What is that STRANGE RATTLE???

[Dandelion]

2006 Stingray 20' with the Merc 4.3 carb, 190hp engine. At top speed, there is a subtle rattle coming from the engine compartment. At first I thought something was loose and either banging around in there or even banging on the hull, because that's what it sounded like, a random 'banging around' sound: tat tat... tattattat, tat..... tat tat. And so on. No fixed rhythm to it.

The engine is not backfiring, and there is nothing loose in the engine compartment or in any of the storage compartments. All hull fittings outside the boat are secure.

Since it ONLY happens at top speed, and more-so once the engine has been running a while, I'm thinking it has to be engine-related, even though it's a very 'physical' sounding noise.

Any ideas are appreciated.

 

[Bondo]

Re: What is that STRANGE RATTLE???

Since it ONLY happens at top speed, and more-so once the engine has been running a while, I'm thinking it has to be engine-related, even though it's a very 'physical' sounding noise.

Ayuh,....

Here's My WAGuess,.......

Change your Fuel Filters,....
Your hearing Detonation caused by a Lean condition......

 

[Don S]

Re: What is that STRANGE RATTLE???

There is always the ever popular noise made by the lifters when the oil is aireated due to high oil level. At higher rpms the lifters clatter a little. If your oil level is over the full mark, drain some down so it isn't and see what happens.

 

[MikDee]

Re: What is that STRANGE RATTLE???

Ayuh,....

Here's My WAGuess,.......

Change your Fuel Filters,....
Your hearing Detonation caused by a Lean condition......

I agree, it sounds like preignition, running lean, high temp, the Death knell of a motor, better check it out, and get it fixed, right quick!

 

[xxxflhrci]

Re: What is that STRANGE RATTLE???

I agree with Don S on it being lifter noise. Back off the throttle a couple of hundred RPMs and the noise will usually go away.

 

[gamarines2]

Re: What is that STRANGE RATTLE???

My first thought was exhaust flappers, but when those go bad, it only evident when at idle, right?

 

[chiefalen]

Re: What is that STRANGE RATTLE???

Do you know what the rpm's supposed to be for that motor at W.O.T? Are you running over? Just a thought. Also in my humble opinion to many people think they can run at W.O.T all day everyday.