86 johnson 25hp overheating

[merc350]

my johnson 25hp overheats, after about 5 minutes out on the water.
it is pumping water, but it gets hot and then the water coming out the telltale, gets hot, and starts steaming.
the motor sat for a long time, and i have put a brand new water pump and impellor, but its still gets hot. im just about to pull my hair out!!
the motor has only done 14 hrs work in its whole life.. any ideas?

 

[ezeke]

Re: 86 johnson 25hp overheating

The tell tale does not let you know if water is passing through the engine's cooling passages; it just lets you know that the water pump is functioning at some level.

The thermostat controls the flow of water through the engine, so check that first.

 

[merc350]

Re: 86 johnson 25hp overheating

ok , now the next question, where is the thermostat? i cant seem to locate it anywhere...

 

[ezeke]

Re: 86 johnson 25hp overheating

Click the thumbnail, please.

It's #19 in the drawing. You have to remove the water cover #53 to get to it. Buy the gasket first.

You also have three water passage deflectors that may be a problem, but check those later.

 

[merc350]

Re: 86 johnson 25hp overheating

thanks, took cover off, snapped 5 bolts in the process, and the thermostat was just a lump of corrosion. noting could possible get past it. damn.
will the motor run without the thermostat?

 

[ezeke]

Re: 86 johnson 25hp overheating

It will run, but running without a good thermostat will shorten the life and contribute to fouling, smoke, etc.

Those 143 degree thermostats are as little as $10.

 

[merc350]

Re: 86 johnson 25hp overheating

thankyou i really appriciate your advice. the seat where the thermostat is supposed to sit, is corroded away. looks like i have no choice . i guess that i wont get too much life out of the engine, but if it runs and doesnt over heat for a few years i will be happy. thanks !

 

[ezeke]

Re: 86 johnson 25hp overheating

You might make an offer on this: http://cgi.ebay.com/ebaymotors/JOHN...2787201QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear

 

[merc350]

Re: 86 johnson 25hp overheating

thanks for that. i bought that head, as my head was corroded to far to be reused. thanks. the water jackets in the block were full of sand also. so its good that the head came off.

 

[ezeke]

Re: 86 johnson 25hp overheating

Great. While you have the cylinder head off it would be a great time to replace your water passage deflectors.

 

[merc350]

Re: 86 johnson 25hp overheating

deflectors?? now you have lost me.
down the bottom there is a little rubber doohicky , is that supposed to be there? where are they and how do i change them? do they have a pourpose?
i really appreciate the advice.

 

[ezeke]

Re: 86 johnson 25hp overheating

The three rubber parts are "water passage deflectors"; click the thumbnail please. They direct the flow of water through the cooling passages.

#9 is OE part # 0335602
#10 is OE part #335603
#10A is OE part #335603

While you are at it, check the water intake screens; They need to be in perfect shape to keep the particles out of your cooling system.