Blog: M-LINE maintenance guide part 2

Regular maintenance is essential to keep your VETUS marine diesel engine running reliably. In this guide, we explain how to service three critical components of your engine’s cooling and drive systems: the impeller, the V-belt, and the coolant.

Routine inspection and replacement of these parts helps prevent overheating, loss of charging power, and unexpected breakdowns on the water.

View VETUS engine service kit

Why this maintenance is important

Your marine diesel engine depends on proper cooling and belt-driven systems to function efficiently:

The impeller ensures seawater circulates through the cooling system.
The V-belt drives essential components such as the alternator and water pump.
The coolant regulates engine temperature and prevents corrosion.

Failure in any of these areas can lead to overheating, reduced performance, or serious engine damage.

Servicing the impeller

The impeller is a wearable rubber component inside the seawater pump. Over time, the vanes can become brittle, cracked, or deformed.

When to check or replace

At least once per season
After winter storage
If the engine overheats
If reduced cooling water flow is visible from the exhaust

Step-by-step overview

Turn off the engine and close the seawater intake valve.
Remove the pump cover carefully.
Extract the impeller using pliers or an impeller puller.
Inspect for:
- Cracked or missing vanes
- Hard or brittle rubber
- Deformation
Lubricate the new impeller with glycerine or soapy water.
Insert the new impeller while rotating it in the correct direction.
Reinstall the cover with a new gasket if necessary.
Reopen the seawater intake valve and test the system.

💡 Tip: Always check that no broken impeller blades remain inside the cooling system.

Inspecting and adjusting the V-Belt

The V-belt transfers power from the crankshaft to components such as the alternator and water pump. A worn or loose belt can reduce charging capacity and cooling efficiency.

Signs of wear

Cracks or fraying
Glazing or shiny surfaces
Squealing noise during operation
Excessive slack

How to Check Tension

Press the belt midway between pulleys. It should deflect slightly under firm thumb pressure (typically 10–15 mm, depending on the engine model — always consult your engine manual).

Replacing or Adjusting the Belt

Loosen the mounting bolts of the driven component (e.g., alternator).
Adjust tension until correct.
Tighten mounting bolts securely.
Recheck tension after initial engine run.

⚠️ An overtightened belt can damage bearings. Too loose, and it may slip.

Checking and replacing coolant

Coolant plays a crucial role in maintaining stable engine temperature and preventing internal corrosion.

When to replace coolant

According to the engine service schedule (often every 2 years)
If coolant appears dirty or contaminated
If corrosion protection is reduced

Coolant service overview

Ensure the engine is cool.
Open the drain point and collect old coolant responsibly.
Flush the system if required.
Refill with the recommended VETUS-approved coolant mixture.
Bleed air from the system if necessary.
Run the engine and recheck levels.

🌊 Always dispose of old coolant according to local environmental regulations.

Maintenance schedule recommendation

For optimal performance:

Inspect the impeller annually
Check V-belt tension regularly
Replace coolant according to the service interval
Follow your VETUS engine manual for model-specific details

Preventative maintenance is significantly more cost-effective than emergency repairs offshore.

Frequently asked questions (FAQ)

Can I replace the impeller without removing the entire pump?

Yes, on most VETUS engines the impeller can be replaced by removing only the pump cover. However, access may vary depending on installation space in your engine compartment.

What should I do if impeller blades are missing?

If vanes are missing, they may have entered the cooling system. It’s important to locate and remove the fragments (often in the heat exchanger) to prevent blockages and overheating.

Can I tension a V-belt without special tools?

In most cases, no special tools are required — just standard spanners to loosen and adjust the alternator. However, always ensure proper alignment and avoid overtightening.

Can I top up coolant instead of replacing it?

Topping up is fine if the level is slightly low, but it does not restore depleted corrosion inhibitors. Full replacement is required at the recommended service interval.