tapping noise in mecruiser 3.0 L engine??

[hannahbear]

tapping noise in mecruiser 3.0 L engine??

After 3000 rpm's I hear a loud tapping noise in the engine. After bringing the rpm's down the tapping noise goes away and oil pressure gauge goes back up. Any idea what is causing this????

 

[Trent]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

Most likely your hearing the shutter in the exhaust. Around that RPM is where you really hear it. Its a "flapper" type valve in the exhaust that keeps water from comming back into the engine after a quick slow down of the boat or a big wave from washing into the engine. Its does sound like a tapping type noise at times. Listen to the engine and make sure its not in the valve cover area. How low does the oil pressure go? What does it do exactly (gage)?

 

[Bondo]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

i would be looking into the oil system.. oil pressure Should be at it's highest at those speeds... the tapping could be, lifters, rod bearing.....maybe piston slap... is the oil full,...what kind of oil pressure #s are we talking here..???? sounds like a serious oil starvation problem going on.....<br /><br />Bondo

 

[hannahbear]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

when the boat reaches 3000 RPM's the oil pressure drops to 0! When the boat is at idle speed and below 3000 RPM's the oil pressure stays between 20 and 40 on the gauge. The tapping noise seems like it does come from under the valve cover when listening to it. <br /> Thanks

 

[Trent]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

Put a manual gage on the engine to verify the oil pressure.

 

[wheels4]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

You have oil starvation problems buy why?First thing I would check would be to pull a valve cover.Check the condition of your valve train is there a lot of carbon buildup?Ive seen a chunk of carbon clog the oil return to the oil pan.If this is not the problem and you have the oil filled to the right capacity I would suspect you have a bad pump or pickup.Hope you find the problem.Wheels

 

[hannahbear]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

Could it be the Oil pressure sending unit. Is it not telling it to pump more oil as the RPMs increase, or does it need a new oil pump? It seems like it runs fine in lower RPMs. After running it at higher RPMs for about 30 seconds the tapping starts. I think all the oil runs back down and isn't being pumped back up fast enough because once you bring the RPMs back down it the tapping stops. About how much is it to get an oil pump replaced, if that's the problem?

 

[Trent]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

The oil pressure sending unit only tells the gage how much pressure is there. It has nothing to do with the oil pump. Your sending unit could be bad and when the pressure builds up the gage goes to zero. You need to verfiy that the engine has pressure. Put a mechanical gage in place of the oil sending unit and check.<br /><br />Replacement of the pump would be about 500.00 but if its bad so is everything else...most likely. Wheels does have a point about oil return blockage. <br /><br />Check the oil pressure first.

 

[kinsey2001]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

Sounds like the pump tp me. Had a Chevy 305 make the same sound and read about the same at the guage (mechanical). Turned out to be the over presure valve in the pump. There is a ball and spring combo that works as a bypass in the oil pump. At 3000 rpm and a weak spring could be causing this valve to open & shut (tick, tick).<br /><br />Either way, new pump.<br /><br />Hope this helps<br />Skipp

 

[Ted S.]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

I had the same problem with my Johnny and I added some tranny fluid to the gas and it went away really quickly. It even cuts the smoke output percentage by half. I know some people say it's a bad thing to do but it worked on my 74 Gremlin. <br /><br />Good luck

 

[FLASH0002]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

Same noise here. I just changed the oil, but before doing so I ran a quart of transmission fluid in the oil for about ten minutes. Went away. I could not figure out what it was. I am assuming that it was a sticking valve. My oil pressure stays steady, so I don't think it has anything to do with that. <br /><br />Let me know if you find out anything different.<br /><br />FLASH<br /><br />1990 Chris Craft 177 Concept OMC 3.0

 

[hannahbear]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

Well, the oil pressure didn't have anything to do with it. It was just a loose connection to the sending unit. It still makes that noise after about 15 seconds at 3000 rpms (loud tapping). Could it have anything to do with the exhaust? I checked the oil and didn't notice any water in it.<br />Will it just go away or is it not safe to run it like that?

 

[Trent]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

Still sounds like the exhaust shutter... NORMAL!!THey make that noise at the RPM you posted. Dont think you have a problem!

 

[denniz]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

I agree with trent on most he posted, check your oil pressure, Im wondering why you would think a exhaust shutter would sound at 3000 rpms??? underload it would be at full open with enough water pressure to hold it there. Normally you hear a shutter at idle/offidle.

 

[Mikevn1500]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

Mine was making a loud clicking/tapping noise. Turns out A bolt came out of the ALT. allowing it to vibrate. Had my but tight on that one! Easy fix.

 

[chesire_catt]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

what does running trans fluid in the oil do and how does one do it?

 

[Trent]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

Rod Knocking..I understand what your saying..But Iv seen several of these make this sound and it turns out to be the shutter "Rattling" Underload.

 

[denniz]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

It definetly worth checking,think your right that oil pressure is the main concern.

 

[C17LoadSmasher]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

Does your engine run rough? Does it not want to stay running at idle? I had the same symptoms and it ended up being a blown valve and a detonated spark plug - Dealer or MerCruiser do not know what caused it. Just some food for thought.

 

[SS MAYFLOAT]

Re: tapping noise in mecruiser 3.0 L engine??

Re: tapping noise in mecruiser 3.0 L engine??

I also will agree with Trent on this one. Does this do it at 3000rpm while sitting still in the water, or while your in gear and crusing? With sitting still at 3K rpm, lake water will create more back pressure on your exhaust, where as while your crusing, the water will work like a vacuum pulling the exhaust out of your engine.