Tale of two mechanics

E

exrescueswimmer

New Member
Jul 17, 2011
32
Pompano Beach, fl
Boat Info
2003 360 Sundancer
Engines
8.1l Mercruisers inboard with v-drives
ok – I could use some experienced opinions here…
so i took possession of my boat (360) a little over a month ago.
on the sea trial everything was fine - we noted a sound around the stbd engine so we did oil samples from the transmission that came back clean. The day I was moving it, the stbd engine would not run over 3200 rpm and has not since except in idle.

Symptoms:
vibration noted on stbd side (stops when the transmission is in neutral and engine not under load)
max 3200 rpm when 6 weeks ago it ran at 4600
when not under load (in neutral) it will run over 4000 rpm
running gear passed survey including the props (visual inspection and a spacer between the blades and the strut to insure equidistance) – again, 6 weeks ago
no oil or fluids in the bilge
looked at running gear recently but was have a difficult time getting very close due to strong current at anchor point – nothing obvious
engines run great, according to the gauges – within a couple of degrees temp at same rpm’s – all other gauges are spot on
no smartcraft alerts

Mechanic #1 thinks it’s the transmission and is working up numbers to replace it – diagnostics won’t pick up a transmission problem.

Mechanic #2 says he’s never seen transmissions cause vibration and that they usually fail catastrophically – the cause is likely in the engine – thinks diagnostics should be run (approx $125 – 150) Feels the engine running over the 3200 mark not under load is meaningless.

could there be a compression issue and would that show up on a diagnostic?

Anyone out there have a similar experience or some thoughts?
I appreciate the help!

there are mercruiser 8.1 with v-drives
 
Personally I would spend the $150 on the diagnostic first instead of replacing the tranny.
 
#2 is the better advise... The gauge is often off, and running not under load is meaningless...
 
Wild a$$ guess here, but I'm going to say it needs plugs/wires. I've seen this before.

Don
 
Had this problem on my 7.4 starboard side. First had injector bad and engine was missing. The mechanic pulled 3 plug wires off to prove the point that you sometimes cant tell the engine is missing because the computer compensates for it. 3 plug wires off and i couldnt even tell.

So, replaced bad injector and still had the problem. Ended up water in gas and the water could have damaged the injector. Not saying this is your issue however the rpm thing was intermittent, one time it would WOT at 4200, 5 minutes later 3200. Vibration was similar too.
 
Mechanic #2 knows what he's doing; mechanic # 1 is guessing.

When a v-drive fails, you may hear a rumble, a rattle, clicking, a whine or it may fail to go into gear, or stop pulling altogether, but they don't vibrate.

Low compression can cause plug fouling and a miss, but you are jumping way ahead in the line of possibilities. Get mechanic #2 to run the engine diagnostics and see what is going on. Most likely, you have a miss under load caused by plug wires, fouled plug, or even an injector that isn't working or isn't working properly.
 
It really sounds like some sort of prop growth to me. My boat did the same thing earlier this season. It was fine when I launched it but then 5-6 weeks later I actually got to use it and it was terrible! Vibrating and couldn't get over 2500 rpms. The only difference was I had it with both motors. I had it hauled & cleaned and no more problems!
 
Hello I had kind of the same problem picked my new 350 up a 2009 left over ran it out ran up to 4600 no problem a week later took it out wouldnt get over 4000 the was my port engine brought it in the hooked it up no errors brought him out and ran it and he picked up a missing cylinder when under load replaced all plugs and wires then no vibration and right up to 4600 a month later my starboard did the same they did the same thing to that engine now im getting 4 gph better fuel economy and no noise or vibration so before I go into replacing big number items id do a complete tune up if it hasnt been done they think mine was from not running it since it was a left over Good luck
 
Either ignition or your running gear is fowled. In my area, it took 3 weeks of non-use for my bottom to foult his year, with new Micron CSC applied.... Mechanic #1 is incorrect. I would tune everything up, and check your running gear/bottom with a quick haul.
 
so - i was able to get under the boat this past weekend and there are probably 20 - 30 small barnacles (BB to pea-sized) on the props.
I assume that would be enough to cause a vibration so i'm going to schedule a cleaning to see if that helps and still get the diagnostics this thursday.
Is there any way to deter or slow growth on the running gear?
 
rcknecht said:
Prop Speed

http://www.propspeedusa.com/...
Click to expand...

Or put that money toward the fuel and run the boat more often.

I see that you're in FL and obviously not everyone can run their boats every weekend. I would agree with Rod that propspeed is a great product and sure will help you.

Also, another good solution (which is very common in your area) is to contract a diver to clean the bottom and the running gear on a monthly basis or whaever is more appropriate frequency.
 
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