1998 90hp Johnson no water in thermostat

[Anderj85]

Hey guys, longtime lurker but finally have my own problems. I have 1998 90hp Johnson that i bought this winter to replace an old worn out mariner on my fishing boat.

Yesterday i put the motor in a tub to get it started before taking it to the lake. Starts and runs fine but after about 3-4 minutes idling the temp alarm went off. I verified temp with infra red temp gun and the heads were 170-180 degrees. So i shut it down. There was a strong stream out of the telltale but i took the hose off between the cylinder and thermostat housing and there was no water in there. Is this a waterpump failure or thermostat stuck? Not sure how to diagnose further.

Im mechanically inclined, raced cars for years and am an engineer, just dont have much experience with outboards. Any help is appreciated.

 

[racerone]

Was the water in your tub 6 to 8" above the water pump ??

 

[Anderj85]

Water was 2"-3" above the anti-cav plate. Is that not enough?

 

[racerone]

Water must be 6 to 8" above the pump !-----These pumps are not self priming.-----And you would now be wise to install a new impeller at the least.

 

[ondarvr]

If you had a strong pee stream then the impeller was doing its job. Normally a small amount of water will bypass the thermostat and you should see water in the cooling system. But it could be the thermostat area is full of corrosion and not letting any water get past.

 

[Anderj85]

FOr my reference at what height is the pump relative to the water intake? I assummed if the water level was well past the intake that was enough.

 

[racerone]

No, water must be 6 to 8" above the pump !----The pump sits just above the joint between the lower unit and exhaust housing !

 

[Anderj85]

Ok, if i try again with deeper water, i can measure water pressure to check the function of the pump correct? Where should that be measured and what is normal? Thanks for the help guys.

 

[boobie]

Edit....

 

[oldboat1]

All good advice re. water depth. Would check out Ondarvr's post again (#5). You may have some corrosion blockage, particularly if you are running in salt or brackish water. If you get in the housing to clean it out, pull out the t.stat (or "vernatherm") and clean and test it.

 

[Anderj85]

After talking to a couple local boat mechanics as well, it sounds like I need to check for a blocked thermostat housing. I ordered thermostats, gaskets, poppet valves/springs, and grommets. Should hopefully be everything I need to replace the thermostats and make sure everything is not blocked.

 

[Fed]

There is no hose between the cylinder & thermostat housing, Model Number?

It sounds like an earlier model with the thermostats down low and removable hoses, water should gush out of those hoses when the engine is running.

Best to figure it out before throwing parts & time at it.

Edit: Just noticed the bubble back so forget the above.

As a quick test you can disconnect the 2 hoses from the thermostat housing and give it a short run on the muffs to see if water flows out of them.

 

[Anderj85]

Which direction does the water flow through the thermostats? Is it through the thermostat then the hoses to the cylinders? Or is it through the cylinders, out the hoses and then through the cylinders?

 

[bob johnson]

There is no hose between the cylinder & thermostat housing, Model Number?

It sounds like an earlier model with the thermostats down low and removable hoses, water should gush out of those hoses when the engine is running.

Best to figure it out before throwing parts & time at it.

Edit: Just noticed the bubble back so forget the above.

As a quick test you can disconnect the 2 hoses from the thermostat housing and give it a short run on the muffs to see if water flows out of them.

I think 1998 was the last year they made v4 crossflows..... they made a 90 and a 115... for sure.... I think those models have a hose ..... bob

 

[Anderj85]

Yes, from everything I've seen, it is a crossflow, no bubble back though, flatback. It's a 90TSLECM. Any input on the water flow direction through the thermostats?

 

[racerone]

Water flows FROM the head to the thermostat.-----Water flows from the head to the thermostat.

 

[Anderj85]

That leads me to believe it's an issue with water supply or impeller then since there was no water coming from the head. I'll need to do some more investigating. thanks guys

 

[ondarvr]

You said the pee stream was strong, if that's the case the issue is passed that point, the impeller is working and pumping water.

 

[Woodonglass]

Ditto, if she's Peeing Water is circulating!!!

 

[racerone]

Very wrong.--------If the water diverters are out of place then water will not flow thru the engine.