Logo
FULL SITE MENU

Overheating plus strange engine rattle

I

inliner

New member
"Just returned my faithful 197

"Just returned my faithful 1977 165 Merc Cruiser to service and it overheated at idle and there is this new "rattle" I never heard before that sounds like it coming from the top of the engine. It sounds as though if you were to toss a few nuts into your clothes dryer....bouncing and loudly clacking around with the clothes.

Overheating should be easy to figure out; check water pump/impellers/themostat, right?

But this sudden new "rattle" kind of bothers me. Pulled the valve cover off and it 'looks' all ok; no busted springs etc. So could a really bad water pump makes these noises? What about loose or bad exhast shutters?

New member. Great board. Hope someone recognizes and can comment on the 'rattle' I'm trying to describe

Regards, John"
 
"Does it do it just idling, or

"Does it do it just idling, or do you hear it when you rev the motor?

Jeff"
 
"Hi Jeff. My mind-set was to r

"Hi Jeff. My mind-set was to rev it as little as possible, maybe 300 rpm above idle and the rattle was still there. I'm back home without the boat or I would give it a better go."
 
"Does the engine shake violent

"Does the engine shake violently when it rattles? If not, then I would pull the belt off the circulating pump for a minute and run the engine to see if it stops. Bearings in the circ. pump can rust and sound like a can of nuts and bolts being shaken. Does the pump weep hole on the bottom side show signs of rusty seepage? Guy"
 
"John;
You could use a mechan

"John;
You could use a mechanics stethoscope (or trusty short length of hose) to try to narrow down where it is coming from. Like Guy says, it could be the circ pump bearings, but it is likely the exhaust shutters. They are notorious for this kind of noise problem.
Rod"
 
Rod: you mentioned shutters;

Rod: you mentioned shutters; how would you check their condition on a 4.3 L V-6? Guy
 
"Visual check is best. You nee

"Visual check is best. You need to remove the funny looking fold-back aluminum exhaust elbows that are between the exhaust riser/elbows and the tops of the Y pipe. If the rubber sleeves are old & hard, it takes some wrestling and prying. Worst case you may need to unbolt the exhaust risers from the manifolds. You will need new gaskets to reassemble the risers, and refitting the rubber sleeves works best with a nice soapy water solution.
The shutters are right at the top of each side of the Y pipe and should be intact with their rubbers. If not, there is a kit to replace them I beleive. If the rubbers are shot, they flap and clank against the Y pipe creating the unhappy noises.
Rod"
 
Back
Top