2005 50hp alarms and WTF is going on here

[tramp666]

I have a 21' toon with 2005 50hp 2 stroke that pumps about 6 lb of water pressure. Last trip out ran great and I usually putt around under 3000rpm but when I kicked it up to 4000rpm the water gauge moved to 8 psi then when I moved to 4600rpm the psi went to 10 and the alarm went off. HMMMM

I shut it down... restarted it and no alarm... run it at 3k and everything is great, psi is back to 6lb psi (whatever) go up to 3.8k and back up goes the presure to 8 psi. bump it to 4.5k and pressure goes to 10 psi and the alarm comes on again. This time I just back it off to 3k and the psi drop to 6psi and the alarm shuts off.

So my question is WTF? Seems like the termostat is sticking or there is a clog of some kind.

I've had the boat for a year now and this just popped up.

Before I bought it, it carried about 10-12 psi then the shop change the pump/implier and the pressure then ran about 0-6psi but pees good.

It does fine on the water hose and muffs at idle. Gauge reads 0 untill bump up the trottle then the gage goes to 2-4 psi.

Any ideas?

 

[mercfixer]

Re: 2005 50hp alarms and WTF is going on here

I have seen five or six of these in the last two years. Tried water pump repair, thermostat replacement, and popet valve replacement, still over heats over 3500-4000 rpm. Under the powerhead, where the water tube connects to the midsection, is a rubber gromet which seals the tube at the top. The surface around the gromet corrodes and restricts the water flow. The motor will still spray a tell tale like a fire hose, but overheats at high rpm.
Seems six year old and older are most common. Two stroke not too bad of a fix.....4-stroke is much more involved. Took me about three hours in the shop with time for cleaning corrosion and zinc chromate primer and paint so as to avoid a repeat performance.

 

[Reloder]

Re: 2005 50hp alarms and WTF is going on here

This is very common and frustrating among 50HP owners. I assume that because you have a pontoon you don't do much sea use which eliminates the idea that this is a saltwater issue. I'm doing my 50HP 4S this weekend. Here is a link w/ decent pics:

http://rib.net/forum/showthread.php?t=35217

As mentioned in that post, the thermostat is easy enough to check.

BTW, my merc water pressure kit says that 50 HP outboards should run between 12-25 PSI above 5000 RPM.

Out of curiosity, do you have an hour gauge?

Took me about three hours in the shop with time for cleaning corrosion and zinc chromate primer and paint so as to avoid a repeat performance

Mercfixer, what difference would zinc chromate primer and paint make? I am under the impression this is a rubber seal? What did you paint?

 

[tramp666]

Re: 2005 50hp alarms and WTF is going on here

First off... thanks for he straight shooting answers and the link from both of you. I'm not looking forward to this at all. But I have to admit it makes sense. I live in Panama City Florida and run the boat in St Andrews Bay. So salt water is the culprit.

I cant believe Mercury in all there experiance and years in business would miss this in R&D on these motors. Blows my mind. It also blows my mind that this can't be unplug externally with a chase/snake of some kind.

I don't have a hour meter so don't know how many hours are on the motor but I know that in Panama City people cross the bay to Shell Island and pretty much hangout all day then go back. Mine is a 2005 so can't have too many hours on it.