Thermostat - 1989 70hp Johnson

[renegade]

How important is it to have the thermostat in the engine. Is it ok to leave it out. I'm asking because my engine is overheating with it in. I went out and bought a new therm. and installed it. It does not overhreat @ idle, but about 10 sec. after planning out it overheats. I have a flats boat and the engine is on a jack plate. I even lowered the plate to give the engine a little more depth in case the inlets were too shallow in the water - it did not help. Please advise.<br /><br />Renegade

 

[clanton]

Re: Thermostat - 1989 70hp Johnson

There is about 5 Service Bulletins for overheat on this engine, will post them tonight. If you bought thermostat at sharp dealer he/she would have informed you of this, and sold you the parts to upgrade the engine,

 

[butlp]

Re: Thermostat - 1989 70hp Johnson

Renegade,<br />Do you use the boat in salt water and do you flush the motor regularly?<br />Apart from this does the engine start and run normally?<br /><br />I would first check the water pump is OK and make sure all the cooling water ways are clear. <br /> <br />If all looks good with the cooling, I would then check the temperature switches. Put them in hot oil, the contact should close at 211 deg F +/- 6 deg. and open at 175 deg +/- 7 deg<br /><br />You can check if the motor is really overheating using Markal Thermomelt Sticks or if you have access to a infrared gun. <br />The manual says to run the motor at 3000 - 4000 RPM in forward (must be in the water) and put a 163 deg F stick on each cylinder head. If it melts then the motor is overheating.<br /><br />According to the trouble check chart, possible cause of overheating are:<br />Thermostats damaged<br />Thermo-cover or gaskets damaged<br />Pressure control valve damaged<br />Exhaust cover gasket leaking<br />Head gasket leaking (warped head) (water in cylinders)<br />Water intake obstructed<br />Pump plate not sealing (bottom)<br />Pump impeller damaged<br />Pump housing worn<br />Pump housing distorted (motor run out of water)<br />Pump housing cover seal (driveshaft grooved)<br />Water tube grommet damaged<br /><br />I wouldn't run it without the thermostat, it's there for a reason.<br /><br />Hope this helps!<br />Good luck!<br />Peter

 

[butlp]

Re: Thermostat - 1989 70hp Johnson

Renegade,<br />Sorry I did not read your post correctly and thought your motor was a 150 hp. I think the checks are the same for a in-line motor as the V though.<br />Sounds like Clanton has all the scoop on your motor!<br />Good luck.

 

[clanton]

Re: Thermostat - 1989 70hp Johnson

SB2221 dated Feb1990 changed tenp sensor, PN 584166 new switch has 7 1/4 inch tan wire with blue stripe.<br /><br />SB 2225 dated April 1990 change thermostat seat from 2 piece to 1 piece, old has stainless cup for rubber seal, you remove old seal and cup, replace with 1 piece seal PN 336416.Also applies to V4/6/8.<br /><br />SB2276R1 dated April 1994 relocated tattle tail nipple from side of block to top of engine to vent air for better cooling at idle.<br /><br />Waterpump kit kit 432955 has SB 2276R1 in kit,a choice of 2 new pressure relief springs depending on model of engine with cover,and inproved inpeller.

 

[clanton]

Re: Thermostat - 1989 70hp Johnson

You should have a strong tattle tale at idle with boat in water, and I would install a water pressure guage. You may be raising the motor to high. When was the waterpump replaced? Yes you need the thermostat.

 

[waterdowg]

Re: Thermostat - 1989 70hp Johnson

clanton,<br /> Seen to have same issue with 89 88spl. Replaced impeller, but still seems to get hot. Do you know of any service updateds on this motor?

 

[clanton]

Re: Thermostat - 1989 70hp Johnson

No SB. If you have high speed overheat check the o-ring between the stainless inpeller cup and plastic housing, and water deflecters behind cylinder heads. Remove thermostat housing check relief springs and valve, check thermostat in hot water should start to open 143, be fully open 150/155. If you are using aftermarket inpeller, they dont have the 0-ring seal between the inpeller and wear plate, does not seal as good as OEM.

 

[garycunn]

Re: Thermostat - 1989 70hp Johnson

My thermostat in my 86 70hp Johnson was removed by mechanic 3yrs ago because of horn going off.Mechanic said it wasn't needed because I run in summer.He said thermostat is problem area and removing it provides bettercooling without problems. I have read postson this board that run contrary to that.<br />Maybe I am just lucky buy no problems now for<br />three years.