johnson 8hp overheating solutions sought

[leda259]

i am tearing my hair out.

1989 j8rcec 8hp. overheating. i had good flow from pee hole, nothing from exhaust relief port in back of down tube except for a lot of steam when hot. inspection stream extremely hot.
-head and exhaust covers removed and all passages cleaned out as well as around cylinders.
-removed thermostat
-new water pump. grommet well seated on tube. (good flow from water tube when hosed through thermo port while disassembled.)
-when i hose water through thermostat housing with exhaust cover off, i get good flow from lower right passage in exhaust housing, somewhat less in lower left.
-when i run the engine with the thermo cover off, (exhaust cover obviously on) i get very little flow through the thermo port unless i put my hand over the below water exhaust port to force back pressure.
-engine fires right up and runs smooth but inspection stream still extremely hot and cylinder head extremely hot to touch after a few minutes. i have tried with hose hook up as well as on boat.


i just did the exact same routine on a virtually identical 1987 j6rcud with good results. i am out of ideas on this one.

what am i missing?

 

[nwcove]

Re: johnson 8hp overheating solutions sought

sounds like you did your homework! i had a similiar problem with my 84 4.5 hp, no thermostat, but it was a head/head gasket issue. the motor blew steam, ran hot......all i did was sanded the head on a flat surface (it was warped).....replaced the head gasket, and the motor runs perfect to this day. (it was hot exhaust gas blowing into the water jackets, boiling the cooling water and fighting against the water pump)

 

[leda259]

Re: johnson 8hp overheating solutions sought

thanks nw.

what you say makes a lot of sense since i have water coming and going every which way. i never thought of blow by on the head. i will give it a try and report back. now i just have to get my hands on the gasket.

i use these small o/b's on my dinghy for my larger sailboat so i have gotten somewhat used to keeping them going. i have accumulated 2 8's, a 6 and a 1974 9.9 sea horse (kind of my favorite). at any one time at least two are working. they are all extremely sensitive to fuel issues and spark plug quality. the overheating thing was coincidental on two. the 6 had a bad impeller but that was the last thing i looked at. i was reluctant to drop the lower unit since i had a nightmare of a time with one of the 8's. when i finally did it, these two dropped right off.
now that i see what salt water does to the insides of these monsters, i am going to be more careful rinsing them out with fresh. the water jackets and passages were caked with salt.