier, wears less during cold start, and gets to work faster.

What You Can Check Yourself

Safe DIY checks:

• Air filter condition
• Oil level and condition
• Coolant level (when cold)
• Battery connections and condition
• Fuel filter age (look at your records)
• Visual inspection for leaks
• Check engine light codes (with basic scanner)

What to leave to professionals:

• Fuel injection system work
• Turbocharger diagnosis
• Emissions system repairs
• Internal engine work
• Electrical diagnosis beyond basics

When to Call for Help

Call immediately if:

• Engine is making knocking or rattling noises
• Oil pressure warning light comes on
• Coolant temperature goes critical
• You see metal in oil or coolant in oil

Call soon if:

• Check engine light is on
• Power loss is significant
• You can't diagnose the problem
• Any problem is getting worse

Don't wait if:

• Small problems become big problems fast on diesel engines under heavy load
• The cost of continued operation may exceed the cost of repair
• You're not confident in your diagnosis

Professional Diesel Service

I provide diesel engine service for all major brands:

Commercial engines:

• Cummins (ISB, ISL, ISX)
• Caterpillar (C7, C9, C13)
• Detroit Diesel (DD13, DD15, DD16)
• PACCAR (MX)
• Navistar/International

Pickup truck engines:

• Ford Power Stroke (6.0, 6.7, 7.3)
• GM Duramax (LB7, LBZ, LML, L5P)
• Ram Cummins (5.9, 6.7)

I work on hydrovac trucks throughout Pennsylvania, New Jersey, New York, and the DC/Maryland area. Mobile service available — I can come to your location for many repairs.

Preventive Maintenance That Matters

Keep your diesel healthy:

Engine oil: Change per manufacturer intervals, using correct spec oil Fuel filters: Don't stretch change intervals Air filter: Check monthly, replace when dirty Coolant: Test annually, change per spec DEF: Keep tank full, use quality fluid Batteries: Test annually, replace when marginal

Pay attention to:

• Oil consumption trends
• Power output changes
• Any unusual sounds or smells
• Warning lights

The Bottom Line

Your diesel engine is the foundation of your hydrovac operation. It works hard, running under sustained load that would be unusual for a typical truck.

Take care of it:

• Proper maintenance at proper intervals
• Address problems early
• Don't ignore warning signs
• Know when to call for professional help

The operators who take care of their diesels don't see me for emergency engine repairs. The ones who don't take care of their engines see me a lot — and those visits are expensive.

For diesel problems or questions, call me at 272-296-9637. Check out the related guides on DPF problems, DEF system failures, and warning signs every operator should recognize.