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1998 35 hp Johnson overheats at 4k+ RPMs

 
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Mike_Smith



Joined: 06 Aug 2010
Posts: 1

PostPosted: Fri Aug 06, 2010 3:28 am    Post subject: 1998 35 hp Johnson overheats at 4k+ RPMs Reply with quote

I have a 1998 Johnson 35 hp, 535 cc, 3 cylinder out board that I use in salt water. If I run the boat at 4,000 rpms or higher, the motor will overheat after about 30 minutes of use. I let it cool off for 20 minutes and it starts right up again. If I stay at about 3,000 rpms, I can go indefinitely without overheating.

I thought "thermostat" was the obvious cause which I replaced but that did not fix the problem - it still overheats. My next best guess is the impeller but after researching the steps for replacement, it sounds like a job that I will wait with until the boat comes off the mooring for the season. The only other item I intend to check is the water intake screen to make sure there is nothing obstructing the passage way.

Do you think it is the impeller and is there anything else anyone can suggest that might cause overheating as I've described?

Thanks!
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MikeW
Senior Member


Joined: 01 May 2006
Posts: 680

PostPosted: Fri Aug 13, 2010 7:58 am    Post subject: Reply with quote

Hello Mike, it sounds like a weak impeller. The impeller should be changed every other season as preventative maintenance. Cool
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