How do you know if you are doing too much — or too little — preventive maintenance?

• some assets are being over-inspected
• some assets are missing important prevention entirely
• and many existing PM plans are not actually working the way the organisation thinks they are

All three problems often exist simultaneously.

And most organisations struggle to see any of them clearly.

On paper, the PM strategy may look structured. The plans exist. The inspections happen. The preventive percentage looks healthy.

Operationally, however, the organisation may still be:

• missing preventable failures
• wasting labour on low-value inspections
• building schedules and budgets on unrealistic estimates
• and slowly drifting away from effective preventive coverage

This article explains:

• why PM strategy drift is difficult to detect
• the three ways PM programmes typically become ineffective
• why standard KPIs rarely expose the problem properly
• and what continuous PM strategy review should actually look like

Why this question is so difficult to answer

Most organisations still review PM strategy in large periodic exercises.

Typically every:

• two years
• three years
• or sometimes even longer

An asset owner or engineer reviews plans one-by-one:

• reading workorders
• checking history
• reviewing failures
• deciding whether plans should stay, change, or disappear

The problem is that this process is extremely slow.

Large sites may have:

• hundreds of PM plans
• thousands of inspections
• years of execution history

By the time one review cycle finishes, the next cycle has already started.

And meanwhile, PM strategy continues drifting operationally underneath the surface.

This creates a deeper issue:

Most organisations do not actually have a continuously measurable answer to: "Are we doing the right amount of preventive maintenance?"

The question itself rarely gets answered systematically.

What the data usually shows

When PM data is analysed deeply across heavy asset operations, three forms of drift appear repeatedly.

The first: too little prevention.

The second: too much prevention.

The third: prevention that exists operationally on paper but is ineffective in practice.

Most sites contain all three.

The first drift: too little preventive maintenance

Some failures are genuinely unpredictable.

Many are not.

Patterns often already exist inside the operational data:

• recurring failure modes
• repeat breakdown behaviour
• similar asset histories
• wear patterns
• escalating condition signals

The organisation often already has enough evidence to justify preventive intervention.

But no meaningful prevention exists operationally inside the PM strategy.

There is also a more subtle version of under-prevention.

Sometimes the PM plan technically exists — but execution timing makes it ineffective.

For example: a preventive intervention is consistently executed too late because lower-priority work keeps slipping.

Officially, the work was completed.

Operationally, the prevention already failed before execution happened.

That distinction matters enormously.

Because organisations often measure PM completion. Not whether the PM timing actually prevented the failure mode.

The second drift: too much preventive maintenance

This problem is often less visible because preventive work usually appears "safe."

But many organisations quietly accumulate large amounts of low-value preventive activity.

Three patterns appear repeatedly.

Inspections nobody meaningfully reviews

The inspection gets completed. The report gets filed. No operational decision follows afterwards.

Eventually the organisation should ask: why are we still performing this inspection?

Inspection findings that never become action

An inspection identifies an issue. A follow-up workorder gets created. The work keeps slipping. Eventually it disappears into the backlog.

Again: what operational value did the inspection actually create?

Inspections that consistently find nothing

Some inspections repeat:

• monthly
• quarterly
• annually

for years without meaningful findings.

That does not automatically mean the inspection is useless.

But it absolutely deserves review.

Because every unnecessary inspection:

• consumes labour
• consumes planning effort
• consumes scheduling capacity
• increases preventive counts artificially

And this is exactly why preventive-vs-corrective KPI ratios can become misleading.

A high preventive percentage does not necessarily mean the PM strategy is effective.

It may simply mean the organisation is performing large volumes of preventive activity.

The third drift: plans built on unrealistic estimates

This issue is hugely underestimated operationally.

PM plans contain:

• labour estimates
• cost estimates
• execution expectations

Those estimates feed:

• schedules
• manpower planning
• budgets
• shutdown forecasting
• resource allocation

Now imagine a PM task consistently estimated at: 8 labour hours

while operationally technicians only ever book: 2 hours.

