Stymied by diesel engine overheating & hull vibration

[algoodman1]

I recently changed the raw water pump impeller on the Yanmar 2GM20FW diesel on my 2000 Hunter 320. After restarting and warming up the engine for about 20 min I put a load on the engine and headed out and 5 minutes later the high temp alarm sounded. I also noticed alot of vibration in the cockpit floor. What could be the problem? Here's what I've checked so far: I rechecked the water pump impeller installation & confirmed the impeller turns OK and was installed in the correct direction, the new O-ring seal is working (no leaks from the pump), and tightened up the pump belt.I cleaned the intake water strainer (it wasn't clogged).I disconnected the antisiphon valve on the hose to the engine exhaust manifold & tested it & it was working properly. Started engine up again, it spit water OK, and it had the same vibration in the cockpit floor/stern area, both when running in nuetral and in gear. I didn't let the engine run long enough to see if it would overheat again. The vibration seems to be coming from the muffler area. The engine runs smoothly, and shakes only a very little bit on its mounts (mechanic said its normal), but the stern and cockpit floor sound and feel like they're rattling? Since the vibrations occur even when not in gear, I don't suspect the shaft alignment of cutless bearing. Do wet exhaust mufflers ever go bad? The exhaust outlet is at the waterline, so its hard to tell how much water is coming out, but it is splashing. The rattling is definetely something new. What else should I check? I'm stymied.
Al

 

[mcaswell]

I'm relatively new to marine diesels, but one thought... check to see if the mixing elbow gets hot. I believe I read here that if it does get hot, that signifies a lack of raw water flow. Also, did you open up the freshwater side? I recently did a flush/coolant change, and encountered problems similar to what you describe as a result of air in the lines to the water heater.

--Michael

 

[Stu Jackson]

...and encountered problems similar to what you describe as a result of air in the lines to the water heater.

http://c34.org/bbs/index.php/topic,4518.0.html

 

[wufibugs]

I had pretty much the same symptoms as Al with the same motor, and it was the elbow. Perhaps changing the impeller increased the raw water flow beyond what the already obstructed elbow could handle. Mine was totally carbonized. As was pointed out in another thread, best accessed from the rear by unbolting the mount from the head and separating the elbow after both are off. I asked about shot-peening the elbow to decarbonize, but was told by a couple of people to forget it and pony up the $180 for the elbow, which I did.

 

[Steve Dion]

Al:

You may also want to consider inspecting the heat exchanger. They can get crapped up (especially on the raw water side).

As far as your vibration it may be your motor mounts. Yes some vibration is normal but how much is the question. Motor mounts are about $400-500 for a complete set so you don't want to change them out unless it is necessary.

Do not discount any of the above suggestions. The elbow is a common but easy fix. You are usually best off by replacing the entire unit (elbow, manifold & coupling)

Is you mechanic a Yanmar guy or general diesel mechanic?

 

[heart of gold]

I also had an over heating problem so I took my heat exchanger and elbow apart this spring and had them cleaned in a high temp parts washer. That cleaned them pretty well, escpecially the exchanger. The elbow was a different story. I worked at it with pointy objects like screw dirivers etc untill I got it acceptable. I had a hole in the side of it that was completely carboned over, and being on the cheap(I was quoted 360 beans for a new one) I found some cast manifold epoxy filler from Lordco and fixed this, seems to have done the trick for this year at least. I re assembled with new gaskets and a new exhaust hose to muffler and all is well. I bet that the muffler could bang around down there if the mixing elbow wasn't working right. Could be causing your noise. I went through this because a bit of black smoke out the back as well, and this has cleared right up and I'm sure it runs smoother. If you are confident and have good access to parts, it is not a difficult job. Cheers

 

[AXEL]

Check the thermostat. The Elbow sounds like a good possiability. It may not be so easy to get off though. I spent 5 days of EB Blaster and a tourch 2 years ago. Heat exchanger is easy to check. Check fresh water cooling, make sure it's got antifreeze (green). If you have a hole in the heat exchanger you'll be pumping sea water. Check your oil, make sure nothiing unusual going on there.

