Indmar Marine Spark Plugs – 5.7L Standard | Non-Catalysed Exhaust System | Part #491008
Keep your Indmar 5.7L firing on all cylinders with this genuine Indmar standard specification spark plug, designed for engines fitted with a non-catalysed exhaust system. Spark plugs are one of the most fundamental tune-up items on any engine — and on a marine engine running hard all summer they deserve the same attention as your impeller and oil filter. Fresh plugs mean reliable starts, smooth power delivery, and optimal fuel efficiency every time you hit the water.
Compatible with: Indmar 5.7L marine engines with non-catalysed exhaust systems fitted to Malibu, Moomba, Supra, MB, Mastercraft and Tige boats. Contact us to verify fitment for your specific model year
Catalysed or Non-Catalysed — why does it matter for spark plugs?
This is one of the most important things to confirm before ordering spark plugs for your Indmar 5.7L. Engines fitted with a catalysed exhaust system require a different spark plug specification to non-catalysed systems. Using the wrong plug specification can cause:
- Premature plug fouling from incorrect heat range
- Damage to the catalytic converter from incorrect combustion temperatures
- Poor engine performance and increased fuel consumption
- Incorrect gap specification causing misfires and ignition system strain
Always confirm whether your exhaust system is catalysed or non-catalysed before ordering. If you are unsure — check your engine documentation or contact us before ordering and we will help you identify the correct plug for your specific setup.
How many spark plugs does my 5.7L need?
The Indmar 5.7L is a V8 engine — it requires 8 spark plugs per engine. Always replace all 8 plugs at the same time — never replace individual plugs unless diagnosing a specific fault. Uneven plug wear across cylinders causes rough running, misfires, and reduced performance. Add quantity 8 to your cart before checkout.
What does a spark plug do?
The spark plug delivers the high voltage electrical spark that ignites the compressed air/fuel mixture in each cylinder. Every single power stroke in your engine begins with a spark plug firing correctly. A worn or fouled plug causes:
- Incomplete combustion — wasting fuel and reducing power
- Misfires — rough running and vibration under load
- Hard starting — especially after winter storage
- Increased fuel consumption — noticeable at the bowser
- Higher exhaust emissions — potentially failing compliance checks
- Increased load on the ignition system — accelerating coil and distributor wear
How often should you replace them?
Replace your spark plugs every season or every 100 hours of operation as part of your annual pre-season service. Marine engines work harder than automotive engines — sustained high RPM operation on the water accelerates plug wear significantly compared to normal road driving.
Signs your spark plugs need replacing:
- Rough idle or misfiring under load
- Hard starting especially after winter storage
- Noticeable drop in fuel economy on the water
- Black sooty deposits on plug electrodes — rich running
- White or grey deposits — lean running or coolant contamination
- Worn or eroded electrode gap
- Engine vibration or hesitation under acceleration
Pro tip: When fitting new spark plugs always use a torque wrench to tighten to the correct specification — overtightening damages the cylinder head threads and undertightening allows the plug to loosen under vibration. Apply a small amount of anti-seize to the plug threads and always fit a new plug washer if required.
The complete annual ignition service for non-catalysed 5.7L — order together:
- 491008 – Spark Plug 5.7L Standard Non-Catalysed x8 (this part)
- 556345GM – Distributor Cap High Voltage Switch
- 636127 – Water/Fuel Separator Filter
- 556003 – Fuel Filter EFI All Models
- 685007 – Raw Water Pump Impeller
- 685008 – Impeller Pump Gasket Johnson
- 872023 – Oil Filter GM 5.7L, 8.1L & 3CSE Special
Pairs perfectly with:
- 556345GM – Distributor Cap High Voltage Switch
- 636127 – Water/Fuel Separator Filter
- 556003 – Fuel Filter EFI All Models
- 872023 – Oil Filter GM 5.7L, 8.1L & 3CSE Special
- 685007 – Raw Water Pump Impeller
- 685008 – Impeller Pump Gasket Johnson
Features:
- Genuine Indmar OEM part
- Standard specification for Indmar 5.7L marine engines
- Correct heat range for non-catalysed exhaust system applications
- OEM electrode gap specification for reliable ignition
- 8 plugs required per V8 engine — order quantity 8
- Not suitable for catalysed exhaust system applications
- Direct replacement — no modifications needed
Part Number: 491008
In stock and shipped fast from Australia 🇦🇺
