Overheat Alarm

ranger · #1 08-21-2005, 10:01 PM

Hey, Maybe someone can give me an idea. Yesterday I took off from the dock and went about 3 miles down the Cumberland river. Boat was running well. My overheat alarm in the control box went off. I immediately shut down the motor and waited for it to cool. When I started it back up the alarm was still going. I was getting a good constant stream from the telltale hole and the heads were hot but I could touch them. I hated to do this but I had to run it back to the dock. The motor would not go over 2000 rpms, but it ran well (I didn't hear things coming apart) and we made it to the dock. It even started back up and went onto the trailer ( the horn was still going). Today I went out and turned the key and the horn was quiet.
I put the muffs on and let it run for about 30 min. No horn.
Water felt cool coming out. I started it up again and the horn started sounding. I fell the water again and it was hot. I pulled the thermostats and they looked like they had seen better days, so I will replace them.

ranger · #2 08-21-2005, 10:03 PM

Oops hit the post button too quick. What I wanted to know was do any of you have any ideas on this slight problem. Its a 1979 Johnson 200 hp V6. Thanks

reelapeelin · #3 08-21-2005, 11:01 PM

I think you're on the right track w/the tstats...pisser wouldn't be runnin' if the impeller was shot... ;)...

jaysea · #4 08-21-2005, 11:52 PM

you may have a defective temp sender,that puts the engine into a safe mode(low rpms) so you cant do any damage ,but get the boat an passengers to a safe place

Skools Out · #5 08-22-2005, 12:08 AM

as i know of the old Johnson Evinrudes didn't have a safe mode for low rpm's. check your compression and make sure you have good or close compression on all cylinders let us know what you find. 79 motors were cross flow motors. Should have high compression like 115 to 130 on all.

steplift20 · #6 08-30-2005, 11:49 AM

ok let me tell you something
i have a merc and it hasd the same problem but it was the switch box
what would happen is the alarm would go off and the motor would be cut in have the speed i mean i would lose half the cylinders and i thought it was a safety feature but it wasnt it didnt come with that feature its a 1988 150 so i opened up my repair manuel and diagnose it myself and it turned out to be the outer switch box check it out your self when the alarm goes off see if you lose half the cylinders good luck

ranger · #7 08-30-2005, 12:29 PM

Update. I installed 2 new thermostats. The old ones looked like they were barely working. Ran her for about 30 min (turning it off and on). Heard no alarm or abnormal sounds and I could get full rpm. Seems like the simple solution was the best solution. When this rain stops I can test her on the water. Thanks for the replies.

reelapeelin · #8 08-30-2005, 07:01 PM

Why ya gotta wait on the rain to stop?

ranger · #9 08-30-2005, 10:20 PM

Its not the rain I am worried about, its the 50 knot wind gusts. ;D

reelapeelin · #10 08-31-2005, 12:33 AM

Got it!...