One of two things is happening:

• the estimate is structurally wrong, or
• the work is not being executed the way the plan assumes

Either way, the organisation is now building schedules and budgets on false assumptions.

And over time, those estimate deviations quietly distort:

• planning quality
• capacity expectations
• resource forecasts
• execution reliability

Why standard KPIs fail to expose this properly

Most organisations rely heavily on aggregated KPIs such as:

• preventive vs corrective ratio
• breakdown counts
• PM compliance
• emergency work percentages

The problem is that these metrics are too aggregated to explain PM effectiveness properly.

Take preventive vs corrective ratio.

If an organisation performs: 52 useless inspections per year

then technically the preventive percentage improves.

But operationally, nothing meaningful improved.

The KPI measures PM volume.

Not PM quality.

Breakdown counts have the same issue.

A breakdown could result from:

• missing preventive coverage
• execution failure
• operational misuse
• random equipment failure
• late intervention
• poor spare strategy

The KPI alone cannot distinguish between them.

This is why organisations often struggle to understand whether:

• they are over-maintaining
• under-maintaining
• or simply maintaining ineffectively

Deeper read: Why your KPI dashboard isn't making things better — on why aggregated maintenance KPIs measure volume rather than operational effectiveness.

The traditional PM review process also has blind spots

The standard review approach usually focuses on existing PM plans.

That means organisations review:

• inspections already happening
• tasks already defined
• plans already existing

This allows organisations to identify:

• outdated inspections
• poor estimates
• ineffective frequencies
• low-value activities

But it misses one critical category completely:

Missing prevention.

Because if no PM plan exists for a recurring preventable failure mode, then the issue never even enters the review scope.

And that means traditional PM reviews are structurally much better at detecting: "doing too much"

than detecting: "not doing enough."

Finding missing prevention requires a completely different analysis approach:

• reading breakdown history
• analysing recurring failures
• comparing similar assets
• identifying patterns that should have been preventable
• asking whether preventive coverage should exist where none currently does

Most organisations simply do not have time to do this systematically.

What a better PM review approach actually looks like

The most effective PM strategy review is:

• continuous
• lightweight
• signal-driven
• plan-specific

Instead of one enormous review project every three years, the organisation should continuously surface meaningful PM signals automatically.

Four signals are especially valuable.

1. No-finding inspections

Plans where repeated inspections consistently produce:

• no findings
• no follow-up work
• no intervention changes

These deserve review.

Not necessarily removal — but review.

Because many organisations continue inspecting assets long after the inspection stopped creating operational value.

2. Estimate deviation

Plans where actual labour repeatedly deviates heavily from planned labour.

This immediately surfaces:

• unrealistic planning assumptions
• poor PM task definitions
• execution inconsistency
• incorrect estimate structures

3. Late prevention linked to breakdowns

This is one of the highest-value signals possible.

Preventive work executed overdue and followed by the exact failure mode it was intended to prevent.

That signal tells the organisation: the prevention itself may have been correct, but operational execution timing failed.

Deeper read: Why execution is often the weakest link in the maintenance process — on why PM plans only matter if the resulting work actually gets executed.

4. Continuous breakdown review

Instead of reviewing every PM plan manually every few years, engineers should continuously review:

• recent breakdowns
• related history
• prior inspections
• recurring patterns
• similar asset failures

The goal becomes: identifying where preventive strategy should evolve continuously instead of waiting years between review cycles.

What asset owners should actually spend their time doing

Asset owners create the most value when they focus on:

• strategy
• reliability judgment
• intervention philosophy
• cost-benefit thinking
• preventive optimisation

But operationally, many spend huge amounts of time on:

• data collection
• Excel work
• manual filtering
• reconstructing timelines
• assembling context

That is backwards.

The system should assemble the picture automatically.

The engineer or asset owner should spend their time: forming judgment, not gathering raw information.

That is the real shift.