Diesel Engine Overload

Diesel engines have reputations for long lives, yet many recreational marine diesels don't make it past the first several hundred hours of operation. Overloading is a common life-reducer in modern marine diesel engines. Yet while many books describe diesel engine maintenance, few discuss overload.

Boat manufacturers want to be able to quote the highest possible cruise speed with a given engine configuration and, as a consequence, are motivated to prop the boat for maximum speed prior to rigging, fueling, provisioning, filling the bait tanks, etc.  The configuration will pass the engine manufacturers sea trial in this configuration but, once the boat is delivered and fully loaded, the engines are in pearl.  For example, our boat is listed by the manufacturer as 24,000 lbs but weighs in at just under 29,000 lbs when lifted at the yard. The boat as delivered is between 1" and 2" over-pitched depending upon eventual use. 

We wanted our engines to last well, so we researched the topic and made some changes to our setup. Later, we posted an article to our website to describe our results. As we write this introduction, our engines have run without issue for over 3,000 hours.  Here is a link to our original diesel engine overload article posted in 2002. Below are selected answers to questions that we have received from readers since then.

Original Article: Avoiding Diesel Engine Overload



Follow-up Questions:


Stern Drives

Comments on stern drives.


Gauge Selection

The specific ISSPRO gauges that we installed.


Fuel Consumption

Determine fuel consumption and HP produced.


Restricted Air Intake

Insufficient engine room ventilation can also cause sooting.


Crankshaft Bearing Failure

Over-propping can occur in many ways.


Exhaust Gas Temperature

To properly use exhaust gas temperature to gauge engine load, you need engine manufacturer specifications for your engine and you need to know where the temperature is measured. 


WOT Measured By RPM

RPM isn't actually the only indication of load. There are actually are others and, in fact, RPM isn't really a good predictor of load.


Diesel RPM Too Low?

Light load is good as long as the engines are at full temperature.


Overloaded for One Season OK?

Fixing an overload is inexpensive compared to the price of an engine.



Select References:


Articles by Tony Athens

Tony Athens of Seaboard Marine is a frequent contributor to and he knows Cummins products incredibly well having installed 100's over the years. We particularly recommend the article "Engine Life vs. Engine Loading."

Why EGT is Important

This article discusses EGT with respect to truck engines, but the advice applies to marine diesels.





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Copyright 2012 Jennifer and James Hamilton