Step-by-Step: How to Inspect a Car Engine Using a Borescope Camera

If you want to know how to inspect an engine with a borescope the right way, you have come to the right place. A borescope camera is one of the most powerful diagnostic tools you can own as a car enthusiast, DIY mechanic, or professional technician. With it, you can peer directly into your engine’s cylinders, check valve condition, spot carbon buildup, and catch developing problems before they turn into four-figure repair bills. No teardown required. No guesswork. Just real, visual evidence of exactly what is happening inside your engine.

This guide walks you through the entire process, from choosing the right scope to knowing what you are actually looking at once the camera is inside.

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Why Bother Inspecting Your Engine with a Borescope?

Most engine damage does not announce itself loudly until it is too late. A cylinder that is slowly losing compression, a valve seat that is pitting, or a piston crown that is starting to score will silently worsen over thousands of kilometres before your check engine light blinks on.

Here is what a borescope inspection can reveal that no scan tool ever will:

• Carbon buildup on intake valves (especially common in direct injection engines)
• Cylinder wall scoring or scuffing from oil starvation
• Piston crown damage from detonation or overheating
• Valve condition, including bent, burnt, or corroded valves
• Rust, moisture intrusion, or debris inside cylinders
• Head gasket failure signs visible from the combustion chamber side

Before buying a used car? A five-minute borescope check can save you from buying someone else’s expensive problem. Running a high-mileage engine? Regular borescope inspections let you catch wear trends before they snowball.

Choosing the Right Borescope for Engine Inspection

Not all borescopes are built for engine work. Camera diameter matters most here. For accessing cylinders through spark plug holes, you need a probe no wider than 5.5mm to 6mm. Anything thicker will not fit most cylinder heads without removing additional components.

Here is a quick breakdown of your options:

Type	Best For	Price Range	Image Quality
Rigid borescope	Straight access (spark plug holes)	$$	Excellent
Semi-rigid borescope	Angled entry, tight spaces	$	Good
Articulating borescope	Deep inspection, full navigation	$$$	Excellent
WiFi borescope	Smartphone pairing, easy sharing	$	Moderate

For engine inspection specifically, a semi-rigid or articulating borescope with a 5.5mm probe and built-in LED lighting is the sweet spot. Budget options around $30 to $80 on Amazon or from industrial suppliers are perfectly capable for this job.

What You Need Before You Start

• A borescope camera (5.5mm diameter or smaller)
• A smartphone or dedicated monitor (depending on your scope model)
• Spark plug socket and ratchet
• Compressed air or a small brush to clean around plug recesses
• A notepad or your phone to record findings per cylinder
• Good lighting in your work area

Optional but useful: a small mirror or secondary light source to illuminate the area around plug holes, and penetrating oil if plugs have been in for a long time.

Step-by-Step: How to Inspect an Engine with a Borescope

Step 1: Let the Engine Cool Down Completely

This is non-negotiable. A hot engine means hot metal, and a hot cylinder can warp your probe tip, destroy your camera, or worse, cause burns. Wait at least two hours after the last engine run. If you are doing a pre-purchase inspection on a cold car, even better.

Step 2: Remove the Spark Plugs

Using your spark plug socket, remove one plug at a time. Before pulling each one, use compressed air to blow out any debris sitting in the plug recess. Dirt and grit falling into an open cylinder during inspection can scratch cylinder walls.

Label which plug came from which cylinder. While they are out, inspect them too. Plug condition tells its own story about combustion health.

Step 3: Prepare Your Borescope

Connect your scope to your phone or its dedicated screen. Turn on the LED lights and confirm the image is clear before inserting. Set your phone screen brightness to maximum. You want a sharp, well-lit feed, not a grainy shadow.

Step 4: Insert the Probe and Navigate

Gently feed the probe down through the spark plug hole. Do not force it. Modern cylinder heads have angled plug locations, so you may need to guide the probe with a slight bend in the cable. Once inside, you have direct visibility of:

• The piston crown (top surface)
• Cylinder walls
• The underside of both intake and exhaust valves
• The combustion chamber roof

Rotate the cylinder to TDC (top dead centre) by turning the engine manually if you want the best view of the piston. With the piston down, you get more cylinder wall exposure.

Step 5: Document What You See

Take photos or video of each cylinder. Most borescope apps and screens allow you to capture stills directly. Inspect and document each cylinder in sequence, noting any visual abnormalities. You want a baseline if this is a health check, or hard evidence if something looks wrong.

Step 6: Reinstall Plugs and Cross-Reference Findings

Once all cylinders are inspected, reinstall your spark plugs to spec using a torque wrench. Then sit down and review your footage. Compare cylinders against each other. Consistent findings across all cylinders often indicate a maintenance or fuel issue. A problem isolated to one cylinder points to a localized mechanical fault.

Interpreting What You See: A Quick Reference Guide

This is where most beginners get stuck. The camera is inside the engine, but what does normal actually look like? Here is a practical reference:

What You See	What It Means	Urgency Level
Carbon buildup on valves	Poor fuel quality or short trips; decarb service needed	Low to Medium
Scoring on cylinder walls	Possible piston ring wear; oil burning likely	High
Rust or pitting on valves	Moisture ingestion; check intake sealing	Medium
Dark oily residue	Head gasket leak or PCV system failure	High
Clean, light grey surfaces	Healthy combustion; engine in good shape	All Good
Bright metallic shavings	Serious internal wear; stop driving immediately	Critical

Normal combustion leaves a light grey to tan residue on piston crowns. Anything black, oily, wet, or metallic needs immediate attention.

Pro Tips to Get Better Results

• Inspect cylinders after an Italian tune-up (a hard highway run) rather than after short cold trips. Carbon deposits are easier to assess on a warm, recently worked engine that has cooled down.
• Use the scope before and after a walnut blasting or chemical decarbonization service to verify the cleaning was effective.
• Check cylinder walls at multiple piston positions. Mid-stroke and bottom of stroke can reveal wear patterns invisible from TDC.
• On turbocharged engines, also scope through the intake manifold and intercooler connections if you suspect oil contamination from a failing turbo seal.
• If you find heavy carbon or deposits on one cylinder only, pull that injector and test it before assuming a mechanical fault.

Conclusion: A Small Tool with a Big Impact

Learning how to inspect an engine with a borescope is one of the highest-return skills you can add to your diagnostic toolkit. It takes less than 30 minutes per inspection, costs almost nothing once you own the tool, and can reveal problems no code reader, compression test, or leak-down test can show you visually.

Whether you are vetting a used car purchase, monitoring a high-mileage daily driver, or just satisfying your curiosity about what is happening inside your engine, the borescope camera gives you something no other tool does: actual eyes inside the machine.

Invest in a decent 5.5mm scope. Learn what healthy looks like. Inspect early, inspect often. Your engine will thank you.

For home use, see our ‘best borescope for home use‘ guide.