beta 20hp BD722 newbie question re-oil alarm

[jaybeegee]

I have a a Beta marine with around 400hrs and around 5 years old just serviced.

Today after around 45mins of engine running at 35k revs in calm waters the oil pressure alarm kicked in! I slowed down considerably and within 30seconds it stopped and we carried on! What could it have been? A mulfuction or this could be considered normal as long as the alarm does not remain on?

thanks!
Jay

[donradclife]

No, it is not normal for the oil pressure alarm to come on at full speed. Generally, the first thing to do is turn the engine off and check the oil level, because you can seriously damage the engine by running it at low oil pressure. In your case, the engine may have been overheating if you were running it wide open, and recovered when you dropped the speed back--did you notice what the temperature reading was??

[NCboatrx]

This is not normal.

If there are no oil leaks and the oil is still full, the other thing to look for is a faulty connection at the oil switch on the engine. This could also be an issue with the type or grade of oil that you are using. You say that you were running at 3500 RPM so if the oil viscosity has dropped because of engine heat and heat in the engine compartment, you could have lost pressure and slowing the engine down will definately have helped here.

Trust the engine alarm system, you may save your engine.
Stanley

[MarkSF]

Running it at 35,000 rpm was probably the cause. Keep it under 3500.

[redhead78]

Ditto 35K sounds, high, what is recomended cruising RPM...Red

[jaybeegee]

thanks for your prompt replies.

My mistake it is infact 3500 RPM !

@Don - thanks for the tip. oil level is ok. unfortunately i dont have a temperature reading but did temp alarm did not kick in!

J.

[JimsCAL]

If your oil level is fine, my vote is for the oil getting hot and the low viscosity resulting in low oil pressure. I generally avoid running at max power or RPM for long periods of time. The engine is happier and fuel consumption is better.

[jaybeegee]

Originally Posted by JimsCAL

If your oil level is fine, my vote is for the oil getting hot and the low viscosity resulting in low oil pressure. I generally avoid running at max power or RPM for long periods of time. The engine is happier and fuel consumption is better.

thanks Jim - what in your mind is long periods? 1hr?

[JohnRPollard]

Originally Posted by jaybeegee

thanks Jim - what in your mind is long periods? 1hr?

Jaybeegee,
Most marine diesels have a "peak" (also called "intermittent") and a "continuous" rating.

Peak is the rated output when the engine is pushed to max rpm, where the max power of the engine is produced. But operating at peak is usually limited to no more than 1 hour.

The "continuous" rating is the power output produced at an rpm where the engine can run literally continuously (assuming plenty of fuel and clean oil). The "continuous" power rating for an engine is the more relevant one in most marine applications.

I am familiar with the Kubota D722 engine. In tractor applications, they rate that engine at 18hp @ 3200 rpm, continuous. It does have a "peak" rating that is higher than that (I believe it's 20-21 hp at 3600 rpm). But that is really pushing the engine VERY hard.

I would urge you to keep the engine rpm at or below 3200 for general use (personally, I'd be looking for a cruise rpm of around 2700-3000 or so). Save the extra rpm for difficult situations where you need a burst of power for brief periods. If you find the prop winds right up to 3500 rpm and yet you are not getting the boat speed you'd expect, that probably means your prop is incorrectly pitched (not enough) and would call for an adjustment.

[JimsCAL]

Good advice John about the continuous and intermittent ratings.

One other thing to check. Make sure the oil isn't overfilled. That can result in the crankshaft whipping the oil into a foam that will lower the oil pressure.