R25 SC Cruise RPM question.

[Bob B.]

We recently became owners of a Ranger 25SC with a Volvo D3 150 hp inboard. I have a cruising RPM question. I realize this has been discussed to death but I am still confused. I have been told by boaters, brokers and service techs to cruise at trawler type rpm 1800 - 2100, and after a few hours run higher RPM, 2700-2800 for 15 to 20 minutes prior to docking.

I have also been told to cruise around 80% of max RPMs (3000) for better engine health.

Fewer RPM causes glazing of cylinders, too many RPMs can cause premature wear. We travel mostly the Upper Mississippi River up and down current. I would love any info relative what the real answer is … we want our engine to live as long as possible.

Bob.

 

[BB marine]

The D3 150 hp is a marinized care engine. It is a small displacement engine capable of 220 hp at 4000 rpm. In a car its normal highway operating rpm is most likely 1800 rpm to 2200 rpm and the engine coolant temperature is usually around 176F. You will not have any cylinder glazing because of reduced rpm with this engine or any common rail Diesel engine. The engine management is continually adjusting fuel and air for a clean burn. The D3 150 hp I believe can be operated at any rpm you want without compromising longevity. Would not be concerned about operating it at 90% of WOT rpm all day long. If the WOT rpm is 3000 rpm You will not wear the engine out operating it at 2700 rpm all day long. This is the same engine that is rated at 220 hp @4000 rpm. I operated the D3 220HP for 5 years 650 hours with an average of 4.5gph and it was just getting broke in. When I say 4.5 gph I mean over all of the 650 hrs the average burn was 4.5 gph. Many times I was at 9 gph and many at 2 gph. The average is total fuel used divided by hours =average. Congrats on the 25 Tug , maintain that engine based on the Volvo service recommendations and enjoy the ride.

 

[Bob B.]

Thanks Brian, that is good news. We prefer to travel at displacement speeds when not racing to make a lock. I guess there is a difference between electronic and mechanically controlled Diesel engines.

Bob.