Mercruiser 5.7 Whining Noise - Intermittent and Independent of rpm

[DuncanDonut]

I just bought a 1997 Sea Ray Sundance 240 with a Mercruiser 5.7 EFI and Bravo outdrive. The boat runs strong but has an intermittent whining noise (I have video/audio but could not upload even after compressing it). A couple of weeks ago I stopped in a cove for about 20 minutes. When I restarted the engine, the belt would not move, resulting in a screaming sound, After sitting for another 15 minutes, I was able to restart and belt was moving again. A mechanic changed the tensioning pulley (he thought that may have been the frozen belt issue and my power steering fluid was very low so I topped it off. I also see some water and oil in the bilge after 20 minute runs up and down the lake.

Even after topping off the power steering and attempting to be sure that there was no air in the line (by turning the steering wheel back and forth with the engine off) I still get this whining noise. It is most noticeable at low rpm (idle) and does not seem to change in frequency when I throttle up. The mechanic at first thought it was air in the power steering line. I guess it still could be.

This morning, when I first started the boat, it was not making the noise. By the time I got through the no wake zone it had started. After our trip, I was idling and it had gone away. Then it came back on the way to the dock. My wife is leery of leaving the dock until we figure out what this is how it might leave us stranded.

 

[DuncanDonut]

New theory - The noise seems to gets worse when there is more water in the bilge and seems to be related to the trim motor/pump system. Can it be that the trim pump is partially submerged resulting in the noise?

 

[alldodge]

Howdy

You won't be able to upload pics or vids until you have posted 3 times. Post anything once more, even Hi, and then you should be able to post

Don't see how water in the bilge would collate to a change in sound. The trim pump only runs when the trim is being used, there should be no sound coming from it when not being used. When the noise starts look in the power steering and see if it's low of is foaming

 

[wahlejim]

I second the power steering examination. Also, you mentioned water in the bilge. It's not your bilge pump going bad, is it?

If water and oil are in your bilge, examine your bellows. Your U-joint Bellow could be cracked, allowing water to get in. The inside of the bellow is typically greasy. If that is bad, change it before your next outing or you could sink your boat.

 

[harleyman1975]

Could be blower motor too if you are one who leaves it on all the time.

 

[Bondo]

Could be blower motor too if you are one who leaves it on all the time.

Ayuh,..... Sounds like he needs to leave the bilge pump runnin' all the time too,......

There shouldn't be Any water enterin' the bilge, that's Priority #1,.....

 

[DuncanDonut]

Thanks all for the feedback. A crawled down into the engine compartment today as far as I can to see what might be affected by water in the bilge. All I found was my bilge pump, float switch, and transducer for the depth sounder.

Today I moved the boat to a new slip since the previous one could have had blowing rain that might have contributed to water in the bilge. I also vacuumed all the water out of the bilge and dried it out really good. I plan to check in the morning to see if any more water came in during the evening. Then I am going to take a short trip to see if I have water intrusion underway. I am going to have the boat pulled in a week or so to change the foot oil, grease all fittings and check the boots.

Now a new theory. The fact that the whining noise did not change with the rpms had me stumped. The whine is almost continuous now. I had checked everything but the trim tabs. Today I activated the trim tabs and it changed the whining sound noticeably. So now I am thinking it has something to do with the trim tab pump or motor. Have any of you ever heard of that? What kind of oil do you use for trim tab systems? I've not had them before.

 

[Pete104]

Insta-trim recommends their fluid but I've used ATF with no issues. Bennett calls for ATF.

 

[DuncanDonut]

Okay fellers - here's the latest. I spent the morning crawling in and out the bilge with a buddy (one at a time). We topped off the trim tab reservoir with ATF and took the boat for a spin. I do not see oil in the bilge - just dirty, oil colored water. That is good news. It appears that the water in the bilge is left over from being stored outside for a little while. When I was coming up on a plane, water came out from under the gas tank. We sopped it up. A little more came out. We sopped it up. A tiny bit came out. We sopped it up. The bilge is currently dry now and I expect it to stay that way now that I am in a dryer slip. I am still going to have the boat pulled to change oil in the foot, grease fittings, and examine the bellows.

