1984 50hp Merc Overheating

[ChrisBrown8]

Hi, I recently bought what I think is a 1984 model 50hp Mercury. I took it out and noticed the tell-tale was spewing out piping hot water. I figured it was the water pump and completely replaced it. I took it out again and once I cranked my motor, it was peeing just fine. After about 5 minutes of running it, it started spewing again. I turned it off to keep from damaging it. What could be causing this? Clogged intake? Something internal? User error? Any help is appreciated!

 

[Chris1956]

Did you install a new higher pitched prop? Overload will cause 'em to overheat.
Are the carbs clean?
Is she running on all 4 cylinders?

 

[ChrisBrown8]

Did you install a new higher pitched prop? Overload will cause 'em to overheat.
Are the carbs clean?
Is she running on all 4 cylinders?

No sir. The prop is still what came on the motor when I bought it. Carbs are clean, I assume all 4 cylinders are still firing. Would a compression test be the best way to see if they are?

 

[racerone]

Testing in the lake or a bucket ?-----In a bucket the water must be 8" above the impeller !

 

[ChrisBrown8]

Testing in the lake or a bucket ?-----In a bucket the water must be 8" above the impeller !

I’ve run it on muffs and in the lake. I can let it idle with muffs on and it does fine. It will idle fine in the lake as well. But after I run it for a few minutes down the lake, it stops peeing and it’s more spewing/steam.

 

[racerone]

I am not there to see , hear or feel your motor.----I do not know the history of your motor.---Is it a long shaft motor on a 20" transom?-----It does sound like there is a blockage in the copper tube or in the motor water jackets.----If it was my motor ( I have a coupe of those ) I would start looking for blockage.

 

[ChrisBrown8]

I took this video a few days ago. I’m not sure about the specifics of the motor. I’m sure I sound like an idiot, but I appreciate any information. I’m taking it to a local mechanic this weekend.

 

[racerone]

I would install a pressure gauge to see what pressures you have.-----Factory parts installed or something else ?

 

[merc850]

Could be you're trimming it out too far or the motor is sitting too high on the transom or both - "Is it a long shaft motor on a 20" transom" is a good question. I am not a fan of those "Whale Tails" they can cause handling problems and might be the reason for your problem. When you're underway at full throttle look at the anti-cavitation plate and see if it's on or below the surface of the water.

 

[ChrisBrown8]

Could be you're trimming it out too far or the motor is sitting too high on the transom or both - "Is it a long shaft motor on a 20" transom" is a good question. I am not a fan of those "Whale Tails" they can cause handling problems and might be the reason for your problem. When you're underway at full throttle look at the anti-cavitation plate and see if it's on or below the surface of the water

I would install a pressure gauge to see what pressures you have.-----Factory parts installed or something else ?

All factory as far as I know, aside from the whale tail.

 

[Faztbullet]

Install the tell-tell nozzle as it acts as a restrictor...could be too much water overboard.

 

[Sea Rider]

Gee that's a 37 year oldie, fresh or slat water use, second, third hand motor ? If haven't checked the thermo(s) current condition, remove them, check the internal housing to see if salted/crusted, if found excessively salted, crusted install new ones in, motor should cool much better.

Before installing a new water pump or impeller, remove both lower leg's water intake screens and with a hard bristle tooth brush brush clean both sides. Poke several times a large thin wooden stick up/down the lower water pump's orifice till seen exiting the water intake housing. The issue is nobody cleans this hidden vertical water passage and over time thru the years will reduce its diameter and the pump will suck less water that it should compared to being impeccable clean.​

Happy Boating

 

[racerone]

There is no thermostat on that 1984 model 50 HP Mercury !

 

[Faztbullet]

As stated no t-stats and passage will not crude up. A small stick is of no use as a mouse can climb thru the passageway as its so large..

 

[Sea Rider]

As stated no t-stats and passage will not crude up. A small stick is of no use as a mouse can climb thru the passageway as its so large..

Need to employ a long wooden stick, stiff wire, thin rod, the lower water passage located on the screen's housing is usually a rectangular water intake with a narrow passage that reduces its diam over the years. Once the cleaning tool employed is seen exiting the lower water passage visually check thru the housing if round or rectangular...

Happy Boating​

 

[Faztbullet]

Dont waste your time on above post as cleaning or a stick isnt going to help anything. The passage ways in powerhead would clog way before any build up in lower unit would effect cooling. If motor has ever overheated it can blow the powerhead gasket causing this. Also if watertube housing melted it will do the same.