1990 Johnson 70 hp

[Mandoman]

I am experiencing a chronic overheat warning alarm for my 1990 Johnson 70 hp. The imeller has been replaced, the head gasket has been replaced, the VRO has been removed to allow me to use premix. and a temp guage has been installed. The engine seems to operate well at below 3800 rpm I am guessing about 150 to 158 degress, over 3800 the temp increases to about 175 and the overheat alarm goes off. I operate the boat in salt water and flush the engine frequently, and use salt-away. My mechanic says the thermo doesn't need to be replaced. Any thoughts on what I should be doing, other than buying a replacement engine ?

 

[Walker]

Re: 1990 Johnson 70 hp

When you replaced the impellor did you put in an entire waterpump kit or just the impellor. The plate and the cup get grooves worn in them and then they let water pass be the impellor. Also pull one of your thermostats and look in the head and see if there is any calcium or crud buildup in there.

 

[ob]

Re: 1990 Johnson 70 hp

What did your mechanic base his decision on as to the T/stat not needing to be repalced ? Did he remove it and reinstall the old one on a visual inspection?Do you have good pressure and a steady stream from the telltale.Did your mechanic apprise you of any technical service bullitens on your engines cooling system?