Hydrovac Blower Oil: When to Change and What to Use

If I could get every hydrovac operator to do just one thing, it would be change their blower oil on time. This single maintenance item prevents more expensive repairs than anything else I know of.

I've been rebuilding hydrovac blowers for 25 years. The difference between a blower that runs 10,000 hours and one that fails at 3,000? Usually comes down to oil changes.

Why Blower Oil Matters So Much

Your PD blower runs at high RPM under continuous load. The rotors spin with tiny clearances — we're talking thousandths of an inch between the lobes and housing. The only thing keeping metal from touching metal is a thin film of oil.

What blower oil does:

• Lubricates bearings (the most critical job)
• Provides a sealing film between rotors and housing
• Carries away heat from high-friction areas
• Protects internal surfaces from corrosion
• Carries away any tiny particles or wear metals

What happens when oil fails:

• Bearings overheat and wear rapidly
• Metal-to-metal contact occurs
• Rotor clearances increase (can't build vacuum)
• Internal damage accelerates
• Eventually: total blower failure

A blower rebuild costs $8,000-12,000 or more. An oil change costs about $50 and takes 30 minutes. This is not a difficult decision.

When to Change Blower Oil

General rule: Every 200 hours of operation or monthly, whichever comes first.

But that's just the starting point. Adjust based on:

More frequent changes (150 hours or less) if:

• Operating in dusty conditions
• Running in extreme temperatures (very hot or cold)
• High-intensity operation (max vacuum, long runs)
• Older blower with higher wear
• Any contamination events

Standard 200-hour changes if:

• Normal operating conditions
• Moderate duty cycles
• Blower in good condition
• Clean operating environment

Never extend beyond 200 hours or monthly. Even if the blower sits unused, oil degrades over time. Annual changes are the absolute minimum for stored equipment.

What Oil to Use

This is where people get confused. Blower manufacturers specify oil grades — use what they specify.

Common blower oil specs:

• Most Roots-type blowers: SAE 30 or 40 weight, non-detergent oil
• Some specify synthetic blower oil
• Cold climate operation: may require lighter weight

What to look for:

• Non-detergent: Detergent oils can cause foaming and poor lubrication
• Correct viscosity: Too thick won't flow; too thin won't protect
• Blower-specific: Oils marketed specifically for PD blowers are formulated for the job
• Quality: Don't cheap out — this oil protects a $12,000 component

Common products:

• Tuthill Corporation blower oil (OEM for many blowers)
• Gardner Denver recommended oils
• Various brands of synthetic blower oil

Do not use:

• Regular motor oil (detergent formula causes problems)
• Hydraulic oil (wrong viscosity and additives)
• Gear oil (too thick)
• Random "all-purpose" oil

When in doubt, call your blower manufacturer and ask. They'll tell you exactly what they want.

How to Change Blower Oil

This is not complicated, but do it right:

You'll need:

• Correct replacement oil (usually 2-4 quarts depending on blower)
• Drain pan
• Basic wrenches
• Clean rags
• Funnel for filling
• New fill plug gasket (if available)

The process:

1. Warm up the blower first — Run it for a few minutes to warm the oil. Warm oil drains more completely.

2. Shut down and let it sit briefly — Give oil time to drain back to the sump.

3. Locate drain and fill plugs — Usually on the bottom (drain) and side (fill). Know which is which before you start.

4. Remove fill plug first — This prevents vacuum lock and ensures oil will actually drain.

5. Position drain pan and remove drain plug — Oil will flow immediately. Let it drain completely (5-10 minutes minimum).

6. Inspect the oil — What does it look like? (More on this below)

7. Replace drain plug — Tighten securely but don't over-torque. Use new gasket if available.

8. Add new oil — Slowly, checking level as you go. Don't overfill.

9. Check level — There's usually a sight glass or level plug. Fill to the specified level, not above.

10. Replace fill plug — Tighten securely.

11. Run the blower briefly — Check for leaks, verify level after oil circulates.

12. Document it — Record date, hours, and oil used.

Reading Your Old Oil

The oil you drain out tells you about your blower's health:

Good oil looks like:

• Golden to light brown color
• Clear, not cloudy
• Consistent texture
• Normal smell

Warning signs:

Dark black color: Oil is breaking down from heat. Might need more frequent changes or to check for cooling issues.