Now the persistent whining noise. It is no longer intermittent but is almost constant (perhaps a deteriorating condition - I sort of wish something would just fail and get it over with. Otherwise, I will start to whine louder than the boat). When we first started out, the whining noise would modulate slightly when I trimmed the tabs up or down (in spite of a now full reservoir). As we pulled back in, activating the trim tabs no longer changed the pitch of the whining noise. My mechanic said that the alternator had a little resistance when he turned it but it is still functional. The whining does not change with increasing rpms, trimming the outdrive or activating the power steering. Could activating the trim tabs place a load on the alternator that resulted in a change in the noise if the alternator is the source. Can a whine come from the alternator that would not be affected by the speed of the motor? How can I check the power steering? I topped off the fluid about two weeks ago. Someone suggested the bilge pump. The next time I go out, I will activate the bilge pump and see what that does, if anything.

I still could upload the video/audio. Sorry. Thanks again for your input. I love this boat, but this whining has got to stop (the boat's - not mine, of course)

 

[alldodge]

Forget the trim, it's not it unless the trim motor is stuck and that would cause other issues.

Is your bilge pump or blower running as others have mentioned?

 

[thumpar]

When it is whining start pulling accessory fuses like bilge pump and blower to see if it stops.

 

[DuncanDonut]

Good idea! Pulling fuses tomorrow. Thanks again for everyone's input.

 

[NHGuy]

Go to an auto parts store or Harbor Freight and get a mechanic's stethoscope, or get a length of small diameter hose. Maybe clear vinyl. Stick the hose or scope in your ear(s) and start moving the pickup point around the motor looking for the sound.
Check all the belt driven pulleys for the sound.
When bearings fail the indicator is a whine sound similar to an airplane noise. The pitch does not change but the volume changes with speed and sometimes with load.
Plus your tech said the alternator has some drag.

 

[DuncanDonut]

All good ideas. I ordered a stethoscope this evening and it will be here on Monday. Thanks again.

 

[DuncanDonut]

More data. Went to the boat again today. The engine made a light chirping noise upon start up (belt or water pump?). After about 2-3 minutes, the whining noise started. Apparently it starts after the engine or bearing warms up. I am leaning toward the alternator as the culprit right now. The description by NHGuy of an airplane engine noise is the closest description I have heard, yet. Stethoscope arrives tomorrow so I should have a better idea by tomorrow evening about the source. Blower works fine, but I discovered that the blower hoses were not hooked up to the transom exhaust nipples so I picked up some clamps on the way home. I could not find the fuses for the bilge pump. Any thoughts on where to look?

I found a loose clamp under the engine (see photo below). Any thoughts about what this might be?

 

[Pete104]

Looks like a clamp that used to secure P/S hoses to the front port motor mount.

 

[DuncanDonut]

Thanks, Pete104. Your observation seems to fit with today's findings. I took my new engine stethoscope to the boat today (one of the best tools every devised). The good news is that the whining noise is not the alternator, water pump, trim tabs, bilge pump, outdrive trim, or any thing associated with the pulleys on the front of the engine. The culprit is a box under the engine that is connected to the "raw water in from Leg" (see diagram below) on the port underside of the engine - right next to the motor mount. Is that the power steering cooler? What could cause whining? cavitation? air in the power steering system? Or is it simply a very high frequency vibration against the engine, engine mount, or hull. It modulates slightly when I activate the trim tab. Does that change something about the hull that is enough to modulate the vibration? Is it related to the loose clamp the I found in the bilge earlier (pictured earlier)? Tomorrow, I plan to go back with a wooden wedge to see if I can make it stop vibrating if that is the source of the noise. If so, what would be a more permanent solution? The boat temperature seems to be fine, so it must be getting enough water for cooling.

 

[DuncanDonut]

One more question. if the source of whining/vibration is the power steering cooler, why does it take a couple of minutes after starting the engine for the noise to start? Is something heating up?

 

[thumpar]

I don't know the 4.3 mercruiser but if that is the power steering cooler you might want to see if there is sound from the steering actuator. It could be resonating through the fluid.

 

[Pete104]

Better put a decal set on that flame arrestor cover! That BOX down by the motor is your Gen II fuel pump & cooler. The P/S cooler on that engine straddled on the ass end of the engine.