I learned about the following diesel engine stress test when I took a class with noted expert Bob Smith several years ago. Smith developed the Lehman Ford diesel engines found in many trawlers and went on to found American Diesel.
To catch engine problems before they occur, write down the base numbers for temperatures and oil pressure when things are running fine, so you’ll know what is normal. Then run this test under load in open water once a month during the boating season.
- Allow your diesel engine to get up to normal operating temperature.
- Run the engine up to maximum rpm for about 60 to 90 seconds, about 2,500 rpm for most engines.
- Back the engine off about 200 rpm and run for about 5 minutes.
- Watch for temperature and oil pressure changes.
- Don’t continue to run the engine if black smoke occurs. This happens because the engine isn’t capable of burning all the fuel.
The three critical temperatures are
- engine coolant temperature 175–180 degrees,
- exhaust gas temperature and
- oil temperature in the base of the engine.
On my boat, the only difference I see after running the test for about five minutes is a slight increase in coolant temperature, which is normal.