Cummins 450C Diamond Series Review

The Cummins 6CTA 8.3 is arguably one of the best mechanical marine engines ever made. They have a variety of horsepower ratings with the most popular being the “450 Diamond.” 

This inline, 6-cylinder motor was released in the late 90s and is still a popular motor to this day. The liners allow for an easy rebuild in frame (leave the engine in the boat). Properly maintained, this engine can have a lifespan of 8000-15,000+ hours and the rebuild costs are marginal compared to some alternative brands. This makes the cost of ownership exceptional for this motor.

The 450C is actually 430 BHP and is rated to 2600 rpm. It’s important to have your boat propped correctly and the motors should do at least 2650 RPM at wide open throttle. This is important because if you overload the engine, there is excess heat and stress on the cylinder head (valves in particular). If you drop a valve, the metal can score a cylinder and take out the turbo on it’s way out. This basically results in a top-end rebuild. 

It’s important to have your boat propped correctly and if you are shopping around, make sure the boat isn’t underpowered. These are phenomenal engines but if you see a Cummins 450 or 480CE in a 45+ foot boat, don’t expect the same kind of lifespan.

Maintaining a Cummins 450C

The maintenance regiment for a Cummins 450C is relatively straightforward. We have a list in our notes that is synchronized with our crew which I’ll post below. We basically list the interval as well as the last set of hours where the work was done.

Oil and Fuel Filters Main & Gen- 250 Hrs

Date/Hrs Completed-  8717/8738

Air Filters- 500 Hrs

Date/Hrs Completed-  8670/8690

Coolant Filter- 500 Hrs

Date/Hrs Completed-  8670 / 8690

Service Aftercoolers- 750 Hrs

Date/Hrs Completed-  8170/8190

All Eng, Gen, and Pump Box Zincs- 750 Hrs or 6 months

Date/Hrs Completed-  8500 Hrs- 5/18/2021

Main and Gen Impellers- 1500 Hrs

Date/Hrs Completed- Port pump done 7800 hrs, Starboard done 7200 hrs

Engine Coolant- 1000 Hrs

Date/Hrs Completed- 7960/ 7980

Change All Belts- 1000 Hrs

Date/Hrs Completed-  8000/8130

These maintenance intervals may vary a bit depending on how much you use your boat but this list has been working pretty well for us.

Servicing Aftercoolers

The aftercoolers are messy job but a service requirement for these engines. SBMAR (headed by Tony) is a wealth of knowledge and they have a helpful article on maintaining aftercoolers here: https://www.sbmar.com/articles/cummins-marine-aftercooler-maintenance/ 

That’s also an insightful article about marine age vs hours and more.

Cummins 450c Performance

Our boat is heavy for a 43 and has a full tower, livewells, extra fuel tank, and more. The boat cruises at 17 knots and tops out at 24 knots. We burn about 25 gallons per hour at cruise with twins.

If you would like to check out the performance curve, check out this list here: 

https://www.sbmar.com/cummins-marine-diesel-performance-curves/