Milky or cloudy: Water contamination. Could be condensation (common in humid climates or temperature swings) or seal failure allowing water intrusion. Serious if persistent.

Metallic particles or flakes: Internal wear happening. If you see this, check particle size. Fine dust is normal wear. Larger pieces or chunks mean something is failing.

Burnt smell: Oil overheated at some point. Check for cooling issues, low oil levels, or running too hard without warm-up.

Gritty or grainy texture: Contamination. Dirt getting in somewhere. Check air filter, seals, and oil fill practices.

If oil looks bad, more frequent changes won't fix the underlying problem. Diagnose and address the root cause.

Oil Level Checks

Between changes, check oil level regularly:

How often: At least weekly, more often for high-hour operation

How to check:

• Most blowers have a sight glass — oil should be visible at the center mark
• Some have a level plug — oil should just reach the plug when removed
• Check when blower is stopped and cooled (hot oil expands)

If level is dropping:

• Small consumption is normal (some oil weeps past seals)
• Rapid consumption indicates a leak or burning oil
• Find and fix leaks rather than just topping off continuously

Cold Weather Considerations

Cold oil is thick oil. Thick oil doesn't lubricate well at startup.

Winter practices:

• Use manufacturer-recommended cold-weather oil grade if available
• Allow extra warm-up time before heavy operation
• Consider oil heaters for extreme cold
• Never run a blower hard with cold, thick oil

Winter preparation includes making sure your blower oil is appropriate for the conditions.

Common Mistakes

Mistake 1: Using the wrong oil I've seen blowers filled with motor oil, hydraulic oil, and worse. Use what the manufacturer specifies.

Mistake 2: Overfilling Too much oil causes churning, overheating, and can blow seals. Fill to the mark, not above.

Mistake 3: Ignoring oil condition Just changing oil on schedule isn't enough. Look at what comes out. It's telling you something.

Mistake 4: Stretching intervals "It's only a few hundred hours over" is how blowers die early. Stick to the schedule.

Mistake 5: Not warming up for oil changes Cold oil doesn't drain completely. You leave old, degraded oil behind.

Mistake 6: Dirty filling practices Introducing dirt during oil changes defeats the purpose. Clean the area, use clean containers, funnel carefully.

Oil Analysis Option

For high-value equipment or large fleets, oil analysis makes sense:

What it tells you:

• Wear metals (indicates internal condition)
• Contamination levels
• Oil breakdown rate
• Optimal change intervals

Cost: $25-35 per sample

Who should do it:

• Fleet operators with multiple trucks
• Anyone running expensive blowers
• Operators wanting to optimize intervals
• Anyone seeing unusual oil conditions

Documentation

Keep records of every oil change:

• Date
• Hour meter reading
• Oil brand and type
• Oil condition observed
• Any issues noted

This documentation:

• Proves maintenance for warranty claims
• Helps diagnose problems later
• Tracks consumption trends
• Provides accountability

The Bottom Line

Blower oil changes are the single most important maintenance task on a hydrovac. They're cheap, quick, and prevent catastrophic damage.

The schedule:

• Every 200 hours or monthly, whichever comes first
• Check level weekly
• Use correct oil type
• Inspect oil condition at every change

The math:

• Oil change cost: ~$50
• Blower rebuild cost: ~$10,000
• Number of oil changes to equal one rebuild: 200

You can buy 200 oil changes for the cost of one rebuild. Do the math.

For blower problems or questions, call me at 272-296-9637. I provide blower repair service throughout Pennsylvania, New Jersey, New York, and the DC area. But I'd rather see you for scheduled maintenance than emergency blower failure.

For more on hydrovac maintenance, check out the complete maintenance guide, proper service intervals, and operator habits that affect equipment life.