2002 Merc Outboard newbie w/ noise questions

[brewer5]

1st time boat owner- 2002 90 hp Merc o/b on 186 bay boat. Most hours on ICW salt water. I have two main concerns. First, there is a knocking sound when I shift to reverse and sometimesd when shifting forward. Once in gear, all is well. Also, twice today when I shifted forward the engine died...shallow water- maybe too shallow and caught in sand? The other concern is the alarm sound from the console. Started today and is very intermittent. Pee hole is fine- don't think is overheating. Almost seems connected to steering wheel...beeping somehow responsive to steering,comes and goes depending on steering wheel...yet very constant when on plane back to boat ramp...Thanks for helping a newbie!@

 

[Don S]

Re: 2002 Merc Outboard newbie w/ noise questions

Is this a 2 stroke or 4 stroke motor?
Is the Knocking sound you hear actually the clunk of the shift dogs engaging in the lower unit? If so, that is normal. If you have a SS prop it will also be worse, and if your idle rpm is too high it will be worse.

 

[brewer5]

Re: 2002 Merc Outboard newbie w/ noise questions

Thanks. It is a SS prop. Any clue on the alarm sound? It just started and seems to be coming from the console and it seems to cut in and out with no real pattern. It's pretty annoying. Thanks again!

 

[Texasmark]

Re: 2002 Merc Outboard newbie w/ noise questions

I have a 2002 90. I bought it used last Dec. The thermostat was frozen shut which caused my overtemp alarm to sound first time I had it out. That engine has a bypass valve also, which opens (I'm told) at around 2500 rpm's (with a good impeller) and when underway if you are going fast enough for water pressure to open it. When that happens the head gets circulating water, cools (where the sensor is) and the alarm goes off. If you slow back down after a few minutes it will sound again cause the bypass valve closes and there is no circulation (with a closed stat).

Stat is under the cover on top left of the rear of the water jacket to the side of plug #1. Stat temp is 120F and you can buy it on here for $10. Also under that cover is the bypass valve (the larger of the two holes). If you are careful removing it you can use some blue RTV and reuse the existing gasket. Otherwise you have to order it separately and don't know if iboats sells that too or not.

Be very careful when you remove the old one and pay attention to how the sealing rubber gasket is installed on the stat so that you can get it on the new one correctly.

Mark

 

[Texasmark]

Re: 2002 Merc Outboard newbie w/ noise questions

Forgot something.

That engine has a 2.3:1 gearbox which is a high ratio, made for using a smaller engine on larger boats (but I run a big engine on a small boat.....if you want to call 90 a big engine).

If you have a big, heavy, high pitched SS prop the gearbox will make funny clunking-banging noises at low speeds and is caused by "clutch dog rattle". Merc says don't worry about it and I have had it since installing props with higher pitch. You can eliminate it by using an alum prop of lower pitch....like 17". BTDT But I wanna run my 24P HP SS so I put up with the noise or just run the engine a little faster (1000-1200rpm's) till it stops. If the engine had a different gearbox (2:1 or so) or an additional cylinder, it probably wouldn't do that because few large cylinders coupled with a high ratio gearbox (causing me to run a high pitched prop) is what causes it.

Idle rpm affects your ability to shift into reverse and the manual says that 675 rpm in F gear boat moving in the water is the correct setting.

Get some Sea Foam and add it to the gas....I use 4 or so ounces per 5 gallons. Engine starts and runs much better.

Mark

 

[brewer5]

Re: 2002 Merc Outboard newbie w/ noise questions

Thanks for all the great info!!