At July Cummins, we love to see everyone get the most out of their maritime activities. If you’re a boater, you may have certain beliefs about your diesel engine that are false or misunderstood and that may actually be harmful. Here are three common marine diesel engine myths along with the reality on each topic.

1. I Can Let My Diesel Engine Idle as Long as I Want

Do you let your diesel engine idle or turn off the engine whenever possible? Diesel engine idle myths are some of the most pervasive ones out there, likely because the idea that it’s okay and sometimes even desirable to leave your engine idling nearly indefinitely is somewhat rooted in truth.

The true part is that in contrast to gasoline engines, diesel engine throttles do not block the amount of air they take in, which allows them to burn much less fuel when they idle than gasoline engines.

However, even though you’re not burning fuel, excessive idling is not good for your engine or the environment. Much of the fuel you do expel when idling does not combust, which creates greater pollution. You’re also still running the engine, which can lead to faster engine wear, especially if some of that non-combusted fuel gets into your oil.

2. Marine Engine Wear Is Highest at Higher RPM

Marine engines are tough, and with the right parts, they should last a long time. That said, it’s understandable if you want to put as little wear on them as possible. It’s important to understand where the most engine wear happens.

It’s counter-intuitive, but often the most wear typically takes place not at high RPMs but when you’re starting the engine up. Why? Because your lubricating oil is cold and hasn’t had a chance to flow through the system yet. There will be residual oil on your components at startup, but not as much as when your engine is in regular operation.

If you have a commercial diesel engine with a block heater and/or pump to circulate the oil before the engine starts, you should not have this problem. If you don’t, you’ll want to give the engine a minute to get warm before advancing the throttles.

3. I Should Never Put Synthetic Oil in a Diesel Engine

It’s a common belief that putting synthetic oil into a diesel engine can cause leaks and other problems. In fact, some people believe that it’s not even safe to switch brands of oil when lubricating a diesel engine. These assertions are all myths. As long as your lubricating oil meets the OEM requirements, you’re free to switch brands and use synthetic oil as you see fit.