Possible Cooling Issue 2007 Johnson 15HP J15RSUA

[Boned]

Hello Folks

I'm stumped. My motor idles at 180 to 190F which according to the service manual is too hot. Idle should be no more than 168F at the head. At full throttle it actually runs cooler. It idles great but the temp just seems too high. I cannot figure out what the problem is. Here is what I've done so far.

-Tried running on the muffs and in a barrel with no difference in temperature
-Pulled the thermostat assembly and ran without it. Temp down to 140F at idle
-Replaced the thermostat unit. (just the brass thermo, not rubber or springs as they look fine)
-Pulled the lower unit and checked the impeller. All looks good.
-Made a hose adapter to connect garden hose to water tube where pump normally feeds. Runs at 180F again. Water flow seems fine through block. Still stumped.
-Pulled block from midsection. Water tube and grommets are in great shape.
-Removed head from block. Looks good. I can blow air (with mouth and a hose) through all passages in block and head with no resistance. I have to remove the thermostat to get air through but that should be normal as it was cold.

Engine is still apart. I have not pulled the side covers and don't think I will need to.
Anyone have any ideas?

 

[oldboat1]

Might check to make sure the t.stat assembly is complete: http://www.iboats.com/Cylinder-Crankcase/dm/cart_id.800961725--session_id.854826494--view_id.1537567

 

[Boned]

It seems like it's all there. I looked at some exploded views and it looks like it's all there. On one view it shows what looks like a washer in front of the diagphram. The washer is listed as a "cup". I suspect that it is the plastic washer that's part of the diagphram on mine. I didn't separate the two of them on mine just in case I tear the rubber.

I'll try to post some pics.

 

[Boned]

http://s800.photobucket.com/user/Bone556/library/Outboard?sort=3&page=1

 

[oldboat1]

couldn't quite see the second spring in your pic, but probably there. Issue seems to be at the t.stat, though, based on your description. Bypass issue, maybe? (blocked bypass in the housing). Your impeller has a "set", and that can affect cooling at idle.

[Edit. That is, I would first replace the impeller if you haven't done that. The impeller shown would probably do the job at higher rpm, when the pump functions as a centrifugal pump. At idle, though, the vanes of the impeller pictured might not push enough water to hold a proper temp.]

 

[Boned]

Looks like it was bypassing at the inner exhaust cover i think. You can see where the water was washing into the exhaust chamber. The covers are warped.

Now to find covers. Everyone seems to not have them or not able to get them.