What is the difference between a marine engine and an automotive engine?

A car engine typically only uses a portion of its horsepower to maintain a decent speed on the road. On the other hand, a marine engine is essentially at full throttle all the time just to move it through the water, so it has to be pretty heavy duty to keep up.

How many rpms should a boat run at?

Most mechanics and engineers suggest the best cruising speeds are achieved at 3400 and 3800 rpm respectively.

Can I put a truck engine in my boat?

Answer: In principle, a diesel engine is a diesel engine, so an automotive diesel will work fine in a boat. And, in fact, many marine diesel engines are nothing more than “marinized” car or truck engines. The engine will want a water-cooled exhaust manifold and a wet exhaust (a dry exhaust is too noisy).

Do marine motors run backwards?

There is no real ‘forward’ or ‘backwards’ in a marine engine. The last couple of ships I worked on had low speed marine diesel engines that could run in either direction. These engines were hooked directly to the propeller shaft and there was no gear box installed.

Why is my boat not reaching max RPM?

If the WOT test shows the motor fails to reach the optimum RPM, the motor is “over propped.” To remedy an over-propped motor, change the propeller to one with a lesser pitch. The lower-pitch prop creates less resistance in the water, which allows the engine’s RPM to increase and achieve optimum speed.

How do you know if your outboard is too high?

Too high usually results in low water pressure, prop letting go in turns, or lack of bow lift are usually the telltale signs. Sometimes porpoising is caused by too much bow lift and dropping the motor will give it more bite and make it worse.

What RPM should an outboard idle at?

1500 RPM is normal for idle. You can see some fluctuation (1500-1800), especially if plugs get old or you are out of the water on the hose with no resistance on the impellers.