 

[Deadline]

To get the elbow off, you have to disonnect four bolts at the manifold, which is easy. Use a hairdryer to warm the hose to get it off the elbow. Don't clean the elbow, buy a new one.

If it isn't the elbow, it could be cavitation. I over-engineered an impeller replacement last year by adding the paper gasket to the black sealant gasket. It created just enough air leakage to prevent the water from flowing, but not enough to present as a leak at the pump. Perhaps the air prevented it from dripping. It led to a spectacular explosion of the exhaust hose. Easy fix, took forever to diagnose.

 

[Steve Dion]

The mixing elbow is around $150 +/- for that part alone. It can be very difficult to seperate the elbow from the manifold.

If you CANNOT get them apart, I suggest that you get two very large pipe wrenches with breaker bars. Try breaking them apart. If this does not work, then try using a torch on the manifold or elbow. If that does not work, you may be stuck purchasing the entire assembly (manifold, coupling & elbow).

Be SURE to use never seize on all the threads when re-assembling the unit. You will also want to use the never seize on the bolts for the manifold too.

 

[Don12364]

Chunk of rope round the prop would also cause all of the above symptoms?
If it will rev freely in neutral it is unlikely to be the exhaust elbow carboned up, though the overheating it could still be a blockage in water injection outlet.

 

[algoodman1]

Thanks everyone for your tips. I will check the elbow temp and check the thermostat on the FW side tomorrow. Also, I'll test the high temp alarm and buzzer to see if they're working properly.The oil checked OK...was replaced a few months ago. I replaced the FW pump last fall and there is plenty of coolant in the expansion tank and no leaks since. The engine runs great since I pulled the injectors and had then cleaned several months ago...that did away with the black smoke I was getting on startup. I think the next step will be to remove the mixing elbow and header for inspection. BTW, this has been a freshwater boat entirely, except for a few weeks during 2008 and 2009 in saltwater. The vibration/rattling sound on the cockpit floor and at the stern lockers is still puzzling. The muffler isn't rattling around though. I scheduled my diesel mechanic (lots of Yanmar and boa deisel experience) to have a look later this week if the problems persist. I''ll post the results.
--Al

 

[Ken13559]

Al, is your exhaust underwater? If yes, you won't be able to tell if water is coming out of it. I've a 326, think its same as 320, and had same problem after changing impeller. Found problem due to air lock, no water going to heat-exchanger. Fill hose between impeller and exchanger, problem solved. Since problem develop after you changed impeller, I don't think mixing elbow to be a problem.

 

[Witzend]

Vibration noise, check that the shaft is centered in the thru-hull...engine alignment.

 

[heart of gold]

one more thing

If you do take the elbow off and try to unscrew it from the manifold fitting, you may find it to be a reverse thread. I did on my 3gmf. Cheers

 

[algoodman1]

Update on fixes -- overheating and vibration

It looks like tightening the water pump belt has fixed the engine overheating. Afterwards, I ran the engine (2GM20FW) for about an hour, mostly under cruising load, while checking the temperature of various places on the cooling system with an infrared thermometer gun. No alarms. Temp stayed under 160 and the mixing elbow was cool enough to place my hand on. The temperature difference (inlet vs outlet) on the raw water side was under 10 degrees. I see no need to inspect the elbow for clogging at this time. As for the vibration, my mechanic agreed with me that its excessive. You can see the shaft wiggling around in the stern tube when cruising. The engine clearly needs an alignment. If that does not eliminate the vibration, then I will haul the boat and inspect the strut, cutlass bearing and max-prop. All of these components looked fine when it was surveyed a year ago, but its always possible debris may have hit them. I sail the Columbia River and each spring high water lifts alot of woody debris into the river. Thanks to everyone for your replies.
Cheers!