Cruising RPM/ Yanmar 2QM15

[bruceyp]

I have a C&C 29 with a Yanmar 2Qm15. She, and it, are oldies but goodies as far as I am concerned. But this weekend I ended up motoring for about 4-5 hours due to a lack of wind. I was running around 2300 RPM the last 35-40and the engine finally heated up enough for the Temperature alarm to sound. I shut the engine down. Luckily, we were very close to our mooring and the wind rose just enough to get back in under the jib. But Now I am wonderig what RPM I should be cruising at? When I went out the next day the engine ran normally inspite of a slight odor in the engine compartment. An oil change is on tap this afternoon as a preventative. Any advise would be appreciated from any of you more experienced with this engine.
Thanks ,
BruceyP

[Gary M]

2300 RPM should be no problem for a Yanmar, I have a 2 GM but they typicaly are rated to run continously around 3200 RPM. I would be checking your cooling water system.

Gary

[NOLAsailing]

Small marine diesels run best around 80% of their max rpms. For the 2QM15, 2300 should be just right. You were not over-revving the motor.

Gary is correct, you'll want to check the cooling system. Also, do you have a temp gauge? If not, then it's possible that the temp climbed suddenly, so you'll also want to check the impeller. Even if that wasn't the original source, running without water can crack the vanes, so inspect it carefully.

If you find it useful, I've uploaded the operation and service manuals to my website in .pdf format. If you don't have them, please feel free to download them. One nice thing about the .pdf manuals is that you can print out the relevant pages and bring them to your boat without worrying about getting the boat dirty.

Here are the links:
Operation Manual: http://www.rambunctiousracing.com/files/2qm15.pdf

Service Manual: http://www.rambunctiousracing.com/fi...m15service.pdf

Webpage: http://www.rambunctiousracing.com/literature.html

[bruceyp]

Jason,
Thanks for the links. I already had the link to your service manual but not the Operations manual. Now that I have a knowledgeable person to ask... between my exhaust mixing elbow and the transom I have a stainless steel pot (for lack of a better term) that takes in the cooling water from the engine and then connects to the transom ( this is a raw water system). What is this thing and what does it do? Do I need to remove and clean it? The service manual doesn't show any such thing.
Thanks again for your help.
You too, Gary

[bruceyp]

Rick,
You tell me. Is that what it is? Do I have to clean it out or anything? This is my first full season with my first keeled boat and I'm finding out all kinds of things I didn't know before. (I've found out some things in a very costly way.) Hobiecats didn't have all these systems to mess with. But then there weren't many creature comforts either.
B

[Gary M]

It is likely the water muffler. How much water is coming out the exhaust when the engine is running ? It is a bit hard to define but on a guess it should fill a pail in about a minute or two. I would find another boat with a 2 cylinder diesel and see if your water flow is comparable.
Every time you start your engine you should look over the transom to see if you have adequate flow.

Do you have a closed loop cooling system ? ie. is there a heat exchanger ?

[NOLAsailing]

You're describing a water lift muffler. It takes the place of the old style exhaust (long jacketed hoses) and works by filling with the engine cooling water. The exhaust pressure is enough to discharge the cooling water when the muffler fills and so the water in the "pot" muffles the engine's exhaust noise.

They do make them out of stainless steel, though plastic or fiberglass may be more common. I suppose it's possible to build up scale or sedimentary deposit in the water lift, but I doubt this is the issue. The much smaller engine passages would probably clog before you noticed a significant degradation at the water lift. However, you can always remove the intake and discharge hoses to see if there is any sedimentary build up.

If you have a cooling system issue, the first thing to check will be the amount of water that exits your exhaust at the transom. Is the flow normal? Note that with a water lift, the flow will sort of sputter at idle; you don't normally get a steady flow until you are running under load as it's exhaust gas pressure that evacuates the water.

It would easy to check, but I suspect you'll find the culprit elsewhere.

[bruceyp]

All,
Thanks. I do check the outflow over the stern whenever I start up. But What is Normal? It sputters at idle. But even at 2000 RPM it isn't a steady stream I don't think. Having said this, I'm not usually hanging over the transom when I'm motoring along, so I will have to recheck this. I am sure I get a "pail in a minute or two". At the beginning of the season I replaced the thermostat and noticed that the old one was pretty gunked up and rusty. Is there a way to flush the cooling jacket? Maybe suck some kind of cleaner stuff into the engine, let is sit awhile and then flush it out? I once did something like this to a car I owned though, and when I was done my waterpump started leaking like crazy. I had cleaned out all the gunk that was blocking all of the leaks.
B

[NOLAsailing]

You can do an acid flush if you suspect the cooling passages might be blocked.

Use about a 1:3 solution of muriatic acid (you can get it at home depot) and water. Fill a bucket and let the engine suck it up with the water intake (just close the seacock and redirect the hose or, if necessary, fit a longer hose to the pump temporarily). When the bucket is empty, let the motor sit for thirty minutes and then thoroughly flush it by letting the motor run with the raw water hose reattached.

Don't over-diagnose, though. Have you checked the impeller?

[southerncross31]

I would second checking the impellar. On my 2qm15 it is on the back side of the water pump. If you have not checked this, it is probably the problem. They should be replaced every season.