Best running speed?

[Xhawk101]

I am a new owner of a 2009 25 ranger tug. It has the 150 hp cummins turbo. Max speed appx 18 mph. 3000 rpm about 13 mph. Seems to run a little hotter over 3k rpm. Wondering the best speed for cruising. Is it harmful to run 3000 plus rpm for extended periods?

I know 2000 rpm is way more efficient. Thanks for the input.

 

[Todd]

Don't know about Cummins. Check owners manual. I have the Yanmar 260. Max RPM 4000 Max continuous power 3600.

 

[Levitation]

Your QSD engine is rated for continuous operation at 3/4 throttle (look in the black cover Cummins/Mercruiser manual).
That is below 3000 rpm based on how the factory props the boat.
What exact temperature is the 'little hotter' you speak of and at what RPM and for what time period?
Mercury rates the engine a bit higher than Ranger's 150 hp.
http://www.mercurymarine.com/engines/diesel/qsd/


Is the sea chest strainer clean?
When was your sea water impeller changed?
When was your coolant/antifreeze changed? (a pita to do - I suspect I know the answer)
Pull the zinc out of the heat exchanger and shine a strong light in there - or use a borescope - and look for scaling or deposits. It may need to be cleaned.
Have you compared the gauge to an infrared temperature gun reading?
*** Do that at multiple throttle settings and make a graph comparing the gauge to the gun - take enough time at each throttle setting to allow the engine to stabilize***
What is full throttle RPM? Is your prop clean? Or dinged?
Is the bottom clean?

And you thought you could just ask a simple question and get away at that, eh grasshopper :mrgreen:

 

[Xhawk101]

Thanks very much for the information. So it's actually a lot hotter, like 196 to 200 if over 65 or 75% throttle. Have had system cleaned, new impeller, etc. Maybe I should try new cooling fluid.

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[NorthernFocus]

Thanks very much for the information. So it's actually a lot hotter, like 196 to 200 if over 65 or 75% throttle. Have had system cleaned, new impeller, etc. Maybe I should try new cooling fluid.

Confused about this thread. It spans several years. So is the overheat situation only a recent issue and boat has been operating OK since 2013?

Design operating temperature for the engine is 176-185F but they don't specify at what water temperature that is achievable.

New coolant isn't likely going to make a difference but flushing the block might help. Which would also mean replacing the coolant but flushing the system is the key.

 

[Xhawk101]

Sorry for the confusion it's basically same recurrent problem I guess but worse recently perhaps warmer water in Florida contributory but it shouldn't be getting over 186 it sounds like.

I've already had the system flushed. I guess I just need to find a decent mechanic... Easier said than done.

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[captstu]

My R25 engine had a chronic overheat problem until I changed out the thru Hull, eliminated the elbow, and replaced the. Sea chest with a strainer, all 1 1/2”. Problem solved.

See shearwater-sailing.com for a full discussion.

 

[NorthernFocus]

My R25 engine had a chronic overheat problem until I changed out the thru Hull, eliminated the elbow, and replaced the. Sea chest with a strainer, all 1 1/2”. Problem solved.

See shearwater-sailing.com for a full discussion.

Along the lines of what I was thinking. The raw water intake system as designed/installed by the factory is marginal at best. But only having experience with It with 50 degree sea water temperature I didn't have any data to back up my opinion. I'd not place any bets on 80 degree water and above. Maybe some other Florida owners will chime in.

 

[chrispangaro]

I have a 2008 25 with the 110hp. At over 80% max rpm temp would creep up. Sea chest setup is poor. By cleaning Seacrest cover I found that at higher rpm the engine intake was creating sufficient vacuum to pull air through the head, more or less depending on the dry bowl setting on the head. This would be evident after a hard run, looking at the sea chest with engine running revealed a mostly empty bowl although it started full.

Problem substantially resolved by putting a high quality one way or check valve in the sea water supply to the head. Bowl on sea chest remains full. I still think the strainer style through hull doesn't allow sufficient flow for WOT. Will resolve that next time boat is slipped by cutting grating off it.

Chris

 

[Xhawk101]

Great advice all thanks! Makes more sense now.

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