2000 25hp Johnson Tech advice only please

[rsl31652]

Even we techs need advice now and then! Working on a year 2000 Johnson 25 hp. This **** thing runs hotter than any o.b. I've ever seen. Appears to melt 175 degree thermostick. Power pack hits SLOW at 180 degrees. Replaced or checked everything including deflectors. Thermostat is same 143 used for last 20 years. Anyone else have a "hot" running newer 2 cylinder? Techline no help. Runs hot enough that it "coughs" (lean condition) when throttling back down. Richen idle circuit to eleininate that problem but then negatively effect idle and trolling operation (too rich). checked lower unit for bearing failure and enough oil, don't think that's it. Any suggestions? Thanks

 

[jegervais]

Re: 2000 25hp Johnson Tech advice only please

For your "cough" when throttling down, adjust the cam/roller pickup point anywhere from 1/4" to 1/2" advanced or retarded. Try advancing first, if the issue worsens, then go towards retarding it. <br /><br />Regarding your overheat, under what conditions is this happening? Are you running it in your test tank? Or??? <br /><br />Sometimes the obvious is difficult to find when you're frustrated (been there/done that/felt real stupid afterwards...), but... 3 deflectors right? And they're the correct ones (they're NOT the same ones as the cross-flows). Also make sure the intake screens aren't on backwards. It sounds like you've done/checked everything regarding water supply to the cylinder head, but how about the water dump? Try dropping the gearcase and hook up a garden hose to the copper tube. turn on the water (not too high pressure). Does the water exit it's designed path at a rate about equal to what you're supplying? Try this a second time with the t-stat removed. Again compare water volume exiting thru the exhaust housing. Don't forget about the water flow diagram in the back of the factory service manual.<br /><br />That's all I've got for now, keep us posted.<br /><br />-John

 

[enn]

Re: 2000 25hp Johnson Tech advice only please

I would:<br />1)check water pressure<br />2)Try run without termostat and see what happens.<br />3) check to see that it there is not an airleak on the inlet side of pump (=a mixture of water/air is pumped inte the engine = poor cooling)<br /><br />I have had a similar case on a Suzuki 30 hp - after messuring pressure etc. I found out the test tank water was app 50celcius - that was the problem <br /><br />After that i often chack the water temp in the test tank - it is incredible how fast an OB can heat up the water.<br />

 

[petryshyn]

Re: 2000 25hp Johnson Tech advice only please

Has this engine ever run at normal temp?<br />Did this just develope out of the blue?<br />Have you measured water pressure?<br />Have you run it with the thermostat housing off?(how's flow?)